Sample records for auxin polar transport

  1. Polar auxin transport: controlling where and how much (United States)

    Muday, G. K.; DeLong, A.; Brown, C. S. (Principal Investigator)


    Auxin is transported through plant tissues, moving from cell to cell in a unique polar manner. Polar auxin transport controls important growth and developmental processes in higher plants. Recent studies have identified several proteins that mediate polar auxin transport and have shown that some of these proteins are asymmetrically localized, paving the way for studies of the mechanisms that regulate auxin transport. New data indicate that reversible protein phosphorylation can control the amount of auxin transport, whereas protein secretion through Golgi-derived vesicles and interactions with the actin cytoskeleton might regulate the localization of auxin efflux complexes.

  2. Polar auxin transport: models and mechanisms

    NARCIS (Netherlands)

    Berkel, van K.; Boer, de R.J.; Scheres, B.; Tusscher, ten K.


    Spatial patterns of the hormone auxin are important drivers of plant development. The observed feedback between the active, directed transport that generates auxin patterns and the auxin distribution that influences transport orientation has rendered this a popular subject for modelling studies. Her

  3. Loss of GSNOR1 Function Leads to Compromised Auxin Signaling and Polar Auxin Transport. (United States)

    Shi, Ya-Fei; Wang, Da-Li; Wang, Chao; Culler, Angela Hendrickson; Kreiser, Molly A; Suresh, Jayanti; Cohen, Jerry D; Pan, Jianwei; Baker, Barbara; Liu, Jian-Zhong


    Cross talk between phytohormones, nitric oxide (NO), and auxin has been implicated in the control of plant growth and development. Two recent reports indicate that NO promoted auxin signaling but inhibited auxin transport probably through S-nitrosylation. However, genetic evidence for the effect of S-nitrosylation on auxin physiology has been lacking. In this study, we used a genetic approach to understand the broader role of S-nitrosylation in auxin physiology in Arabidopsis. We compared auxin signaling and transport in Col-0 and gsnor1-3, a loss-of-function GSNOR1 mutant defective in protein de-nitrosylation. Our results showed that auxin signaling was impaired in the gsnor1-3 mutant as revealed by significantly reduced DR5-GUS/DR5-GFP accumulation and compromised degradation of AXR3NT-GUS, a useful reporter in interrogating auxin-mediated degradation of Aux/IAA by auxin receptors. In addition, polar auxin transport was compromised in gsnor1-3, which was correlated with universally reduced levels of PIN or GFP-PIN proteins in the roots of the mutant in a manner independent of transcription and 26S proteasome degradation. Our results suggest that S-nitrosylation and GSNOR1-mediated de-nitrosylation contribute to auxin physiology, and impaired auxin signaling and compromised auxin transport are responsible for the auxin-related morphological phenotypes displayed by the gsnor1-3 mutant.

  4. PIN protein phosphorylation by plant AGC3 kinases and its role in polar auxin transport

    NARCIS (Netherlands)

    Huang, Fang


    Polar cell-to-cell transport of plant hormone auxin mediated by plasma membrane (PM)-localized PIN-FORMED (PIN) auxin efflux carriers generates auxin gradients that provide positional information for various plant developmental processes. The apical-basal polar localization of the PIN proteins that

  5. Foliar modifications induced by inhibition of polar transport of auxin

    Institute of Scientific and Technical Information of China (English)



    The effects of auxin polar transport inhibitors,9-hydroxy-fluorene-9-carboxylic acid (HFCA);2,3,5-triiodobenzoic acid(TIBA) and trans-cinnamic acid (CA) on leaf pattern formation were investigated with shoots formed from cultured leaf explants of tobacco and cultured pedicel explants of Orychophragmus violaceus,and the seedlings of tobacco and Brassica chinensis,Although the effective concentration varies with the inhibitors used,all of the inhibitors induced the formation of trumpet-shaped and/or fused leaves.The frequency of trumpet-shaped leaf formation was related to the concentration of inhibitors in the medium.Histological observation of tobacco seedlings showed that there was only one main vascular bundle and several minor vascular bundles in normal leaves of the control,but there were several vascular bundles of more or less the same size in the trumpet-shaped leaves of treated ones.These results indicated that auxin polar transport played an important role on bilateral symmetry of leaf growth.

  6. The Role of PIN Auxin Efflux Carriers in Polar Auxin Transport and Accumulation and Their Effect on Shaping Maize Development

    Institute of Scientific and Technical Information of China (English)

    Cristian Forestan; Serena Varotto


    In plants,proper seed development and the continuing post-embryonic organogenesis both require that different cell types are correctly differentiated in response to internal and external stimuli.Among internal stimuli,plant hormones and particularly auxin and its polar transport(PAT)have been shown to regulate a multitude of plant physiological processes during vegetative and reproductive development.Although our current auxin knowledge is almost based on the results from researches on the eudicot Arabidopsis thaliana,during the last few years,many studies tried to transfer this knowledge from model to crop species,maize in particular.Applications of auxin transport inhibitors,mutant characterization,and molecular and cell biology approaches,facilitated by the sequencing of the maize genome,allowed the identification of genes involved in auxin metabolism,signaling,and particularly in polar auxin transport.PIN auxin efflux carriers have been shown to play an essential role in regulating PAT during both seed and post-embryonic development in maize.In this review,we provide a summary of the recent findings on PIN-mediated polar auxin transport during maize development.Similarities and differences between maize and Arabidopsis are analyzed and discussed,also considering that their different plant architecture depends on the differentiation of structures whose development is controlled by auxins.

  7. Suitable experimental design for determination of auxin polar transport in space using a spacecraft. (United States)

    Shimazu, T; Miyamoto, K; Hoson, T; Kamisaka, S; Ueda, J


    It is necessary to establish a suitable experimental design for the determination of auxin (indole-3-acetic acid: IAA) polar transport in space using a spacecraft in concerning with the role of gravity. Problems in space experiments are as follows: I) Selection of suitable plant species; II) Preservation of integrity of plant segments for activities of auxin polar transport; III) Stop of auxin polar transport of the segments after the transport experiment in space. Segments of etiolated pea epicotyls and etiolated maize coleoptiles showed relatively high activities of auxin polar transport among dicotyledonous and monocotyledonous plants tested, respectively. The activities decreased dramatically when the segments were pre-stored at 25 degrees C only for 1 day. On the other hand, the storage at low temperature (5 degrees C) in the presence of antioxidants or chelating agents, especially EGTA, maintained relatively high activities of auxin polar transport in pea epicotyl segments. Low temperature (5 degrees C) substantially inhibited the activity of auxin polar transport. Based on the results in this study, a suitable experimental design for the space experiment of auxin polar transport using a spacecraft is also proposed.

  8. S-nitrosylation mediates nitric oxide -auxin crosstalk in auxin signaling and polar auxin transport (United States)

    Nitric oxide (NO) and auxin phytohormone cross talk has been implicated in plant development and growth. Addition and removal of NO moieties to cysteine residues of proteins, is termed S-nitrosylation and de-nitrosylation, respectively and functions as an on/off switch of protein activity. This dyna...

  9. The actin cytoskeleton may control the polar distribution of an auxin transport protein (United States)

    Muday, G. K.; Hu, S.; Brady, S. R.; Davies, E. (Principal Investigator)


    The gravitropic bending of plants has long been linked to the changes in the transport of the plant hormone auxin. To understand the mechanism by which gravity alters auxin movement, it is critical to know how polar auxin transport is initially established. In shoots, polar auxin transport is basipetal (i.e., from the shoot apex toward the base). It is driven by the basal localization of the auxin efflux carrier complex. One mechanism for localizing this efflux carrier complex to the basal membrane may be through attachment to the actin cytoskeleton. The efflux carrier protein complex is believed to consist of several polypeptides, including a regulatory subunit that binds auxin transport inhibitors, such as naphthylphthalamic acid (NPA). Several lines of experimentation have been used to determine if the NPA binding protein interacts with actin filaments. The NPA binding protein has been shown to partition with the actin cytoskeleton during detergent extraction. Agents that specifically alter the polymerization state of the actin cytoskeleton change the amount of NPA binding protein and actin recovered in these cytoskeletal pellets. Actin-affinity columns were prepared with polymers of actin purified from zucchini hypocotyl tissue. NPA binding activity was eluted in a single peak from the actin filament column. Cytochalasin D, which fragments the actin cytoskeleton, was shown to reduce polar auxin transport in zucchini hypocotyls. The interaction of the NPA binding protein with the actin cytoskeleton may localize it in one plane of the plasma membrane, and thereby control the polarity of auxin transport.

  10. Auxin polar transport in arabidopsis under simulated microgravity conditions - relevance to growth and development (United States)

    Miyamoto, K.; Oka, M.; Yamamoto, R.; Masuda, Y.; Hoson, T.; Kamisaka, S.; Ueda, J.


    Activity of auxin polar transport in inflorescence axes of Arabidopsis thaliana grown under simulated microgravity conditions was studied in relation to the growth and development. Seeds were germinated and allowed to grow on an agar medium in test tubes on a horizontal clinostat. Horizontal clinostat rotation substantially reduced the growth of inflorescence axes and the productivity of seeds of Arabidopsis thaliana (ecotypes Landsberg erecta and Columbia), although it little affected seed germination, development of rosette leaves and flowering. The activity of auxin polar transport in inflorescence axes decreased when Arabidopsis plants were grown on a horizontal clinostat from germination stage, being ca. 60% of 1 g control. On the other hand, the auxin polar transport in inflorescence axes of Arabidopsis grown in 1 g conditions was not affected when the segments were exposed to various gravistimuli, including 3-dimensional clinorotation, during transport experiments. Pin-formed mutant of Arabidopsis, having a unique structure of the inflorescence axis with no flower and extremely low levels of the activity of auxin polar transport in inflorescence axes and endogenous auxin, did not continue its vegetative growth under clinostat rotation. These facts suggest that the development of the system of auxin polar transport in Arabidopsis is affected by microgravity, resulting in the inhibition of growth and development, especially during reproductive growth.

  11. Brassinosteroids stimulate plant tropisms through modulation of polar auxin transport in Brassica and Arabidopsis. (United States)

    Li, Li; Xu, Jian; Xu, Zhi-Hong; Xue, Hong-Wei


    Brassinosteroids (BRs) are important plant growth regulators in multiple developmental processes. Previous studies have indicated that BR treatment enhanced auxin-related responses, but the underlying mechanisms remain unknown. Using (14)C-labeled indole-3-acetic acid and Arabidopsis thaliana plants harboring an auxin-responsive reporter construct, we show that the BR brassinolide (BL) stimulates polar auxin transport capacities and modifies the distribution of endogenous auxin. In plants treated with BL or defective in BR biosynthesis or signaling, the transcription of PIN genes, which facilitate functional auxin transport in plants, was differentially regulated. In addition, BL enhanced plant tropistic responses by promoting the accumulation of the PIN2 protein from the root tip to the elongation zone and stimulating the expression and dispersed localization of ROP2 during tropistic responses. Constitutive overexpression of ROP2 results in enhanced polar accumulation of PIN2 protein in the root elongation region and increased gravitropism, which is significantly affected by latrunculin B, an inhibitor of F-actin assembly. The ROP2 dominant negative mutants (35S-ROP2-DA/DN) show delayed tropistic responses, and this delay cannot be reversed by BL addition, strongly supporting the idea that ROP2 modulates the functional localization of PIN2 through regulation of the assembly/reassembly of F-actins, thereby mediating the BR effects on polar auxin transport and tropistic responses.

  12. A major facilitator superfamily transporter plays a dual role in polar auxin transport and drought stress tolerance in Arabidopsis. (United States)

    Remy, Estelle; Cabrito, Tânia R; Baster, Pawel; Batista, Rita A; Teixeira, Miguel C; Friml, Jiri; Sá-Correia, Isabel; Duque, Paula


    Many key aspects of plant development are regulated by the polarized transport of the phytohormone auxin. Cellular auxin efflux, the rate-limiting step in this process, has been shown to rely on the coordinated action of PIN-formed (PIN) and B-type ATP binding cassette (ABCB) carriers. Here, we report that polar auxin transport in the Arabidopsis thaliana root also requires the action of a Major Facilitator Superfamily (MFS) transporter, Zinc-Induced Facilitator-Like 1 (ZIFL1). Sequencing, promoter-reporter, and fluorescent protein fusion experiments indicate that the full-length ZIFL1.1 protein and a truncated splice isoform, ZIFL1.3, localize to the tonoplast of root cells and the plasma membrane of leaf stomatal guard cells, respectively. Using reverse genetics, we show that the ZIFL1.1 transporter regulates various root auxin-related processes, while the ZIFL1.3 isoform mediates drought tolerance by regulating stomatal closure. Auxin transport and immunolocalization assays demonstrate that ZIFL1.1 indirectly modulates cellular auxin efflux during shootward auxin transport at the root tip, likely by regulating plasma membrane PIN2 abundance. Finally, heterologous expression in yeast revealed that ZIFL1.1 and ZIFL1.3 share H(+)-coupled K(+) transport activity. Thus, by determining the subcellular and tissue distribution of two isoforms, alternative splicing dictates a dual function for the ZIFL1 transporter. We propose that this MFS carrier regulates stomatal movements and polar auxin transport by modulating potassium and proton fluxes in Arabidopsis cells.

  13. ROP3 GTPase contributes to polar auxin transport and auxin responses and is important for embryogenesis and seedling growth in Arabidopsis. (United States)

    Huang, Jia-bao; Liu, Huili; Chen, Min; Li, Xiaojuan; Wang, Mingyan; Yang, Yali; Wang, Chunling; Huang, Jiaqing; Liu, Guolan; Liu, Yuting; Xu, Jian; Cheung, Alice Y; Tao, Li-zhen


    ROP GTPases are crucial for the establishment of cell polarity and for controlling responses to hormones and environmental signals in plants. In this work, we show that ROP3 plays important roles in embryo development and auxin-dependent plant growth. Loss-of-function and dominant-negative (DN) mutations in ROP3 induced a spectrum of similar defects starting with altered cell division patterning during early embryogenesis to postembryonic auxin-regulated growth and developmental responses. These resulted in distorted embryo development, defective organ formation, retarded root gravitropism, and reduced auxin-dependent hypocotyl elongation. Our results showed that the expression of AUXIN RESPONSE FACTOR5/MONOPTEROS and root master regulators PLETHORA1 (PLT1) and PLT2 was reduced in DN-rop3 mutant embryos, accounting for some of the observed patterning defects. ROP3 mutations also altered polar localization of auxin efflux proteins (PINs) at the plasma membrane (PM), thus disrupting auxin maxima in the root. Notably, ROP3 is induced by auxin and prominently detected in root stele cells, an expression pattern similar to those of several stele-enriched PINs. Our results demonstrate that ROP3 is important for maintaining the polarity of PIN proteins at the PM, which in turn ensures polar auxin transport and distribution, thereby controlling plant patterning and auxin-regulated responses.

  14. Model of polar auxin transport coupled to mechanical forces retrieves robust morphogenesis along the Arabidopsis root (United States)

    Romero-Arias, J. Roberto; Hernández-Hernández, Valeria; Benítez, Mariana; Alvarez-Buylla, Elena R.; Barrio, Rafael A.


    Stem cells are identical in many scales, they share the same molecular composition, DNA, genes, and genetic networks, yet they should acquire different properties to form a functional tissue. Therefore, they must interact and get some external information from their environment, either spatial (dynamical fields) or temporal (lineage). In this paper we test to what extent coupled chemical and physical fields can underlie the cell's positional information during development. We choose the root apical meristem of Arabidopsis thaliana to model the emergence of cellular patterns. We built a model to study the dynamics and interactions between the cell divisions, the local auxin concentration, and physical elastic fields. Our model recovers important aspects of the self-organized and resilient behavior of the observed cellular patterns in the Arabidopsis root, in particular, the reverse fountain pattern observed in the auxin transport, the PIN-FORMED (protein family of auxin transporters) polarization pattern and the accumulation of auxin near the region of maximum curvature in a bent root. Our model may be extended to predict altered cellular patterns that are expected under various applied auxin treatments or modified physical growth conditions.

  15. The effect of polar auxin transport on adventitious branches formation in Gracilaria lichenoides in vitro. (United States)

    Wang, Wenlei; Li, Huanqin; Lin, Xiangzhi; Zhang, Fang; Fang, Baishan; Wang, Zhaokai


    Seaweed tissue culture (STC) is an important micropropagation tool that has been applied for strain improvement, micropropagation and genetic engineering. Because the mechanisms associated with STC are poorly understood, its application to these organisms lags far behind that of tissue culture propagation of higher plants. Auxin, calcium (Ca(2+) ) and hydrogen peroxide (H2 O2 ) fluxes all play key roles during plant growth and development. In this study, we therefore measured indole-3-acetic acid, Ca(2+) and H2 O2 fluxes of Gracilaria lichenoides explants during adventitious branches (ABs) formation for the first time using noninvasive micro-test technology. We confirmed that polar auxin transport (PAT) also occurs in the marine red alga G. lichenoides. We additionally found that N-1-naphthylphthalamic acid may suppress auxin efflux via ABCB1 transporters and then inhibit ABs formation from the apical region of G. lichenoides segments. The involvement of Ca(2+) and H2 O2 fluxes in PAT-mediated AB formation in G. lichenoides was also investigated. We propose that complex feedback among Ca(2+) , H2 O2 and auxin signaling and response systems may occur during ABs polar formation in G. lichenoides explants, similar to that in higher plants. Our results provide innovative insights that should aid future elucidation of mechanisms operative during STC.

  16. Differential effects of auxin polar transport inhibitors on rooting in some Crassulaceae species


    Marian Saniewski; Justyna Góraj; Elżbieta Węgrzynowicz-Lesiak; Kensuke Miyamoto; Junichi Ueda


    Effects of auxin polar transport inhibitors, 2,3,5-triio-dobenzoic acid (TIBA), 1-N-naphthylphthalamic acid (NPA) and methyl 2-chloro-9-hydroxyfluorene-9-carboxylate (morphactin IT 3456), as a lanolin paste, on root formation in cuttings of some species of Crassulaceae, such as Bryophyllum daigremontianum, B. calycinum, Kalanchoe blossfeldiana and K. tubiflora, were studied. Cuttings of these plants were easily rooted in water without any treatment. TIBA and morphactin IT 3456 completely inhi...

  17. Differential effects of auxin polar transport inhibitors on rooting in some Crassulaceae species

    Directory of Open Access Journals (Sweden)

    Marian Saniewski


    Full Text Available Effects of auxin polar transport inhibitors, 2,3,5-triio-dobenzoic acid (TIBA, 1-N-naphthylphthalamic acid (NPA and methyl 2-chloro-9-hydroxyfluorene-9-carboxylate (morphactin IT 3456, as a lanolin paste, on root formation in cuttings of some species of Crassulaceae, such as Bryophyllum daigremontianum, B. calycinum, Kalanchoe blossfeldiana and K. tubiflora, were studied. Cuttings of these plants were easily rooted in water without any treatment. TIBA and morphactin IT 3456 completely inhibited root formation in the cuttings of these plants but NPA did not when these inhibitors were applied around the stem below the leaves. When TIBA and morphactin were applied around the stem near the top, but leaves were present below the treatment, the root formation was observed in B. calycinum and K. blossfeldiana but in a smaller degree than in control cuttings. These results strongly suggest that endogenous auxin is required for root formation in cuttings of Crassulaceae plants. The differential mode of action of NPA is discussed together with its effect on auxin polar transport.

  18. Auxin transport sites are visualized in planta using fluorescent auxin analogs. (United States)

    Hayashi, Ken-ichiro; Nakamura, Shouichi; Fukunaga, Shiho; Nishimura, Takeshi; Jenness, Mark K; Murphy, Angus S; Motose, Hiroyasu; Nozaki, Hiroshi; Furutani, Masahiko; Aoyama, Takashi


    The plant hormone auxin is a key morphogenetic signal that controls many aspects of plant growth and development. Cellular auxin levels are coordinately regulated by multiple processes, including auxin biosynthesis and the polar transport and metabolic pathways. The auxin concentration gradient determines plant organ positioning and growth responses to environmental cues. Auxin transport systems play crucial roles in the spatiotemporal regulation of the auxin gradient. This auxin gradient has been analyzed using SCF-type E3 ubiquitin-ligase complex-based auxin biosensors in synthetic auxin-responsive reporter lines. However, the contributions of auxin biosynthesis and metabolism to the auxin gradient have been largely elusive. Additionally, the available information on subcellular auxin localization is still limited. Here we designed fluorescently labeled auxin analogs that remain active for auxin transport but are inactive for auxin signaling and metabolism. Fluorescent auxin analogs enable the selective visualization of the distribution of auxin by the auxin transport system. Together with auxin biosynthesis inhibitors and an auxin biosensor, these analogs indicated a substantial contribution of local auxin biosynthesis to the formation of auxin maxima at the root apex. Moreover, fluorescent auxin analogs mainly localized to the endoplasmic reticulum in cultured cells and roots, implying the presence of a subcellular auxin gradient in the cells. Our work not only provides a useful tool for the plant chemical biology field but also demonstrates a new strategy for imaging the distribution of small-molecule hormones.

  19. Polar transport of auxin across gravistimulated roots of maize and its enhancement by calcium (United States)

    Lee, J. S.; Evans, M. L.


    The effect of Ca on the polar movement of [3H]indoleacetic acid ([3H]IAA) in gravistimulated roots was examined using 3-day-old seedlings of maize (Zea mays L.). Transport of label was measured by placing an agar donor block containing [3H]IAA on one side of the elongation zone and measuring movement of label across the root into an agar receiver block on the opposite side. In vertically oriented roots, movement of label across the elongation zone into the receiver was slight and was not enhanced by incorporating 10 millimolar CaCl2 into the receiver block. In horizontally oriented roots, movement of label across the root was readily detectable and movement to a receiver on the bottom was about 3-fold greater than movement in the opposite direction. This polarity was abolished in roots from which the caps were removed prior to gravistimulation. When CaCl2 was incorporated into the receivers, movement of label across horizontally oriented intact roots was increased about 3-fold in both the downward and upward direction. The ability of Ca to enhance the movement of label from [3H]IAA increased with increasing Ca concentration in the receiver up to 5 to 10 millimolar CaCl2. With the inclusion of CaCl2 in the receiver blocks, gravity-induced polar movement of label into receiver blocks from applied [3H]IAA was detectable within 30 minutes, and asymmetric distribution of label within the tissue was detectable within 20 minutes. The results indicate that gravistimulation induces a physiological asymmetry in the auxin transport system of maize roots and that Ca increases the total transport of auxin across the root.

  20. Gravistimulation changes expression of genes encoding putative carrier proteins of auxin polar transport in etiolated pea epicotyls (United States)

    Hoshino, T.; Hitotsubashi, R.; Miyamoto, K.; Tanimoto, E.; Ueda, J.

    STS-95 space experiment has showed that auxin polar transport in etiolated epicotyls of pea (Pisum sativum L. cv. Alaska) seedlings is controlled by gravistimulation. In Arabidopsis thaliana auxin polar transport has considered to be regulated by efflux and influx carrier proteins in plasma membranes, AtPIN1 and AtAUX1, respectively. In order to know how gravistimuli control auxin polar transport in etiolated pea epicotyls at molecular levels, strenuous efforts have been made, resulting in successful isolation of full-length cDNAs of a putative auxin efflux and influx carriers, PsPIN2 and PsAUX1, respectively. Significantly high levels in homology were found on nucleotide and deduced amino acid sequences among PsPIN2, PsPIN1 (accession no. AY222857, Chawla and DeMason, 2003) and AtPINs, and also among PsAUX1, AtAUX1 and their related genes. Phylogenetic analyses based on the deduced amino acid sequences revealed that PsPIN2 belonged to a subclade including AtPIN3, AtPIN4 relating to lateral transport of auxin, while PsPIN1 belonged to the same clade as AtPIN1 relating to auxin polar transport. In the present study, we examined the effects of gravistimuli on the expression of PsPINs and PsAUX1 in etiolated pea seedlings by northern blot analysis. Expression of PsPIN1, PsPIN2 and PsAUX1 in hook region of 3.5-d-old etiolated pea seedlings grown under simulated microgravity conditions on a 3-D clinostat increased as compared with that of the seedlings grown under 1 g conditions. On the other hand, that of PsPIN1 and PsAUX1 in the 1st internode region under simulated microgravity conditions on a 3-D clinostat also increased, while that of PsPIN2 was affected little. These results suggest that expression of PsPIN1, PsPIN2 and PsAUX1 regulating polar/lateral transport of auxin is substantially under the control of gravity. A possible role of PsPINs and PsAUX1 of auxin polar transport in etiolated pea seedlings will also be discussed.

  1. Extracellular ATP inhibits root gravitropism at concentrations that inhibit polar auxin transport (United States)

    Tang, Wenqiang; Brady, Shari R.; Sun, Yu; Muday, Gloria K.; Roux, Stanley J.


    Raising the level of extracellular ATP to mM concentrations similar to those found inside cells can block gravitropism of Arabidopsis roots. When plants are grown in Murashige and Skoog medium supplied with 1 mM ATP, their roots grow horizontally instead of growing straight down. Medium with 2 mM ATP induces root curling, and 3 mM ATP stimulates lateral root growth. When plants are transferred to medium containing exogenous ATP, the gravity response is reduced or in some cases completely blocked by ATP. Equivalent concentrations of ADP or inorganic phosphate have slight but usually statistically insignificant effects, suggesting the specificity of ATP in these responses. The ATP effects may be attributable to the disturbance of auxin distribution in roots by exogenously applied ATP, because extracellular ATP can alter the pattern of auxin-induced gene expression in DR5-beta-glucuronidase transgenic plants and increase the response sensitivity of plant roots to exogenously added auxin. The presence of extracellular ATP also decreases basipetal auxin transport in a dose-dependent fashion in both maize (Zea mays) and Arabidopsis roots and increases the retention of [(3)H]indole-3-acetic acid in root tips of maize. Taken together, these results suggest that the inhibitory effects of extracellular ATP on auxin distribution may happen at the level of auxin export. The potential role of the trans-plasma membrane ATP gradient in auxin export and plant root gravitropism is discussed.

  2. Auxin polar transport of etiolated Ageotropum pea epicotyls is not affected by gravistimulation: Relevance to automorphosis-like growth and development (United States)

    Miyamoto, Kensuke; Hoshino, Tomoki; Takahashi, Yoshinori; Ueda, Junichi

    There appears to be a close relationship between automorphosis and changes in auxin polar transport due to the fact that microgravity conditions cause both changes in the activity of auxin polar transport and in automorphosis of etiolated Alaska pea epicotyls. In addition, the application of inhibitors of auxin polar transport results in automorphosis-like growth and development. To elucidate the role of auxin polar transport in gravimorphogenesis in etiolated pea seedlings, we have studied the effects of gravistimulation on growth and development, and auxin polar transport in epicotyls of an agravitropic pea mutant " Ageotropum" seedlings and the normal "Alaska" seedlings. When the embryo axes in seeds of Alaska pea were set in a vertical (parallel to the direction of gravity) or a horizontal (vertical to the direction of gravity) position, and allowed to germinate and grow under 1 g conditions in the dark for 3 or 6.5 days, the epicotyls grew upward due to negative gravitropic responses regardless of gravistimulation during seed germination. On the other hand, epicotyls of etiolated Ageotropum pea seedlings showed automorphosis-like bending away from the cotyledons regardless of gravistimulation during seed germination. Automorphosis-like epicotyl bending of etiolated Ageotropum pea seedlings was also unaffected by clinorotation on a three-dimensional (3-D) clinostat. The activity of auxin polar transport in the 2nd internodes of 6.5-d-old etiolated Ageotropum pea seedlings was lower than those of Alaska pea seedlings, and was not affected by clinorotation on a 3-D clinostat or by changes in gravity conditions during seed germination. These findings strongly support our previous studies that showed that normal auxin polar transport is required for the normal graviresponse of epicotyls in etiolated pea seedlings.

  3. Flavonol-induced changes in PIN2 polarity and auxin transport in the Arabidopsis thaliana rol1-2 mutant require phosphatase activity (United States)

    Kuhn, Benjamin M.; Nodzyński, Tomasz; Errafi, Sanae; Bucher, Rahel; Gupta, Shibu; Aryal, Bibek; Dobrev, Petre; Bigler, Laurent; Geisler, Markus; Zažímalová, Eva; Friml, Jiří; Ringli, Christoph


    The phytohormone auxin is a major determinant and regulatory component important for plant development. Auxin transport between cells is mediated by a complex system of transporters such as AUX1/LAX, PIN, and ABCB proteins, and their localization and activity is thought to be influenced by phosphatases and kinases. Flavonols have been shown to alter auxin transport activity and changes in flavonol accumulation in the Arabidopsis thaliana rol1-2 mutant cause defects in auxin transport and seedling development. A new mutation in ROOTS CURL IN NPA 1 (RCN1), encoding a regulatory subunit of the phosphatase PP2A, was found to suppress the growth defects of rol1-2 without changing the flavonol content. rol1-2 rcn1-3 double mutants show wild type-like auxin transport activity while levels of free auxin are not affected by rcn1-3. In the rol1-2 mutant, PIN2 shows a flavonol-induced basal-to-apical shift in polar localization which is reversed in the rol1-2 rcn1-3 to basal localization. In vivo analysis of PINOID action, a kinase known to influence PIN protein localization in a PP2A-antagonistic manner, revealed a negative impact of flavonols on PINOID activity. Together, these data suggest that flavonols affect auxin transport by modifying the antagonistic kinase/phosphatase equilibrium. PMID:28165500

  4. Auxin polar transport of etiolated epicotyls of ageotropum pea seedlings is not affected by gravistimulation: Relevance to automorphosis-like growth and development (United States)

    Miyamoto, K.; Hoshino, T.; Takahashi, Y.; Ueda, J.

    Both true microgravity conditions in space STS-95 space experiment and simulated ones on a three-dimensional 3-D clinostat have been demonstrated to induce automorphosis in etiolated pea Pisum sativum L cv Alaska seedlings represented as epicotyl bending as well as changes in root growth direction and inhibition of hook formation and to alter the activities of auxin polar transport of epicotyls The fact that the application of inhibitors of auxin polar transport phenocopied automorphosis together with the result of detail kinetic analyses of epicotyl bending on the 3-D clinostat suggests that automorphosis of etiolated pea epicotyls is due to suppression of a negative gravitropic response on 1 g conditions and graviresponse of etiolated pea seedlings under 1 g conditions requires normal activities of auxin polar transport To study the role of auxin polar transport in graviresponse in early growth stage of etiolated pea seedlings effect of gravistimulation on auxin polar transport in epicotyls of Alaska pea seedlings was studied in comparison with that of the agravitropic pea mutant ageotropum seedlings Dry pea seeds whose embryo axes were set in a horizontal position referred to as horizontal position or an inclinational one to the gravity vector referred to as inclinational position allowed to germinate and grow in the dark for 2 5 days Epicotyls of etiolated Alaska pea seedlings grown under horizontal position showed negative gravitropisum due to relatively larger elongation in the proximal side to the cotyledons

  5. Auxin Polar Transport In Stamen Formation And Development: How Many Actors?

    Directory of Open Access Journals (Sweden)

    Maura eCardarelli


    Full Text Available In flowering plants, proper development of stamens, the male reproductive organs, is required for successful sexual reproduction. In Arabidopsis thaliana normally six stamen primordia arise in the third whorl of floral organs and subsequently differentiate into stamen filaments and anthers, where male meiosis occurs, thus ending the early developmental phase. This early phase is followed by a late developmental phase, which consists of a rapid elongation of stamen filaments coordinated with anther dehiscence and pollen maturation, and terminates with mature pollen grain release at anthesis. Increasing evidence suggests that auxin transport is necessary for both early and late phases of stamen development. It has been shown that different members of PIN (PIN-FORMED family are involved in the early phase, whereas members of both PIN and P-glycoproteins of the ABCB (PGP transporter families are required during the late developmental phase. In this review we provide an overview of the increasing knowledge on auxin transporters involved in Arabidopsis stamen formation and development and we discuss their role and functional conservation across plant species.

  6. myo-Inositol-1-phosphate synthase is required for polar auxin transport and organ development

    KAUST Repository

    Chen, Hao


    myo-Inositol-1-phosphate synthase is a conserved enzyme that catalyzes the first committed and rate-limiting step in inositol biosynthesis. Despite its wide occurrence in all eukaryotes, the role of myo-inositol-1-phosphate synthase and de novo inositol biosynthesis in cell signaling and organism development has been unclear. In this study, we isolated loss-of-function mutants in the Arabidopsis MIPS1 gene from different ecotypes. It was found that all mips1 mutants are defective in embryogenesis, cotyledon venation patterning, root growth, and root cap development. The mutant roots are also agravitropic and have reduced basipetal auxin transport. mips1 mutants have significantly reduced levels of major phosphatidylinositols and exhibit much slower rates of endocytosis. Treatment with brefeldin A induces slower PIN2 protein aggregation in mips1, indicating altered PIN2 trafficking. Our results demonstrate that MIPS1 is critical for maintaining phosphatidylinositol levels and affects pattern formation in plants likely through regulation of auxin distribution. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.

  7. Auxin transport sites are visualized in planta using fluorescent auxin analogs



    Fluorescent auxin analogs are designed to function as active auxins for the auxin transport system but to be inactive for auxin signaling. These fluorescent auxin analogs can mimic auxin via the transport system and be used to visualize inter- and intracellular auxin distribution in roots. These analogs allow imaging of auxin transport sites with high spatiotemporal resolution. Our fluorescent auxin system provides insight into auxin transport dynamics and subcellular auxin distribution.

  8. Novel auxin transport inhibitors phenocopy the auxin influx carrier mutation aux1. (United States)

    Parry, G; Delbarre, A; Marchant, A; Swarup, R; Napier, R; Perrot-Rechenmann, C; Bennett, M J


    The hormone auxin is transported in plants through the combined actions of diffusion and specific auxin influx and efflux carriers. In contrast to auxin efflux, for which there are well documented inhibitors, understanding the developmental roles of carrier-mediated auxin influx has been hampered by the absence of specific competitive inhibitors. However, several molecules that inhibit auxin influx in cultured cells have been described recently. The physiological effects of two of these novel influx carrier inhibitors, 1-naphthoxyacetic acid (1-NOA) and 3-chloro-4-hydroxyphenylacetic acid (CHPAA), have been investigated in intact seedlings and tissue segments using classical and new auxin transport bioassays. Both molecules do disrupt root gravitropism, which is a developmental process requiring rapid auxin redistribution. Furthermore, the auxin-insensitive and agravitropic root-growth characteristics of aux1 plants were phenocopied by 1-NOA and CHPAA. Similarly, the agravitropic phenotype of inhibitor-treated seedlings was rescued by the auxin 1-naphthaleneacetic acid, but not by 2,4-dichlorophenoxyacetic acid, again resembling the relative abilities of these two auxins to rescue the phenotype of aux1. Further investigations have shown that none of these compounds block polar auxin transport, and that CHPAA exhibits some auxin-like activity at high concentrations. Whilst results indicate that 1-NOA and CHPAA represent useful tools for physiological studies addressing the role of auxin influx in planta, 1-NOA is likely to prove the more useful of the two compounds.

  9. Species differences in ligand specificity of auxin-controlled elongation and auxin transport: comparing Zea and Vigna (United States)

    Zhao, Hu; Hertel, Rainer; Ishikawa, Hideo; Evans, Michael L.


    The plant hormone auxin affects cell elongation in both roots and shoots. In roots, the predominant action of auxin is to inhibit cell elongation while in shoots auxin, at normal physiological levels, stimulates elongation. The question of whether the primary receptor for auxin is the same in roots and shoots has not been resolved. In addition to its action on cell elongation in roots and shoots, auxin is transported in a polar fashion in both organs. Although auxin transport is well characterized in both roots and shoots, there is relatively little information on the connection, if any, between auxin transport and its action on elongation. In particular, it is not clear whether the protein mediating polar auxin movement is separate from the protein mediating auxin action on cell elongation or whether these two processes might be mediated by one and the same receptor. We examined the identity of the auxin growth receptor in roots and shoots by comparing the response of roots and shoots of the grass Zea mays L. and the legume Vigna mungo L. to indole-3-acetic acid, 2-naphthoxyacetic acid, 4,6-dichloroindoleacetic acid, and 4,7-dichloroindoleacetic acid. We also studied whether or not a single protein might mediate both auxin transport and auxin action by comparing the polar transport of indole-3-acetic acid and 2-naphthoxyacetic acid through segments from Vigna hypocotyls and maize coleoptiles. For all of the assays performed (root elongation, shoot elongation, and polar transport) the action and transport of the auxin derivatives was much greater in the dicots than in the grass species. The preservation of ligand specificity between roots and shoots and the parallels in ligand specificity between auxin transport and auxin action on growth are consistent with the hypothesis that the auxin receptor is the same in roots and shoots and that this protein may mediate auxin efflux as well as auxin action in both organ types.

  10. Role of the Arabidopsis PIN6 Auxin Transporter in Auxin Homeostasis and Auxin-Mediated Development



    Plant-specific PIN-formed (PIN) efflux transporters for the plant hormone auxin are required for tissue-specific directional auxin transport and cellular auxin homeostasis. The Arabidopsis PIN protein family has been shown to play important roles in developmental processes such as embryogenesis, organogenesis, vascular tissue differentiation, root meristem patterning and tropic growth. Here we analyzed roles of the less characterised Arabidopsis PIN6 auxin transporter. PIN6 is auxin-inducible...

  11. Role of actin in auxin transport and transduction of gravity (United States)

    Hu, S.; Basu, S.; Brady, S.; Muday, G.

    Transport of the plant hormone auxin is polar and the direction of the hormone movement appears to be controlled by asymmetric distribution of auxin transport protein complexes. Changes in the direction of auxin transport are believed to drive asymmetric growth in response to changes in the gravity vector. To test the possibility that asymmetric distribution of the auxin transport protein complex is mediated by attachment to the actin cytoskeleton, a variety of experimental approaches have been used. The most direct demonstration of the role of the actin cytoskeleton in localization of the protein complex is the ability of one protein in this complex to bind to affinity columns containing actin filaments. Additionally, treatments of plant tissues with drugs that fragment the actin c toskeleton reducey polar transport. In order to explore this actin interaction and the affect of gravity on auxin transport and developmental polarity, embryos of the brown alga, Fucus have been examined. Fucus zygotes are initially symmetrical, but develop asymmetry in response to environmental gradients, with light gradients being the best- characterized signal. Gravity will polarize these embryos and gravity-induced polarity is randomized by clinorotation. Auxin transport also appears necessary for environmental controls of polarity, since auxin efflux inhibitors perturb both photo- and gravity-polarization at a very discrete temporal window within six hours after fertilization. The actin cytoskeleton has previously been shown to reorganize after fertilization of Fucus embryos leading to formation of an actin patch at the site of polar outgrowth. These actin patches still form in Fucus embryos treated with auxin efflux inhibitors, yet the position of these patches is randomized. Together, these results suggest that there are connections between the actin cytoskeleton, auxin transport, and gravity oriented growth and development. (Supported by NASA Grant: NAG2-1203)

  12. Arabidopsis phosphatidylinositol monophosphate 5-kinase 2 is involved in root gravitropism through regulation of polar auxin transport by affecting the cycling of PIN proteins

    Institute of Scientific and Technical Information of China (English)

    Yu Mei; Wen-Jing Jia; Yu-Jia Chu; Hong-Wei Xue


    Phosphatidylinositol monophosphate 5-kinase(PIP5K)catalyzes the synthesis of PI-4,5-bisphosphate(PtdIns(4,5)P2)by phosphorylation of PI-4-phosphate at the 5 position of the inositol ring,and is involved in regulating multiple developmental processes and stress responses.We here report on the functional characterization of Arabidopsis PIP5K2,which is expressed during lateral root initiation and elongation,and whose expression is enhanced by exogenous auxin.The knockout mutant pip5k2 shows reduced lateral root formation,which could be recovered with exogenous auxin,and interestingly,delayed root gravity response that could not be recovered with exogenous auxin.Crossing with the DR5-GUS marker line and measurement of free IAA content confirmed the reduced auxin accumulation in pip5k2.In addition,analysis using the membrane-selective dye FM4-64 revealed the decelerated vesicle trafficking caused by PtdIns(4,5)P2 reduction,which hence results in suppressed cycling of PIN proteins(PIN2 and 3),and delayed redistribution of PIN2 and auxin under gravistimulation in pipSk2 roots.On the contrary,PtdIns(4,5)P2 significantly enhanced the vesicle trafficking and cycling of PIN proteins.These results demonstrate that PIP5K2 is involved in regulating lateral root formation and root gravity response,and reveal a critical role of PIP5K2/Ptdlns(4,5)P2 in root development through regulation of PIN proteins,providing direct evidence of crosstalk between the phosphatidylinositol signaling pathway and auxin response,and new insights into the control of polar auxin transport.

  13. The role of polar auxin transport through pedicels of Prunus avium L. in relation to fruit development and retention. (United States)

    Else, Mark A; Stankiewicz-Davies, Anna P; Crisp, Carol M; Atkinson, Christopher J


    It was investigated whether premature fruit abscission in Prunus avium L. was triggered by a reduction in polar auxin transport (PAT). The capacity of pedicels to transport tritiated IAA ([3H]-IAA) via the PAT pathway was measured at intervals throughout flower and fruit development. The extent of passive diffusion, assessed by concurrent applications of [14C]-benzoic acid ([14C]-BA), was negligible. Transported radioactivity recovered from agar blocks eluted at the same retention time as authentic [3H]-IAA during HPLC fractionation. The capacity for PAT was already high 7 d before anthesis and increased further following the fertilization of flowers at anthesis. PAT intensity was greatest immediately following fertilization and at the beginning of the cell expansion phase of fruit growth; the transport intensity in fruitlets destined to abscind was negligible. The amount of endogenous IAA moving through the PAT pathway was greatest during the first 3 weeks after fertilization and was again high at the beginning of the fruit expansion stage. IAA export in the phloem increased following fertilization then declined below detectable levels. ABA export in the phloem increased markedly during stone formation and at the onset of fruit expansion. TIBA applied to pedicels of fruit in situ promoted fruitlet abscission in 2000 but not in 2001, despite PAT capacity being reduced by over 98% in the treated pedicels. The application of TIBA to pedicels did not affect fruit expansion. The role of PAT and IAA in relation to the development and retention of Prunus avium fruit is discussed.

  14. The Relationship between auxin transport and maize branching. (United States)

    Gallavotti, Andrea; Yang, Yan; Schmidt, Robert J; Jackson, David


    Maize (Zea mays) plants make different types of vegetative or reproductive branches during development. Branches develop from axillary meristems produced on the flanks of the vegetative or inflorescence shoot apical meristem. Among these branches are the spikelets, short grass-specific structures, produced by determinate axillary spikelet-pair and spikelet meristems. We investigated the mechanism of branching in maize by making transgenic plants expressing a native expressed endogenous auxin efflux transporter (ZmPIN1a) fused to yellow fluorescent protein and a synthetic auxin-responsive promoter (DR5rev) driving red fluorescent protein. By imaging these plants, we found that all maize branching events during vegetative and reproductive development appear to be regulated by the creation of auxin response maxima through the activity of polar auxin transporters. We also found that the auxin transporter ZmPIN1a is functional, as it can rescue the polar auxin transport defects of the Arabidopsis (Arabidopsis thaliana) pin1-3 mutant. Based on this and on the groundbreaking analysis in Arabidopsis and other species, we conclude that branching mechanisms are conserved and can, in addition, explain the formation of axillary meristems (spikelet-pair and spikelet meristems) that are unique to grasses. We also found that BARREN STALK1 is required for the creation of auxin response maxima at the flanks of the inflorescence meristem, suggesting a role in the initiation of polar auxin transport for axillary meristem formation. Based on our results, we propose a general model for branching during maize inflorescence development.

  15. Seven Things We Think We Know about Auxin Transport

    Institute of Scientific and Technical Information of China (English)

    Wendy Ann Peer; Joshua J. Blakeslee; Haibing Yang; Angus S. Murphy


    T Polar transport of the phytohormone auxin and the establishment of localized auxin maxima regulate embryonic development, stem cell maintenance, root and shoot architecture, and tropic growth responses. The past decade has been marked by dramatic progress in efforts to elucidate the complex mechanisms by which auxin transport regulates plant growth. As the understanding of auxin transport regulation has been increasingly elaborated, it has become clear that this process is involved in almost all plant growth and environmental responses in some way. However, we still lack information about some basic aspects of this fundamental regulatory mechanism. In this review, we present what we know (or what we think we know) and what we do not know about seven auxin-regulated processes. We discuss the role of auxin transport in gravitropism in primary and lateral roots, phototropism, shoot branching, leaf expansion, and venation. We also discuss the auxin reflux/fountain model at the root tip, flavonoid modulation of auxin transport processes, and outstanding aspects of post-translational regulation of auxin transporters. This discussion is not meant to be exhaustive, but highlights areas in which generally held assumptions require more substantive validation.

  16. Auxin regulation of cell polarity in plants. (United States)

    Pan, Xue; Chen, Jisheng; Yang, Zhenbiao


    Auxin is well known to control pattern formation and directional growth at the organ/tissue levels via the nuclear TIR1/AFB receptor-mediated transcriptional responses. Recent studies have expanded the arena of auxin actions as a trigger or key regulator of cell polarization and morphogenesis. These actions require non-transcriptional responses such as changes in the cytoskeleton and vesicular trafficking, which are commonly regulated by ROP/Rac GTPase-dependent pathways. These findings beg for the question about the nature of auxin receptors that regulate these responses and renew the interest in ABP1 as a cell surface auxin receptor, including the work showing auxin-binding protein 1 (ABP1) interacts with the extracellular domain of the transmembrane kinase (TMK) receptor-like kinases in an auxin-dependent manner, as well as the debate on this auxin binding protein discovered about 40 years ago. This review highlights recent work on the non-transcriptional auxin signaling mechanisms underscoring cell polarity and shape formation in plants.

  17. Regulation of auxin transport during gravitropism (United States)

    Rashotte, A.; Brady, S.; Kirpalani, N.; Buer, C.; Muday, G.

    Plants respond to changes in the gravity vector by differential growth across the gravity-stimulated organ. The plant hormone auxin, which is normally basipetally transported, changes in direction and auxin redistribution has been suggested to drive this differential growth or gravitropism. The mechanisms by which auxin transport directionality changes in response to a change in gravity vector are largely unknown. Using the model plant, Arabidopsis thaliana, we have been exploring several regulatory mechanisms that may control auxin transport. Mutations that alter protein phosphorylation suggest that auxin transport in arabidopsis roots may be controlled via phosphorylation and this signal may facilitate gravitropic bending. The protein kinase mutant pinoid (pid9) has reduced auxin transport; whereas the protein phosphatase mutant, rcn1, has elevated transport, suggesting reciprocal regulation of auxin transport by reversible protein phosphorylation. In both of these mutants, the auxin transport defects are accompanied by gravitropic defects, linking phosphorylation signaling to gravity-induced changes in auxin transport. Additionally, auxin transport may be regulated during gravity response by changes in an endogenous auxin efflux inhibitor. Flavonoids, such as quercetin and kaempferol, have been implicated in regulation of auxin transport in vivo and in vitro. Mutants that make no flavonoids have reduced root gravitropic bending. Furthermore, changes in auxin-induced gene expression and flavonoid accumulation patterns have been observed during gravity stimulation. Current studies are examining whether there are spatial and temporal changes in flavonoid accumulation that precede gravitropic bending and whether the absence of these changes are the cause of the altered gravity response in plants with mutations that block flavonoid synthesis. These results support the idea that auxin transport may be regulated during gravity response by several mechanisms including

  18. Auxin transport in the evolution of branching forms. (United States)

    Harrison, C Jill


    I. II. III. IV. V. VI. VII. Acknowledgements References SUMMARY: Branching is one of the most striking aspects of land plant architecture, affecting resource acquisition and yield. Polar auxin transport by PIN proteins is a primary determinant of flowering plant branching patterns regulating both branch initiation and branch outgrowth. Several lines of experimental evidence suggest that PIN-mediated polar auxin transport is a conserved regulator of branching in vascular plant sporophytes. However, the mechanisms of branching and auxin transport and relationships between the two are not well known outside the flowering plants, and the paradigm for PIN-regulated branching in flowering plants does not fit bryophyte gametophytes. The evidence reviewed here suggests that divergent auxin transport routes contributed to the diversification of branching forms in distinct land plant lineages.

  19. A tetratricopeptide repeat domain-containing protein SSR1 located in mitochondria is involved in root development and auxin polar transport in Arabidopsis. (United States)

    Zhang, Min; Wang, Cuiping; Lin, Qingfang; Liu, Aihua; Wang, Ting; Feng, Xuanjun; Liu, Jie; Han, Huiling; Ma, Yan; Bonea, Diana; Zhao, Rongmin; Hua, Xuejun


    Auxin polar transport mediated by a group of Pin-formed (PIN) transporters plays important roles in plant root development. However, the mechanism underlying the PIN expression and targeting in response to different developmental and environmental stimuli is still not fully understood. Here, we report a previously uncharacterized gene SSR1, which encodes a mitochondrial protein with tetratricopeptide repeat (TPR) domains, and show its function in root development in Arabidopsis thaliana. In ssr1-2, a SSR1 knock-out mutant, the primary root growth was dramatically inhibited due to severely impaired cell proliferation and cell elongation. Significantly lowered level of auxin was found in ssr1-2 roots by auxin measurement and was further supported by reduced expression of DR5-driven reporter gene. As a result, the maintenance of the root stem cell niche is compromised in ssr1-2. It is further revealed that the expression level of several PIN proteins, namely, PIN1, PIN2, PIN3, PIN4 and PIN7, were markedly reduced in ssr1-2 roots. In particular, we showed that the reduced protein level of PIN2 on cell membrane in ssr1-2 is due to impaired retrograde trafficking, possibly resulting from a defect in retromer sorting system, which destines PIN2 for degradation in vacuoles. In conclusion, our results indicated that SSR1 is functioning in root development in Arabidopsis, possibly by affecting PIN protein expression and subcellular targeting.

  20. Maintenance of asymmetric cellular localization of an auxin transport protein through interaction with the actin cytoskeleton (United States)

    Muday, G. K.


    In shoots, polar auxin transport is basipetal (that is, from the shoot apex toward the base) and is driven by the basal localization of the auxin efflux carrier complex. The focus of this article is to summarize the experiments that have examined how the asymmetric distribution of this protein complex is controlled and the significance of this polar distribution. Experimental evidence suggests that asymmetries in the auxin efflux carrier may be established through localized secretion of Golgi vesicles, whereas an attachment of a subunit of the efflux carrier to the actin cytoskeleton may maintain this localization. In addition, the idea that this localization of the efflux carrier may control both the polarity of auxin movement and more globally regulate developmental polarity is explored. Finally, evidence indicating that the gravity vector controls auxin transport polarity is summarized and possible mechanisms for the environmentally induced changes in auxin transport polarity are discussed.

  1. Connective Auxin Transport in the Shoot Facilitates Communication between Shoot Apices. (United States)

    Bennett, Tom; Hines, Geneviève; van Rongen, Martin; Waldie, Tanya; Sawchuk, Megan G; Scarpella, Enrico; Ljung, Karin; Leyser, Ottoline


    The bulk polar movement of the plant signaling molecule auxin through the stem is a long-recognized but poorly understood phenomenon. Here we show that the highly polar, high conductance polar auxin transport stream (PATS) is only part of a multimodal auxin transport network in the stem. The dynamics of auxin movement through stems are inconsistent with a single polar transport regime and instead suggest widespread low conductance, less polar auxin transport in the stem, which we term connective auxin transport (CAT). The bidirectional movement of auxin between the PATS and the surrounding tissues, mediated by CAT, can explain the complex auxin transport kinetics we observe. We show that the auxin efflux carriers PIN3, PIN4, and PIN7 are major contributors to this auxin transport connectivity and that their activity is important for communication between shoot apices in the regulation of shoot branching. We propose that the PATS provides a long-range, consolidated stream of information throughout the plant, while CAT acts locally, allowing tissues to modulate and be modulated by information in the PATS.

  2. 滇杨倒置插穗的生长素极性运输%The Polarity of Auxin Transport in Inverted Cuttings of Populus yunnanensis

    Institute of Scientific and Technical Information of China (English)

    李佳蔓; 员涛; 王军民; 郑元; 周安佩; 纵丹; 何承忠


    生长素是唯一具有极性运输的内源激素,在植株生长发育过程中发挥着重要的调控作用。为探讨倒置插穗在生根发芽过程中生长素的极性运输规律,以滇杨1年生根萌苗主干制作插穗,分别正向放置和倒向放置后进行水培,采用高效液相色谱法(HPLC)测定正置、倒置插穗不同部位树皮与侧芽内生长素(IAA)和脱落酸(ABA)含量的动态变化。结果表明,不同时期滇杨正置、倒置插穗树皮和侧芽内IAA和ABA总含量的动态变化规律存在差异,极性对倒置插穗的生理生化活性有一定的影响。滇杨正置插穗树皮和侧芽内IAA的运输符合极性运输规律。倒置插穗分别在21 d和28 d之前,其树皮和侧芽内IAA的运输符合极性运输规律,即从形态学上端(插穗的下端)向形态学下端(插穗的上端)运输;之后,倒置插穗内重新建立了IAA的运输方向,即从形态学下端(插穗的上端)向形态学上端(插穗的下端)运输。正置与倒置插穗不同部位树皮和侧芽内ABA的含量从上到下依次递增,运输规律遵循向重力性。研究结果初步表明:滇杨倒置插穗内IAA的极性运输可能会发生逆转。%Polar transport within plant tissues is unique to auxin, and it plays an important role to regulate plant growth and development. In order to investigate the polar auxin transport regularity in inverted cutting of Popu-lus yunnanensis for the duration of rooting and shooting, cuttings made of one-year-old main stem of P. yunna-nensis rootlings, upright and inverted cuttings cultured in water, high performance liquid chromatography (HPLC) was used to measure the dynamic changes of IAA and ABA contents in different parts of bark and lat-eral buds of upright and inverted cuttings. The results showed that differences existed in amount contents of IAA and ABA in bark and lateral buds between upright cuttings and inverted cuttings, and the polarity made

  3. Auxin distribution and transport during embryogenesis and seed germi-nation of Arabidopsis

    Institute of Scientific and Technical Information of China (English)


    Auxin distribution during embryogenesis and seed germination were studied with transgenic Arabidopsis plants expressing GUS gene driven by a synthetic DR5 promoter, an auxin responsive promoter. The results showed that GUS activity is higher in ends of hypophysis and cotyledon primordia of heart-, torpedo- and cotyledon-stage embryos, leaf tip area, lateral root primordia, root apex and cotyledon of young seedlings.And GUS accumulated in root apex of the seedlings grown on auxin transport inhibitor containing media.All these suggested that above-mentioned part of the organs and tissues have a higher level of auxin, and auxin polar transport inhibitor could cause the accumulation of auxin in root apex. And auxin transport inhibitor also resulted in aberration of Arabidopsis leaf pattern formation, root gravitropism and elongation.

  4. Aluminium toxicity targets PIN2 in Arabidopsis root apices: Effects on PIN2 endocytosis, vesicular recycling,and polar auxin transport

    Institute of Scientific and Technical Information of China (English)

    SHEN Hong; HOU NingYan; Markus SCHLICHT; WAN YingLang; Stefano MANCUSO; Frantisek BALUSKA


    The most obvious symptom of AI toxicity is the inhibition of root growth.However,the mechanism of AI-inhibiting root growth remains to be elucidated.In this study,auxin transport and vesicle movement of an auxin-efflux carrier (PIN2) were investigated in Arabidopsis roots in response to AI stress.Results indicated that AI inhibited the apical transport of auxin in root tips of Arabidopsis significantly.The severe inhibition was localized in the cells of transition zone,where the concentration of auxin was only 34% that of the control.Brefeldin A (BFA),an inhibitor of vesicle transport,induced the dot-like structure of PIN2 vesicle significantly.Al decreased the size of dot-like structure of PIN2 vesicles.Re-sults of real-time RT-PCR and Western-blotting analysis showed that Al increased the transcript level of PIN2 and the accumulation of PIN2 protein in horizontal direction of plasma membrane,but decreased its distribution in endosomes,suggesting that AI inhibited the transport of PIN2 vesicles from plasma membrane to endosomes.Results of cytoskeleton-depolymering drugs indicated that it was via the pathway of disruption of actin microfilaments that AI inhibited the transport of PIN2 vesicles.Exposed to AI stress,the cells of elongation zone had less AI uptake and less transport frequency of vesicles than cells of transition zone.Taken together,our results suggested that AI inhibited root growth mainly by modulating the transport of PIN2 vesicles between plasma membrane and endosomes,thus block-ing auxin transport and root growth.

  5. Quercetin Promotes Auxin Transport in Arabidopsis thaliana%槲皮素促进拟南芥生长素极性运输的研究

    Institute of Scientific and Technical Information of China (English)

    高静; 黄华孙; 程汉


    Study on the role of quercentin in polar auxin transportation. Arabidopsis was cultured on medium supplemented with quercetin to observe the growth of hypocotyls, 14C-IAA transport assays were conducted to measure the auxin transport activity. The results showed that Arabidopsis mutant auxl which had been deficient in auxin influx transportion obviously recovered the ability after cultured on the medium with quercetin. The polar auxin transport was promoted by the addition of quercetin. These results indicated that quereetin could promote polar auxin transport in vivo.

  6. Auxin Acts through MONOPTEROS to Regulate Plant Cell Polarity and Pattern Phyllotaxis. (United States)

    Bhatia, Neha; Bozorg, Behruz; Larsson, André; Ohno, Carolyn; Jönsson, Henrik; Heisler, Marcus G


    The periodic formation of plant organs such as leaves and flowers gives rise to intricate patterns that have fascinated biologists and mathematicians alike for hundreds of years [1]. The plant hormone auxin plays a central role in establishing these patterns by promoting organ formation at sites where it accumulates due to its polar, cell-to-cell transport [2-6]. Although experimental evidence as well as modeling suggest that feedback from auxin to its transport direction may help specify phyllotactic patterns [7-12], the nature of this feedback remains unclear [13]. Here we reveal that polarization of the auxin efflux carrier PIN-FORMED 1 (PIN1) is regulated by the auxin response transcription factor MONOPTEROS (MP) [14]. We find that in the shoot, cell polarity patterns follow MP expression, which in turn follows auxin distribution patterns. By perturbing MP activity both globally and locally, we show that localized MP activity is necessary for the generation of polarity convergence patterns and that localized MP expression is sufficient to instruct PIN1 polarity directions non-cell autonomously, toward MP-expressing cells. By expressing MP in the epidermis of mp mutants, we further show that although MP activity in a single-cell layer is sufficient to promote polarity convergence patterns, MP in sub-epidermal tissues helps anchor these polarity patterns to the underlying cells. Overall, our findings reveal a patterning module in plants that determines organ position by orienting transport of the hormone auxin toward cells with high levels of MP-mediated auxin signaling. We propose that this feedback process acts broadly to generate periodic plant architectures.

  7. [Role of auxin in induction of polarity in zygotes of Fucus vesiculosus L]. (United States)

    Polevoĭ, V V; Tarakhovskaia, E R; Maslov, Iu I; Polevoĭ, A V


    We studied the effects of auxin (indolyl-3 acetic acid) on formation of the primary polarity axis in zygotes of the brown algae Fucus vesiculosus. Within the first 2.5 h after fertilization, the zygotes release this phytohormone in the environment. The treatment of developing zygotes with the inhibitor of indolyl-3-acetic acid transport from the cell triiodobenzoic acid at 5 mg/l arrests the auxin secretion and leads to its accumulation in the cells. This causes a significant delay in zygote polarization. The treatment of zygotes with the exogenous indolyl-3-acetic acid at 1 mg/l stimulates cell polarization and formation of a rhizoid process. When auxin was added to the medium with triiodobenzoic acid, the inhibitory effect of the latter was fully relieved. It has been proposed that the content of indolyl-3-acetic acid in the environment is a key factor in the induction of polarity of the F. vesiculosus zygotes.

  8. Characterization of transmembrane auxin transport in Arabidopsis suspension-cultured cells. (United States)

    Seifertová, Daniela; Skůpa, Petr; Rychtář, Jan; Laňková, Martina; Pařezová, Markéta; Dobrev, Petre I; Hoyerová, Klára; Petrášek, Jan; Zažímalová, Eva


    Polar auxin transport is a crucial process for control and coordination of plant development. Studies of auxin transport through plant tissues and organs showed that auxin is transported by a combination of phloem flow and the active, carrier-mediated cell-to-cell transport. Since plant organs and even tissues are too complex for determination of the kinetics of carrier-mediated auxin uptake and efflux on the cellular level, simplified models of cell suspension cultures are often used, and several tobacco cell lines have been established for auxin transport assays. However, there are very few data available on the specificity and kinetics of auxin transport across the plasma membrane for Arabidopsis thaliana suspension-cultured cells. In this report, the characteristics of carrier-mediated uptake (influx) and efflux for the native auxin indole-3-acetic acid and synthetic auxins, naphthalene-1-acetic and 2,4-dichlorophenoxyacetic acids (NAA and 2,4-D, respectively) in A. thaliana ecotype Landsberg erecta suspension-cultured cells (LE line) are provided. By auxin competition assays and inhibitor treatments, we show that, similarly to tobacco cells, uptake carriers have high affinity towards 2,4-D and that NAA is a good tool for studies of auxin efflux in LE cells. In contrast to tobacco cells, metabolic profiling showed that only a small proportion of NAA is metabolized in LE cells. These results show that the LE cell line is a useful experimental system for measurements of kinetics of auxin carriers on the cellular level that is complementary to tobacco cells.

  9. Reduced phototropism in pks mutants may be due to altered auxin-regulated gene expression or reduced lateral auxin transport. (United States)

    Kami, Chitose; Allenbach, Laure; Zourelidou, Melina; Ljung, Karin; Schütz, Frédéric; Isono, Erika; Watahiki, Masaaki K; Yamamoto, Kotaro T; Schwechheimer, Claus; Fankhauser, Christian


    Phototropism allows plants to orient their photosynthetic organs towards the light. In Arabidopsis, phototropins 1 and 2 sense directional blue light such that phot1 triggers phototropism in response to low fluence rates, while both phot1 and phot2 mediate this response under higher light conditions. Phototropism results from asymmetric growth in the hypocotyl elongation zone that depends on an auxin gradient across the embryonic stem. How phototropin activation leads to this growth response is still poorly understood. Members of the phytochrome kinase substrate (PKS) family may act early in this pathway, because PKS1, PKS2 and PKS4 are needed for a normal phototropic response and they associate with phot1 in vivo. Here we show that PKS proteins are needed both for phot1- and phot2-mediated phototropism. The phototropic response is conditioned by the developmental asymmetry of dicotyledonous seedlings, such that there is a faster growth reorientation when cotyledons face away from the light compared with seedlings whose cotyledons face the light. The molecular basis for this developmental effect on phototropism is unknown; here we show that PKS proteins play a role at the interface between development and phototropism. Moreover, we present evidence for a role of PKS genes in hypocotyl gravi-reorientation that is independent of photoreceptors. pks mutants have normal levels of auxin and normal polar auxin transport, however they show altered expression patterns of auxin marker genes. This situation suggests that PKS proteins are involved in auxin signaling and/or lateral auxin redistribution.

  10. Auxin Biosynthesis, Accumulation, Action and Transport are Involved in Stress-Induced Microspore Embryogenesis Initiation and Progression in Brassica napus. (United States)

    Rodríguez-Sanz, Héctor; Solís, María-Teresa; López, María-Fernanda; Gómez-Cadenas, Aurelio; Risueño, María C; Testillano, Pilar S


    Isolated microspores are reprogrammed in vitro by stress, becoming totipotent cells and producing embryos and plants via a process known as microspore embryogenesis. Despite the abundance of data on auxin involvement in plant development and embryogenesis, no data are available regarding the dynamics of auxin concentration, cellular localization and the expression of biosynthesis genes during microspore embryogenesis. This work involved the analysis of auxin concentration and cellular accumulation; expression of TAA1 and NIT2 encoding enzymes of two auxin biosynthetic pathways; expression of the PIN1-like efflux carrier; and the effects of inhibition of auxin transport and action by N-1-naphthylphthalamic acid (NPA) and α-(p-chlorophenoxy) isobutyric acid (PCIB) during Brassica napus microspore embryogenesis. The results indicated de novo auxin synthesis after stress-induced microspore reprogramming and embryogenesis initiation, accompanying the first cell divisions. The progressive increase of auxin concentration during progression of embryogenesis correlated with the expression patterns of TAA1 and NIT2 genes of auxin biosynthetic pathways. Auxin was evenly distributed in early embryos, whereas in heart/torpedo embryos auxin was accumulated in apical and basal embryo regions. Auxin efflux carrier PIN1-like gene expression was induced in early multicellular embryos and increased at the globular/torpedo embryo stages. Inhibition of polar auxin transport (PAT) and action, by NPA and PCIB, impaired embryo development, indicating that PAT and auxin action are required for microspore embryo progression. NPA also modified auxin embryo accumulation patterns. These findings indicate that endogenous auxin biosynthesis, action and polar transport are required in stress-induced microspore reprogramming, embryogenesis initiation and progression.

  11. Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins. (United States)

    Geisler, Markus; Bailly, Aurélien; Ivanchenko, Maria


    Plant development and architecture are greatly influenced by the polar distribution of the essential hormone auxin. The directional influx and efflux of auxin from plant cells depends primarily on AUX1/LAX, PIN, and ABCB/PGP/MDR families of auxin transport proteins. The functional analysis of these proteins has progressed rapidly within the last decade thanks to the establishment of heterologous auxin transport systems. Heterologous co-expression allowed also for the testing of protein-protein interactions involved in the regulation of transporters and identified relationships with members of the FK506-Binding Protein (FKBP) and cyclophilin protein families, which are best known in non-plant systems as cellular receptors for the immunosuppressant drugs, FK506 and cyclosporin A, respectively. Current evidence that such interactions affect membrane trafficking, and potentially the activity of auxin transporters is reviewed. We also propose that FKBPs andcyclophilins might integrate the action of auxin transport inhibitors, such as NPA, on members of the ABCB and PIN family, respectively. Finally, we outline open questions that might be useful for further elucidation of the role of immunophilins as regulators (servants) of auxin transporters (masters).

  12. SAUR39, a small auxin-up RNA gene, acts as a negative regulator of auxin synthesis and transport in rice. (United States)

    Kant, Surya; Bi, Yong-Mei; Zhu, Tong; Rothstein, Steven J


    The phytohormone auxin plays a critical role for plant growth by regulating the expression of a set of genes. One large auxin-responsive gene family of this type is the small auxin-up RNA (SAUR) genes, although their function is largely unknown. The expression of the rice (Oryza sativa) SAUR39 gene showed rapid induction by transient change in different environmental factors, including auxin, nitrogen, salinity, cytokinin, and anoxia. Transgenic rice plants overexpressing the SAUR39 gene resulted in lower shoot and root growth, altered shoot morphology, smaller vascular tissue, and lower yield compared with wild-type plants. The SAUR39 gene was expressed at higher levels in older leaves, unlike auxin biosynthesis, which occurs largely in the meristematic region. The transgenic plants had a lower auxin level and a reduced polar auxin transport as well as the down-regulation of some putative auxin biosynthesis and transporter genes. Biochemical analysis also revealed that transgenic plants had lower chlorophyll content, higher levels of anthocyanin, abscisic acid, sugar, and starch, and faster leaf senescence compared with wild-type plants at the vegetative stage. Most of these phenomena have been shown to be negatively correlated with auxin level and transport. Transcript profiling revealed that metabolic perturbations in overexpresser plants were largely due to transcriptional changes of genes involved in photosynthesis, senescence, chlorophyll production, anthocyanin accumulation, sugar synthesis, and transport. The lower growth and yield of overexpresser plants was largely recovered by exogenous auxin application. Taken together, the results suggest that SAUR39 acts as a negative regulator for auxin synthesis and transport.

  13. Flavonoids and Auxin Transport Inhibitors Rescue Symbiotic Nodulation in the Medicago truncatula Cytokinin Perception Mutant cre1. (United States)

    Ng, Jason Liang Pin; Hassan, Samira; Truong, Thy T; Hocart, Charles H; Laffont, Carole; Frugier, Florian; Mathesius, Ulrike


    Initiation of symbiotic nodules in legumes requires cytokinin signaling, but its mechanism of action is largely unknown. Here, we tested whether the failure to initiate nodules in the Medicago truncatula cytokinin perception mutant cre1 (cytokinin response1) is due to its altered ability to regulate auxin transport, auxin accumulation, and induction of flavonoids. We found that in the cre1 mutant, symbiotic rhizobia cannot locally alter acro- and basipetal auxin transport during nodule initiation and that these mutants show reduced auxin (indole-3-acetic acid) accumulation and auxin responses compared with the wild type. Quantification of flavonoids, which can act as endogenous auxin transport inhibitors, showed a deficiency in the induction of free naringenin, isoliquiritigenin, quercetin, and hesperetin in cre1 roots compared with wild-type roots 24 h after inoculation with rhizobia. Coinoculation of roots with rhizobia and the flavonoids naringenin, isoliquiritigenin, and kaempferol, or with the synthetic auxin transport inhibitor 2,3,5,-triiodobenzoic acid, rescued nodulation efficiency in cre1 mutants and allowed auxin transport control in response to rhizobia. Our results suggest that CRE1-dependent cytokinin signaling leads to nodule initiation through the regulation of flavonoid accumulation required for local alteration of polar auxin transport and subsequent auxin accumulation in cortical cells during the early stages of nodulation.

  14. Transport of the two natural auxins, indole-3-butyric acid and indole-3-acetic acid, in Arabidopsis (United States)

    Rashotte, Aaron M.; Poupart, Julie; Waddell, Candace S.; Muday, Gloria K.; Brown, C. S. (Principal Investigator)


    Polar transport of the natural auxin indole-3-acetic acid (IAA) is important in a number of plant developmental processes. However, few studies have investigated the polar transport of other endogenous auxins, such as indole-3-butyric acid (IBA), in Arabidopsis. This study details the similarities and differences between IBA and IAA transport in several tissues of Arabidopsis. In the inflorescence axis, no significant IBA movement was detected, whereas IAA is transported in a basipetal direction from the meristem tip. In young seedlings, both IBA and IAA were transported only in a basipetal direction in the hypocotyl. In roots, both auxins moved in two distinct polarities and in specific tissues. The kinetics of IBA and IAA transport appear similar, with transport rates of 8 to 10 mm per hour. In addition, IBA transport, like IAA transport, is saturable at high concentrations of auxin, suggesting that IBA transport is protein mediated. Interestingly, IAA efflux inhibitors and mutations in genes encoding putative IAA transport proteins reduce IAA transport but do not alter IBA movement, suggesting that different auxin transport protein complexes are likely to mediate IBA and IAA transport. Finally, the physiological effects of IBA and IAA on hypocotyl elongation under several light conditions were examined and analyzed in the context of the differences in IBA and IAA transport. Together, these results present a detailed picture of IBA transport and provide the basis for a better understanding of the transport of these two endogenous auxins.

  15. The Relationship between Auxin Transport and Maize Branching1[C][W][OA (United States)

    Gallavotti, Andrea; Yang, Yan; Schmidt, Robert J.; Jackson, David


    Maize (Zea mays) plants make different types of vegetative or reproductive branches during development. Branches develop from axillary meristems produced on the flanks of the vegetative or inflorescence shoot apical meristem. Among these branches are the spikelets, short grass-specific structures, produced by determinate axillary spikelet-pair and spikelet meristems. We investigated the mechanism of branching in maize by making transgenic plants expressing a native expressed endogenous auxin efflux transporter (ZmPIN1a) fused to yellow fluorescent protein and a synthetic auxin-responsive promoter (DR5rev) driving red fluorescent protein. By imaging these plants, we found that all maize branching events during vegetative and reproductive development appear to be regulated by the creation of auxin response maxima through the activity of polar auxin transporters. We also found that the auxin transporter ZmPIN1a is functional, as it can rescue the polar auxin transport defects of the Arabidopsis (Arabidopsis thaliana) pin1-3 mutant. Based on this and on the groundbreaking analysis in Arabidopsis and other species, we conclude that branching mechanisms are conserved and can, in addition, explain the formation of axillary meristems (spikelet-pair and spikelet meristems) that are unique to grasses. We also found that BARREN STALK1 is required for the creation of auxin response maxima at the flanks of the inflorescence meristem, suggesting a role in the initiation of polar auxin transport for axillary meristem formation. Based on our results, we propose a general model for branching during maize inflorescence development. PMID:18550681

  16. Auxin conjugated to fluorescent dyes--a tool for the analysis of auxin transport pathways. (United States)

    Sokołowska, K; Kizińska, J; Szewczuk, Z; Banasiak, A


    Auxin is a small molecule involved in most processes related to plant growth and development. Its effect usually depends on the distribution in tissues and the formation of concentration gradients. Until now there has been no tool for the direct tracking of auxin transport at the cellular and tissue level; therefore the majority of studies have been based on various indirect methods. However, due to their various restrictions, relatively little is known about the relationship between various pathways of auxin transport and specific developmental processes. We present a new research tool: fluorescently labelled auxin in the form of a conjugate with two different fluorescent tracers, FITC and RITC, which allows direct observation of auxin transport in plant tissues. Chemical analysis and biological tests have shown that our conjugates have auxin-like biological activity and transport; therefore they can be used in all experimental systems as an alternative to IAA. In addition, the conjugates are a universal tool that can be applied in studies of all plant groups and species. The conjugation procedure presented in this paper can be adapted to other fluorescent dyes, which are constantly being improved. In our opinion, the conjugates greatly expand the possibilities of research concerning the role of auxin and its transport in different developmental processes in plants.

  17. Auxin transport inhibitors impair vesicle motility and actin cytoskeleton dynamics in diverse eukaryotes

    NARCIS (Netherlands)

    P. Dhonukshe (Pankaj); I. Grigoriev (Ilya); R. Fischer (Rainer); M. Tominaga (Motoki); D.G. Robinson (David); J. Hašek (Jiří); T. Paciorek (Tomasz); J. Petrášek (Jan); D. Seifertová (Daniela); R. Tejos (Ricardo); L.A. Meisel (Lee); E. Zažímalová (Eva); T.W.J. Gadella (Theodorus); Y.D. Stierhof; T. Ueda (Takashi); K. Oiwa (Kazuhiro); A.S. Akhmanova (Anna); R. Brock (Roland); A. Spang (Anne); J. Friml (Jiří)


    textabstractMany aspects of plant development, including patterning and tropisms, are largely dependent on the asymmetric distribution of the plant signaling molecule auxin. Auxin transport inhibitors (ATIs), which interfere with directional auxin transport, have been essential tools in formulating

  18. Heterologous expression of a membrane-spanning auxin importer: implications for functional analyses of auxin transporters. (United States)

    Carrier, David John; Abu Bakar, Norliza Tendot; Lawler, Karen; Dorrian, James Matthew; Haider, Ameena; Bennett, Malcolm John; Kerr, Ian Derek


    Biochemical studies of plant auxin transporters in vivo are made difficult by the presence of multiple auxin transporters and auxin-interacting proteins. Furthermore, the expression level of most such transporters in plants is likely to be too low for purification and downstream functional analysis. Heterologous expression systems should address both of these issues. We have examined a number of such systems for their efficiency in expressing AUX1 from Arabidopsis thaliana. We find that a eukaryotic system based upon infection of insect cells with recombinant baculovirus provides a high level, easily scalable expression system capable of delivering a functional assay for AUX1. Furthermore, a transient transfection system in mammalian cells enables localization of AUX1 and AUX1-mediated transport of auxin to be investigated. In contrast, we were unable to utilise P. pastoris or L. lactis expression systems to reliably express AUX1.

  19. A Role for Auxin in Flower Development

    Institute of Scientific and Technical Information of China (English)

    Youfa Cheng; Yunde Zhao


    Auxin has long been implicated in many aspects of plant growth and development including flower development. However, the exact roles of auxin in flower development have not been well defined until the recent identification of auxin biosynthesis mutants. Auxin is necessary for the initiation of floral primordia,and the disruption of auxin biosynthesis, polar auxin transport or auxin signaling leads to the failure of flower formation. Auxin also plays an essential role in specifying the number and identity of floral organs.Further analysis of the relationship between the auxin pathways and the known flower development genes will provide critical information regarding mechanisms of organogenesis and pattern formation in plants.

  20. Protein ubiquitination in auxin signaling and transport

    NARCIS (Netherlands)

    Santos Maraschin, Felipe dos


    What makes plant shoots grow towards the light, and plant roots grow down into the soil? This was a question that Charles Darwin asked himself, and his experiments more than a century ago to find the answer laid the basis for the identification of the growth hormone auxin. Auxin, or indole-3-acetic

  1. Complex regulation of Arabidopsis AGR1/PIN2-mediated root gravitropic response and basipetal auxin transport by cantharidin-sensitive protein phosphatases (United States)

    Shin, Heungsop; Shin, Hwa-Soo; Guo, Zibiao; Blancaflor, Elison B.; Masson, Patrick H.; Chen, Rujin


    Polar auxin transport, mediated by two distinct plasma membrane-localized auxin influx and efflux carrier proteins/complexes, plays an important role in many plant growth and developmental processes including tropic responses to gravity and light, development of lateral roots and patterning in embryogenesis. We have previously shown that the Arabidopsis AGRAVITROPIC 1/PIN2 gene encodes an auxin efflux component regulating root gravitropism and basipetal auxin transport. However, the regulatory mechanism underlying the function of AGR1/PIN2 is largely unknown. Recently, protein phosphorylation and dephosphorylation mediated by protein kinases and phosphatases, respectively, have been implicated in regulating polar auxin transport and root gravitropism. Here, we examined the effects of chemical inhibitors of protein phosphatases on root gravitropism and basipetal auxin transport, as well as the expression pattern of AGR1/PIN2 gene and the localization of AGR1/PIN2 protein. We also examined the effects of inhibitors of vesicle trafficking and protein kinases. Our data suggest that protein phosphatases, sensitive to cantharidin and okadaic acid, are likely involved in regulating AGR1/PIN2-mediated root basipetal auxin transport and gravitropism, as well as auxin response in the root central elongation zone (CEZ). BFA-sensitive vesicle trafficking may be required for the cycling of AGR1/PIN2 between plasma membrane and the BFA compartment, but not for the AGR1/PIN2-mediated root basipetal auxin transport and auxin response in CEZ cells.

  2. Basipetal auxin transport is required for gravitropism in roots of Arabidopsis (United States)

    Rashotte, A. M.; Brady, S. R.; Reed, R. C.; Ante, S. J.; Muday, G. K.; Davies, E. (Principal Investigator)


    Auxin transport has been reported to occur in two distinct polarities, acropetally and basipetally, in two different root tissues. The goals of this study were to determine whether both polarities of indole-3-acetic acid (IAA) transport occur in roots of Arabidopsis and to determine which polarity controls the gravity response. Global application of the auxin transport inhibitor naphthylphthalamic acid (NPA) to roots blocked the gravity response, root waving, and root elongation. Immediately after the application of NPA, the root gravity response was completely blocked, as measured by an automated video digitizer. Basipetal [(3)H]IAA transport in Arabidopsis roots was inhibited by NPA, whereas the movement of [(14)C]benzoic acid was not affected. Inhibition of basipetal IAA transport by local application of NPA blocked the gravity response. Inhibition of acropetal IAA transport by application of NPA at the root-shoot junction only partially reduced the gravity response at high NPA concentrations. Excised root tips, which do not receive auxin from the shoot, exhibited a normal response to gravity. The Arabidopsis mutant eir1, which has agravitropic roots, exhibited reduced basipetal IAA transport but wild-type levels of acropetal IAA transport. These results support the hypothesis that basipetally transported IAA controls root gravitropism in Arabidopsis.

  3. Auxin-responsive DR5 promoter coupled with transport assays suggest separate but linked routes of auxin transport during woody stem development in Populus. (United States)

    Spicer, Rachel; Tisdale-Orr, Tracy; Talavera, Christian


    Polar auxin transport (PAT) is a major determinant of plant morphology and internal anatomy with important roles in vascular patterning, tropic growth responses, apical dominance and phyllotactic arrangement. Woody plants present a highly complex system of vascular development in which isolated bundles of xylem and phloem gradually unite to form concentric rings of conductive tissue. We generated several transgenic lines of hybrid poplar (Populus tremula x alba) with the auxin-responsive DR5 promoter driving GUS expression in order to visualize an auxin response during the establishment of secondary growth. Distinct GUS expression in the cambial zone and developing xylem-side derivatives supports the current view of this tissue as a major stream of basipetal PAT. However, we also found novel sites of GUS expression in the primary xylem parenchyma lining the outer perimeter of the pith. Strands of primary xylem parenchyma depart the stem as a leaf trace, and showed GUS expression as long as the leaves to which they were connected remained attached (i.e., until just prior to leaf abscission). Tissue composed of primary xylem parenchyma strands contained measurable levels of free indole-3-acetic acid (IAA) and showed basipetal transport of radiolabeled auxin ((3)H-IAA) that was both significantly faster than diffusion and highly sensitive to the PAT inhibitor NPA. Radiolabeled auxin was also able to move between the primary xylem parenchyma in the interior of the stem and the basipetal stream in the cambial zone, an exchange that was likely mediated by ray parenchyma cells. Our results suggest that (a) channeling of leaf-derived IAA first delineates isolated strands of pre-procambial tissue but then later shifts to include basipetal transport through the rapidly expanding xylem elements, and (b) the transition from primary to secondary vascular development is gradual, with an auxin response preceding the appearance of a unified and radially-organized vascular cambium.

  4. Identification and Analysis of Medicago truncatula Auxin Transporter Gene Families Uncover their Roles in Responses to Sinorhizobium meliloti Infection. (United States)

    Shen, Chenjia; Yue, Runqing; Bai, Youhuang; Feng, Rong; Sun, Tao; Wang, Xiaofei; Yang, Yanjun; Tie, Shuanggui; Wang, Huizhong


    Auxin transport plays a pivotal role in the interaction between legume species and nitrogen-fixing bacteria to form symbioses. Auxin influx carriers auxin resistant 1/like aux 1 (AUX/LAX), efflux carriers pin-formed (PIN) and efflux/conditional P-glycoprotein (PGP/ABCB) are three major protein families participating in auxin polar transport. We used the latest Medicago truncatula genome sequence to characterize and analyze the M. truncatula LAX (MtLAX), M. truncatula PIN (MtPIN) and M. truncatula ABCB (MtABCB) families. Transient expression experiments indicated that three representative auxin transporters (MtLAX3, MtPIN7 and MtABCB1) showed cell plasma membrane localizations. The expression of most MtLAX, MtPIN and MtABCB genes was up-regulated in the roots and was down-regulated in the shoots by Sinorhizobium meliloti infection in the wild type (WT). However, the expression of these genes was down-regulated in both the roots and shoots of an infection-resistant mutant, dmi3. The different expression patterns between the WT and the mutant roots indicated that auxin relocation may be involved in rhizobial infection responses. Furthermore, IAA contents were significantly up-regulated in the shoots and down-regulated in the roots after Sinorhizobium meliloti infection in the WT. Inoculation of roots with rhizobia may reduce the auxin loading from shoots to roots by inhibiting the expression of most auxin transporter genes. However, the rate of change of gene expression and IAA contents in the dmi3 mutant were obviously lower than in the WT. The identification and expression analysis of auxin transporter genes helps us to understand the roles of auxin in the regulation of nodule formation in M. truncatula.

  5. Auxin transport is sufficient to generate a maximumand gradient guiding root growth

    NARCIS (Netherlands)

    Grieneisen, V.; Xu, J.; Marée, A.F.M.; Hogeweg, P.; Scheres, B.J.G.


    The plant growth regulator auxin controls cell identity, cell division and cell expansion. Auxin efflux facilitators (PINs) are associated with auxin maxima in distal regions of both shoots and roots. Here we model diffusion and PIN-facilitated auxin transport in and across cells within a structured

  6. Rooting of carnation cuttings: The auxin signal


    Acosta, Manuel; Oliveros-Valenzuela, M Rocío; Nicolás, Carlos; Sánchez-Bravo, José


    The rooting of stem cuttings is a common vegetative propagation practice in many ornamental species. Among other signals, auxin polarly transported through the stem plays a key role in the formation and growth of adventitious roots. Unlike in other plant species, auxin from mature leaves plays a decisive role in the rooting of carnation (Dianthus caryophyllus. L) cuttings. The gene DcAUX1, which codifies an auxin influx carrier involved in polar auxin transport, has now been cloned and charac...

  7. Bioassay for investigation of auxin transport in single cell layers

    Directory of Open Access Journals (Sweden)

    Alina B. Wodzicki


    Full Text Available Auxin was collected from the cambial region of Pinus sylvestris by applying agar strips to the cut surfaces of stem sections which comprised a single layer of 2 to 4-mm long, mainly intact fusiform cells. Sections of the agar strips were either bioassayed immediately to determine their auxin content or stored for several months at -80oC, extracted with 80% MeOH and redissolved in hot agar prior to bioassay. Auxin concentrations were determined by Went's oat coleoptile test, as described by Funke, which was modified considerably to give highly reproducible results. The modifications proved essential for good replication of results and are described in detail together with the use of the bioassay to determine changes in cambial cell polarity during ageing and senescence in P. sylvestris.

  8. BARREN INFLORESCENCE2 interaction with ZmPIN1a suggests a role in auxin transport during maize inflorescence development. (United States)

    Skirpan, Andrea; Culler, Angela Hendrickson; Gallavotti, Andrea; Jackson, David; Cohen, Jerry D; McSteen, Paula


    Polar auxin transport, mediated by the PIN-FORMED (PIN) class of auxin efflux carriers, controls organ initiation in plants. In maize, BARREN INFLORESCENCE2 (BIF2) encodes a serine/threonine protein kinase co-orthologous to PINOID (PID), which regulates the subcellular localization of AtPIN1 in Arabidopsis. We show that BIF2 phosphorylates ZmPIN1a, a maize homolog of AtPIN1, in vitro and regulates ZmPIN1a subcellular localization in vivo, similar to the role of PID in Arabidopsis. In addition, bif2 mutant inflorescences have lower auxin levels later in development. We propose that BIF2 regulates auxin transport through direct regulation of ZmPIN1a during maize inflorescence development.

  9. Auxin and chloroplast movements. (United States)

    Eckstein, Aleksandra; Krzeszowiec, Weronika; Waligórski, Piotr; Gabryś, Halina


    Auxin is involved in a wide spectrum of physiological processes in plants, including responses controlled by the blue light photoreceptors phototropins: phototropic bending and stomatal movement. However, the role of auxin in phototropin-mediated chloroplast movements has never been studied. To address this question we searched for potential interactions between auxin and the chloroplast movement signaling pathway using different experimental approaches and two model plants, Arabidopsis thaliana and Nicotiana tabacum. We observed that the disturbance of auxin homeostasis by shoot decapitation caused a decrease in chloroplast movement parameters, which could be rescued by exogenous auxin application. In several cases, the impairment of polar auxin transport, by chemical inhibitors or in auxin carrier mutants, had a similar negative effect on chloroplast movements. This inhibition was not correlated with changes in auxin levels. Chloroplast relocations were also affected by the antiauxin p-chlorophenoxyisobutyric acid and mutations in genes encoding some of the elements of the SCF(TIR1)-Aux/IAA auxin receptor complex. The observed changes in chloroplast movement parameters are not prominent, which points to a modulatory role of auxin in this process. Taken together, the obtained results suggest that auxin acts indirectly to regulate chloroplast movements, presumably by regulating gene expression via the SCF(TIR1)-Aux/IAA-ARF pathway. Auxin does not seem to be involved in controlling the expression of phototropins.

  10. An auxin transport mechanism restricts positive orthogravitropism in lateral roots. (United States)

    Rosquete, Michel Ruiz; von Wangenheim, Daniel; Marhavý, Peter; Barbez, Elke; Stelzer, Ernst H K; Benková, Eva; Maizel, Alexis; Kleine-Vehn, Jürgen


    As soon as a seed germinates, plant growth relates to gravity to ensure that the root penetrates the soil and the shoot expands aerially. Whereas mechanisms of positive and negative orthogravitropism of primary roots and shoots are relatively well understood, lateral organs often show more complex growth behavior. Lateral roots (LRs) seemingly suppress positive gravitropic growth and show a defined gravitropic set-point angle (GSA) that allows radial expansion of the root system (plagiotropism). Despite its eminent importance for root architecture, it so far remains completely unknown how lateral organs partially suppress positive orthogravitropism. Here we show that the phytohormone auxin steers GSA formation and limits positive orthogravitropism in LR. Low and high auxin levels/signaling lead to radial or axial root systems, respectively. At a cellular level, it is the auxin transport-dependent regulation of asymmetric growth in the elongation zone that determines GSA. Our data suggest that strong repression of PIN4/PIN7 and transient PIN3 expression limit auxin redistribution in young LR columella cells. We conclude that PIN activity, by temporally limiting the asymmetric auxin fluxes in the tip of LRs, induces transient, differential growth responses in the elongation zone and, consequently, controls root architecture.

  11. A ROP GTPase-dependent auxin signaling pahtway regulates the subcellular distribution of PIN2 in Arabidopsis roots

    NARCIS (Netherlands)

    Lin, D.; Nagawa, S.; Chen, J.; Cao, L.; Scheres, B.


    PIN-FORMED (PIN) protein-mediated auxin polar transport is critically important for development, pattern formation, and morphogenesis in plants. Auxin has been implicated in the regulation of polar auxin transport by inhibiting PIN endocytosis [1 and 2], but how auxin regulates this process is poorl

  12. ROTUNDA3 function in plant development by phosphatase 2A-mediated regulation of auxin transporter recycling. (United States)

    Karampelias, Michael; Neyt, Pia; De Groeve, Steven; Aesaert, Stijn; Coussens, Griet; Rolčík, Jakub; Bruno, Leonardo; De Winne, Nancy; Van Minnebruggen, Annemie; Van Montagu, Marc; Ponce, María Rosa; Micol, José Luis; Friml, Jiří; De Jaeger, Geert; Van Lijsebettens, Mieke


    The shaping of organs in plants depends on the intercellular flow of the phytohormone auxin, of which the directional signaling is determined by the polar subcellular localization of PIN-FORMED (PIN) auxin transport proteins. Phosphorylation dynamics of PIN proteins are affected by the protein phosphatase 2A (PP2A) and the PINOID kinase, which act antagonistically to mediate their apical-basal polar delivery. Here, we identified the ROTUNDA3 (RON3) protein as a regulator of the PP2A phosphatase activity in Arabidopsis thaliana. The RON3 gene was map-based cloned starting from the ron3-1 leaf mutant and found to be a unique, plant-specific gene coding for a protein with high and dispersed proline content. The ron3-1 and ron3-2 mutant phenotypes [i.e., reduced apical dominance, primary root length, lateral root emergence, and growth; increased ectopic stages II, IV, and V lateral root primordia; decreased auxin maxima in indole-3-acetic acid (IAA)-treated root apical meristems; hypergravitropic root growth and response; increased IAA levels in shoot apices; and reduced auxin accumulation in root meristems] support a role for RON3 in auxin biology. The affinity-purified PP2A complex with RON3 as bait suggested that RON3 might act in PIN transporter trafficking. Indeed, pharmacological interference with vesicle trafficking processes revealed that single ron3-2 and double ron3-2 rcn1 mutants have altered PIN polarity and endocytosis in specific cells. Our data indicate that RON3 contributes to auxin-mediated development by playing a role in PIN recycling and polarity establishment through regulation of the PP2A complex activity.

  13. Expression profile of PIN, AUX/LAX and PGP auxin transporter gene families in Sorghum bicolor under phytohormone and abiotic stress. (United States)

    Shen, ChenJia; Bai, YouHuang; Wang, SuiKang; Zhang, SaiNa; Wu, YunRong; Chen, Ming; Jiang, DeAn; Qi, YanHua


    Auxin is transported by the influx carriers auxin resistant 1/like aux1 (AUX/LAX), and the efflux carriers pin-formed (PIN) and P-glycoprotein (PGP), which play a major role in polar auxin transport. Several auxin transporter genes have been characterized in dicotyledonous Arabidopsis, but most are unknown in monocotyledons, especially in sorghum. Here, we analyze the chromosome distribution, gene duplication and intron/exon of SbPIN, SbLAX and SbPGP gene families, and examine their phylogenic relationships in Arabidopsis, rice and sorghum. Real-time PCR analysis demonstrated that most of these genes were differently expressed in the organs of sorghum. SbPIN3 and SbPIN9 were highly expressed in flowers, SbLAX2 and SbPGP17 were mainly expressed in stems, and SbPGP7 was strongly expressed in roots. This suggests that individual genes might participate in specific organ development. The expression profiles of these gene families were analyzed after treatment with: (a) the phytohormones indole-3-acetic acid and brassinosteroid; (b) the polar auxin transport inhibitors 1-naphthoxyacetic acids, 1-naphthylphthalamic acid and 2,3,5-triiodobenzoic acid; and (c) abscissic acid and the abiotic stresses of high salinity and drought. Most of the auxin transporter genes were strongly induced by indole-3-acetic acid and brassinosteroid, providing new evidence for the synergism of these phytohormones. Interestingly, most genes showed similar trends in expression under polar auxin transport inhibitors and each also responded to abscissic acid, salt and drought. This study provides new insights into the auxin transporters of sorghum.

  14. Pinoid kinase regulates root gravitropism through modulation of PIN2-dependent basipetal auxin transport in Arabidopsis thaliana (United States)

    Muday, Gloria; Sukumar, Poornima; Edwards, Karin; Delong, Alison; Rahman, Abidur

    Reversible protein phosphorylation is a key regulatory mechanism governing polar auxin transport. We tested the hypothesis that PINOID (PID)-mediated phosphorylation and RCN1- regulated dephosphorylation might antagonistically regulate auxin transport and gravity response in seedling roots. Here we show that basipetal IAA transport and gravitropism are reduced in pid mutant seedlings, while acropetal transport and lateral root development are unchanged. Treatment of wild-type seedlings with the protein kinase inhibitor, staurosporine, phenocopied the reduced auxin transport and gravity response of pid-9 and reduced formation of asymmetric DR5-revGFP expression at the root tip after reorientation relative to gravity. Gravitropism and auxin transport in pid are resistant to further inhibition by staurosporine. Gravity response defects of rcn1 and pid-9 are partially rescued by treatment with staurosporine or the phosphatase inhibitor, cantharidin, respectively, and in the pid-9 rcn1 double mutant. Furthermore, the effect of staurosporine is lost in pin2, and a PIN2::GFP fusion protein accumulates in endomembrane compartments after staurosporine treatment. In the pid-9 mutant, immunological techniques find a similar PIN2 localization. These data suggest that staurosporine inhibits gravitropism and basipetal IAA transport by blocking PID action and altering PIN2 localization and support the model that PID and RCN1 reciprocally regulate root gravitropic curvature.

  15. Keeping it all together: auxin-actin crosstalk in plant development. (United States)

    Zhu, Jinsheng; Geisler, Markus


    Polar auxin transport and the action of the actin cytoskeleton are tightly interconnected, which is documented by the finding that auxin transporters reach their final destination by active movement of secretory vesicles along F-actin tracks. Moreover, auxin transporter polarity and flexibility is thought to depend on transporter cycling that requires endocytosis and exocytosis of vesicles. In this context, we have reviewed the current literature on an involvement of the actin cytoskeleton in polar auxin transport and identify known similarities and differences in its structure, function and dynamics in comparison to non-plant organisms. By describing how auxin modulates actin expression and actin organization and how actin and its stability affects auxin-transporter endocytosis and recycling, we discuss the current knowledge on regulatory auxin-actin feedback loops. We focus on known effects of auxin and of auxin transport inhibitors on the stability and organization of actin and examine the functionality of auxin and/or auxin transport inhibitor-binding proteins with respect to their suitability to integrate auxin/auxin transport inhibitor action. Finally, we indicate current difficulties in the interpretation of organ, time and concentration-dependent auxin/auxin transport inhibitor treatments and formulate simple future experimental guidelines.

  16. Gibberellins inhibit adventitious rooting in hybrid aspen and Arabidopsis by affecting auxin transport. (United States)

    Mauriat, Mélanie; Petterle, Anna; Bellini, Catherine; Moritz, Thomas


    Knowledge of processes involved in adventitious rooting is important to improve both fundamental understanding of plant physiology and the propagation of numerous plants. Hybrid aspen (Populus tremula × tremuloïdes) plants overexpressing a key gibberellin (GA) biosynthesis gene (AtGA20ox1) grow rapidly but have poor rooting efficiency, which restricts their clonal propagation. Therefore, we investigated the molecular basis of adventitious rooting in Populus and the model plant Arabidopsis. The production of adventitious roots (ARs) in tree cuttings is initiated from the basal stem region, and involves the interplay of several endogenous and exogenous factors. The roles of several hormones in this process have been characterized, but the effects of GAs have not been fully investigated. Here, we show that a GA treatment negatively affects the numbers of ARs produced by wild-type hybrid aspen cuttings. Furthermore, both hybrid aspen plants and intact Arabidopsis seedlings overexpressing AtGA20ox1, PttGID1.1 or PttGID1.3 genes (with a 35S promoter) produce few ARs, although ARs develop from the basal stem region of hybrid aspen and the hypocotyl of Arabidopsis. In Arabidopsis, auxin and strigolactones are known to affect AR formation. Our data show that the inhibitory effect of GA treatment on adventitious rooting is not mediated by perturbation of the auxin signalling pathway, or of the strigolactone biosynthetic and signalling pathways. Instead, GAs appear to act by perturbing polar auxin transport, in particular auxin efflux in hybrid aspen, and both efflux and influx in Arabidopsis.

  17. Activation of Big Grain1 significantly improves grain size by regulating auxin transport in rice. (United States)

    Liu, Linchuan; Tong, Hongning; Xiao, Yunhua; Che, Ronghui; Xu, Fan; Hu, Bin; Liang, Chengzhen; Chu, Jinfang; Li, Jiayang; Chu, Chengcai


    Grain size is one of the key factors determining grain yield. However, it remains largely unknown how grain size is regulated by developmental signals. Here, we report the identification and characterization of a dominant mutant big grain1 (Bg1-D) that shows an extra-large grain phenotype from our rice T-DNA insertion population. Overexpression of BG1 leads to significantly increased grain size, and the severe lines exhibit obviously perturbed gravitropism. In addition, the mutant has increased sensitivities to both auxin and N-1-naphthylphthalamic acid, an auxin transport inhibitor, whereas knockdown of BG1 results in decreased sensitivities and smaller grains. Moreover, BG1 is specifically induced by auxin treatment, preferentially expresses in the vascular tissue of culms and young panicles, and encodes a novel membrane-localized protein, strongly suggesting its role in regulating auxin transport. Consistent with this finding, the mutant has increased auxin basipetal transport and altered auxin distribution, whereas the knockdown plants have decreased auxin transport. Manipulation of BG1 in both rice and Arabidopsis can enhance plant biomass, seed weight, and yield. Taking these data together, we identify a novel positive regulator of auxin response and transport in a crop plant and demonstrate its role in regulating grain size, thus illuminating a new strategy to improve plant productivity.

  18. Gravity-induced modification of auxin transport and distribution for peg formation in cucumber seedlings (United States)

    Kamada, M.; Fujii, N.; Higashitani, A.; Takahashi, H.

    Cucumber seedlings grown in microgravity developed a peg on each side of the transition zone between hypocotyl and root, whereas seedlings grown in a horizontal position on the ground developed a peg on the concave (lower) side of the gravitropically bending transition zone. Using an auxin-inducible gene, CS-IAA1, we showed that upon gravistimulation the auxin concentration on the upper side of the horizontally placed transition zone is reduced to a level below the threshold necessary for peg formation. In this study, to elucidate the role of auxin in the lateral placement of peg formation, we measured the contents of endogenous auxin in the transition zone. The content of free IAA was lower and conjugated IAA was more abundant on the upper side of the transition zone of the gravistimulated seedlings compared with the lower side. These results support the idea that a decrease in auxin level due to a modification of auxin transport or metabolism causes the suppression of peg formation on the upper side of the transition zone in a horizontal position. Cucumber seedlings treated with auxin transport inhibitors exhibited agravitropic growth and developed a peg on each side of the transition zone. Application of auxin transport inhibitors caused an increase in CS-IAA1 mRNA (an auxin-inducible gene) at the transition zone. To analyze auxin transport system for peg formation, we isolated auxin influx carrier, CS-AUX1, and auxin efflux carrier, CS-PIN1, from cucumber plants. The accumulation of CS-AUX1 and CS-PIN1 mRNAs was observed at vascular tissue and epidermis in the transition zone. The level of CS-AUX1 mRNA was lower on the upper side of the transition zone in a horizontal position. The results suggest that the transition zone is an additional source of auxin, and that both influx and efflux of auxin in the cells of the transition zone control cytoplasmic concentration of auxin for peg formation.

  19. Advances on Carriers of Plant Auxin Transport%植物生长素运输载体研究进展

    Institute of Scientific and Technical Information of China (English)

    陈晓阳; 谢文军; 罗海山; 罗红兵


    生长素运输载体通过影响极性运输而作用于植物组织器官的形成、生长等过程.植物中存在三种类型生长素运输载体:AUX1(Auxin Resistant)蛋白、PIN (PIN-FORMED)蛋白家族和MDR/PGP(Multidrug-Resistant/P-glycoprotein)蛋白家族.对拟南芥、玉米、水稻中生长素运输载体的最新研究进行了综述,并对未来可能研究领域提出了展望.%Auxin transport carriers modulate organogenesis and growth by affecting polar auxin transport. Three types of auxin transport carriers have been identified: AUX1 (Auxin Resistant) protein PIN (PIN-FORMED) protein families and MDR/PGP(Multidrug-Resistant/P-glycoprotein) protein families. Recent advances on auxin transport carriers in Arabidopsis, Maize.Rice are summarized,and research perspectives in this field are discussed in this review.

  20. Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response, and lateral root growth (United States)

    Rashotte, A. M.; DeLong, A.; Muday, G. K.; Brown, C. S. (Principal Investigator)


    Auxin transport is required for important growth and developmental processes in plants, including gravity response and lateral root growth. Several lines of evidence suggest that reversible protein phosphorylation regulates auxin transport. Arabidopsis rcn1 mutant seedlings exhibit reduced protein phosphatase 2A activity and defects in differential cell elongation. Here we report that reduced phosphatase activity alters auxin transport and dependent physiological processes in the seedling root. Root basipetal transport was increased in rcn1 or phosphatase inhibitor-treated seedlings but showed normal sensitivity to the auxin transport inhibitor naphthylphthalamic acid (NPA). Phosphatase inhibition reduced root gravity response and delayed the establishment of differential auxin-induced gene expression across a gravity-stimulated root tip. An NPA treatment that reduced basipetal transport in rcn1 and cantharidin-treated wild-type plants also restored a normal gravity response and asymmetric auxin-induced gene expression, indicating that increased basipetal auxin transport impedes gravitropism. Increased auxin transport in rcn1 or phosphatase inhibitor-treated seedlings did not require the AGR1/EIR1/PIN2/WAV6 or AUX1 gene products. In contrast to basipetal transport, root acropetal transport was normal in phosphatase-inhibited seedlings in the absence of NPA, although it showed reduced NPA sensitivity. Lateral root growth also exhibited reduced NPA sensitivity in rcn1 seedlings, consistent with acropetal transport controlling lateral root growth. These results support the role of protein phosphorylation in regulating auxin transport and suggest that the acropetal and basipetal auxin transport streams are differentially regulated.

  1. Localized auxin peaks in concentration-based transport models of the shoot apical meristem. (United States)

    Draelants, Delphine; Avitabile, Daniele; Vanroose, Wim


    We study the formation of auxin peaks in a generic class of concentration-based auxin transport models, posed on static plant tissues. Using standard asymptotic analysis, we prove that, on bounded domains, auxin peaks are not formed via a Turing instability in the active transport parameter, but via simple corrections to the homogeneous steady state. When the active transport is small, the geometry of the tissue encodes the peaks' amplitude and location: peaks arise where cells have fewer neighbours, that is, at the boundary of the domain. We test our theory and perform numerical bifurcation analysis on two models that are known to generate auxin patterns for biologically plausible parameter values. In the same parameter regimes, we find that realistic tissues are capable of generating a multitude of stationary patterns, with a variable number of auxin peaks, that can be selected by different initial conditions or by quasi-static changes in the active transport parameter. The competition between active transport and production rate determines whether peaks remain localized or cover the entire domain. In particular, changes in the auxin production that are fast with respect to the cellular life cycle affect the auxin peak distribution, switching from localized spots to fully patterned states. We relate the occurrence of localized patterns to a snaking bifurcation structure, which is known to arise in a wide variety of nonlinear media, but has not yet been reported in plant models.

  2. Low-fluence red light increases the transport and biosynthesis of auxin. (United States)

    Liu, Xing; Cohen, Jerry D; Gardner, Gary


    In plants, light is an important environmental signal that induces photomorphogenesis and interacts with endogenous signals, including hormones. We found that light increased polar auxin transport in dark-grown Arabidopsis (Arabidopsis thaliana) and tomato (Solanum lycopersicum) hypocotyls. In tomato, this increase was induced by low-fluence red or blue light followed by 1 d of darkness. It was reduced in phyA, phyB1, and phyB2 tomato mutants and was reversed by far-red light applied immediately after the red or blue light exposure, suggesting that phytochrome is involved in this response. We further found that the free indole-3-acetic acid (IAA) level in hypocotyl regions below the hook was increased by red light, while the level of conjugated IAA was unchanged. Analysis of IAA synthesized from [¹³C]indole or [¹³C]tryptophan (Trp) revealed that both Trp-dependent and Trp-independent IAA biosynthesis were increased by low-fluence red light in the top section (meristem, cotyledons, and hook), and the Trp-independent pathway appears to become the primary route for IAA biosynthesis after red light exposure. IAA biosynthesis in tissues below the top section was not affected by red light, suggesting that the increase of free IAA in this region was due to increased transport of IAA from above. Our study provides a comprehensive view of light effects on the transport and biosynthesis of IAA, showing that red light increases both IAA biosynthesis in the top section and polar auxin transport in hypocotyls, leading to unchanged free IAA levels in the top section and increased free IAA levels in the lower hypocotyl regions.

  3. A mutation in protein phosphatase 2A regulatory subunit A affects auxin transport in Arabidopsis (United States)

    Garbers, C.; DeLong, A.; Deruere, J.; Bernasconi, P.; Soll, D.; Evans, M. L. (Principal Investigator)


    The phytohormone auxin controls processes such as cell elongation, root hair development and root branching. Tropisms, growth curvatures triggered by gravity, light and touch, are also auxin-mediated responses. Auxin is synthesized in the shoot apex and transported through the stem, but the molecular mechanism of auxin transport is not well understood. Naphthylphthalamic acid (NPA) and other inhibitors of auxin transport block tropic curvature responses and inhibit root and shoot elongation. We have isolated a novel Arabidopsis thaliana mutant designated roots curl in NPA (rcn1). Mutant seedlings exhibit altered responses to NPA in root curling and hypocotyl elongation. Auxin efflux in mutant seedlings displays increased sensitivity to NPA. The rcn1 mutation was transferred-DNA (T-DNA) tagged and sequences flanking the T-DNA insert were cloned. Analysis of the RCN1 cDNA reveals that the T-DNA insertion disrupts a gene for the regulatory A subunit of protein phosphatase 2A (PP2A-A). The RCN1 gene rescues the rcn1 mutant phenotype and also complements the temperature-sensitive phenotype of the Saccharomyces cerevisiae PP2A-A mutation, tpd3-1. These data implicate protein phosphatase 2A in the regulation of auxin transport in Arabidopsis.

  4. Comprehensive Analysis and Expression Profiling of the OsLAX and OsABCB Auxin Transporter Gene Families in Rice (Oryza sativa under Phytohormone Stimuli and Abiotic Stresses

    Directory of Open Access Journals (Sweden)

    Chenglin eChai


    Full Text Available The plant hormone auxin regulates many aspects of plant growth and developmental processes. Auxin gradient is formed in plant as a result of polar auxin transportation by three types of auxin transporters such as OsLAX, OsPIN, and OsABCB. We report here the analysis of two rice auxin transporter gene families, OsLAX and OsABCB, using bioinformatics tools, publicly accessible microarray data, and quantitative RT-PCR. There are 5 putative OsLAXs and 22 putative OsABCBs in rice genome, which were mapped on 8 chromosomes. The exon-intron structure of OsLAX genes and properties of deduced proteins were relatively conserved within grass family, while that of OsABCB genes varied greatly. Both constitutive and organ/tissue specific expression patterns were observed in OsLAXs and OsABCBs. Analysis of evolutionarily closely related gene pairs together with organ/tissue specific expression revealed possible function gaining and function losing events during rice evolution. Most OsLAX and OsABCB genes were regulated by drought and salt stress, as well as hormonal stimuli [auxin and Abscisic Acid (ABA], which suggests extensive crosstalk between abiotic stresses and hormone signaling pathways. The existence of large number of auxin and stress related cis-regulatory elements in promoter regions might account for their massive responsiveness of these genes to these environmental stimuli, indicating complexity of regulatory networks involved in various developmental and physiological processes. The comprehensive analysis of OsLAX and OsABCB auxin transporter genes in this study would be helpful for understanding the biological significance of these gene families in hormone signaling and adaptation of rice plants to unfavorable environments.

  5. MAB4-induced auxin sink generates local auxin gradients in Arabidopsis organ formation. (United States)

    Furutani, Masahiko; Nakano, Yasukazu; Tasaka, Masao


    In Arabidopsis, leaves and flowers form cyclically in the shoot meristem periphery and are triggered by local accumulations of the plant hormone auxin. Auxin maxima are established by the auxin efflux carrier PIN-formed1 (PIN1). During organ formation, two distinct types of PIN1 polarization occur. First, convergence of PIN1 polarity in the surface of the meristem creates local auxin peaks. Second, basipetal PIN1 polarization causes auxin to move away from the surface in the middle of an incipient organ primordium, thought to contribute to vascular formation. Several mathematical models have been developed in attempts to explain the PIN1 localization pattern. However, the molecular mechanisms that control these dynamic changes are unknown. Here, we show that loss-of-function in the MACCHI-BOU 4 (MAB4) family genes, which encode nonphototropic hypocotyl 3-like proteins and regulate PIN endocytosis, cause deletion of basipetal PIN1 polarization, resulting in extensive auxin accumulation all over the meristem surface from lack of a sink for auxin. These results indicate that the MAB4 family genes establish inward auxin transport from the L1 surface of incipient organ primordia by basipetal PIN1 polarization, and that this behavior is essential for the progression of organ development. Furthermore, the expression of the MAB4 family genes depends on auxin response. Our results define two distinct molecular mechanisms for PIN1 polarization during organ development and indicate that an auxin response triggers the switching between these two mechanisms.

  6. D6PK AGCVIII kinases are required for auxin transport and phototropic hypocotyl bending in Arabidopsis. (United States)

    Willige, Björn C; Ahlers, Siv; Zourelidou, Melina; Barbosa, Inês C R; Demarsy, Emilie; Trevisan, Martine; Davis, Philip A; Roelfsema, M Rob G; Hangarter, Roger; Fankhauser, Christian; Schwechheimer, Claus


    Phototropic hypocotyl bending in response to blue light excitation is an important adaptive process that helps plants to optimize their exposure to light. In Arabidopsis thaliana, phototropic hypocotyl bending is initiated by the blue light receptors and protein kinases phototropin1 (phot1) and phot2. Phototropic responses also require auxin transport and were shown to be partially compromised in mutants of the PIN-FORMED (PIN) auxin efflux facilitators. We previously described the D6 PROTEIN KINASE (D6PK) subfamily of AGCVIII kinases, which we proposed to directly regulate PIN-mediated auxin transport. Here, we show that phototropic hypocotyl bending is strongly dependent on the activity of D6PKs and the PIN proteins PIN3, PIN4, and PIN7. While early blue light and phot-dependent signaling events are not affected by the loss of D6PKs, we detect a gradual loss of PIN3 phosphorylation in d6pk mutants of increasing complexity that is most severe in the d6pk d6pkl1 d6pkl2 d6pkl3 quadruple mutant. This is accompanied by a reduction of basipetal auxin transport in the hypocotyls of d6pk as well as in pin mutants. Based on our data, we propose that D6PK-dependent PIN regulation promotes auxin transport and that auxin transport in the hypocotyl is a prerequisite for phot1-dependent hypocotyl bending.

  7. Roles of auxin transport and action in the gravity-regulated morphogenesis of cucumber seedlings (United States)

    Saito, Y.; Shimizu, M.; Hotta, T.; Dai-Hee, K.; Yanai, K.; Kamada, M.; Fujii, N.; Miyazawa, Y.; Takahashi, H.

    Cucumber Cucumis sativus L seedlings develop a specialized protuberance peg on the lower side of the transition zone between the hypocotyl and the root when seeds germinate in a horizontal position The peg plays an important role in pulling seedling out from the seed coat We have reported that cucumber seedlings potentially develop a peg on each side of the transition zone but peg development on the upper side is suppressed in response to gravity Auxin is the primary factor responsible for the induction or the suppression of peg formation Here we investigated the roles of auxin transport and action in the gravity-regulated formation suppression of the peg in cucumber seedlings When cucumber seedlings were treated with inhibitors of auxin efflux carrier a peg was formed not only on the lower side but also on the upper side of the gravistimulated transition zone suggesting that activation of auxin efflux carriers is required for the suppression of peg formation To identify auxin efflux carriers involved in the suppression of peg formation by graviresponse we isolated six cucumber cDNAs of PIN auxin efflux carrier genes and investigated their mRNA accumulation and protein expression Our results show that CsPIN1 and CsPIN6 could play a role in the redistribution of auxin in the transition zone To understand auxin action on peg formation suppression we next examined the transcriptional regulators for the expressions of auxin-responsive genes The results suggest that a higher level of auxin in the lower side of the

  8. Ethylene regulates root growth through effects on auxin biosynthesis and transport-dependent auxin distribution



    In plants, each developmental process integrates a network of signaling events that are regulated by different phytohormones, and interactions among hormonal pathways are essential to modulate their effect. Continuous growth of roots results from the postembryonic activity of cells within the root meristem that is controlled by the coordinated action of several phytohormones, including auxin and ethylene. Although their interaction has been studied intensively, the molecular and cellular mech...

  9. Regulation of Auxin Transport by Phosphorylation and Flavonoids during Gravitropism in Arabidopsis (United States)

    Muday, Gloria K.


    The focus of this research includes: 1) Regulation of Axin transport by flavonoids during gravitropism; 2) Phosphorylation control of auxin transport during gravity response; 3) Ethylene regulation of gravitropic curvature; 4) IBA transport and gravitropic response; and 5) Other collaborative projects.

  10. Revisiting Apoplastic Auxin Signaling Mediated by AUXIN BINDING PROTEIN 1. (United States)

    Feng, Mingxiao; Kim, Jae-Yean


    It has been suggested that AUXIN BINDING PROTEIN 1 (ABP1) functions as an apoplastic auxin receptor, and is known to be involved in the post-transcriptional process, and largely independent of the already well-known SKP-cullin-F-box-transport inhibitor response (TIR1) /auxin signaling F-box (AFB) (SCF(TIR1/AFB)) pathway. In the past 10 years, several key components downstream of ABP1 have been reported. After perceiving the auxin signal, ABP1 interacts, directly or indirectly, with plasma membrane (PM)-localized transmembrane proteins, transmembrane kinase (TMK) or SPIKE1 (SPK1), or other unidentified proteins, which transfer the signal into the cell to the Rho of plants (ROP). ROPs interact with their effectors, such as the ROP interactive CRIB motif-containing protein (RIC), to regulate the endocytosis/exocytosis of the auxin efflux carrier PIN-FORMED (PIN) proteins to mediate polar auxin transport across the PM. Additionally, ABP1 is a negative regulator of the traditional SCF(TIR1/AFB) auxin signaling pathway. However, Gao et al. (2015) very recently reported that ABP1 is not a key component in auxin signaling, and the famous abp1-1 and abp1-5 mutant Arabidopsis lines are being called into question because of possible additional mutantion sites, making it necessary to reevaluate ABP1. In this review, we will provide a brief overview of the history of ABP1 research.

  11. Action of Abscisic Acid on Auxin Transport and its Relation to Phototropism

    DEFF Research Database (Denmark)

    Naqvi, S. M.; Engvild, Kjeld Christensen


    The action of abscisic acid on the kinetics of auxin transport through Zea mays L. (cv. Goudster) coleoptiles has been investigated. Abscisic acid applied simultaneously with indoleacetic acid-2-14C in the donor block reduced the transport intensity without materially affecting the basipetal...

  12. Auxin influx inhibitors 1-NOA, 2-NOA, and CHPAA interfere with membrane dynamics in tobacco cells. (United States)

    Lanková, Martina; Smith, Richard S; Pesek, Bedrich; Kubes, Martin; Zazímalová, Eva; Petrásek, Jan; Hoyerová, Klára


    The phytohormone auxin is transported through the plant body either via vascular pathways or from cell to cell by specialized polar transport machinery. This machinery consists of a balanced system of passive diffusion combined with the activities of auxin influx and efflux carriers. Synthetic auxins that differ in the mechanisms of their transport across the plasma membrane together with polar auxin transport inhibitors have been used in many studies on particular auxin carriers and their role in plant development. However, the exact mechanism of action of auxin efflux and influx inhibitors has not been fully elucidated. In this report, the mechanism of action of the auxin influx inhibitors (1-naphthoxyacetic acid (1-NOA), 2-naphthoxyacetic acid (2-NOA), and 3-chloro-4-hydroxyphenylacetic acid (CHPAA)) is examined by direct measurements of auxin accumulation, cellular phenotypic analysis, as well as by localization studies of Arabidopsis thaliana L. auxin carriers heterologously expressed in Nicotiana tabacum L., cv. Bright Yellow cell suspensions. The mode of action of 1-NOA, 2-NOA, and CHPAA has been shown to be linked with the dynamics of the plasma membrane. The most potent inhibitor, 1-NOA, blocked the activities of both auxin influx and efflux carriers, whereas 2-NOA and CHPAA at the same concentration preferentially inhibited auxin influx. The results suggest that these, previously unknown, activities of putative auxin influx inhibitors regulate overall auxin transport across the plasma membrane depending on the dynamics of particular membrane vesicles.

  13. Separating the roles of acropetal and basipetal auxin transport on gravitropism with mutations in two Arabidopsis multidrug resistance-like ABC transporter genes. (United States)

    Lewis, Daniel R; Miller, Nathan D; Splitt, Bessie L; Wu, Guosheng; Spalding, Edgar P


    Two Arabidopsis thaliana ABC transporter genes linked to auxin transport by various previous results were studied in a reverse-genetic fashion. Mutations in Multidrug Resistance-Like1 (MDR1) reduced acropetal auxin transport in roots by 80% without affecting basipetal transport. Conversely, mutations in MDR4 blocked 50% of basipetal transport without affecting acropetal transport. Developmental and auxin distribution phenotypes associated with these altered auxin flows were studied with a high-resolution morphometric system and confocal microscopy, respectively. Vertically grown mdr1 roots produced positive and negative curvatures threefold greater than the wild type, possibly due to abnormal auxin distribution observed in the elongation zone. However, upon 90 degrees reorientation, mdr1 gravitropism was inseparable from the wild type. Thus, acropetal auxin transport maintains straight growth but contributes surprisingly little to gravitropism. Conversely, vertically maintained mdr4 roots grew as straight as the wild type, but their gravitropism was enhanced. Upon reorientation, curvature in this mutant developed faster, was distributed more basally, and produced a greater total angle than the wild type. An amplified auxin asymmetry may explain the mdr4 hypertropism. Double mutant analysis indicated that the two auxin transport streams are more independent than interdependent. The hypothesis that flavanols regulate MDR-dependent auxin transport was supported by the epistatic relationship of mdr4 to the tt4 phenylpropanoid pathway mutation.

  14. Non-invasive quantification of endogenous root auxin transport using an integrated flux microsensor technique. (United States)

    McLamore, Eric S; Diggs, Alfred; Calvo Marzal, Percy; Shi, Jin; Blakeslee, Joshua J; Peer, Wendy A; Murphy, Angus S; Porterfield, D Marshall


    Indole-3-acetic acid (IAA) is a primary phytohormone that regulates multiple aspects of plant development. Because polar transport of IAA is an essential determinant of organogenesis and dynamic tropic growth, methods to monitor IAA movement in vivo are in demand. A self-referencing electrochemical microsensor was optimized to non-invasively measure endogenous IAA flux near the surface of Zea mays roots without the addition of exogenous IAA. Enhanced sensor surface modification, decoupling of acquired signals, and integrated flux analyses were combined to provide direct, real time quantification of endogenous IAA movement in B73 maize inbred and brachytic2 (br2) auxin transport mutant roots. BR2 is localized in epidermal and hypodermal tissues at the root apex. br2 roots exhibit reduced shootward IAA transport at the root apex in radiotracer experiments and reduced gravitropic growth. IAA flux data indicates that maximal transport occurs in the distal elongation zone of maize roots, and net transport in/out of br2 roots was decreased compared to B73. Integration of short term real time flux data in this zone revealed oscillatory patterns, with B73 exhibiting shorter oscillatory periods and greater amplitude than br2. IAA efflux and influx were inhibited using 1-N-naphthylphthalamic acid (NPA), and 2-naphthoxyacetic acid (NOA), respectively. A simple harmonic oscillation model of these data produced a correlation between modeled and measured values of 0.70 for B73 and 0.69 for br2. These results indicate that this technique is useful for real-time IAA transport monitoring in surface tissues and that this approach can be performed simultaneously with current live imaging techniques.

  15. Antagonistic regulation of PIN phosphorylation by PP2A and PINOID directs auxin flux

    NARCIS (Netherlands)

    Michniewicz, M.; Zago, M.K.; Abas, L.; Weijers, D.; Schweighofer, A.; Meskiene, I.; Heisler, M.G.; Ohno, C.; Zhang, J.; Huang, F.; Schwab, R.; Weigel, D.; Meyerowitz, E.M.; Luschnig, C.; Offringa, R.; Friml, J.


    In plants, cell polarity and tissue patterning are connected by intercellular flow of the phytohormone auxin, whose directional signaling depends on polar subcellular localization of PIN auxin transport proteins. The mechanism of polar targeting of PINs or other cargos in plants is largely unidentif

  16. Auxin-driven patterning with unidirectional fluxes. (United States)

    Cieslak, Mikolaj; Runions, Adam; Prusinkiewicz, Przemyslaw


    The plant hormone auxin plays an essential role in the patterning of plant structures. Biological hypotheses supported by computational models suggest that auxin may fulfil this role by regulating its own transport, but the plausibility of previously proposed models has been questioned. We applied the notion of unidirectional fluxes and the formalism of Petri nets to show that the key modes of auxin-driven patterning-the formation of convergence points and the formation of canals-can be implemented by biochemically plausible networks, with the fluxes measured by dedicated tally molecules or by efflux and influx carriers themselves. Common elements of these networks include a positive feedback of auxin efflux on the allocation of membrane-bound auxin efflux carriers (PIN proteins), and a modulation of this allocation by auxin in the extracellular space. Auxin concentration in the extracellular space is the only information exchanged by the cells. Canalization patterns are produced when auxin efflux and influx act antagonistically: an increase in auxin influx or concentration in the extracellular space decreases the abundance of efflux carriers in the adjacent segment of the membrane. In contrast, convergence points emerge in networks in which auxin efflux and influx act synergistically. A change in a single reaction rate may result in a dynamic switch between these modes, suggesting plausible molecular implementations of coordinated patterning of organ initials and vascular strands predicted by the dual polarization theory.

  17. Auxin transport through PIN-FORMED 3 (PIN3) controls shade avoidance and fitness during competition (United States)

    Keuskamp, Diederik H.; Pollmann, Stephan; Voesenek, Laurentius A. C. J.; Peeters, Anton J. M.; Pierik, Ronald


    Plants grow in dense vegetations at the risk of being out-competed by neighbors. To increase their competitive power, plants display adaptive responses, such as rapid shoot elongation (shade avoidance) to consolidate light capture. These responses are induced upon detection of proximate neighbors through perception of the reduced ratio between red (R) and far-red (FR) light that is typical for dense vegetations. The plant hormone auxin is a central regulator of plant development and plasticity, but until now it has been unknown how auxin transport is controlled to regulate shade-avoidance responses. Here, we show that low R:FR detection changes the cellular location of the PIN-FORMED 3 (PIN3) protein, a regulator of auxin efflux, in Arabidopsis seedlings. As a result, auxin levels in the elongating hypocotyls are increased under low R:FR. Seedlings of the pin3-3 mutant lack this low R:FR-induced increase of endogenous auxin in the hypocotyl and, accordingly, have no elongation response to low R:FR. We hypothesize that low R:FR-induced stimulation of auxin biosynthesis drives the regulation of PIN3, thus allowing shade avoidance to occur. The adaptive significance of PIN3-mediated control of shade-avoidance is shown in plant competition studies. It was found that pin3 mutants are outcompeted by wild-type neighbors who suppress fitness of pin3-3 by 40%. We conclude that low R:FR modulates the auxin distribution by a change in the cellular location of PIN3, and that this control can be of great importance for plants growing in dense vegetations. PMID:21149713

  18. Transport and Metabolism of the Endogenous Auxin Precursor lndole-3-Butyric Acid

    Institute of Scientific and Technical Information of China (English)

    Lucia C. Strader; Bonnie Bartel


    T Plant growth and morphogenesis depend on the levels and distribution of the plant hormone auxin. Plants tightly regulate cellular levels of the active auxin indole-3-acetic acid (IAA) through synthesis, inactivation, and transport. Although the transporters that move IAA into and out of cells are well characterized and play important roles in development, little is known about the transport of IAA precursors. In this review, we discuss the accumulating evidence suggesting that the IAA precursor indole-3-butyric acid (IBA) is transported independently of the characterized IAA transport machinery along with the recent identification of specific IBA efflux carriers and enzymes suggested to metabolize IBA. These studies have revealed important roles for IBA in maintaining IAA levels and distribution within the plant to support normal development.

  19. Auxin and its transport play a role in plant tolerance to arsenite-induced oxidative stress in Arabidopsis thaliana. (United States)

    Krishnamurthy, Aparna; Rathinasabapathi, Bala


    The role of auxin in plant development is well known; however, its possible function in root response to abiotic stress is poorly understood. In this study, we demonstrate a novel role of auxin transport in plant tolerance to oxidative stress caused by arsenite. Plant response to arsenite [As(III)] was evaluated by measuring root growth and markers for stress on seedlings treated with control or As(III)-containing medium. Auxin transporter mutants aux1, pin1 and pin2 were significantly more sensitive to As(III) than the wild type (WT). Auxin transport inhibitors significantly reduced plant tolerance to As(III) in the WT, while exogenous supply of indole-3-acetic acid improved As(III) tolerance of aux1 and not that of WT. Uptake assays using H(3) -IAA showed As(III) affected auxin transport in WT roots. As(III) increased the levels of H2 O2 in WT but not in aux1, suggesting a positive role for auxin transport through AUX1 on plant tolerance to As(III) stress via reactive oxygen species (ROS)-mediated signalling. Compared to the WT, the mutant aux1 was significantly more sensitive to high-temperature stress and salinity, also suggesting auxin transport influences a common element shared by plant tolerance to arsenite, salinity and high-temperature stress.

  20. Local auxin sources orient the apical-basal axis in Arabidopsis embryos. (United States)

    Robert, Hélène S; Grones, Peter; Stepanova, Anna N; Robles, Linda M; Lokerse, Annemarie S; Alonso, Jose M; Weijers, Dolf; Friml, Jiří


    Establishment of the embryonic axis foreshadows the main body axis of adults both in plants and in animals, but underlying mechanisms are considered distinct. Plants utilize directional, cell-to-cell transport of the growth hormone auxin to generate an asymmetric auxin response that specifies the embryonic apical-basal axis. The auxin flow directionality depends on the polarized subcellular localization of PIN-FORMED (PIN) auxin transporters. It remains unknown which mechanisms and spatial cues guide cell polarization and axis orientation in early embryos. Herein, we provide conceptually novel insights into the formation of embryonic axis in Arabidopsis by identifying a crucial role of localized tryptophan-dependent auxin biosynthesis. Local auxin production at the base of young embryos and the accompanying PIN7-mediated auxin flow toward the proembryo are required for the apical auxin response maximum and the specification of apical embryonic structures. Later in embryogenesis, the precisely timed onset of localized apical auxin biosynthesis mediates PIN1 polarization, basal auxin response maximum, and specification of the root pole. Thus, the tight spatiotemporal control of distinct local auxin sources provides a necessary, non-cell-autonomous trigger for the coordinated cell polarization and subsequent apical-basal axis orientation during embryogenesis and, presumably, also for other polarization events during postembryonic plant life.

  1. Auxin biosynthesis and storage forms. (United States)

    Korasick, David A; Enders, Tara A; Strader, Lucia C


    The plant hormone auxin drives plant growth and morphogenesis. The levels and distribution of the active auxin indole-3-acetic acid (IAA) are tightly controlled through synthesis, inactivation, and transport. Many auxin precursors and modified auxin forms, used to regulate auxin homeostasis, have been identified; however, very little is known about the integration of multiple auxin biosynthesis and inactivation pathways. This review discusses the many ways auxin levels are regulated through biosynthesis, storage forms, and inactivation, and the potential roles modified auxins play in regulating the bioactive pool of auxin to affect plant growth and development.

  2. Enquiry into the Topology of Plasma Membrane-Localized PIN Auxin Transport Components. (United States)

    Nodzyński, Tomasz; Vanneste, Steffen; Zwiewka, Marta; Pernisová, Markéta; Hejátko, Jan; Friml, Jiří


    Auxin directs plant ontogenesis via differential accumulation within tissues depending largely on the activity of PIN proteins that mediate auxin efflux from cells and its directional cell-to-cell transport. Regardless of the developmental importance of PINs, the structure of these transporters is poorly characterized. Here, we present experimental data concerning protein topology of plasma membrane-localized PINs. Utilizing approaches based on pH-dependent quenching of fluorescent reporters combined with immunolocalization techniques, we mapped the membrane topology of PINs and further cross-validated our results using available topology modeling software. We delineated the topology of PIN1 with two transmembrane (TM) bundles of five α-helices linked by a large intracellular loop and a C-terminus positioned outside the cytoplasm. Using constraints derived from our experimental data, we also provide an updated position of helical regions generating a verisimilitude model of PIN1. Since the canonical long PINs show a high degree of conservation in TM domains and auxin transport capacity has been demonstrated for Arabidopsis representatives of this group, this empirically enhanced topological model of PIN1 will be an important starting point for further studies on PIN structure-function relationships. In addition, we have established protocols that can be used to probe the topology of other plasma membrane proteins in plants.

  3. Auxin physiology of the tomato mutant diageotropica (United States)

    Daniel, S. G.; Rayle, D. L.; Cleland, R. E.


    The tomato (Lycopersicon esculentum, Mill.) mutant diageotropica (dgt) exhibits biochemical, physiological, and morphological abnormalities that suggest the mutation may have affected a primary site of auxin perception or action. We have compared two aspects of the auxin physiology of dgt and wild-type (VFN8) seedlings: auxin transport and cellular growth parameters. The rates of basipetal indole-3-acetic acid (IAA) polar transport are identical in hypocotyl sections of the two genotypes, but dgt sections have a slightly greater capacity for IAA transport. 2,3,5-Triiodobenzoic acid and ethylene reduce transport in both mutant and wild-type sections. The kinetics of auxin uptake into VFN8 and dgt sections are nearly identical. These results make it unlikely that an altered IAA efflux carrier or IAA uptake symport are responsible for the pleiotropic effects resulting from the dgt mutation. The lack of auxin-induced cell elongation in dgt plants is not due to insufficient turgor, as the osmotic potential of dgt cell sap is less (more negative) than that of VFN8. An auxin-induced increase in wall extensibility, as measured by the Instron technique, only occurs in the VFN8 plants. These data suggest dgt hypocotyls suffer a defect in the sequence of events culminating in auxin-induced cell wall loosening.

  4. D6PK AGCVIII Kinases Are Required for Auxin Transport and Phototropic Hypocotyl Bending in Arabidopsis[C][W (United States)

    Willige, Björn C.; Ahlers, Siv; Zourelidou, Melina; Barbosa, Inês C.R.; Demarsy, Emilie; Trevisan, Martine; Davis, Philip A.; Roelfsema, M. Rob G.; Hangarter, Roger; Fankhauser, Christian; Schwechheimer, Claus


    Phototropic hypocotyl bending in response to blue light excitation is an important adaptive process that helps plants to optimize their exposure to light. In Arabidopsis thaliana, phototropic hypocotyl bending is initiated by the blue light receptors and protein kinases phototropin1 (phot1) and phot2. Phototropic responses also require auxin transport and were shown to be partially compromised in mutants of the PIN-FORMED (PIN) auxin efflux facilitators. We previously described the D6 PROTEIN KINASE (D6PK) subfamily of AGCVIII kinases, which we proposed to directly regulate PIN-mediated auxin transport. Here, we show that phototropic hypocotyl bending is strongly dependent on the activity of D6PKs and the PIN proteins PIN3, PIN4, and PIN7. While early blue light and phot-dependent signaling events are not affected by the loss of D6PKs, we detect a gradual loss of PIN3 phosphorylation in d6pk mutants of increasing complexity that is most severe in the d6pk d6pkl1 d6pkl2 d6pkl3 quadruple mutant. This is accompanied by a reduction of basipetal auxin transport in the hypocotyls of d6pk as well as in pin mutants. Based on our data, we propose that D6PK-dependent PIN regulation promotes auxin transport and that auxin transport in the hypocotyl is a prerequisite for phot1-dependent hypocotyl bending. PMID:23709629

  5. OsPIN5b modulates rice (Oryza sativa) plant architecture and yield by changing auxin homeostasis, transport and distribution. (United States)

    Lu, Guangwen; Coneva, Viktoriya; Casaretto, José A; Ying, Shan; Mahmood, Kashif; Liu, Fang; Nambara, Eiji; Bi, Yong-Mei; Rothstein, Steven J


    Plant architecture attributes such as tillering, plant height and panicle size are important agronomic traits that determine rice (Oryza sativa) productivity. Here, we report that altered auxin content, transport and distribution affect these traits, and hence rice yield. Overexpression of the auxin efflux carrier-like gene OsPIN5b causes pleiotropic effects, mainly reducing plant height, leaf and tiller number, shoot and root biomass, seed-setting rate, panicle length and yield parameters. Conversely, reduced expression of OsPIN5b results in higher tiller number, more vigorous root system, longer panicles and increased yield. We show that OsPIN5b is an endoplasmic reticulum (ER) -localized protein that participates in auxin homeostasis, transport and distribution in vivo. This work describes an example of an auxin-related gene where modulating its expression can simultaneously improve plant architecture and yield potential in rice, and reveals an important effect of hormonal signaling on these traits.

  6. Genome-wide identification and expression profiling analysis of ZmPIN, ZmPILS, ZmLAX and ZmABCB auxin transporter gene families in maize (Zea mays L. under various abiotic stresses.

    Directory of Open Access Journals (Sweden)

    Runqing Yue

    Full Text Available The auxin influx carriers auxin resistant 1/like aux 1 (AUX/LAX, efflux carriers pin-formed (PIN (together with PIN-like proteins and efflux/conditional P-glycoprotein (ABCB are major protein families involved in auxin polar transport. However, how they function in responses to exogenous auxin and abiotic stresses in maize is largely unknown. In this work, the latest updated maize (Zea mays L. reference genome sequence was used to characterize and analyze the ZmLAX, ZmPIN, ZmPILS and ZmABCB family genes from maize. The results showed that five ZmLAXs, fifteen ZmPINs, nine ZmPILSs and thirty-five ZmABCBs were mapped on all ten maize chromosomes. Highly diversified gene structures, nonconservative transmembrane helices and tissue-specific expression patterns suggested the possibility of function diversification for these genes. Quantitative real-time polymerase chain reaction (qRT-PCR was used to analyze the expression patterns of ZmLAX, ZmPIN, ZmPILS and ZmABCB genes under exogenous auxin and different environmental stresses. The expression levels of most ZmPIN, ZmPILS, ZmLAX and ZmABCB genes were induced in shoots and were reduced in roots by various abiotic stresses (drought, salt and cold stresses. The opposite expression response patterns indicated the dynamic auxin transport between shoots and roots under abiotic stresses. Analysis of the expression patterns of ZmPIN, ZmPILS, ZmLAX and ZmABCB genes under drought, salt and cold treatment may help us to understand the possible roles of maize auxin transporter genes in responses and tolerance to environmental stresses.

  7. Pavement cells: a model system for non-transcriptional auxin signalling and crosstalks. (United States)

    Chen, Jisheng; Wang, Fei; Zheng, Shiqin; Xu, Tongda; Yang, Zhenbiao


    Auxin (indole acetic acid) is a multifunctional phytohormone controlling various developmental patterns, morphogenetic processes, and growth behaviours in plants. The transcription-based pathway activated by the nuclear TRANSPORT INHIBITOR RESISTANT 1/auxin-related F-box auxin receptors is well established, but the long-sought molecular mechanisms of non-transcriptional auxin signalling remained enigmatic until very recently. Along with the establishment of the Arabidopsis leaf epidermal pavement cell (PC) as an exciting and amenable model system in the past decade, we began to gain insight into non-transcriptional auxin signalling. The puzzle-piece shape of PCs forms from intercalated or interdigitated cell growth, requiring local intra- and inter-cellular coordination of lobe and indent formation. Precise coordination of this interdigitated pattern requires auxin and an extracellular auxin sensing system that activates plasma membrane-associated Rho GTPases from plants and subsequent downstream events regulating cytoskeletal reorganization and PIN polarization. Apart from auxin, mechanical stress and cytokinin have been shown to affect PC interdigitation, possibly by interacting with auxin signals. This review focuses upon signalling mechanisms for cell polarity formation in PCs, with an emphasis on non-transcriptional auxin signalling in polarized cell expansion and pattern formation and how different auxin pathways interplay with each other and with other signals.

  8. D6 PROTEIN KINASE activates auxin transport-dependent growth and PIN-FORMED phosphorylation at the plasma membrane. (United States)

    Barbosa, Inês C R; Zourelidou, Melina; Willige, Björn C; Weller, Benjamin; Schwechheimer, Claus


    The directed cell-to-cell transport of the phytohormone auxin by efflux and influx transporters is essential for proper plant growth and development. Like auxin efflux facilitators of the PIN-FORMED (PIN) family, D6 PROTEIN KINASE (D6PK) from Arabidopsis thaliana localizes to the basal plasma membrane of many cells, and evidence exists that D6PK may directly phosphorylate PINs. We find that D6PK is a membrane-bound protein that is associated with either the basal domain of the plasma membrane or endomembranes. Inhibition of the trafficking regulator GNOM leads to a rapid internalization of D6PK to endomembranes. Interestingly, the dissociation of D6PK from the plasma membrane is also promoted by auxin. Surprisingly, we find that auxin transport-dependent tropic responses are critically and reversibly controlled by D6PK and D6PK-dependent PIN phosphorylation at the plasma membrane. We conclude that D6PK abundance at the plasma membrane and likely D6PK-dependent PIN phosphorylation are prerequisites for PIN-mediated auxin transport.

  9. Phytochrome B promotes branching in Arabidopsis by suppressing auxin signaling. (United States)

    Krishna Reddy, Srirama; Finlayson, Scott A


    Many plants respond to competition signals generated by neighbors by evoking the shade avoidance syndrome, including increased main stem elongation and reduced branching. Vegetation-induced reduction in the red light:far-red light ratio provides a competition signal sensed by phytochromes. Plants deficient in phytochrome B (phyB) exhibit a constitutive shade avoidance syndrome including reduced branching. Because auxin in the polar auxin transport stream (PATS) inhibits axillary bud outgrowth, its role in regulating the phyB branching phenotype was tested. Removing the main shoot PATS auxin source by decapitation or chemically inhibiting the PATS strongly stimulated branching in Arabidopsis (Arabidopsis thaliana) deficient in phyB, but had a modest effect in the wild type. Whereas indole-3-acetic acid (IAA) levels were elevated in young phyB seedlings, there was less IAA in mature stems compared with the wild type. A split plate assay of bud outgrowth kinetics indicated that low auxin levels inhibited phyB buds more than the wild type. Because the auxin response could be a result of either the auxin signaling status or the bud's ability to export auxin into the main shoot PATS, both parameters were assessed. Main shoots of phyB had less absolute auxin transport capacity compared with the wild type, but equal or greater capacity when based on the relative amounts of native IAA in the stems. Thus, auxin transport capacity was unlikely to restrict branching. Both shoots of young phyB seedlings and mature stem segments showed elevated expression of auxin-responsive genes and expression was further increased by auxin treatment, suggesting that phyB suppresses auxin signaling to promote branching.

  10. Stochastic and deterministic multiscale models for systems biology: an auxin-transport case study

    Directory of Open Access Journals (Sweden)

    King John R


    Full Text Available Abstract Background Stochastic and asymptotic methods are powerful tools in developing multiscale systems biology models; however, little has been done in this context to compare the efficacy of these methods. The majority of current systems biology modelling research, including that of auxin transport, uses numerical simulations to study the behaviour of large systems of deterministic ordinary differential equations, with little consideration of alternative modelling frameworks. Results In this case study, we solve an auxin-transport model using analytical methods, deterministic numerical simulations and stochastic numerical simulations. Although the three approaches in general predict the same behaviour, the approaches provide different information that we use to gain distinct insights into the modelled biological system. We show in particular that the analytical approach readily provides straightforward mathematical expressions for the concentrations and transport speeds, while the stochastic simulations naturally provide information on the variability of the system. Conclusions Our study provides a constructive comparison which highlights the advantages and disadvantages of each of the considered modelling approaches. This will prove helpful to researchers when weighing up which modelling approach to select. In addition, the paper goes some way to bridging the gap between these approaches, which in the future we hope will lead to integrative hybrid models.

  11. Posttranslational modification and trafficking of PIN auxin efflux carriers. (United States)

    Löfke, Christian; Luschnig, Christian; Kleine-Vehn, Jürgen


    Cell-to-cell communication is absolutely essential for multicellular organisms. Both animals and plants use chemicals called hormones for intercellular signaling. However, multicellularity of plants and animals has evolved independently, which led to establishment of distinct strategies in order to cope with variations in an ever-changing environment. The phytohormone auxin is crucial to plant development and patterning. PIN auxin efflux carrier-driven polar auxin transport regulates plant development as it controls asymmetric auxin distribution (auxin gradients), which in turn modulates a wide range of developmental processes. Internal and external cues trigger a number of posttranslational PIN auxin carrier modifications that were demonstrated to decisively influence variations in adaptive growth responses. In this review, we highlight recent advances in the analysis of posttranslational modification of PIN auxin efflux carriers, such as phosphorylation and ubiquitylation, and discuss their eminent role in directional vesicle trafficking, PIN protein de-/stabilization and auxin transport activity. We conclude with updated models, in which we attempt to integrate the mechanistic relevance of posttranslational modifications of PIN auxin carriers for the dynamic nature of plant development.

  12. Auxin: simply complicated. (United States)

    Sauer, Michael; Robert, Stéphanie; Kleine-Vehn, Jürgen


    Auxin is a plant hormone involved in an extraordinarily broad variety of biological mechanisms. These range from basic cellular processes, such as endocytosis, cell polarity, and cell cycle control over localized responses such as cell elongation and differential growth, to macroscopic phenomena such as embryogenesis, tissue patterning, and de novo formation of organs. Even though the history of auxin research reaches back more than a hundred years, we are still far from a comprehensive understanding of how auxin governs such a wide range of responses. Some answers to this question may lie in the auxin molecule itself. Naturally occurring auxin-like substances have been found and they may play roles in specific developmental and cellular processes. The molecular mode of auxin action can be further explored by the utilization of synthetic auxin-like molecules. A second area is the perception of auxin, where we know of three seemingly independent receptors and signalling systems, some better understood than others, but each of them probably involved in distinct physiological processes. Lastly, auxin is actively modified, metabolized, and intracellularly compartmentalized, which can have a great impact on its availability and activity. In this review, we will give an overview of these rather recent and emerging areas of auxin research and try to formulate some of the open questions. Without doubt, the manifold facets of auxin biology will not cease to amaze us for a long time to come.

  13. Morphometric Analysis of Auxin-Mediated Development (United States)

    Lewis, Daniel

    Auxin controls many aspects of plant development through its effects on growth. Its distribution is controlled by specific tissue and organ level polar transport streams. The responses to environmental cues such as gravity light, nutrient availability are largely controlled by coordinated regulation of distinct auxin transport streams. Many plant responses to the environment involve changes in shape. Much can be learned about the underlying processes controlling plant form if the response is measured with sufficient resolution. Computer-aided analysis of digital images or 'machine vision' can be used to greatly increase the speed and consistency of data from a morphometric study of plant form. Advances in image acquisition and analysis pioneered at UW-Madison have allowed unprecedented resolution of the growth and gravitropism of Arabidopsis. A reverse genetic analysis was used to determine if the MDR-like ABC transporters influence auxin distribution important for plant development and the response to environmental cues in Arabidopsis. Mutations in MDR1 (At3g28860) reduce acropetal auxin transport in the root. This is correlated with deviation from the vertical axis. Mutations in MDR4 (At2g47000) reduce basipetal auxin transport in the root. This is correlated with hypergravitropism. It was theorized that reduced transport whithin the elongation zone is responsible for the increased curvature. Flavanols were found to regulate gravitropism upstream of MDR4. The mdr1 mdr4 double mutant showed additive but not synergistic phenotypes, suggesting that the two auxin transport streams are more independent than interdependent. MDR proteins seem to enhance auxin transport in situations where PIN-type effux alone is insufficient.

  14. Diversification and expression of the PIN, AUX/LAX and ABCB families of putative auxin transporters in Populus

    Directory of Open Access Journals (Sweden)

    Nicola eCarraro


    Full Text Available Intercellular transport of the plant hormone auxin is mediated by three families of membrane-bound protein carriers, with the PIN and ABCB families coding primarily for efflux proteins and the AUX/LAX family coding for influx proteins. In the last decade our understanding of gene and protein function for these transporters in Arabidopsis has expanded rapidly but very little is known about their role in woody plant development. Here we present a comprehensive account of all three families in the model woody species Populus, including chromosome distribution, protein structure, quantitative gene expression, and evolutionary relationships. The PIN and AUX/LAX gene families in Populus comprise 16 and 8 members respectively, and show evidence for the retention of paralogs following a relatively recent whole genome duplication. There is also evidence for differential expression across tissues within many gene pairs. The ABCB family is previously undescribed in Populus and includes 20 members, showing a much deeper evolutionary history including both tandem and whole genome duplication as well as probable loss. A striking number of these transporters are expressed in developing Populus stems and we suggest that evolutionary and structural relationships with known auxin transporters in Arabidopsis can point toward candidate genes for further study in Populus. This is especially important for the ABCBs, which is a large family and includes members in Arabidopsis that are able to transport other substrates in addition to auxin. Protein modeling, sequence alignment and expression data all point to ABCB1.1 as a likely auxin transport protein in Populus. Given that basipetal auxin flow through the cambial zone shapes the development of woody stems, it is important that we identify the full complement of proteins involved in this process. This work should lay the foundation for studies targeting specific proteins for functional characterization and in situ

  15. The inter-kingdom volatile signal indole promotes root development by interfering with auxin signalling. (United States)

    Bailly, Aurélien; Groenhagen, Ulrike; Schulz, Stefan; Geisler, Markus; Eberl, Leo; Weisskopf, Laure


    Recently, emission of volatile organic compounds (VOCs) has emerged as a mode of communication between bacteria and plants. Although some bacterial VOCs that promote plant growth have been identified, their underlying mechanism of action is unknown. Here we demonstrate that indole, which was identified using a screen for Arabidopsis growth promotion by VOCs from soil-borne bacteria, is a potent plant-growth modulator. Its prominent role in increasing the plant secondary root network is mediated by interfering with the auxin-signalling machinery. Using auxin reporter lines and classic auxin physiological and transport assays we show that the indole signal invades the plant body, reaches zones of auxin activity and acts in a polar auxin transport-dependent bimodal mechanism to trigger differential cellular auxin responses. Our results suggest that indole, beyond its importance as a bacterial signal molecule, can serve as a remote messenger to manipulate plant growth and development.

  16. A novel putative auxin carrier family regulates intracellular auxin homeostasis in plants



    The phytohormone auxin acts as a prominent signal, providing, by its local accumulation or depletion in selected cells, a spatial and temporal reference for changes in the developmental program. The distribution of auxin depends on both auxin metabolism (biosynthesis, conjugation and degradation) and cellular auxin transport. We identified in silico a novel putative auxin transport facilitator family, called PIN-LIKES (PILS). Here we illustrate that PILS proteins are required for auxin-depend...

  17. Decarboxylation and transport of auxin in segments of sunflower and cabbage roots. (United States)

    Iversen, T H; Aasheim, T


    The movement of (14)C from indole-3-acetic acid (IAA) (14)C has been examined in 5 mm root segments of dark-grown seedlings of Helianthus annuus and Brassica oleracea. Contaminants from distilled water, phosphate buffer and the razor-blade cutter increase the decarboxylation of IAA-(14)C, and cutting of root segments results in an activation of IAA-destroying enzymes at the cut surfaces. When these sources of errors were eliminated the following was shown: a) Both in sunflower and cabbage there is a slight acropetal flux of (14)C through the root segments into the agar receiver blocks. The amount of (14)C found in the receiver blocks increases with the lenght of the transport period. b) When the root segments, after the transport period, are cut in two equal parts and these assayed separately, the amounts of (14)C in the two parts indicate a greater acropetal than basipetal transport. c) The total radioactivity of the receiver blocks is in part due to IAA-(14)C and in part to (14)CO2, the latter being a result of enzymatic destruction of auxin. d) Addition of ferulic acid, an inhibitor of IAA oxidases, to the receiver blocks markedly inhibits the decarboxylation of IAA-(14)C and thus increases the amount transported. This effect is more pronounced after a 20 hr than after a 6 hr transport period.

  18. Auxin as an inducer of asymmetrical division generating the subsidiary cells in stomatal complexes of Zea mays. (United States)

    Livanos, Pantelis; Giannoutsou, Eleni; Apostolakos, Panagiotis; Galatis, Basil


    The data presented in this work revealed that in Zea mays the exogenously added auxins indole-3-acetic acid (IAA) and 1-napthaleneacetic acid (NAA), promoted the establishment of subsidiary cell mother cell (SMC) polarity and the subsequent subsidiary cell formation, while treatment with auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and 1-napthoxyacetic acid (NOA) specifically blocked SMC polarization and asymmetrical division. Furthermore, in young guard cell mother cells (GMCs) the PIN1 auxin efflux carriers were mainly localized in the transverse GMC faces, while in the advanced GMCs they appeared both in the transverse and the lateral ones adjacent to SMCs. Considering that phosphatidyl-inositol-3-kinase (PI3K) is an active component of auxin signal transduction and that phospholipid signaling contributes in the establishment of polarity, treatments with the specific inhibitor of the PI3K LY294002 were carried out. The presence of LY294002 suppressed polarization of SMCs and prevented their asymmetrical division, whereas combined treatment with exogenously added NAA and LY294002 restricted the promotional auxin influence on subsidiary cell formation. These findings support the view that auxin is involved in Z. mays subsidiary cell formation, probably functioning as inducer of the asymmetrical SMC division. Collectively, the results obtained from treatments with auxin transport inhibitors and the appearance of PIN1 proteins in the lateral GMC faces indicate a local transfer of auxin from GMCs to SMCs. Moreover, auxin signal transduction seems to be mediated by the catalytic function of PI3K.

  19. Inhibition of auxin transport and auxin signaling and treatment with far red light induces root coiling in the phospholipase-A mutant ppla-I-1. Significance for surface penetration? (United States)

    Perrineau, F; Wimalasekera, R; Effendi, Y; Scherer, G F E


    When grown on a non-penetretable at a surface angle of 45°, Arabidopsis roots form wave-like structures and, in wild type rarely, but in certain mutants the tip root even may form circles. These circles are called coils. The formation of coils depends on the complex interaction of circumnutation, gravitropism and negative thigmotropism where - at least - gravitropism is intimately linked to auxin transport and signaling. The knockout mutant of patatin-related phospholipase-AI-1 (pplaI-1) is an auxin-signaling mutant which forms moderately increased numbers of coils on tilted agar plates. We tested the effects of the auxin efflux transport inhibitor NPA (1-naphthylphtalamic acid) and of the influx transport inhibitor 1-NOA (1-naphthoxyacetic acid) which both further increased root coil formation. The pPLAI-1 inhibitors HELSS (haloenol lactone suicide substrate=E-6-(bromomethylene)tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one) and ETYA (eicosatetraynoic acid) which are auxin signaling inhibitors also increased coil formation. In addition, far red light treatment increased coil formation. The results point out that a disturbance of auxin transport and signaling is one potential cause for root coils. As we show that the mutant pplaI-1 penetrates horizontal agar plates better than wild type plants root movements may help penetrating the soil.

  20. Early embryo development in Fucus distichus is auxin sensitive (United States)

    Basu, Swati; Sun, Haiguo; Brian, Leigh; Quatrano, Ralph L.; Muday, Gloria K.


    Auxin and polar auxin transport have been implicated in controlling embryo development in land plants. The goal of these studies was to determine if auxin and auxin transport are also important during the earliest stages of development in embryos of the brown alga Fucus distichus. Indole-3-acetic acid (IAA) was identified in F. distichus embryos and mature tissues by gas chromatography-mass spectroscopy. F. distichus embryos accumulate [(3)H]IAA and an inhibitor of IAA efflux, naphthylphthalamic acid (NPA), elevates IAA accumulation, suggesting the presence of an auxin efflux protein complex similar to that found in land plants. F. distichus embryos normally develop with a single unbranched rhizoid, but growth on IAA leads to formation of multiple rhizoids and growth on NPA leads to formation of embryos with branched rhizoids, at concentrations that are active in auxin accumulation assays. The effects of IAA and NPA are complete before 6 h after fertilization (AF), which is before rhizoid germination and cell division. The maximal effects of IAA and NPA are between 3.5 and 5 h AF and 4 and 5.5 h AF, respectively. Although, the location of the planes of cell division was significantly altered in NPA- and IAA-treated embryos, these abnormal divisions occurred after abnormal rhizoid initiation and branching was observed. The results of this study suggest that auxin acts in the formation of apical basal patterns in F. distichus embryo development.

  1. Cellular Auxin Homeostasis:Gatekeeping Is Housekeeping

    Institute of Scientific and Technical Information of China (English)

    Michel Ruiz Rosquete; Elke Barbez; Jürgen Kleine-Vehn


    The phytohormone auxin is essential for plant development and contributes to nearly every aspect of the plant life cycle.The spatio-temporal distribution of auxin depends on a complex interplay between auxin metabolism and cell-to-cell auxin transport.Auxin metabolism and transport are both crucial for plant development;however,it largely remains to be seen how these processes are integrated to ensure defined cellular auxin levels or even gradients within tissues or organs.In this review,we provide a glance at very diverse topics of auxin biology,such as biosynthesis,conjugation,oxidation,and transport of auxin.This broad,but certainly superficial,overview highlights the mutual importance of auxin metabolism and transport.Moreover,it allows pinpointing how auxin metabolism and transport get integrated to jointly regulate cellular auxin homeostasis.Even though these processes have been so far only separately studied,we assume that the phytohormonal crosstalk integrates and coordinates auxin metabolism and transport.Besides the integrative power of the global hormone signaling,we additionally introduce the hypothetical concept considering auxin transport components as gatekeepers for auxin responses.

  2. WOX5-1AA17 Feedback Circuit-Mediated CellularAuxin Response Is Crucial for the Patterning ofRoot Stem Cell Niches in Arabidopsis

    Institute of Scientific and Technical Information of China (English)


    In plants, the patterning of stem cell-enriched meristems requires a graded auxin response maximum thatemerges from the concerted action of polar auxin transport, auxin biosynthesis, auxin metabolism, and cellular auxinresponse machinery. However, mechanisms underlying this auxin response maximum-mediated root stem cell mainte-nance are not fully understood. Here, we present unexpected evidence that WUSCHEL-RELATED HOMEOBOX 5 (WOX5)transcription factor modulates expression of auxin biosynthetic genes in the quiescent center (QC) of the root and thusprovides a robust mechanism for the maintenance of auxin response maximum in the root tip. This WOX5 action is bal-anced through the activity of indole-3-acetic acid 17 (IAA17) auxin response repressor. Our combined genetic, cell biol-ogy, and computational modeling studies revealed a previously uncharacterized feedback loop linking WOX5-mediatedauxin production to IAA17-dependent repression of auxin responses. This WOX5-1AA17 feedback circuit further assuresthe maintenance of auxin response maximum in the root tip and thereby contributes to the maintenance of distal stemcell (DSC) populations. Our experimental studies and in silico computer simulations both demonstrate that the WOX5-iAA17 feedback circuit is essential for the maintenance of auxin gradient in the root tip and the auxin-mediated root DSCdifferentiation.

  3. Emergence of tissue polarization from synergy of intracellular and extracellular auxin signaling

    NARCIS (Netherlands)

    Wabnik, K.; Kleine-Vehn, J.; Balla, J.; Sauer, M.; Naramoto, S.; Reinöhl, V.; Merks, R.M.H.; Govaerts, W.; Friml, J.


    Plant development is exceptionally flexible as manifested by its potential for organogenesis and regeneration, which are processes involving rearrangements of tissue polarities. Fundamental questions concern how individual cells can polarize in a coordinated manner to integrate into the multicellular

  4. Cell plate-restricted association of Arabidopsis dynamin related proteins and PIN auxin efflux carriers is required for PIN endocytic trafficking during cytokinesis.

    NARCIS (Netherlands)

    Mravec, J.; Petrasek, J.; Li, N.; Boeren, J.A.; Karlova, R.B.; Kitakura, S.; Naramoto, S.; Nodzynski, T.; Dhonukshe, P.B.; Vries, de S.C.; Zazimalova, E.; Friml, J.


    The polarized transport of the phytohormone auxin [1], which is crucial for the regulation of different stages of plant development [ [2] and [3] ], depends on the asymmetric plasma membrane distribution of the PIN-FORMED (PIN) auxin efflux carriers [4 A. Vieten, M. Sauer, P.B. Brewer and J. Friml,

  5. Arabidopsis ABCB21 is a facultative auxin importer/exporter regulated by cytoplasmic auxin concentration. (United States)

    Kamimoto, Yoshihisa; Terasaka, Kazuyoshi; Hamamoto, Masafumi; Takanashi, Kojiro; Fukuda, Shoju; Shitan, Nobukazu; Sugiyama, Akifumi; Suzuki, Hideyuki; Shibata, Daisuke; Wang, Bangjun; Pollmann, Stephan; Geisler, Markus; Yazaki, Kazufumi


    The phytohormone auxin is critical for plant growth and many developmental processes. Members of the P-glycoprotein (PGP/ABCB) subfamily of ATP-binding cassette (ABC) transporters have been shown to function in the polar movement of auxin by transporting auxin over the plasma membrane in both monocots and dicots. Here, we characterize a new Arabidopsis member of the ABCB subfamily, ABCB21/PGP21, a close homolog of ABCB4, for which conflicting transport directionalities have been reported. ABCB21 is strongly expressed in the abaxial side of cotyledons and in junctions of lateral organs in the aerial part, whereas in roots it is specifically expressed in pericycle cells. Membrane fractionation by sucrose density gradient centrifugation followed by Western blot showed that ABCB21 is a plasma membrane-localized ABC transporter. A transport assay with Arabidopsis protoplasts suggested that ABCB21 was involved in IAA transport in an outward direction, while naphthalene acetic acid (NAA) was a less preferable substrate for ABCB21. Further functional analysis of ABCB21 using yeast import and export assays showed that ABCB21 mediates the 1-N-naphthylphthalamic acid (NPA)-sensitive translocation of auxin in an inward direction when the cytoplasmic IAA concentration is low, whereas this transporter mediates outward transport under high internal IAA. An increase in the cytoplasmic IAA concentration by pre-loading of IAA into yeast cells abolished the IAA uptake activity by ABCB21 as well as ABCB4. These findings suggest that ABCB21 functions as a facultative importer/exporter controlling auxin concentrations in plant cells.

  6. Regulation of ABCB1/PGP1-catalysed auxin transport by linker phosphorylation

    DEFF Research Database (Denmark)

    Henrichs, Sina; Wang, Bangjun; Fukao, Yoichiro;


    -IP) and shotgun LC-MS/MS analysis, we identified PID as a valid partner in the interaction with TWD1. In-vitro and yeast expression analyses indicated that PID specifically modulates ABCB1-mediated auxin efflux in an action that is dependent on its kinase activity and that is reverted by quercetin binding...

  7. Dust transport into Martian polar latitudes (United States)

    Murphy, J. R.; Pollack, J. B.


    The presence of suspended dust in the Martian atmosphere, and its return to the planet's surface, is implicated in the formation of the polar layered terrain and the dichotomy in perennial CO2 polar cap retention in the two hemispheres. A three dimensional model was used to study Martian global dust storms. The model accounts for the interactive feedbacks between the atmospheric thermal and dynamical states and an evolving radiatively active suspended dust load. Results from dust storm experiments, as well as from simulations in which there is interest in identifying the conditions under which surface dust lifting occurs at various locations and times, indicate that dust transport due to atmospheric eddy motions is likely to be important in the arrival of suspended dust at polar latitudes. The layered terrain in both polar regions of Mars is interpreted as the reality of cyclical episodes of volatile (CO2, H2O) and dust deposition.

  8. The transparent testa4 mutation prevents flavonoid synthesis and alters auxin transport and the response of Arabidopsis roots to gravity and light. (United States)

    Buer, Charles S; Muday, Gloria K


    We examined whether flavonoids act as endogenous auxin transport regulators during gravity vector and light intensity changes in Arabidopsis thaliana roots. Flavonoid deficient transparent testa4 [tt4(2YY6)] seedlings had elevated root basipetal auxin transport compared with the wild type, consistent with the absence of a negative auxin transport regulator. The tt4(2YY6) roots had delayed gravitropism that was chemically complemented with a flavonoid intermediate. Flavonoid accumulation was found in wild-type columella cells, the site of gravity perception, and in epidermal and cortical cells, the site of differential growth, but flavonoid accumulation was absent in tt4(2YY6) roots. Flavonoid accumulation was higher in gravity-stimulated root tips as compared with vertical controls, with maximum differences coinciding with the timing of gravitropic bending, and was located in epidermal cells. Exogenous indole-3-acetic acid (IAA) also elevated flavonoid accumulation, suggesting that flavonoid changes in response to gravity might be partly as a result of changing IAA distribution. Acropetal IAA transport was also elevated in roots of tt4(2YY6). Flavonoid synthesis was repressed in the dark, as were differences in root acropetal transport in tt4(2YY6). These results are consistent with light- and gravity-induced flavonoid stimulation that alters auxin transport in roots and dependent physiological processes, including gravitropic bending and root development.

  9. Overexpression of OsWRKY72 gene interferes in the abscisic acid signal and auxin transport pathway of Arabidopsis

    Indian Academy of Sciences (India)

    Song Yu; Chen Ligang; Zhang Liping; Yu Diqiu


    Through activating specific transcriptional programmes, plants can launch resistance mechanisms to stressful environments and acquire a new equilibrium between development and defence. To screen the rice WRKY transcription factor which functions in abiotic stress tolerance and modulates the abscisic acid (ABA) response, we generated a whole array of 35S-OsWRKY transgenic Arabidopsis. In this study, we report that 35S-OsWRKY72 transgenic Arabidopsis, whose seed germination was retarded under normal conditions, emerged more sensitive to mannitol, NaCl, ABA stresses and sugar starvation than vector plants. Meanwhile, 35S-OsWRKY72 transgenic Arabidopsis displayed early flowering, reduced apical dominance, lost high temperature-induced hypocotyl elongation response, and enhanced gravitropism response, which were similar to the auxin-related gene mutants aux1, axr1 and bud1. Further, semi-quantitative RT-PCR showed that the expression patterns of three auxin-related genes AUX1, AXR1 and BUD1 were significantly altered in rosette leaves and inflorescences of 35S-OsWRKY72 plants compared with control Arabidopsis, and two ABA-related genes ABA2 and ABI4 were induced in 35S-OsWRKY72 seedlings. In addition, northern blot analysis indicated that, in rice, OsWRKY72 was inducible by polyethylene glycol (PEG), NaCl, naphthalene acetic acid (NAA), ABA and 42°C, similar to its orthologue AtWRKY75 in Arabidopsis, implying that these two WRKY genes might be required for multiple physiological processes in their plants. Together, these results suggest that OsWRKY72 interferes in the signal cross-talk between the ABA signal and auxin transport pathway in transgenic Arabidopsis.

  10. Fusarium Oxysporum Volatiles Enhance Plant Growth Via Affecting Auxin Transport and Signaling. (United States)

    Bitas, Vasileios; McCartney, Nathaniel; Li, Ningxiao; Demers, Jill; Kim, Jung-Eun; Kim, Hye-Seon; Brown, Kathleen M; Kang, Seogchan


    Volatile organic compounds (VOCs) have well-documented roles in plant-plant communication and directing animal behavior. In this study, we examine the less understood roles of VOCs in plant-fungal relationships. Phylogenetically and ecologically diverse strains of Fusarium oxysporum, a fungal species complex that often resides in the rhizosphere of assorted plants, produce volatile compounds that augment shoot and root growth of Arabidopsis thaliana and tobacco. Growth responses of A. thaliana hormone signaling mutants and expression patterns of a GUS reporter gene under the auxin-responsive DR5 promoter supported the involvement of auxin signaling in F. oxysporum volatile-mediated growth enhancement. In addition, 1-naphthylthalamic acid, an inhibitor of auxin efflux, negated F. oxysporum volatile-mediated growth enhancement in both plants. Comparison of the profiles of volatile compounds produced by F. oxysporum strains that differentially affected plant growth suggests that the relative compositions of both growth inhibitory and stimulatory compounds may determine the degree of plant growth enhancement. Volatile-mediated signaling between fungi and plants may represent a potentially conserved, yet mostly overlooked, mechanism underpinning plant-fungus interactions and fungal niche adaption.

  11. Fusarium oxysporum volatiles enhance plant growth via affecting auxin transport and signaling

    Directory of Open Access Journals (Sweden)

    Vasileios eBitas


    Full Text Available Volatile organic compounds (VOCs have well-documented roles in plant-plant communication and directing animal behavior. In this study, we examine the less understood roles of VOCs in plant-fungal relationships. Phylogenetically and ecologically diverse strains of Fusarium oxysporum, a fungal species complex that often resides in the rhizosphere of assorted plants, produce volatile compounds that augment shoot and root growth of Arabidopsis thaliana and tobacco. Growth responses of A. thaliana hormone signaling mutants and expression patterns of a GUS reporter gene under the auxin-responsive DR5 promoter supported the involvement of auxin signaling in F. oxysporum volatile-mediated growth enhancement. In addition, 1-naphthylthalamic acid, an inhibitor of auxin efflux, negated F. oxysporum volatile-mediated growth enhancement in both plants. Comparison of the profiles of volatile compounds produced by F. oxysporum strains that differentially affected plant growth suggests that the relative compositions of both growth inhibitory and stimulatory compounds may determine the degree of plant growth enhancement. Volatile-mediated signaling between fungi and plants may represent a potentially conserved, yet mostly overlooked, mechanism underpinning plant-fungus interactions and fungal niche adaption.

  12. The auxin transporter, OsAUX1, is involved in primary root and root hair elongation and in Cd stress responses in rice (Oryza sativa L.). (United States)

    Yu, ChenLiang; Sun, ChenDong; Shen, Chenjia; Wang, Suikang; Liu, Fang; Liu, Yan; Chen, YunLong; Li, Chuanyou; Qian, Qian; Aryal, Bibek; Geisler, Markus; Jiang, De An; Qi, YanHua


    Auxin and cadmium (Cd) stress play critical roles during root development. There are only a few reports on the mechanisms by which Cd stress influences auxin homeostasis and affects primary root (PR) and lateral root (LR) development, and almost nothing is known about how auxin and Cd interfere with root hair (RH) development. Here, we characterize rice osaux1 mutants that have a longer PR and shorter RHs in hydroponic culture, and that are more sensitive to Cd stress compared to wild-type (Dongjin). OsAUX1 expression in root hair cells is different from that of its paralogous gene, AtAUX1, which is expressed in non-hair cells. However, OsAUX1, like AtAUX1, localizes at the plasma membrane and appears to function as an auxin tranporter. Decreased auxin distribution and contents in the osaux1 mutant result in reduction of OsCyCB1;1 expression and shortened PRs, LRs and RHs under Cd stress, but may be rescued by treatment with the membrane-permeable auxin 1-naphthalene acetic acid. Treatment with the auxin transport inhibitors 1-naphthoxyacetic acid and N-1-naphthylphthalamic acid increased the Cd sensitivity of WT rice. Cd contents in the osaux1 mutant were not altered, but reactive oxygen species-mediated damage was enhanced, further increasing the sensitivity of the osaux1 mutant to Cd stress. Taken together, our results indicate that OsAUX1 plays an important role in root development and in responses to Cd stress.

  13. Distinct Characteristics of Indole-3-Acetic Acid and Phenylacetic Acid, Two Common Auxins in Plants (United States)

    Sugawara, Satoko; Mashiguchi, Kiyoshi; Tanaka, Keita; Hishiyama, Shojiro; Sakai, Tatsuya; Hanada, Kousuke; Kinoshita-Tsujimura, Kaori; Yu, Hong; Dai, Xinhua; Takebayashi, Yumiko; Takeda-Kamiya, Noriko; Kakimoto, Tatsuo; Kawaide, Hiroshi; Natsume, Masahiro; Estelle, Mark; Zhao, Yunde; Hayashi, Ken-ichiro; Kamiya, Yuji; Kasahara, Hiroyuki


    The phytohormone auxin plays a central role in many aspects of plant growth and development. IAA is the most studied natural auxin that possesses the property of polar transport in plants. Phenylacetic acid (PAA) has also been recognized as a natural auxin for >40 years, but its role in plant growth and development remains unclear. In this study, we show that IAA and PAA have overlapping regulatory roles but distinct transport characteristics as auxins in plants. PAA is widely distributed in vascular and non-vascular plants. Although the biological activities of PAA are lower than those of IAA, the endogenous levels of PAA are much higher than those of IAA in various plant tissues in Arabidopsis. PAA and IAA can regulate the same set of auxin-responsive genes through the TIR1/AFB pathway in Arabidopsis. IAA actively forms concentration gradients in maize coleoptiles in response to gravitropic stimulation, whereas PAA does not, indicating that PAA is not actively transported in a polar manner. The induction of the YUCCA (YUC) genes increases PAA metabolite levels in Arabidopsis, indicating that YUC flavin-containing monooxygenases may play a role in PAA biosynthesis. Our results provide new insights into the regulation of plant growth and development by different types of auxins. PMID:26076971

  14. Polarity, Continuity, and Alignment in Plant Vascular Strands

    Institute of Scientific and Technical Information of China (English)

    Megan G. Sawchuk; Enrico Scarpella


    Plant vascular cells are joined end to end along uninterrupted lines to connect shoot organs with roots;vascular strands are thus polar, continuous, and internally aligned. What controls the formation of vascular strands with these properties? The “auxin canalization hypothesis”-based on positive feedback between auxin flow through a cell and the cell’s capacity for auxin transport-predicts the selection of continuous files of cells that transport auxin polarly, thus accounting for the polarity and continuity of vascular strands. By contrast, polar, continuous auxin transport-though required-is insufficient to promote internal alignment of vascular strands, implicating additional factors. The auxin canalization hypothesis was derived from the response of mature tissue to auxin application but is consistent with molecular and cellular events in embryo axis formation and shoot organ development. Objections to the hypothesis have been raised based on vascular organizations in callus tissue and shoot organs but seem unsupported by available evidence. Other objections call instead for further research; yet the inductive and orienting influence of auxin on continuous vascular differentiation remains unique.

  15. Auxin Transport and Ribosome Biogenesis Mutant/Reporter Lines to Study Plant Cell Growth and Proliferation under Altered Gravity (United States)

    Valbuena, Miguel A.; Manzano, Ana I.; van Loon, Jack JWA.; Saez-Vasquez, Julio; Carnero-Diaz, Eugenie; Herranz, Raul; Medina, F. J.


    We tested different Arabidopsis thaliana strains to check their availability for space use in the International Space Station (ISS). We used mutants and reporter gene strains affecting factors of cell proliferation and cell growth, to check variations induced by an altered gravity vector. Seedlings were grown either in a Random Positioning Machine (RPM), under simulated microgravity (μg), or in a Large Diameter Centrifuge (LDC), under hypergravity (2g). A combination of the two devices (μgRPM+LDC) was also used. Under all gravity alterations, seedling roots were longer than in control 1g conditions, while the levels of the nucleolar protein nucleolin were depleted. Alterations in the pattern of expression of PIN2, an auxin transporter, and of cyclin B1, a cell cycle regulator, were shown. All these alterations are compatible with previous space data, so the use of these strains will be useful in the next experiments in ISS, under real microgravity.

  16. Auxin response under osmotic stress. (United States)

    Naser, Victoria; Shani, Eilon


    The phytohormone auxin (indole-3-acetic acid, IAA) is a small organic molecule that coordinates many of the key processes in plant development and adaptive growth. Plants regulate the auxin response pathways at multiple levels including biosynthesis, metabolism, transport and perception. One of the most striking aspects of plant plasticity is the modulation of development in response to changing growth environments. In this review, we explore recent findings correlating auxin response-dependent growth and development with osmotic stresses. Studies of water deficit, dehydration, salt, and other osmotic stresses point towards direct and indirect molecular perturbations in the auxin pathway. Osmotic stress stimuli modulate auxin responses by affecting auxin biosynthesis (YUC, TAA1), transport (PIN), perception (TIR/AFB, Aux/IAA), and inactivation/conjugation (GH3, miR167, IAR3) to coordinate growth and patterning. In turn, stress-modulated auxin gradients drive physiological and developmental mechanisms such as stomata aperture, aquaporin and lateral root positioning. We conclude by arguing that auxin-mediated growth inhibition under abiotic stress conditions is one of the developmental and physiological strategies to acclimate to the changing environment.

  17. GH3-Mediated Auxin Conjugation Can Result in Either Transient or Oscillatory Transcriptional Auxin Responses. (United States)

    Mellor, Nathan; Bennett, Malcolm J; King, John R


    The conjugation of the phytohormone auxin to amino acids via members of the gene family GH3 is an important component in the auxin-degradation pathway in the model plant species Arabidopsis thaliana, as well as many other plant species. Since the GH3 genes are themselves up-regulated in response to auxin, providing a negative feedback on intracellular auxin levels, it is hypothesised that the GH3s have a role in auxin homoeostasis. To investigate this, we develop a mathematical model of auxin signalling and response that includes the auxin-inducible negative feedback from GH3 on the rate of auxin degradation. In addition, we include a positive feedback on the rate of auxin input via the auxin influx transporter LAX3, shown previously to be expressed in response to auxin and to have an important role during lateral root emergence. In the absence of the LAX3 positive feedback, we show that the GH3 negative feedback suffices to generate a transient transcriptional response to auxin in the shape of damped oscillations of the model system. When LAX3 positive feedback is present, sustained oscillations of the system are possible. Using steady-state analyses, we identify and discuss key parameters affecting the oscillatory behaviour of the model. The transient peak of auxin and subsequent transcriptional response caused by the up-regulation of GH3 represents a possible protective homoeostasis mechanism that may be used by plant cells in response to excess auxin.

  18. Basipetal auxin versus acropetal cytokinin transport, and their interaction with NO3 fertilisation in cotyledon senescence and sink:source relationships in cucumber (Cucumis sativus L.). (United States)

    Bangerth, K-F


    The paramount role of cytokinins (CKs) in initiation, as well as prevention, of senescence is well established. In recent years, experimental methods have become available to raise and lower the CK concentration and experimentally manipulate senescence. Decapitating the apical shoot and adding the synthetic auxin naphthylacetic acid to the cut stem reduced endogenous CKs to low levels. Conversely, if no auxin was applied, xylem and leaf CK levels increased dramatically, indicating that basipolar auxin transport is a key determinant in the synthesis of CKs and is potentially more important than NO(3). Manipulating the concentration of applied NO(3) caused considerable variation in leaf CK levels and concomitant changes in senescence. These and other results suggest that the frequently discussed decrease in nitrogen use efficiency (NUE) may be more highly regulated by CKs than by NO(3). Analysis of the re-metabolisation and re-allocation of chlorophyll, proteins, amino acids and starch in three different cucumber cultivars indirectly showed that these metabolites were significantly affected by the concentration of CKs in the leaves. Further research in this area may allow leaf senescence and plant yield to be more efficiently regulated by manipulating CKs and/or basipolar auxin transport instead of nitrate.

  19. The carrier AUXIN RESISTANT (AUX1) dominates auxin flux into Arabidopsis protoplasts. (United States)

    Rutschow, Heidi L; Baskin, Tobias I; Kramer, Eric M


    The ability of the plant hormone auxin to enter a cell is critical to auxin transport and signaling. Auxin can cross the cell membrane by diffusion or via auxin-specific influx carriers. There is little knowledge of the magnitudes of these fluxes in plants. Radiolabeled auxin uptake was measured in protoplasts isolated from roots of Arabidopsis thaliana. This was done for the wild-type, under treatments with additional unlabeled auxin to saturate the influx carriers, and for the influx carrier mutant auxin resistant 1 (aux1). We also used flow cytometry to quantify the relative abundance of cells expressing AUX1-YFP in the assayed population. At pH 5.7, the majority of auxin influx into protoplasts - 75% - was mediated by the influx carrier AUX1. An additional 20% was mediated by other saturable carriers. The diffusive influx of auxin was essentially negligible at pH 5.7. The influx of auxin mediated by AUX1, expressed as a membrane permeability, was 1.5 ± 0.3 μm s(-1) . This value is comparable in magnitude to estimates of efflux permeability. Thus, auxin-transporting tissues can sustain relatively high auxin efflux and yet not become depleted of auxin.

  20. Inhibition of auxin movement from the shoot into the root inhibits lateral root development in Arabidopsis (United States)

    Reed, R. C.; Brady, S. R.; Muday, G. K.


    In roots two distinct polar movements of auxin have been reported that may control different developmental and growth events. To test the hypothesis that auxin derived from the shoot and transported toward the root controls lateral root development, the two polarities of auxin transport were uncoupled in Arabidopsis. Local application of the auxin-transport inhibitor naphthylphthalamic acid (NPA) at the root-shoot junction decreased the number and density of lateral roots and reduced the free indoleacetic acid (IAA) levels in the root and [3H]IAA transport into the root. Application of NPA to the basal half of or at several positions along the root only reduced lateral root density in regions that were in contact with NPA or in regions apical to the site of application. Lateral root development was restored by application of IAA apical to NPA application. Lateral root development in Arabidopsis roots was also inhibited by excision of the shoot or dark growth and this inhibition was reversible by IAA. Together, these results are consistent with auxin transport from the shoot into the root controlling lateral root development.

  1. A Division in PIN-Mediated Auxin Patterning during Organ Initiation in Grasses (United States)

    O'Connor, Devin L.; Runions, Adam; Sluis, Aaron; Bragg, Jennifer; Vogel, John P.


    The hormone auxin plays a crucial role in plant morphogenesis. In the shoot apical meristem, the PIN-FORMED1 (PIN1) efflux carrier concentrates auxin into local maxima in the epidermis, which position incipient leaf or floral primordia. From these maxima, PIN1 transports auxin into internal tissues along emergent paths that pattern leaf and stem vasculature. In Arabidopsis thaliana, these functions are attributed to a single PIN1 protein. Using phylogenetic and gene synteny analysis we identified an angiosperm PIN clade sister to PIN1, here termed Sister-of-PIN1 (SoPIN1), which is present in all sampled angiosperms except for Brassicaceae, including Arabidopsis. Additionally, we identified a conserved duplication of PIN1 in the grasses: PIN1a and PIN1b. In Brachypodium distachyon, SoPIN1 is highly expressed in the epidermis and is consistently polarized toward regions of high expression of the DR5 auxin-signaling reporter, which suggests that SoPIN1 functions in the localization of new primordia. In contrast, PIN1a and PIN1b are highly expressed in internal tissues, suggesting a role in vascular patterning. PIN1b is expressed in broad regions spanning the space between new primordia and previously formed vasculature, suggesting a role in connecting new organs to auxin sinks in the older tissues. Within these regions, PIN1a forms narrow canals that likely pattern future veins. Using a computer model, we reproduced the observed spatio-temporal expression and localization patterns of these proteins by assuming that SoPIN1 is polarized up the auxin gradient, and PIN1a and PIN1b are polarized to different degrees with the auxin flux. Our results suggest that examination and modeling of PIN dynamics in plants outside of Brassicaceae will offer insights into auxin-driven patterning obscured by the loss of the SoPIN1 clade in Brassicaceae. PMID:24499933

  2. Plant AGC protein kinases orient auxin-mediated differential growth and organogenesis

    NARCIS (Netherlands)

    Galván Ampudia, Carlos Samuel


    In view of their predominant sessile lifestyle, plants need to be able to adapt to changes in their environment. Environmental signals such as light and gravity modulate plant growth and architecture by redirecting polar cell-to-cell transport of auxin, thus causing changes in the distribution of th

  3. Arabidopsis thaliana AUCSIA-1 regulates auxin biology and physically interacts with a kinesin-related protein.

    Directory of Open Access Journals (Sweden)

    Barbara Molesini

    Full Text Available Aucsia is a green plant gene family encoding 44-54 amino acids long miniproteins. The sequenced genomes of most land plants contain two Aucsia genes. RNA interference of both tomato (Solanum lycopersicum Aucsia genes (SlAucsia-1 and SlAucsia-2 altered auxin sensitivity, auxin transport and distribution; it caused parthenocarpic development of the fruit and other auxin-related morphological changes. Here we present data showing that the Aucsia-1 gene of Arabidopsis thaliana alters, by itself, root auxin biology and that the AtAUCSIA-1 miniprotein physically interacts with a kinesin-related protein. The AtAucsia-1 gene is ubiquitously expressed, although its expression is higher in roots and inflorescences in comparison to stems and leaves. Two allelic mutants for AtAucsia-1 gene did not display visible root morphological alterations; however both basipetal and acropetal indole-3-acetic acid (IAA root transport was reduced as compared with wild-type plants. The transcript steady state levels of the auxin efflux transporters ATP BINDING CASSETTE subfamily B (ABCB ABCB1, ABCB4 and ABCB19 were reduced in ataucsia-1 plants. In ataucsia-1 mutant, lateral root growth showed an altered response to i exogenous auxin, ii an inhibitor of polar auxin transport and iii ethylene. Overexpression of AtAucsia-1 inhibited primary root growth. In vitro and in vivo protein-protein interaction experiments showed that AtAUCSIA-1 interacts with a 185 amino acids long fragment belonging to a 2712 amino acids long protein of unknown function (At4g31570. Bioinformatics analysis indicates that the AtAUCSIA-1 interacting protein (AtAUCSIA-1IP clusters with a group of CENP-E kinesin-related proteins. Gene ontology predictions for the two proteins are consistent with the hypothesis that the AtAUCSIA-1/AtAUCSIA-1IP complex is involved in the regulation of the cytoskeleton dynamics underlying auxin biology.

  4. Inhibition of auxin transport from the ovary or from the apical shoot induces parthenocarpic fruit-set in tomato mediated by gibberellins. (United States)

    Serrani, Juan Carlos; Carrera, Esther; Ruiz-Rivero, Omar; Gallego-Giraldo, Lina; Peres, Lázaro Eustáquio Pereira; García-Martínez, José Luis


    Fruit-set in tomato (Solanum lycopersicum) depends on gibberellins and auxins (GAs). Here, we show, using the cv MicroTom, that application of N-1-naphthylphthalamic acid (NPA; an inhibitor of auxin transport) to unpollinated ovaries induced parthenocarpic fruit-set, associated with an increase of indole-3-acetic acid (IAA) content, and that this effect was negated by paclobutrazol (an inhibitor of GA biosynthesis). NPA-induced ovaries contained higher content of GA(1) (an active GA) and transcripts of GA biosynthetic genes (SlCPS, SlGA20ox1, and -2). Interestingly, application of NPA to pollinated ovaries prevented their growth, potentially due to supraoptimal IAA accumulation. Plant decapitation and inhibition of auxin transport by NPA from the apical shoot also induced parthenocarpic fruit growth of unpollinated ovaries. Application of IAA to the severed stump negated the plant decapitation effect, indicating that the apical shoot prevents unpollinated ovary growth through IAA transport. Parthenocarpic fruit growth induced by plant decapitation was associated with high levels of GA(1) and was counteracted by paclobutrazol treatment. Plant decapitation also produced changes in transcript levels of genes encoding enzymes of GA biosynthesis (SlCPS and SlGA20ox1) in the ovary, quite similar to those found in NPA-induced fruits. All these results suggest that auxin can have opposing effects on fruit-set, either inducing (when accumulated in the ovary) or repressing (when transported from the apical shoot) that process, and that GAs act as mediators in both cases. The effect of NPA application and decapitation on fruit-set induction was also observed in MicroTom lines bearing introgressed DWARF and SELF-PRUNING wild-type alleles.

  5. Studies of aberrant phyllotaxy1 mutants of maize indicate complex interactions between auxin and cytokinin signaling in the shoot apical meristem. (United States)

    Lee, Byeong-ha; Johnston, Robyn; Yang, Yan; Gallavotti, Andrea; Kojima, Mikiko; Travençolo, Bruno A N; Costa, Luciano da F; Sakakibara, Hitoshi; Jackson, David


    One of the most fascinating aspects of plant morphology is the regular geometric arrangement of leaves and flowers, called phyllotaxy. The shoot apical meristem (SAM) determines these patterns, which vary depending on species and developmental stage. Auxin acts as an instructive signal in leaf initiation, and its transport has been implicated in phyllotaxy regulation in Arabidopsis (Arabidopsis thaliana). Altered phyllotactic patterns are observed in a maize (Zea mays) mutant, aberrant phyllotaxy1 (abph1, also known as abphyl1), and ABPH1 encodes a cytokinin-inducible type A response regulator, suggesting that cytokinin signals are also involved in the mechanism by which phyllotactic patterns are established. Therefore, we investigated the interaction between auxin and cytokinin signaling in phyllotaxy. Treatment of maize shoots with a polar auxin transport inhibitor, 1-naphthylphthalamic acid, strongly reduced ABPH1 expression, suggesting that auxin or its polar transport is required for ABPH1 expression. Immunolocalization of the PINFORMED1 (PIN1) polar auxin transporter revealed that PIN1 expression marks leaf primordia in maize, similarly to Arabidopsis. Interestingly, maize PIN1 expression at the incipient leaf primordium was greatly reduced in abph1 mutants. Consistently, auxin levels were reduced in abph1, and the maize PIN1 homolog was induced not only by auxin but also by cytokinin treatments. Our results indicate distinct roles for ABPH1 as a negative regulator of SAM size and a positive regulator of PIN1 expression. These studies highlight a complex interaction between auxin and cytokinin signaling in the specification of phyllotactic patterns and suggest an alternative model for the generation of altered phyllotactic patterns in abph1 mutants. We propose that reduced auxin levels and PIN1 expression in abph1 mutant SAMs delay leaf initiation, contributing to the enlarged SAM and altered phyllotaxy of these mutants.

  6. Studies of aberrant phyllotaxy1 Mutants of Maize Indicate Complex Interactions between Auxin and Cytokinin Signaling in the Shoot Apical Meristem1[W][OA (United States)

    Lee, Byeong-ha; Johnston, Robyn; Yang, Yan; Gallavotti, Andrea; Kojima, Mikiko; Travençolo, Bruno A.N.; Costa, Luciano da F.; Sakakibara, Hitoshi; Jackson, David


    One of the most fascinating aspects of plant morphology is the regular geometric arrangement of leaves and flowers, called phyllotaxy. The shoot apical meristem (SAM) determines these patterns, which vary depending on species and developmental stage. Auxin acts as an instructive signal in leaf initiation, and its transport has been implicated in phyllotaxy regulation in Arabidopsis (Arabidopsis thaliana). Altered phyllotactic patterns are observed in a maize (Zea mays) mutant, aberrant phyllotaxy1 (abph1, also known as abphyl1), and ABPH1 encodes a cytokinin-inducible type A response regulator, suggesting that cytokinin signals are also involved in the mechanism by which phyllotactic patterns are established. Therefore, we investigated the interaction between auxin and cytokinin signaling in phyllotaxy. Treatment of maize shoots with a polar auxin transport inhibitor, 1-naphthylphthalamic acid, strongly reduced ABPH1 expression, suggesting that auxin or its polar transport is required for ABPH1 expression. Immunolocalization of the PINFORMED1 (PIN1) polar auxin transporter revealed that PIN1 expression marks leaf primordia in maize, similarly to Arabidopsis. Interestingly, maize PIN1 expression at the incipient leaf primordium was greatly reduced in abph1 mutants. Consistently, auxin levels were reduced in abph1, and the maize PIN1 homolog was induced not only by auxin but also by cytokinin treatments. Our results indicate distinct roles for ABPH1 as a negative regulator of SAM size and a positive regulator of PIN1 expression. These studies highlight a complex interaction between auxin and cytokinin signaling in the specification of phyllotactic patterns and suggest an alternative model for the generation of altered phyllotactic patterns in abph1 mutants. We propose that reduced auxin levels and PIN1 expression in abph1 mutant SAMs delay leaf initiation, contributing to the enlarged SAM and altered phyllotaxy of these mutants. PMID:19321707

  7. Transcriptomic analysis reveals ethylene as stimulator and auxin as regulator of adventitious root formation in petunia cuttings

    Directory of Open Access Journals (Sweden)

    Uwe eDruege


    Full Text Available Adventitious root (AR formation in the stem base of cuttings is the basis for propagation of many plant species and petunia is used as model to study this developmental process. Following AR formation from 2 to 192 hours after excision (hpe of cuttings, transcriptome analysis by microarray revealed a change of the character of the rooting zone from stem base to root identity. The greatest shift in the number of differentially expressed genes was observed between 24 and 72 hpe, when the categories storage, mineral nutrient acquisition, anti-oxidative and secondary metabolism, and biotic stimuli showed a notable high number of induced genes. Analyses of phytohormone-related genes disclosed multifaceted changes of the auxin transport system, auxin conjugation and the auxin signal perception machinery indicating a reduction in auxin sensitivity and phase-specific responses of particular auxin-regulated genes. Genes involved in ethylene biosynthesis and action showed a more uniform pattern as a high number of respective genes were generally induced during the whole process of AR formation. The important role of ethylene for stimulating AR formation was demonstrated by the application of inhibitors of ethylene biosynthesis and perception as well as of the precursor aminocyclopropane-1-carboxylic acid, all changing the number and length of AR. A model is proposed showing the putative role of polar auxin transport and resulting auxin accumulation in initiation of subsequent changes in auxin homeostasis and signal perception with a particular role of Aux/IAA expression. These changes might in turn guide the entrance into the different phases of AR formation. Ethylene biosynthesis, which is stimulated by wounding and does probably also respond to other stresses and auxin, acts as important stimulator of AR formation probably via the expression of ethylene responsive transcription factor genes, whereas the timing of different phases seems to be controlled

  8. Overexpression of 3β-hydroxysteroid dehydrogenases/C-4 decarboxylases causes growth defects possibly due to abnormal auxin transport in Arabidopsis. (United States)

    Kim, Bokyung; Kim, Gyusik; Fujioka, Shozo; Takatsuto, Suguru; Choe, Sunghwa


    Sterols play crucial roles as membrane components and precursors of steroid hormones (e.g., brassinosteroids, BR). Within membranes, sterols regulate membrane permeability and fluidity by interacting with other lipids and proteins. Sterols are frequently enriched in detergent-insoluble membranes (DIMs), which organize molecules involved in specialized signaling processes, including auxin transporters. To be fully functional, the two methyl groups at the C-4 position of cycloartenol, a precursor of plant sterols, must be removed by bifunctional 3β-hydroxysteroid dehydrogenases/C-4 decarboxylases (3βHSD/D). To understand the role of 3βHSD/D in Arabidopsis development, we analyzed the phenotypes of knock-out mutants and overexpression lines of two 3βHSD/D genes (At1g47290 and At2g26260). Neither single nor double knock-out mutants displayed a noticeable phenotype; however, overexpression consistently resulted in plants with wrinkled leaves and short inflorescence internodes. Interestingly, the internode growth defects were opportunistic; even within a plant, some stems were more severely affected than others. Endogenous levels of BRs were not altered in the overexpression lines, suggesting that the growth defect is not primarily due to a flaw in BR biosynthesis. To determine if overexpression of the sterol biosynthetic genes affects the functions of membrane-localized auxin transporters, we subjected plants to the auxin efflux carrier inhibitor, 1-N-naphthylphthalamic acid (NPA). Where-as the gravity vectors of wild-type roots became randomly scattered in response to NPA treatment, those of the overexpression lines continued to grow in the direction of gravity. Overexpression of the two Arabidopsis 3βHSD/D genes thus appears to affect auxin transporter activity, possibly by altering sterol composition in the membranes.

  9. The rice FISH BONE gene encodes a tryptophan aminotransferase, which affects pleiotropic auxin-related processes. (United States)

    Yoshikawa, Takanori; Ito, Momoyo; Sumikura, Tsuyoshi; Nakayama, Akira; Nishimura, Takeshi; Kitano, Hidemi; Yamaguchi, Isomaro; Koshiba, Tomokazu; Hibara, Ken-Ichiro; Nagato, Yasuo; Itoh, Jun-Ichi


    Auxin is a fundamental plant hormone and its localization within organs plays pivotal roles in plant growth and development. Analysis of many Arabidopsis mutants that were defective in auxin biosynthesis revealed that the indole-3-pyruvic acid (IPA) pathway, catalyzed by the TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) and YUCCA (YUC) families, is the major biosynthetic pathway of indole-3-acetic acid (IAA). In contrast, little information is known about the molecular mechanisms of auxin biosynthesis in rice. In this study, we identified a auxin-related rice mutant, fish bone (fib). FIB encodes an orthologue of TAA genes and loss of FIB function resulted in pleiotropic abnormal phenotypes, such as small leaves with large lamina joint angles, abnormal vascular development, small panicles, abnormal organ identity and defects in root development, together with a reduction in internal IAA levels. Moreover, we found that auxin sensitivity and polar transport activity were altered in the fib mutant. From these results, we suggest that FIB plays a pivotal role in IAA biosynthesis in rice and that auxin biosynthesis, transport and sensitivity are closely interrelated.

  10. CgOpt1, a putative oligopeptide transporter from Colletotrichum gloeosporioides that is involved in responses to auxin and pathogenicity

    Directory of Open Access Journals (Sweden)

    Maor Rudy


    Full Text Available Abstract Background The fungus Colletotrichum gloeosporioides f. sp. aeschynomene produces high levels of indole-3-acetic acid (IAA in axenic cultures and during plant infection. We generated a suppression subtractive hybridization library enriched for IAA-induced genes and identified a clone, which was highly expressed in IAA-containing medium. Results The corresponding gene showed similarity to oligopeptide transporters of the OPT family and was therefore named CgOPT1. Expression of CgOPT1 in mycelia was low, and was enhanced by external application of IAA. cgopt1-silenced mutants produced less spores, had reduced pigmentation, and were less pathogenic to plants than the wild-type strain. IAA enhanced spore formation and caused changes in colony morphology in the wild-type strain, but had no effect on spore formation or colony morphology of the cgopt1-silenced mutants. Conclusion Our results show that IAA induces developmental changes in C. gloeosporioides. These changes are blocked in cgopt1-silenced mutants, suggesting that this protein is involved in regulation of fungal response to IAA. CgOPT1 is also necessary for full virulence, but it is unclear whether this phenotype is related to auxin.

  11. Arabidopsis monothiol glutaredoxin, AtGRXS17, is critical for temperature-dependent postembryonic growth and development via modulating auxin response. (United States)

    Cheng, Ning-Hui; Liu, Jian-Zhong; Liu, Xing; Wu, Qingyu; Thompson, Sean M; Lin, Julie; Chang, Joyce; Whitham, Steven A; Park, Sunghun; Cohen, Jerry D; Hirschi, Kendal D


    Global environmental temperature changes threaten innumerable plant species. Although various signaling networks regulate plant responses to temperature fluctuations, the mechanisms unifying these diverse processes are largely unknown. Here, we demonstrate that an Arabidopsis monothiol glutaredoxin, AtGRXS17 (At4g04950), plays a critical role in redox homeostasis and hormone perception to mediate temperature-dependent postembryonic growth. AtGRXS17 expression was induced by elevated temperatures. Lines altered in AtGRXS17 expression were hypersensitive to elevated temperatures and phenocopied mutants altered in the perception of the phytohormone auxin. We show that auxin sensitivity and polar auxin transport were perturbed in these mutants, whereas auxin biosynthesis was not altered. In addition, atgrxs17 plants displayed phenotypes consistent with defects in proliferation and/or cell cycle control while accumulating higher levels of reactive oxygen species and cellular membrane damage under high temperature. Together, our findings provide a nexus between reactive oxygen species homeostasis, auxin signaling, and temperature responses.

  12. The role of auxin signaling in early embryo pattern formation

    NARCIS (Netherlands)

    Smit, Margot E.; Weijers, Dolf


    Pattern formation of the early Arabidopsis embryo generates precursors to all major cell types, and is profoundly controlled by the signaling molecule auxin. Here we discuss recent milestones in our understanding of auxin-dependent embryo patterning. Auxin biosynthesis, transport and response mec

  13. Effects of cations on hormone transport in primary roots of Zea mays (United States)

    Hasenstein, K. H.; Evans, M. L.


    We examined the influence of aluminum and calcium (and certain other cations) on hormone transport in corn roots. When aluminum was applied unilaterally to the caps of 15 mm apical root sections the roots curved strongly away from the aluminum. When aluminum was applied unilaterally to the cap and 3H-indole-3-acetic acid was applied to the basal cut surface twice as much radioactivity (assumed to be IAA) accumulated on the concave side of the curved root as on the convex side. Auxin transport in the apical region of intact roots was preferentially basipetal, with a polarity (basipetal transport divided by acropetal transport) of 6.3. In decapped 5 mm apical root segments, auxin transport was acropetally polar (polarity = 0.63). Application of aluminum to the root cap strongly promoted acropetal transport of auxin reducing polarity from 6.3 to 2.1. Application of calcium to the root cap enhanced basipetal movement of auxin, increasing polarity from 6.3 to 7.6. Application of the calcium chelator, ethylene-glycol-bis-(beta-aminoethylether)-N,N,N',N'-tetraacetic acid, greatly decreased basipetal auxin movement, reducing polarity from 6.3 to 3.7. Transport of label after application of tritiated abscisic acid showed no polarity and was not affected by calcium or aluminum. The results indicate that the root cap is particularly important in maintaining basipetal polarity of auxin transport in primary roots of corn. The induction of root curvature by unilateral application of aluminum or calcium to root caps is likely to result from localized effects of these ions on auxin transport. The findings are discussed relative to the possible role of calcium redistribution in the gravitropic curvature of roots and the possibility of calmodulin involvement in the action of calcium and aluminum on auxin transport.

  14. Pattern formation in a cell based auxin transport model with numerical bifurcation analysis

    CERN Document Server

    Draelants, Delphine; Beemster, Gerrit T S; Vanroose, Wim


    Transport models of growth hormones can be used to reproduce the hormone accumulations that occur in plant organs. Mostly, these accumulation patterns are calculated using time step methods, even though only the resulting steady state patterns of the model are of interest. We examine the steady state solutions of the hormone transport model of Smith et al (2006) for a one-dimensional row of plant cells. We search for the steady state solutions as a function of three of the model parameters by using numerical continuation methods and bifurcation analysis. These methods are more adequate for solving steady state problems than time step methods. We discuss a trivial solution where the concentrations of hormones are equal in all cells and examine its stability region. We identify two generic bifurcation scenarios through which the trivial solution loses its stability. The trivial solution becomes either a steady state pattern with regular spaced peaks or a pattern where the concentration is periodic in time.

  15. Transcriptional Responses to the Auxin Hormone

    NARCIS (Netherlands)

    Weijers, Dolf; Wagner, Doris


    Auxin is arguably the most important signaling molecule in plants, and the last few decades have seen remarkable breakthroughs in understanding its production, transport, and perception. Recent investigations have focused on transcriptional responses to auxin, providing novel insight into the fun

  16. Genetic evidence for auxin involvement in arbuscular mycorrhiza initiation. (United States)

    Hanlon, Meredith T; Coenen, Catharina


    • Formation of arbuscular mycorrhiza (AM) is controlled by a host of small, diffusible signaling molecules, including phytohormones. To test the hypothesis that the plant hormone auxin controls mycorrhiza development, we assessed mycorrhiza formation in two mutants of tomato (Solanum lycopersicum): diageotropica (dgt), an auxin-resistant mutant, and polycotyledon (pct), a mutant with hyperactive polar auxin transport. • Mutant and wild-type (WT) roots were inoculated with spores of the AM fungus Glomus intraradices. Presymbiotic root-fungus interactions were observed in root organ culture (ROC) and internal fungal colonization was quantified both in ROC and in intact seedlings. • In ROC, G. intraradices stimulated presymbiotic root branching in pct but not in dgt roots. pct roots stimulated production of hyphal fans indicative of appressorium formation and were colonized more rapidly than WT roots. By contrast, approaching hyphae reversed direction to grow away from cultured dgt roots and failed to colonize them. In intact seedlings, pct and dgt roots were colonized poorly, but development of hyphae, arbuscules, and vesicles was morphologically normal within roots of both mutants. • We conclude that auxin signaling within host roots is required for the early stages of AM formation, including during presymbiotic signal exchange.


    Directory of Open Access Journals (Sweden)

    N.V. Tabakov


    Full Text Available The article deals with the theoretic and methodological questions regarding the formation of a transport corridor "Urals industrial – Urals Polar". Analyzed are the main factors that affect the formation of the transport infrastructure. A big effect is centered around the world-view problem, which has to do with the occupation of a human, and the effect of it on nature. Put forth is the possibility to look upon the question of the formation of ma transport corridor "Urals industrial – Urals Polar" in the frame of the forming of the Ural-West-Siberian TPK, taking into account the global transport web.

  18. Comprehensive Transcriptome Analysis of Auxin Responses in Arabidopsis

    Institute of Scientific and Technical Information of China (English)

    Ivan A.Paponov; Martina Paponov; William Teale; Margit Menges; Sohini Chakrabortee; James A.H.Murray; Klaus Palme


    In plants,the hormone auxin shapes gene expression to regulate growth and development.Despite the detailed characterization of auxin-inducible genes,a comprehensive overview of the temporal and spatial dynamics of auxinregulated gene expression is lacking.Here,we analyze transcriptome data from many publicly available Arabidopsis profiling experiments and assess tissue-specific gene expression both in response to auxin concentration and exposure time and in relation to other plant growth regulators.Our analysis shows that the primary response to auxin over a wide range of auxin application conditions and in specific tissues comprises almost exclusively the up-regulation of genes and identifies the most robust auxin marker genes.Tissue-specific auxin responses correlate with differential expression of Aux/IAA genes and the subsequent regulation of context- and sequence-specific patterns of gene expression.Changes in transcript levels were consistent with a distinct sequence of conjugation,increased transport capacity and down-regulation of biosynthesis in the temperance of high cellular auxin concentrations.Our data show that auxin regulates genes associated with the biosynthesis,catabolism and signaling pathways of other phytohormones.We present a transcriptional overview of the auxin response.Specific interactions between auxin and other phytohormones are highlighted,particularly the regulation of their metabolism.Our analysis provides a roadmap for auxin-dependent processes that underpins the concept of an 'auxin code'-a tissue-specific fingerprint of gene expression that initiates specific developmental processes.

  19. The role of auxin signaling in early embryo pattern formation. (United States)

    Smit, Margot E; Weijers, Dolf


    Pattern formation of the early Arabidopsis embryo generates precursors to all major cell types, and is profoundly controlled by the signaling molecule auxin. Here we discuss recent milestones in our understanding of auxin-dependent embryo patterning. Auxin biosynthesis, transport and response mechanisms interact to generate local auxin accumulation in the early embryo. New auxin-dependent reporters help identifying these sites, while atomic structures of transcriptional response mediators help explain the diverse outputs of auxin signaling. Key auxin outputs are control of cell identity and cell division orientation, and progress has been made towards understanding the cellular basis of each. Importantly, a number of studies have combined computational modeling and experiments to analyze the developmental role, genetic circuitry and molecular mechanisms of auxin-dependent cell division control.

  20. Noncoding transcription by alternative RNA polymerases dynamically regulates an auxin-driven chromatin loop. (United States)

    Ariel, Federico; Jegu, Teddy; Latrasse, David; Romero-Barrios, Natali; Christ, Aurélie; Benhamed, Moussa; Crespi, Martin


    The eukaryotic epigenome is shaped by the genome topology in three-dimensional space. Dynamic reversible variations in this epigenome structure directly influence the transcriptional responses to developmental cues. Here, we show that the Arabidopsis long intergenic noncoding RNA (lincRNA) APOLO is transcribed by RNA polymerases II and V in response to auxin, a phytohormone controlling numerous facets of plant development. This dual APOLO transcription regulates the formation of a chromatin loop encompassing the promoter of its neighboring gene PID, a key regulator of polar auxin transport. Altering APOLO expression affects chromatin loop formation, whereas RNA-dependent DNA methylation, active DNA demethylation, and Polycomb complexes control loop dynamics. This dynamic chromatin topology determines PID expression patterns. Hence, the dual transcription of a lincRNA influences local chromatin topology and directs dynamic auxin-controlled developmental outputs on neighboring genes. This mechanism likely underscores the adaptive success of plants in diverse environments and may be widespread in eukaryotes.

  1. Specificity patterns indicate that auxin exporters and receptors are the same proteins. (United States)

    Hössel, D; Schmeiser, C; Hertel, R


    A study of transport and action of synthetic auxin analogues can help to identify transporters and receptors of this plant hormone. Both aspects--transportability and action on growth--were tested with 2-naphthoxyacetic acid (2-NOA) and compared across several plant species. 2-NOA stimulates elongation effectively at low concentrations in petioles of the gymnosperm Ginkgo biloba L., in hypocotyls or internodes of the dicot legumes, mung bean (Vigna mungo L.) and pea (Pisum sativum L.), in cotyledons of onion (Allium cepa L.) and in leaf bases of chive (Allium schoenoprasum L.), the latter two of the monocot order Asparagales. In contrast, elongation of coleoptile segments of maize (Zea mays L.) is poorly responsive to 2-NOA. Significant auxin-like transport of 2-NOA was observed in segments of mung bean hypocotyls, pea internodes, and chive leaf bases, but not in segments of the grass coleoptiles. Thus, for the two assays, elongation and polar transportability, the same difference in ligand specificity was observed between the grass and all other species assayed. This finding supports the hypothesis that a common protein mediates auxin efflux as well as auxin action on elongation.

  2. Do trees grow on money? Auxin as the currency of the cellular economy. (United States)

    Stewart, Jodi L; Nemhauser, Jennifer L


    Auxin plays a role in nearly every aspect of a plant's life. Signals from the developmental program, physiological status, and encounters with other organisms all converge on the auxin pathway. The molecular mechanisms facilitating these interactions are diverse; yet, common themes emerge. Auxin can be regulated by modulating rates of biosynthesis, conjugation, and transport, as well as sensitivity of a cell to the auxin signal. In this article, we describe some well-studied examples of auxin's interactions with other pathways.

  3. Auxin-Cytokinin Interaction Regulates Meristem Development

    Institute of Scientific and Technical Information of China (English)

    Ying-Hua Su; Yu-Bo Liu; Xian-Sheng Zhang


    Plant hormones regulate many aspects of plant growth and development. Both auxin and cytokinin have been known for a long time to act either synergistically or antagonistically to control several significant developmental processes, such as the formation and maintenance of meristem. Over the past few years, exciting progress has been made to reveal the molecular mechanisms underlying the auxin-cytokinin action and interaction. In this review, we shall briefly discuss the major progress made in auxin and cytokinin biosynthesis, auxin transport, and auxin and cytokinin signaling.The frameworks for the complicated interaction of these two hormones in the control of shoot apical meristem and root apical meristem formation as well as their roles in in vitro organ regeneration are the major focus of this review.

  4. The auxin-resistant diageotropica mutant of tomato responds to gravity via an auxin-mediated pathway (United States)

    Rice, M. S.; Lomax, T. L.


    Hypocotyls of the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) do not elongate in response to exogenous auxin, but can respond to gravity. This appears paradoxical in light of the Cholodny-Went hypothesis, which states that shoot gravicurvature results from asymmetric stimulation of elongation by auxin. While light-grown dgt seedlings can achieve correct gravitropic reorientation, the response is slow compared to wild-type seedlings. The sensitivity of dgt seedlings to inhibition of gravicurvature by immersion in auxin or auxin-transport inhibitors is similar to that of wild-type plants, indicating that both an auxin gradient and auxin transport are required for the gravitropic response and that auxin uptake, efflux, and at least one auxin receptor are functional in dgt. Furthermore, dgt gravicurvature is the result of asymmetrically increased elongation as would be expected for an auxin-mediated response. Our results suggest differences between elongation in response to exogenous auxin (absent in dgt) and elongation in response to gravistimulation (present but attenuated in dgt) and confirm the presence of two phases during the gravitropic response, both of which are dependent on functional auxin transport.

  5. Spin-polarized transport in graphene nanoribbon superlattices

    Institute of Scientific and Technical Information of China (English)

    Yu Xin-Xin; Xie Yue-E; OuYang Tao; Chen Yuan-Ping


    By the Green's function method,we investigate spin transport properties of a zigzag graphene nanoribbon superlattice (ZGNS) under a ferromagnetic insulator and edge effect.The exchange splitting induced by the ferromagnetic insulator eliminates the spin degeneracy,which leads to spin-polarized transport in structure.Spin-dependent minibands and minigaps are exhibited in the conductance profile near the Fermi energy.The location and width of the miniband are associated with the geometry of the ZGNS.In the optimal structure,the spin-up and spin-down minibands can be separated completely near the Fermi energy.Therefore,a wide,perfect spin polarization with clear stepwise pattern is observed,i.e.,the perfect spin-polarized transport can be tuned from spin up to spin down by varying the electron energy.

  6. N-glycan containing a core α1,3-fucose residue is required for basipetal auxin transport and gravitropic response in rice (Oryza sativa). (United States)

    Harmoko, Rikno; Yoo, Jae Yong; Ko, Ki Seong; Ramasamy, Nirmal Kumar; Hwang, Bo Young; Lee, Eun Ji; Kim, Ho Soo; Lee, Kyung Jin; Oh, Doo-Byoung; Kim, Dool-Yi; Lee, Sanghun; Li, Yang; Lee, Sang Yeol; Lee, Kyun Oh


    In plants, α1,3-fucosyltransferase (FucT) catalyzes the transfer of fucose from GDP-fucose to asparagine-linked GlcNAc of the N-glycan core in the medial Golgi. To explore the physiological significance of this processing, we isolated two Oryza sativa (rice) mutants (fuct-1 and fuct-2) with loss of FucT function. Biochemical analyses of the N-glycan structure confirmed that α1,3-fucose is missing from the N-glycans of allelic fuct-1 and fuct-2. Compared with the wild-type cv Kitaake, fuct-1 displayed a larger tiller angle, shorter internode and panicle lengths, and decreased grain filling as well as an increase in chalky grains with abnormal shape. The mutant allele fuct-2 gave rise to similar developmental abnormalities, although they were milder than those of fuct-1. Restoration of a normal tiller angle in fuct-1 by complementation demonstrated that the phenotype is caused by the loss of FucT function. Both fuct-1 and fuct-2 plants exhibited reduced gravitropic responses. Expression of the genes involved in tiller and leaf angle control was also affected in the mutants. We demonstrate that reduced basipetal auxin transport and low auxin accumulation at the base of the shoot in fuct-1 account for both the reduced gravitropic response and the increased tiller angle.

  7. Endosidin1 defines a compartment involved in endocytosis of the brassinosteroid receptor BRI1 and the auxin transporters PIN2 and AUX1. (United States)

    Robert, Stéphanie; Chary, S Narasimha; Drakakaki, Georgia; Li, Shundai; Yang, Zhenbiao; Raikhel, Natasha V; Hicks, Glenn R


    Although it is known that proteins are delivered to and recycled from the plasma membrane (PM) via endosomes, the nature of the compartments and pathways responsible for cargo and vesicle sorting and cellular signaling is poorly understood. To define and dissect specific recycling pathways, chemical effectors of proteins involved in vesicle trafficking, especially through endosomes, would be invaluable. Thus, we identified chemicals affecting essential steps in PM/endosome trafficking, using the intensely localized PM transport at the tips of germinating pollen tubes. The basic mechanisms of this localized growth are likely similar to those of non-tip growing cells in seedlings. The compound endosidin 1 (ES1) interfered selectively with endocytosis in seedlings, providing a unique tool to dissect recycling pathways. ES1 treatment induced the rapid agglomeration of the auxin translocators PIN2 and AUX1 and the brassinosteroid receptor BRI1 into distinct endomembrane compartments termed "endosidin bodies"; however, the markers PIN1, PIN7, and other PM proteins were unaffected. Endosidin bodies were defined by the syntaxin SYP61 and the V-ATPase subunit VHA-a1, two trans-Golgi network (TGN)/endosomal proteins. Interestingly, brassinosteroid (BR)-induced gene expression was inhibited by ES1 and treated seedlings displayed a brassinolide (BL)-insensitive phenotype similar to a bri1 loss-of-function mutant. No effect was detected in auxin signaling. Thus, PIN2, AUX1, and BRI1 use interactive pathways involving an early SYP61/VHA-a1 endosomal compartment.

  8. Auxin metabolism rates and implications for plant development

    Directory of Open Access Journals (Sweden)

    Eric M Kramer


    Full Text Available Studies of auxin metabolism rarely express their results as a metabolic rate, although the data obtained would often permit such a calculation to be made. We analyze data from 31 previously published papers to quantify the rates of auxin biosynthesis, conjugation, conjugate hydrolysis, and catabolism in seed plants. Most metabolic pathways have rates in the range 10 nM/h to 1 μM/h, with the exception of auxin conjugation, which has rates as high as ~100 μM/h. The highest rates of auxin conjugation suggests that auxin metabolic sinks may be very small, perhaps as small as a single cell. By contrast, the relatively low rate of auxin biosynthesis requires plants to conserve and recycle auxin during long-distance transport. The consequences for plant development are discussed.

  9. Auxin activity: Past, present, and future. (United States)

    Enders, Tara A; Strader, Lucia C


    Long before its chemical identity was known, the phytohormone auxin was postulated to regulate plant growth. In the late 1800s, Sachs hypothesized that plant growth regulators, present in small amounts, move differentially throughout the plant to regulate growth. Concurrently, Charles Darwin and Francis Darwin were discovering that light and gravity were perceived by the tips of shoots and roots and that the stimulus was transmitted to other tissues, which underwent a growth response. These ideas were improved upon by Boysen-Jensen and Paál and were later developed into the Cholodny-Went hypothesis that tropisms were caused by the asymmetric distribution of a growth-promoting substance. These observations led to many efforts to identify this elusive growth-promoting substance, which we now know as auxin. In this review of auxin field advances over the past century, we start with a seminal paper by Kenneth Thimann and Charles Schneider titled "The relative activities of different auxins" from the American Journal of Botany, in which they compare the growth altering properties of several auxinic compounds. From this point, we explore the modern molecular understanding of auxin-including its biosynthesis, transport, and perception. Finally, we end this review with a discussion of outstanding questions and future directions in the auxin field. Over the past 100 yr, much of our progress in understanding auxin biology has relied on the steady and collective advance of the field of auxin researchers; we expect that the next 100 yr of auxin research will likewise make many exciting advances.

  10. Changes in starch and inositol 1,4,5-trisphosphate levels and auxin transport are interrelated in graviresponding oat (Avena sativa) shoots. (United States)

    Yun, Hye Sup; Joo, Se-Hwan; Kaufman, Peter B; Kim, Tae-Wuk; Kirakosyan, Ara; Philosoph-Hadas, Sonia; Kim, Seong-Ki; Chang, Soo Chul


    This study was conducted to unravel a mechanism for the gravitropic curvature response in oat (Avena sativa) shoot pulvini. For this purpose, we examined the downward movement of starch-filled chloroplast gravisensors, differential changes in inositol 1,4,5-trisphosphate (IP(3)) levels, transport of indole-3-acetic acid (IAA) and gravitropic curvature. Upon gravistimulation, the ratio for IAA levels in lower halves versus those in upper halves (L/U) increased from 1.0 at 0 h and reached a maximum value of 1.45 at 8 h. When shoots were grown in the dark for 10 d, to deplete starch in the chloroplast, the gravity-induced L/U of IAA was reduced to 1.0. N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), both auxin transport inhibitors, significantly reduced the amount of gravitropic curvature and gravity-induced lateral IAA transport, but did not reduce the gravity-induced late change in the L/U ratio of IP(3) levels. U73122, a specific phospholipase C (PLC) inhibitor, decreased gravity-induced curvature. Because U73122 reduced the ratio of L/U of IAA imposed by gravistimulation, it is clear that IAA transport is correlated with changes in IP(3) levels upon gravistimulation. These results indicate that gravistimulation-induced differential lateral IAA transport may result from the onset of graviperception in the chloroplast gravisensors coupled with gravity-induced asymmetric changes in IP(3) levels in oat shoot pulvini.

  11. Phyllotaxis involves auxin drainage through leaf primordia

    DEFF Research Database (Denmark)

    Deb, Yamini; Marti, Dominik; Frenz, Martin;


    of phyllotaxis invoke the accumulation of auxin at leaf initials and removal of auxin through their developing vascular strand, the midvein. We have developed a precise microsurgical tool to ablate the midvein at high spatial and temporal resolution in order to test its function in leaf formation and phyllotaxis...... and to an increase in their width. Phyllotaxis was transiently affected after midvein ablations, but readjusted after two plastochrons. These results indicate that the developing midvein is involved in the basipetal transport of auxin through young primordia, which contributes to phyllotactic spacing and stability...

  12. Is ABP1 an Auxin Receptor Yet?

    Institute of Scientific and Technical Information of China (English)

    Jing-Hua Shi; Zhen-Biao Yang


    AUXIN BINDING PROTEIN 1 (ABP1)has long been proposed as an auxin receptor to regulate cell expansion. The embryo lethality of ABPI-null mutants demonstrates its fundamental role in plant development, but also hinders inves-tigation of its involvement in post-embryonic processes and its mode of action. By taking advantage of weak alleles and inducible systems, several recent studies have revealed a role for ABP1 in organ development, cell polarization, and shape formation. In addition to its role in the regulation of auxin-induced gene expression, ABP1 has now been shown to mod-ulate non-transcriptional auxin responses. ABP1 is required for activating two antagonizing ROP GTPase signaling path-ways involved in cytoskeletal reorganization and cell shape formation, and participates in the regulation of clathrin-mediated endocytosis to subsequently affect PIN protein distribution. These exciting discoveries provide indisputable ev-idence for the auxin-induced signaling pathways that are downstream of ABP1 function, and suggest intriguing mech-anisms for ABPl-mediated polar cell expansion and spatial coordination in response to auxin.

  13. Diffusion equation and spin drag in spin-polarized transport

    DEFF Research Database (Denmark)

    Flensberg, Karsten; Jensen, Thomas Stibius; Mortensen, Asger


    We study the role of electron-electron interactions for spin-polarized transport using the Boltzmann equation, and derive a set of coupled transport equations. For spin-polarized transport the electron-electron interactions are important, because they tend to equilibrate the momentum of the two-spin...... species. This "spin drag" effect enhances the resistivity of the system. The enhancement is stronger the lower the dimension is, and should be measurable in, for example, a two-dimensional electron gas with ferromagnetic contacts. We also include spin-flip scattering, which has two effects......: it equilibrates the spin density imbalance and, provided it has a non-s-wave component, also a current imbalance....

  14. Cell polarity and patterning by PIN trafficking through early endosomal compartments in Arabidopsis thaliana.

    Directory of Open Access Journals (Sweden)

    Hirokazu Tanaka


    Full Text Available PIN-FORMED (PIN proteins localize asymmetrically at the plasma membrane and mediate intercellular polar transport of the plant hormone auxin that is crucial for a multitude of developmental processes in plants. PIN localization is under extensive control by environmental or developmental cues, but mechanisms regulating PIN localization are not fully understood. Here we show that early endosomal components ARF GEF BEN1 and newly identified Sec1/Munc18 family protein BEN2 are involved in distinct steps of early endosomal trafficking. BEN1 and BEN2 are collectively required for polar PIN localization, for their dynamic repolarization, and consequently for auxin activity gradient formation and auxin-related developmental processes including embryonic patterning, organogenesis, and vasculature venation patterning. These results show that early endosomal trafficking is crucial for cell polarity and auxin-dependent regulation of plant architecture.

  15. 生长素调控极性运输载体PIN2质膜丰度与降解%Auxin regulation of its efflux transporter PIN2 plasma membrane abundance and degradation

    Institute of Scientific and Technical Information of China (English)

    付伟; 严旭; 王超; 潘建伟


    The effects of long-term (8 h) treatments with exogenous auxins on auxin efflux transporter PIN2-GFP plasma membrane (PM) abundance,and low temperature,KCN and auxin receptors TIR1/AFBs mutation on auxin regulation of PIN2-GFP PM abundance,and ConA,a vacuolar H +-ATPase inhibitor,on vacuolar accumulation of PIN2-GFP in wild-type and auxin receptor quadruple mutants tir1afb1,2,3 cells in Arabidopsis were systematically studied.The results revealed that exogenous auxins down-regulated PIN2-GFP PM abundance through TIR1/AFB-mediated signaling and promoted PIN2-GFP internalization,intracellular membrane trafficking,and vacuolar degradation,indicating that auxin feedback regulates PIN2-GFP PM levels through TIR1/AFB-mediated signaling and inhibits excessive transport of intracellular auxin out of the cell.%主要观察了外源生长素长时间(8 h)处理对拟南芥生长素极性输出载体PIN2-GFP质膜丰度的影响,低温、KCN处理和生长素受体突变对生长素调控质膜PIN2-GFP丰度的影响,以及液泡H+-ATPase抑制剂ConA对野生型和生长素受体四突变体tir1aafb1,2,3液泡中PIN2-GFP积累的影响.结果表明:外源生长素通过其受体TIR1/AFB介导的信号途径下调质膜PIN2-GFP的丰度,促进PIN2-GFP的内吞、胞内运输和液泡降解.暗示生长素通过TIR1/AFB介导的信号途径反馈调控质膜PIN2-GFP的水平,从而阻止了胞内生长素的过多输出.

  16. Plant embryogenesis requires AUX/LAX-mediated auxin influx

    NARCIS (Netherlands)

    Robert, H.S.; Grunewald, W.; Cannoot, B.; Soriano, M.; Swarup, R.; Weijers, D.; Bennett, M.; Boutilier, K.A.; Friml, J.


    The plant hormone auxin and its directional transport are known to play a crucial role in defining the embryonic axis and subsequent development of the body plan. Although the role of PIN auxin efflux transporters has been clearly assigned during embryonic shoot and root specification, the role of t

  17. Evidence of oxidative attenuation of auxin signalling. (United States)

    Peer, Wendy Ann; Cheng, Yan; Murphy, Angus S


    Indole-3-acetic acid (IAA) is the principle auxin in Arabidopsis and is synthesized primarily in meristems and nodes. Auxin is transported to distal parts of the plant in response to developmental programming or environmental stimuli to activate cell-specific responses. As with any signalling event, the signal must be attenuated to allow the system to reset. Local auxin accumulations are thus reduced by conjugation or catabolism when downstream responses have reached their optima. In most cell types, localized auxin accumulation increases both reactive oxygen species (ROS) and an irreversible catabolic product 2-oxindole-3-acid acid (oxIAA). oxIAA is inactive and does not induce expression of the auxin-responsive reporters DR5 or 2XD0. Here it is shown that oxIAA is not transported from cell to cell, although it appears to be a substrate for the ATP-binding cassette subfamily G (ABCG) transporters that are positioned primarily on the outer lateral surface of the root epidermis. However, oxIAA and oxIAA-Glc levels are higher in ABCB mutants that accumulate auxin due to defective cellular export. Auxin-induced ROS production appears to be at least partially mediated by the NAD(P)H oxidase RbohD. oxIAA levels are higher in mutants that lack ROS-scavenging flavonoids (tt4) and are lower in mutants that accumulate excess flavonols (tt3). These data suggest a model where IAA signalling is attenuated by IAA catabolism to oxIAA. Flavonoids appear to buffer ROS accumulations that occur with localized increases in IAA. This buffering of IAA oxidation would explain some growth responses observed in flavonoid-deficient mutants that cannot be explained by their established role in partially inhibiting auxin transport.

  18. Evolution and structural diversification of PILS putative auxin carriers in plants

    Directory of Open Access Journals (Sweden)

    Elena eFeraru


    Full Text Available The phytohormone auxin contributes to virtually every aspect of the plant development. The spatiotemporal distribution of auxin depends on a complex interplay between auxin metabolism and intercellular auxin transport. Intracellular auxin compartmentalization provides another link between auxin transport processes and auxin metabolism. The PIN-LIKES (PILS putative auxin carriers localize to the endoplasmic reticulum (ER and contribute to cellular auxin homeostasis. PILS proteins regulate intracellular auxin accumulation, the rate of auxin conjugation and subsequently, affect nuclear auxin signalling. Here, we investigate sequence diversification of the PILS family in Arabidopsis thaliana and provide insights into the evolution of these novel putative auxin carriers in plants. Our data suggest that PILS proteins are conserved throughout the plant lineage and expanded during higher plant evolution. PILS proteins diversified early during plant evolution into three clades. Besides the ancient Clade I encompassing non-land plant species, PILS proteins evolved into two clades. The diversification of Clade II and Clade III occurred already at the level of non-vascular plant evolution and, hence, both clades contain vascular and non-vascular plant species. Nevertheless, Clade III contains fewer non- and increased numbers of vascular plants, indicating higher importance of Clade III for vascular plant evolution. Notably, PILS proteins are distinct and appear evolutionarily older than the prominent PIN-FORMED auxin carriers. Moreover, we revealed particular PILS sequence divergence in Arabidopsis and assume that these alterations could contribute to distinct gene regulations and protein functions.

  19. Concentration polarization: Electrodeposition and transport phenomena at overlimiting current

    DEFF Research Database (Denmark)

    Nielsen, Christoffer Peder

    and the boundary layer model, we reveal a number of issues, which invalidate most previous attempts at modeling microchannel concentration polarization using a slip model. Returning to concentration polarization in a bulk system, we study the effects of water splitting at a permselective membrane. We investigate...... this coupled chemical and transport effect using two simple models of the reaction kinetics. The principal investigations are performed using numerical simulations, but in addition we derive an analytical model for the transport in the system. The analytical model reveals an important link between the current...... of salt ions and the current of water ions. This link seemingly exists independent of the specific reaction kinetics, and could help in furthering the understanding of the water splitting process. A fit of the model to experimental data from the literature shows quite good agreement, and provides some...

  20. Spin-polarized transport in Rashba controlled rings

    Energy Technology Data Exchange (ETDEWEB)

    Romeo, F. [Dipartimento di Fisica ' E. R. Caianiello' and Unita C.N.I.S.M., Universita di Salerno, I-84081 Baronissi (Italy); Citro, R. [Dipartimento di Fisica ' E. R. Caianiello' and Unita C.N.I.S.M., Universita di Salerno, I-84081 Baronissi (Italy)]. E-mail:


    We study spin-polarized transport in a Rashba one-dimensional ring interrupted by a tunnel barrier placed in one arm and symmetrically coupled to two external leads. By means of the scattering matrix approach, we investigate the effects on the transport properties of both an applied magnetic flux (Aharonov-Bohm flux) and an effective Aharonov-Casher flux induced by the spin-orbit (SO) Rashba interaction. By varying the model parameters we show a spin-filtering effect relevant for the experimental detection of SO interaction in mesoscopic structures.

  1. Heme and non-heme iron transporters in non-polarized and polarized cells

    Directory of Open Access Journals (Sweden)

    Yasui Yumiko


    Full Text Available Abstract Background Heme and non-heme iron from diet, and recycled iron from hemoglobin are important products of the synthesis of iron-containing molecules. In excess, iron is potentially toxic because it can produce reactive oxygen species through the Fenton reaction. Humans can absorb, transport, store, and recycle iron without an excretory system to remove excess iron. Two candidate heme transporters and two iron transporters have been reported thus far. Heme incorporated into cells is degraded by heme oxygenases (HOs, and the iron product is reutilized by the body. To specify the processes of heme uptake and degradation, and the reutilization of iron, we determined the subcellular localizations of these transporters and HOs. Results In this study, we analyzed the subcellular localizations of 2 isoenzymes of HOs, 4 isoforms of divalent metal transporter 1 (DMT1, and 2 candidate heme transporters--heme carrier protein 1 (HCP1 and heme responsive gene-1 (HRG-1--in non-polarized and polarized cells. In non-polarized cells, HCP1, HRG-1, and DMT1A-I are located in the plasma membrane. In polarized cells, they show distinct localizations: HCP1 and DMT1A-I are located in the apical membrane, whereas HRG-1 is located in the basolateral membrane and lysosome. 16Leu at DMT1A-I N-terminal cytosolic domain was found to be crucial for plasma membrane localization. HOs are located in smooth endoplasmic reticulum and colocalize with NADPH-cytochrome P450 reductase. Conclusions HCP1 and DMT1A-I are localized to the apical membrane, and HRG-1 to the basolateral membrane and lysosome. These findings suggest that HCP1 and DMT1A-I have functions in the uptake of dietary heme and non-heme iron. HRG-1 can transport endocytosed heme from the lysosome into the cytosol. These localization studies support a model in which cytosolic heme can be degraded by HOs, and the resulting iron is exported into tissue fluids via the iron transporter ferroportin 1, which is

  2. Auxin and ethylene interactions control mitotic activity of the quiescent centre, root cap size, and pattern of cap cell differentiation in maize. (United States)

    Ponce, Georgina; Barlow, Peter W; Feldman, Lewis J; Cassab, Gladys I


    Root caps (RCs) are the terminal tissues of higher plant roots. In the present study the factors controlling RC size, shape and structure were examined. It was found that this control involves interactions between the RC and an adjacent population of slowly dividing cells, the quiescent centre, QC. Using the polar auxin transport inhibitor 1-N-naphthylphthalamic acid (NPA), the effects of QC activation on RC gene expression and border cell release was characterized. Ethylene was found to regulate RC size and cell differentiation, since its addition, or the inhibition of its synthesis, affected RC development. The stimulation of cell division in the QC following NPA treatment was reversed by ethylene, and quiescence was re-established. Moreover, inhibition of both ethylene synthesis and auxin polar transport triggered a new pattern of cell division in the root epidermis and led to the appearance of supernumerary epidermal cell files with cap-like characteristics. The data suggest that the QC ensures an ordered internal distribution of auxin, and thereby regulates not only the planes of growth and division in both the root apex proper and the RC meristem, but also regulates cell fate in the RC. Ethylene appears to regulate the auxin redistribution system that resides in the RC. Experiments with Arabidopsis roots also reveal that ethylene plays an important role in regulating the auxin sink, and consequently cell fate in the RC.

  3. Auxin efflux facilitator and auxin dynamism responsible for the gravity-regulated development of peg in cucumber seedlings (United States)

    Takahashi, Hideyuki; Watanabe, Chiaki; Fujii, Nobuharu; Miyazawa, Yutaka

    next to the cortex. This CsPIN1 localization could play a role in transporting auxin from cortex to vascular bundle. In both vascular and pith tissues, CsPIN1 was localized on the bottom plasma membrane of the cells, which could allow auxin to move toward the roots. In the seedlings grown in a horizontal position, endoder-mal cells situated above the vascular bundle localized CsPIN1 on the lower plasma membrane, whereas the polarized localization of CsPIN1 in endodermal cells situated below the vascular bundle became less clear. This differential expression of CsPIN1 in the endodermis commenced within 30 min after gravistimulation. We measured endogenous IAA contents in the transi-tion zone of the 24-hour-old seedlings. In the longitudinally halved transition zone of seedlings grown in a horizontal position, free IAA content was significantly lowered in the upper side, compared to that of the lower side or either side of the transition zone in a vertical position. When 24-hour-old seedlings grown in a vertical position were gravistimulated by reorienting them to the horizontal, free IAA in the lower side of the transition zone increased by 30 min after gravistimulation and eventually decreased to the control level by 180 min after gravistim-ulation. IAA content in the upper side of the transition zone did not change much and was comparable to that in the vertical transition zone during 180 min after gravistimulation. Thus, it appears that gravistimulation causes an immediate increase of IAA level in the lower side and its eventual decrease in the upper side of the transition zone. The gravity-induced changes in CsPIN1 localization in endodermal cells could be involved in auxin redistribution that leads to unilateral positioning of a peg in cucumber seedlings.

  4. Forward genetic screen for auxin-deficient mutants by cytokinin. (United States)

    Wu, Lei; Luo, Pan; Di, Dong-Wei; Wang, Li; Wang, Ming; Lu, Cheng-Kai; Wei, Shao-Dong; Zhang, Li; Zhang, Tian-Zi; Amakorová, Petra; Strnad, Miroslav; Novák, Ondřej; Guo, Guang-Qin


    Identification of mutants with impairments in auxin biosynthesis and dynamics by forward genetic screening is hindered by the complexity, redundancy and necessity of the pathways involved. Furthermore, although a few auxin-deficient mutants have been recently identified by screening for altered responses to shade, ethylene, N-1-naphthylphthalamic acid (NPA) or cytokinin (CK), there is still a lack of robust markers for systematically isolating such mutants. We hypothesized that a potentially suitable phenotypic marker is root curling induced by CK, as observed in the auxin biosynthesis mutant CK-induced root curling 1 / tryptophan aminotransferase of Arabidopsis 1 (ckrc1/taa1). Phenotypic observations, genetic analyses and biochemical complementation tests of Arabidopsis seedlings displaying the trait in large-scale genetic screens showed that it can facilitate isolation of mutants with perturbations in auxin biosynthesis, transport and signaling. However, unlike transport/signaling mutants, the curled (or wavy) root phenotypes of auxin-deficient mutants were significantly induced by CKs and could be rescued by exogenous auxins. Mutants allelic to several known auxin biosynthesis mutants were re-isolated, but several new classes of auxin-deficient mutants were also isolated. The findings show that CK-induced root curling provides an effective marker for discovering genes involved in auxin biosynthesis or homeostasis.

  5. Auxin response factors. (United States)

    Chandler, John William


    Auxin signalling involves the activation or repression of gene expression by a class of auxin response factor (ARF) proteins that bind to auxin response elements in auxin-responsive gene promoters. The release of ARF repression in the presence of auxin by the degradation of their cognate auxin/indole-3-acetic acid repressors forms a paradigm of transcriptional response to auxin. However, this mechanism only applies to activating ARFs, and further layers of complexity of ARF function and regulation are being revealed, which partly reflect their highly modular domain structure. This review summarizes our knowledge concerning ARF binding site specificity, homodimer and heterodimer multimeric ARF association and cooperative function and how activator ARFs activate target genes via chromatin remodelling and evolutionary information derived from phylogenetic comparisons from ARFs from diverse species. ARFs are regulated in diverse ways, and their importance in non-auxin-regulated pathways is becoming evident. They are also embedded within higher-order transcription factor complexes that integrate signalling pathways from other hormones and in response to the environment. The ways in which new information concerning ARFs on many levels is causing a revision of existing paradigms of auxin response are discussed.

  6. Isolation and functional analysis of a Brassica juncea gene encoding a component of auxin efflux carrier

    Institute of Scientific and Technical Information of China (English)



    Polar auxin transport plays a divergent role in plant growth and developmental processes including rootand embryo development, vascular pattern formation and cell elongation. Recently isolated Arabidopsispin gene family was believed to encode a component of auxin efflux carrier (Galweiler et al, 1998). Basedon the Arabidopsis pin1 sequence we have isolated a Brassica juncea cDNA (designated Bjpinl), whichencoded a 70-kDa putative auxin efflux carrier. Deduced BjPIN1 shared 65% identities at protein level withAtPIN1 and was highly homologous to other putative PIN proteins of Arabidopsis (with highest homologyto AtPIN3). Hydrophobic analysis showed similar structures between BjPIN1 and AtPIN proteins. Presenceof 6 exons (varying in size between 65 bp and 1229 bp) and 5 introns (sizes between 89 bp and 463 bp)in the genomic fragment was revealed by comparing the genomic and cDNA sequences. Northern blotanalysis indicated that Bjpinl was expressed in most of the tissues tested, with a relatively higher levelof transcript in flowers and a lower level in root tissues. Promoter-reporter gene fusion studies furtherrevealed the expression of Bjpinl in the mature pollen grains, young seeds, root tip, leaf vascular tissue andtrace bundle, stem epidermis, cortex and vascular cells. BjPIN1 was localized on the plasma membraneas demonstrated through fusion expression of green fluorescent protein (GFP). Auxin efflux carrier activitywas elevated in transgenic Arabidopsis expressing BjPIN1.

  7. Ectopic localization of auxin and cytokinin in tobacco seedlings by the plant-oncogenic AK-6b gene of Agrobacterium tumefaciens AKE10. (United States)

    Takahashi, Sachiko; Sato, Rui; Takahashi, Miho; Hashiba, Noriko; Ogawa, Atsushi; Toyofuku, Kyoko; Sawata, Taiki; Ohsawa, Yuki; Ueda, Kenji; Wabiko, Hiroetsu


    The oncogenic 6b gene of Agrobacterium tumefaciens induces a number of morphological and metabolic alterations in plants. Although molecular functions associated with the 6b genes have been proposed, including auxin transport, sugar transport, transcriptional regulation, and miRNA metabolism, so far an unequivocal conclusion has not been obtained. We investigated the association between auxin accumulation and tumor development of the tobacco seedlings expressing the AK-6b gene under the control of the dexamethasone-inducible promoter. Indole-3-acetic acid (IAA) localization was examined by immunochemical staining with monoclonal antibody against IAA and by histochemical analysis using the IAA-specific induced construct, DR5::GUS (β-glucuronidase). Both procedures indicated that IAA preferentially accumulated in the tumorous protrusions as well as in newly developing vascular bundles in the tumors. Furthermore, true leaves also showed abaxial IAA localization, leading to altered leaves in which the adaxial and abaxial identities were no longer evident. Co-localization of cytokinin and auxin in the abaxial tumors was verified by immunochemical staining with an antibody against cytokinin. Treatment of AK-6b-seedlings with N-1-naphthylphthalamic acid, an inhibitor of polar auxin transport, promoted the morphological severity of phenotypes, whereas 1-naphthoxyacetic acid, a specific auxin influx carrier inhibitor, induced tumor regression on cotyledons and new tumorous proliferations on hypocotyls. Prominent accumulation of both auxin and cytokinin was observed in both regressed and newly developing tumors. We suggest from these results that modulation of auxin/cytokinin localization as a result of AK-6b gene expression is responsible for the tumorous proliferation.

  8. Cadmium interferes with maintenance of auxin homeostasis in Arabidopsis seedlings. (United States)

    Hu, Yan Feng; Zhou, Guoying; Na, Xiao Fan; Yang, Lijing; Nan, Wen Bin; Liu, Xu; Zhang, Yong Qiang; Li, Jiao Long; Bi, Yu Rong


    Auxin and its homeostasis play key roles in many aspects of plant growth and development. Cadmium (Cd) is a phytotoxic heavy metal and its inhibitory effects on plant growth and development have been extensively studied. However, the underlying molecular mechanism of the effects of Cd stress on auxin homeostasis is still unclear. In the present study, we found that the root elongation, shoot weight, hypocotyl length and chlorophyll content in wild-type (WT) Arabidopsis seedlings were significantly reduced after exposure to Cd stress. However, the lateral root (LR) formation was markedly promoted by Cd stress. The level and distribution of auxin were both greatly altered in primary root tips and cotyledons of Cd-treated plants. The results also showed that after Cd treatment, the IAA content was significantly decreased, which was accompanied by increases in the activity of the IAA oxidase and alteration in the expression of several putative auxin biosynthetic and catabolic genes. Application of the auxin transport inhibitor, 1-naphthylphthalamic acid (NPA) and 1-naphthoxyacetic acid (1-NOA), reversed the effects of Cd on LR formation. Additionally, there was less promotion of LR formation by Cd treatment in aux1-7 and pin2 mutants than that in the WT. Meanwhile, Cd stress also altered the expression of PINs and AUX1 in Arabidopsis roots, implying that the auxin transport pathway is required for Cd-modulated LR development. Taken together, these findings suggest that Cd stress disturbs auxin homeostasis through affecting auxin level, distribution, metabolism, and transport in Arabidopsis seedling.

  9. Modelling of Arabidopsis LAX3 expression suggests auxin homeostasis. (United States)

    Mellor, Nathan; Péret, Benjamin; Porco, Silvana; Sairanen, Ilkka; Ljung, Karin; Bennett, Malcolm; King, John


    Emergence of new lateral roots from within the primary root in Arabidopsis has been shown to be regulated by the phytohormone auxin, via the expression of the auxin influx carrier LAX3, mediated by the ARF7/19 IAA14 signalling module (Swarup et al., 2008). A single cell model of the LAX3 and IAA14 auxin response was formulated and used to demonstrate that hysteresis and bistability may explain the experimentally observed 'all-or-nothing' LAX3 spatial expression pattern in cortical cells containing a gradient of auxin concentrations. The model was tested further by using a parameter fitting algorithm to match model output with qRT-PCR mRNA expression data following exogenous auxin treatment. It was found that the model is able to show good agreement with the data, but only when the exogenous auxin signal is degraded over time, at a rate higher than that measured in the experimental medium, suggesting the triggering of an endogenous auxin homeostasis mechanism. Testing the model over a more physiologically relevant range of extracellular auxin shows bistability and hysteresis still occur when using the optimised parameters, providing the rate of LAX3 active auxin transport is sufficiently high relative to passive diffusion.

  10. Vacuolar CAX1 and CAX3 influence auxin transport in guard cells via regulation of apoplastic pH (United States)

    Cation exchangers CAX1 and CAX3 are vacuolar ion transporters involved in ion homeostasis in plants. Widely expressed in the plant, they mediate calcium transport from the cytosol to the vacuole lumen using the proton gradient across the tonoplast. Here, we report an unexpected role of CAX1 and CAX3...

  11. Auxin efflux by PIN-FORMED proteins is activated by two different protein kinases, D6 PROTEIN KINASE and PINOID

    KAUST Repository

    Zourelidou, Melina


    The development and morphology of vascular plants is critically determined by synthesis and proper distribution of the phytohormone auxin. The directed cell-to-cell distribution of auxin is achieved through a system of auxin influx and efflux transporters. PIN-FORMED (PIN) proteins are proposed auxin efflux transporters, and auxin fluxes can seemingly be predicted based on the-in many cells-asymmetric plasma membrane distribution of PINs. Here, we show in a heterologous Xenopus oocyte system as well as in Arabidopsis thaliana inflorescence stems that PIN-mediated auxin transport is directly activated by D6 PROTEIN KINASE (D6PK) and PINOID (PID)/WAG kinases of the Arabidopsis AGCVIII kinase family. At the same time, we reveal that D6PKs and PID have differential phosphosite preferences. Our study suggests that PIN activation by protein kinases is a crucial component of auxin transport control that must be taken into account to understand auxin distribution within the plant.

  12. Auxin efflux by PIN-FORMED proteins is activated by two different protein kinases, D6 PROTEIN KINASE and PINOID. (United States)

    Zourelidou, Melina; Absmanner, Birgit; Weller, Benjamin; Barbosa, Inês C R; Willige, Björn C; Fastner, Astrid; Streit, Verena; Port, Sarah A; Colcombet, Jean; de la Fuente van Bentem, Sergio; Hirt, Heribert; Kuster, Bernhard; Schulze, Waltraud X; Hammes, Ulrich Z; Schwechheimer, Claus


    The development and morphology of vascular plants is critically determined by synthesis and proper distribution of the phytohormone auxin. The directed cell-to-cell distribution of auxin is achieved through a system of auxin influx and efflux transporters. PIN-FORMED (PIN) proteins are proposed auxin efflux transporters, and auxin fluxes can seemingly be predicted based on the--in many cells--asymmetric plasma membrane distribution of PINs. Here, we show in a heterologous Xenopus oocyte system as well as in Arabidopsis thaliana inflorescence stems that PIN-mediated auxin transport is directly activated by D6 PROTEIN KINASE (D6PK) and PINOID (PID)/WAG kinases of the Arabidopsis AGCVIII kinase family. At the same time, we reveal that D6PKs and PID have differential phosphosite preferences. Our study suggests that PIN activation by protein kinases is a crucial component of auxin transport control that must be taken into account to understand auxin distribution within the plant.

  13. Negative phototropism is seen in Arabidopsis inflorescences when auxin signaling is reduced to a minimal level by an Aux/IAA dominant mutation, axr2. (United States)

    Sato, Atsuko; Sasaki, Shu; Matsuzaki, Jun; Yamamoto, Kotaro T


    Inflorescences of a dominant mutant of Arabidopsis Aux/IAA7, axr2, showed negative phototropism with a similar fluence response curve to the positive phototropism of wild-type stems. Application of a synthetic auxin, NAA, and an inhibitor of polar auxin transport, NPA, increased and decreased respectively the magnitude of the phototropic response in the wild type, while in axr2 application of NAA reduced the negative phototropic response and NPA had no effect. Decapitation of the apex induced a small negative phototropism in wild-type stems, and had no effect in axr2 plants. Inflorescences of the double mutants of auxin transporters, pgp1 pgp19, showed no phototropic response, while decapitation resulted in a negative phototropic response. These results suggest that negative phototropism can occur when the level of auxin or of auxin signaling is reduced to a minimal level, and that in plant axial organs the default phototropic response to unilateral blue light may be negative. Expression of axr2 protein by an endodermis-specific promoter resulted in agravitropism of inflorescences in a similar way to that of axr2, but phototropism was normal, confirming that the endodermis does not play a critical role in phototropism.

  14. Endoplasmic reticulum localization and activity of maize auxin biosynthetic enzymes. (United States)

    Kriechbaumer, Verena; Seo, Hyesu; Park, Woong June; Hawes, Chris


    Auxin is a major growth hormone in plants and the first plant hormone to be discovered and studied. Active research over >60 years has shed light on many of the molecular mechanisms of its action including transport, perception, signal transduction, and a variety of biosynthetic pathways in various species, tissues, and developmental stages. The complexity and redundancy of the auxin biosynthetic network and enzymes involved raises the question of how such a system, producing such a potent agent as auxin, can be appropriately controlled at all. Here it is shown that maize auxin biosynthesis takes place in microsomal as well as cytosolic cellular fractions from maize seedlings. Most interestingly, a set of enzymes shown to be involved in auxin biosynthesis via their activity and/or mutant phenotypes and catalysing adjacent steps in YUCCA-dependent biosynthesis are localized to the endoplasmic reticulum (ER). Positioning of auxin biosynthetic enzymes at the ER could be necessary to bring auxin biosynthesis in closer proximity to ER-localized factors for transport, conjugation, and signalling, and allow for an additional level of regulation by subcellular compartmentation of auxin action. Furthermore, it might provide a link to ethylene action and be a factor in hormonal cross-talk as all five ethylene receptors are ER localized.

  15. Isolation and characterization of a cDNA clone encoding an auxin influx carrier in carnation cuttings. Expression in different organs and cultivars and its relationship with cold storage. (United States)

    Oliveros-Valenzuela, María Del Rocío; Reyes, David; Sánchez-Bravo, José; Acosta, Manuel; Nicolás, Carlos


    Polar auxin transport (PAT) is necessary for the formation of adventitious roots in the base of leafy stem cuttings, as has been demonstrated in several studies in which the application of PAT inhibitors strongly inhibited the rooting of cuttings. However, unlike in the case of lateral roots, there is almost no information on the molecular mechanism that controls PAT in the formation of adventitious roots. A novel cDNA encoding an auxin influx carrier has been isolated and characterized from carnation (Dianthus caryophyllus) cuttings. The full length of DcAUX1 was obtained and the deduced aminoacid sequence revealed a high degree of identity with the corresponding auxin carrier proteins from several species. The expression of this gene depended on the organ, the carnation cultivar and the length of time cuttings had been stored in a cold chamber. As a rule, expression was higher in stem than in leaves, in the basal than in the first internode and in mature than in young leaves irrespective of the cultivar and the duration of the storage. This pattern of expression agrees with the results of a previous study showing that auxin from mature leaves was essential for rooting, while exogenous auxin applied to mature leaves was polarly transported in the stem and accumulated in the basal internode (the rooting zone). Variations in the expression observed during storage (depending of the cultivar) might be related to the variation in PAT and rooting reported in previous studies.

  16. Role of auxin and protons in plant shoot gravitropism (United States)

    Rayle, D. L.; Migliaccio, F.; Watson, E.


    Experiments designed to probe the relationship between asymmetric acid efflux and auxin redistribution during gravitropism are reported. Gravistimulation of sunflower hypocotyls results in the retardation of growth on the upper surface and the acceleration of growth on the lower surface relative to a vertically oriented control. Auxin and H(+) both elicit growth over a similarly broad region of the hypocotyl. The correspondence between auxin, H(+), and gravisensitive tissues is consistent with the notion that auxin redistribution may initiate asymmetric acid efflux during gravistimulation. Data are presented showing a redistribution of C-14-IAA and H-3-IAA occurs within 20-30 minutes of gravistimulation. Data on the effects of selected inhibitors of shoot gravitropism are also presented. Taken together, the data suggest that lateral transport of auxin initiates asymmetric acid efflux in gravitropically stimulated shoots.

  17. Auxin and nitric oxide control indeterminate nodule formation

    Directory of Open Access Journals (Sweden)

    Spena Angelo


    Full Text Available Abstract Background Rhizobia symbionts elicit root nodule formation in leguminous plants. Nodule development requires local accumulation of auxin. Both plants and rhizobia synthesise auxin. We have addressed the effects of bacterial auxin (IAA on nodulation by using Sinorhizobium meliloti and Rhizobium leguminosarum bacteria genetically engineered for increased auxin synthesis. Results IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules. Indeterminate legumes (Medicago species bearing IAA-overproducing nodules showed an enhanced lateral root development, a process known to be regulated by both IAA and nitric oxide (NO. Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia. The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains. Conclusion The data hereby presented demonstrate that auxin synthesised by rhizobia and nitric oxide positively affect indeterminate nodule formation and, together with the observation of increased expression of an auxin efflux carrier in roots bearing nodules with higher IAA and NO content, support a model of nodule formation that involves auxin transport regulation and NO synthesis.

  18. 生长素调节植物花发育的研究进展%Research Progress on Auxin Regulation in Flower DeveloPment

    Institute of Scientific and Technical Information of China (English)

    严希; 彭剑涛


    花是被子植物的繁殖器官,花的发育是植物繁衍后代的关键环节。大量研究表明,花发育受到基因、植物激素、温度等多种内外因素的调控,生长素在此过程中扮演着不可或缺的角色。本文介绍了国内外生长素调控花发育研究的进展,尤其是生长素极性运输、生长素含量变化以及生长素信号转导在花器官发育过程中的作用。%Flower is the reproductive organ of angiosperm,and flower development is the key step in the progress of reproduction. Numerous researches have indicated that flower development is regulated by genes,plant hor-mones,temperature,and so on. Plant hormones,especially auxin,play indispensable roles in regulation of flow-er development. In this review we introduced the research progress on auxin regulation in flower development. Effects of polar auxin transport,changes in auxin contents and auxin signal transduction on the development of flower were reviewed in particular.

  19. Auxin activates the plasma membrane H+-ATPase by phosphorylation during hypocotyl elongation in Arabidopsis. (United States)

    Takahashi, Koji; Hayashi, Ken-ichiro; Kinoshita, Toshinori


    The phytohormone auxin is a major regulator of diverse aspects of plant growth and development. The ubiquitin-ligase complex SCF(TIR1/AFB) (for Skp1-Cul1-F-box protein), which includes the TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F-BOX (TIR1/AFB) auxin receptor family, has recently been demonstrated to be critical for auxin-mediated transcriptional regulation. Early-phase auxin-induced hypocotyl elongation, on the other hand, has long been explained by the acid-growth theory, for which proton extrusion by the plasma membrane H(+)-ATPase is a functional prerequisite. However, the mechanism by which auxin mediates H(+)-ATPase activation has yet to be elucidated. Here, we present direct evidence for H(+)-ATPase activation in etiolated hypocotyls of Arabidopsis (Arabidopsis thaliana) by auxin through phosphorylation of the penultimate threonine during early-phase hypocotyl elongation. Application of the natural auxin indole-3-acetic acid (IAA) to endogenous auxin-depleted hypocotyl sections induced phosphorylation of the penultimate threonine of the H(+)-ATPase and increased H(+)-ATPase activity without altering the amount of the enzyme. Changes in both the phosphorylation level of H(+)-ATPase and IAA-induced elongation were similarly concentration dependent. Furthermore, IAA-induced H(+)-ATPase phosphorylation occurred in a tir1-1 afb2-3 double mutant, which is severely defective in auxin-mediated transcriptional regulation. In addition, α-(phenylethyl-2-one)-IAA, the auxin antagonist specific for the nuclear auxin receptor TIR1/AFBs, had no effect on IAA-induced H(+)-ATPase phosphorylation. These results suggest that the TIR1/AFB auxin receptor family is not involved in auxin-induced H(+)-ATPase phosphorylation. Our results define the activation mechanism of H(+)-ATPase by auxin during early-phase hypocotyl elongation; this is the long-sought-after mechanism that is central to the acid-growth theory.

  20. Auxin influx carriers control vascular patterning and xylem differentiation in Arabidopsis thaliana.

    Directory of Open Access Journals (Sweden)

    Norma Fàbregas


    Full Text Available Auxin is an essential hormone for plant growth and development. Auxin influx carriers AUX1/LAX transport auxin into the cell, while auxin efflux carriers PIN pump it out of the cell. It is well established that efflux carriers play an important role in the shoot vascular patterning, yet the contribution of influx carriers to the shoot vasculature remains unknown. Here, we combined theoretical and experimental approaches to decipher the role of auxin influx carriers in the patterning and differentiation of vascular tissues in the Arabidopsis inflorescence stem. Our theoretical analysis predicts that influx carriers facilitate periodic patterning and modulate the periodicity of auxin maxima. In agreement, we observed fewer and more spaced vascular bundles in quadruple mutants plants of the auxin influx carriers aux1lax1lax2lax3. Furthermore, we show AUX1/LAX carriers promote xylem differentiation in both the shoot and the root tissues. Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation. In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation. Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants.

  1. Gibberellins regulate lateral root formation in Populus through interactions with auxin and other hormones. (United States)

    Gou, Jiqing; Strauss, Steven H; Tsai, Chung Jui; Fang, Kai; Chen, Yiru; Jiang, Xiangning; Busov, Victor B


    The role of gibberellins (GAs) in regulation of lateral root development is poorly understood. We show that GA-deficient (35S:PcGA2ox1) and GA-insensitive (35S:rgl1) transgenic Populus exhibited increased lateral root proliferation and elongation under in vitro and greenhouse conditions, and these effects were reversed by exogenous GA treatment. In addition, RNA interference suppression of two poplar GA 2-oxidases predominantly expressed in roots also decreased lateral root formation. GAs negatively affected lateral root formation by inhibiting lateral root primordium initiation. A whole-genome microarray analysis of root development in GA-modified transgenic plants revealed 2069 genes with significantly altered expression. The expression of 1178 genes, including genes that promote cell proliferation, growth, and cell wall loosening, corresponded to the phenotypic severity of the root traits when transgenic events with differential phenotypic expression were compared. The array data and direct hormone measurements suggested crosstalk of GA signaling with other hormone pathways, including auxin and abscisic acid. Transgenic modification of a differentially expressed gene encoding an auxin efflux carrier suggests that GA modulation of lateral root development is at least partly imparted by polar auxin transport modification. These results suggest a mechanism for GA-regulated modulation of lateral root proliferation associated with regulation of plant allometry during the stress response.

  2. Noncoding transcription by alternative rna polymerases dynamically regulates an auxin-driven chromatin loop

    KAUST Repository

    Ariel, Federico D.


    The eukaryotic epigenome is shaped by the genome topology in three-dimensional space. Dynamic reversible variations in this epigenome structure directly influence the transcriptional responses to developmental cues. Here, we show that the Arabidopsis long intergenic noncoding RNA (lincRNA) APOLO is transcribed by RNA polymerases II and V in response to auxin, a phytohormone controlling numerous facets of plant development. This dual APOLO transcription regulates the formation of a chromatin loop encompassing the promoter of its neighboring gene PID, a key regulator of polar auxin transport. Altering APOLO expression affects chromatin loop formation, whereas RNA-dependent DNA methylation, active DNA demethylation, and Polycomb complexes control loop dynamics. This dynamic chromatin topology determines PID expression patterns. Hence, the dual transcription of a lincRNA influences local chromatin topology and directs dynamic auxin-controlled developmental outputs on neighboring genes. This mechanism likely underscores the adaptive success of plants in diverse environments and may be widespread in eukaryotes. © 2014 Elsevier Inc.

  3. Microtubule polarity and the direction of pigment transport reverse simultaneously in surgically severed melanophore arms. (United States)

    McNiven, M A; Wang, M; Porter, K R


    The transport of pigment through the long cytoplasmic extensions (arms) of teleost melanophores is a microtubule-dependent event. We have severed the arms from melanophores to test whether microtubules isolated from the centrosome maintain their original polarity and disposition. In addition, we have tested whether arms containing microtubules of mixed polarities alter the direction of pigment transport. We find that microtubules within severed arms eventually change their polarity and reorganize from the arm center as if to form a new minicell. Concomitant with this change is a reversal in the direction of pigment transport.

  4. Small molecules unravel complex interplay between auxin biology and endomembrane trafficking. (United States)

    Doyle, Siamsa M; Vain, Thomas; Robert, Stéphanie


    The establishment and maintenance of controlled auxin gradients within plant tissues are essential for a multitude of developmental processes. Auxin gradient formation is co-ordinated via local biosynthesis and transport. Cell to cell auxin transport is facilitated and precisely regulated by complex endomembrane trafficking mechanisms that target auxin carrier proteins to their final destinations. In turn, auxin and cross-talk with other phytohormones regulate the endomembrane trafficking of auxin carriers. Dissecting such rapid and complicated processes is challenging for classical genetic experiments due to trafficking pathway diversity, gene functional redundancy, and lethality in loss-of-function mutants. Many of these difficulties can be bypassed via the use of small molecules to modify or disrupt the function or localization of proteins. Here, we will review examples of the knowledge acquired by the use of such chemical tools in this field, outlining the advantages afforded by chemical biology approaches.

  5. Enhancement of spin polarization in transport through protein-like single-helical molecules (United States)

    Wu, Hai-Na; Wang, Xiao; Zhang, Ya-Jing; Yi, Guang-Yu; Gong, Wei-Jiang


    We investigate the spin-polarized electron transport through the single-helical molecules connected with two normal metallic leads. On the basis of an effective model Hamiltonian, influences of the structural parameters on the conductance and the spin polarization are calculated by using the Landauer-Büttiker formula. The optimal structural parameters for the maximal spin polarization are analyzed. Our results show that the dephasing term is an important factor to enhance the spin polarization, in addition to the intrinsic parameters of the single-helical molecule. This work can be helpful in optimizing the spin polarization in the protein-like single-helical molecules.

  6. Implementation of polarization processes in a charge transport model applied on poly(ethylene naphthalate) films (United States)

    Hoang, M.-Q.; Le Roy, S.; Boudou, L.; Teyssedre, G.


    One of the difficulties in unravelling transport processes in electrically insulating materials is the fact that the response, notably charging current transients, can have mixed contributions from orientation polarization and from space charge processes. This work aims at identifying and characterizing the polarization processes in a polar polymer in the time and frequency-domains and to implement the contribution of the polarization into a charge transport model. To do so, Alternate Polarization Current (APC) and Dielectric Spectroscopy measurements have been performed on poly(ethylene naphthalene 2,6-dicarboxylate) (PEN), an aromatic polar polymer, providing information on polarization mechanisms in the time- and frequency-domain, respectively. In the frequency-domain, PEN exhibits 3 relaxation processes termed β, β* (sub-glass transitions), and α relaxations (glass transition) in increasing order of temperature. Conduction was also detected at high temperatures. Dielectric responses were treated using a simplified version of the Havriliak-Negami model (Cole-Cole (CC) model), using 3 parameters per relaxation process, these parameters being temperature dependent. The time dependent polarization obtained from the CC model is then added to a charge transport model. Simulated currents issued from the transport model implemented with the polarization are compared with the measured APCs, showing a good consistency between experiments and simulations in a situation where the response comes essentially from dipolar processes.

  7. Clathrin-Mediated Auxin Efflux and Maxima Regulate Hypocotyl Hook Formation and Light-Stimulated Hook Opening in Arabidopsis. (United States)

    Yu, Qinqin; Zhang, Ying; Wang, Juan; Yan, Xu; Wang, Chao; Xu, Jian; Pan, Jianwei


    The establishment of auxin maxima by PIN-FORMED 3 (PIN3)- and AUXIN RESISTANT 1/LIKE AUX1 (LAX) 3 (AUX1/LAX3)-mediated auxin transport is essential for hook formation in Arabidopsis hypocotyls. Until now, however, the underlying regulatory mechanism has remained poorly understood. Here, we show that loss of function of clathrin light chain CLC2 and CLC3 genes enhanced auxin maxima and thereby hook curvature, alleviated the inhibitory effect of auxin overproduction on auxin maxima and hook curvature, and delayed blue light-stimulated auxin maxima reduction and hook opening. Moreover, pharmacological experiments revealed that auxin maxima formation and hook curvature in clc2 clc3 were sensitive to auxin efflux inhibitors 1-naphthylphthalamic acid and 2,3,5-triiodobenzoic acid but not to the auxin influx inhibitor 1-naphthoxyacetic acid. Live-cell imaging analysis further uncovered that loss of CLC2 and CLC3 function impaired PIN3 endocytosis and promoted its lateralization in the cortical cells but did not affect AUX1 localization. Taken together, these results suggest that clathrin regulates auxin maxima and thereby hook formation through modulating PIN3 localization and auxin efflux, providing a novel mechanism that integrates developmental signals and environmental cues to regulate plant skotomorphogenesis and photomorphogenesis.

  8. Polarized protein transport and lumen formation during epithelial tissue morphogenesis. (United States)

    Blasky, Alex J; Mangan, Anthony; Prekeris, Rytis


    One of the major challenges in biology is to explain how complex tissues and organs arise from the collective action of individual polarized cells. The best-studied model of this process is the cross talk between individual epithelial cells during their polarization to form the multicellular epithelial lumen during tissue morphogenesis. Multiple mechanisms of apical lumen formation have been proposed. Some epithelial lumens form from preexisting polarized epithelial structures. However, de novo lumen formation from nonpolarized cells has recently emerged as an important driver of epithelial tissue morphogenesis, especially during the formation of small epithelial tubule networks. In this review, we discuss the latest findings regarding the mechanisms and regulation of de novo lumen formation in vitro and in vivo.

  9. Lysine63-linked ubiquitylation of PIN2 auxin carrier protein governs hormonally controlled adaptation of Arabidopsis root growth. (United States)

    Leitner, Johannes; Petrášek, Jan; Tomanov, Konstantin; Retzer, Katarzyna; Pařezová, Markéta; Korbei, Barbara; Bachmair, Andreas; Zažímalová, Eva; Luschnig, Christian


    Cross-talk between plant cells and their surroundings requires tight regulation of information exchange at the plasma membrane (PM), which involves dynamic adjustments of PM protein localization and turnover to modulate signal perception and solute transport at the interface between cells and their surroundings. In animals and fungi, turnover of PM proteins is controlled by reversible ubiquitylation, which signals endocytosis and delivery to the cell's lytic compartment, and there is emerging evidence for related mechanisms in plants. Here, we describe the fate of Arabidopsis PIN2 protein, required for directional cellular efflux of the phytohormone auxin, and identify cis- and trans-acting mediators of PIN2 ubiquitylation. We demonstrate that ubiquitin acts as a principal signal for PM protein endocytosis in plants and reveal dynamic adjustments in PIN2 ubiquitylation coinciding with variations in vacuolar targeting and proteolytic turnover. We show that control of PIN2 proteolytic turnover via its ubiquitylation status is of significant importance for auxin distribution in root meristems and for environmentally controlled adaptations of root growth. Moreover, we provide experimental evidence indicating that PIN2 vacuolar sorting depends on modification specifically by lysine(63)-linked ubiquitin chains. Collectively, our results establish lysine(63)-linked PM cargo ubiquitylation as a regulator of polar auxin transport and adaptive growth responses in higher plants.

  10. Identification of auxin responsive genes in Arabidopsis by cDNA array

    Institute of Scientific and Technical Information of China (English)


    The plant hormone auxin influences a variety of developmental and physiological processes. But the mechanism of its action is quite unclear. In order to identify and analyze the expression of auxin responsive genes, a cDNA array approach was used to screen for genes with altered expression from Arabidopsis suspension culture after IAA treatment and was identified 50 differentially expressed genes from 13824 cDNA clones. These genes were related to signal transduction, stress responses, senescence, photosynthesis, protein biosynthesis and transportation. The results provide the molecular evidence that auxin influences a variety of physiological processes and pave a way for further investigation of the mechanism of auxin action. Furthermore,we found that the expression of a ClpC (regulation subunit of Clp protease) was repressed by exogenous auxin, but increased in dark-induced senescing leaves. This suggests that ClpC may be a senescence-associated gene and can be regulated by auxin.

  11. Dynamic Regulation of Auxin Response during Rice Development Revealed by Newly Established Hormone Biosensor Markers (United States)

    Yang, Jing; Yuan, Zheng; Meng, Qingcai; Huang, Guoqiang; Périn, Christophe; Bureau, Charlotte; Meunier, Anne-Cécile; Ingouff, Mathieu; Bennett, Malcolm J.; Liang, Wanqi; Zhang, Dabing


    The hormone auxin is critical for many plant developmental processes. Unlike the model eudicot plant Arabidopsis (Arabidopsis thaliana), auxin distribution and signaling in rice tissues has not been systematically investigated due to the absence of suitable auxin response reporters. In this study we observed the conservation of auxin signaling components between Arabidopsis and model monocot crop rice (Oryza sativa), and generated complementary types of auxin biosensor constructs, one derived from the Aux/IAA-based biosensor DII-VENUS but constitutively driven by maize ubiquitin-1 promoter, and the other termed DR5-VENUS in which a synthetic auxin-responsive promoter (DR5rev) was used to drive expression of the yellow fluorescent protein (YFP). Using the obtained transgenic lines, we observed that during the vegetative development, accumulation of DR5-VENUS signal was at young and mature leaves, tiller buds and stem base. Notably, abundant DR5-VENUS signals were observed in the cytoplasm of cortex cells surrounding lateral root primordia (LRP) in rice. In addition, auxin maxima and dynamic re-localization were seen at the initiation sites of inflorescence and spikelet primordia including branch meristems (BMs), female and male organs. The comparison of these observations among Arabidopsis, rice and maize suggests the unique role of auxin in regulating rice lateral root emergence and reproduction. Moreover, protein localization of auxin transporters PIN1 homologs and GFP tagged OsAUX1 overlapped with DR5-VENUS during spikelet development, helping validate these auxin response reporters are reliable markers in rice. This work firstly reveals the direct correspondence between auxin distribution and rice reproductive and root development at tissue and cellular level, and provides high-resolution auxin tools to probe fundamental developmental processes in rice and to establish links between auxin, development and agronomical traits like yield or root architecture. PMID

  12. Effect of the degree of polar mismatching on traffic jam formation in fast axonal transport. (United States)

    Kuznetsov, A V


    This paper simulates an axon with a region of reversed microtubule (MT) polarity, and investigates how the degree of polar mismatching in this region affects the formation of organelle traps in the axon. The model is based on modified Smith-Simmons equations governing molecular-motor-assisted transport in neurons. It is established that the structure that develops as a result of a region with disoriented MTs consists of two organelle traps, the trap to the left of this region accumulates plus-end-oriented organelles and the trap to the right of this region accumulates minus-end-oriented organelles. The presence of such a structure is shown to inhibit the transport of organelles down the axon. The degree by which the transport of organelles is inhibited depends on the degree of polar mismatching of MTs in the region between MT traps. Four cases with a different degree of polar mismatching are investigated.

  13. Redirection of auxin flow in Arabidopsis thaliana roots after infection by root-knot nematodes

    NARCIS (Netherlands)

    Kyndt, Tina; Goverse, Aska; Haegeman, Annelies; Warmerdam, Sonja; Wanjau, Cecilia; Jahani, Mona; Engler, Gilbert; Almeida Engler, De Janice; Gheysen, Godelieve


    Plant-parasitic root-knot nematodes induce the formation of giant cells within the plant root, and it has been recognized that auxin accumulates in these feeding sites. Here, we studied the role of the auxin transport system governed by AUX1/LAX3 influx proteins and different PIN efflux proteins dur

  14. Local Auxin Sources Orient the Apical-Basal Axis in Arabidopsis Embryos

    NARCIS (Netherlands)

    Robert, H.S.; Grones, P.; Stepanova, A.N.; Robles, L.M.; Lokerse, A.S.; Alonso, J.M.; Weijers, D.; Friml, J.


    Establishment of the embryonic axis foreshadows the main body axis of adults both in plants and in animals, but underlying mechanisms are considered distinct. Plants utilize directional, cell-to-cell transport of the growth hormone auxin [1 and 2] to generate an asymmetric auxin response that specif

  15. Auxin and ethylene induce flavonol accumulation through distinct transcriptional networks. (United States)

    Lewis, Daniel R; Ramirez, Melissa V; Miller, Nathan D; Vallabhaneni, Prashanthi; Ray, W Keith; Helm, Richard F; Winkel, Brenda S J; Muday, Gloria K


    Auxin and ethylene are key regulators of plant growth and development, and thus the transcriptional networks that mediate responses to these hormones have been the subject of intense research. This study dissected the hormonal cross talk regulating the synthesis of flavonols and examined their impact on root growth and development. We analyzed the effects of auxin and an ethylene precursor on roots of wild-type and hormone-insensitive Arabidopsis (Arabidopsis thaliana) mutants at the transcript, protein, and metabolite levels at high spatial and temporal resolution. Indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) differentially increased flavonol pathway transcripts and flavonol accumulation, altering the relative abundance of quercetin and kaempferol. The IAA, but not ACC, response is lost in the transport inhibitor response1 (tir1) auxin receptor mutant, while ACC responses, but not IAA responses, are lost in ethylene insensitive2 (ein2) and ethylene resistant1 (etr1) ethylene signaling mutants. A kinetic analysis identified increases in transcripts encoding the transcriptional regulators MYB12, Transparent Testa Glabra1, and Production of Anthocyanin Pigment after hormone treatments, which preceded increases in transcripts encoding flavonoid biosynthetic enzymes. In addition, myb12 mutants were insensitive to the effects of auxin and ethylene on flavonol metabolism. The equivalent phenotypes for transparent testa4 (tt4), which makes no flavonols, and tt7, which makes kaempferol but not quercetin, showed that quercetin derivatives are the inhibitors of basipetal root auxin transport, gravitropism, and elongation growth. Collectively, these experiments demonstrate that auxin and ethylene regulate flavonol biosynthesis through distinct signaling networks involving TIR1 and EIN2/ETR1, respectively, both of which converge on MYB12. This study also provides new evidence that quercetin is the flavonol that modulates basipetal auxin transport.

  16. A multi-ion generalized transport model of the polar wind (United States)

    Demars, H. G.; Schunk, R. W.


    The higher-order generalizations of the equations of standard hydrodynamics, known collectively as generalized transport theories, have been used since the early 1980s to describe the terrestrial polar wind. Inherent in the structure of generalized transport theories is the ability to describe not only interparticle collisions but also certain non-Maxwellian processes, such as heat flow and viscous stress, that are characteristic of any plasma flow that is not collision dominated. Because the polar wind exhibits a transition from collision-dominated to collisionless flow, generalized transport theories possess advantages for polar wind modeling not shared by either collision-dominated models (such as standard hydrodynamics) or collisionless models (such as those based on solving the collisionless Boltzmann equation). In general, previous polar wind models have used generalized transport equations to describe electrons and only one species of ion (H(+)). If other ion species were included in the models at all, it was in a simplified or semiempirical manner. The model described in this paper is the first polar wind model that uses a generalized transport theory (bi-Maxwellian-based 16-moment theory) to describe all of the species, both major and minor, in the polar wind plasma. In the model, electrons and three ion species (H(+), He(+), O(+)) are assumed to be major and several ion species are assumed to be minor (NO(+), Fe(+), O(++)). For all species, a complete 16-moment transport formulation is used, so that profiles of density, drift velocity, parallel and perpendicular temperatures, and the field-aligned parallel and perpendicular energy flows are obtained. In the results presented here, emphasis is placed on describing those constituents of the polar wind that have received little attention in past studies. In particular, characteristic solutions are presented for supersonic H(+) outflow and for both supersonic and subsonic outflows of the major ion He


    mechanism of auxin action on the enhancement of ethylene production is the formation of enzymes involved in ethylene biogenesis....The stimulation of ethylene production by auxin was inhibited by actinomycin D and other inhibitors of protein synthesis. It is concluded that the

  18. The importance of localized auxin production for morphogenesis of reproductive organs and embryos in Arabidopsis. (United States)

    Robert, Hélène S; Crhak Khaitova, Lucie; Mroue, Souad; Benková, Eva


    Plant sexual reproduction involves highly structured and specialized organs: stamens (male) and gynoecia (female, containing ovules). These organs synchronously develop within protective flower buds, until anthesis, via tightly coordinated mechanisms that are essential for effective fertilization and production of viable seeds. The phytohormone auxin is one of the key endogenous signalling molecules controlling initiation and development of these, and other, plant organs. In particular, its uneven distribution, resulting from tightly controlled production, metabolism and directional transport, is an important morphogenic factor. In this review we discuss how developmentally controlled and localized auxin biosynthesis and transport contribute to the coordinated development of plants' reproductive organs, and their fertilized derivatives (embryos) via the regulation of auxin levels and distribution within and around them. Current understanding of the links between de novo local auxin biosynthesis, auxin transport and/or signalling is presented to highlight the importance of the non-cell autonomous action of auxin production on development and morphogenesis of reproductive organs and embryos. An overview of transcription factor families, which spatiotemporally define local auxin production by controlling key auxin biosynthetic enzymes, is also presented.

  19. Redirection of auxin flow in Arabidopsis thaliana roots after infection by root-knot nematodes (United States)

    Kyndt, Tina; Goverse, Aska; Haegeman, Annelies; Warmerdam, Sonja; Wanjau, Cecilia; Jahani, Mona; Engler, Gilbert; de Almeida Engler, Janice; Gheysen, Godelieve


    Plant-parasitic root-knot nematodes induce the formation of giant cells within the plant root, and it has been recognized that auxin accumulates in these feeding sites. Here, we studied the role of the auxin transport system governed by AUX1/LAX3 influx proteins and different PIN efflux proteins during feeding site development in Arabidopsis thaliana roots. Data generated via promoter–reporter line and protein localization analyses evoke a model in which auxin is being imported at the basipetal side of the feeding site by the concerted action of the influx proteins AUX1 and LAX3, and the efflux protein PIN3. Mutants in auxin influx proteins AUX1 and LAX3 bear significantly fewer and smaller galls, revealing that auxin import into the feeding sites is needed for their development and expansion. The feeding site development in auxin export (PIN) mutants was only slightly hampered. Expression of some PINs appears to be suppressed in galls, probably to prevent auxin drainage. Nevertheless, a functional PIN4 gene seems to be a prerequisite for proper nematode development and gall expansion, most likely by removing excessive auxin to stabilize the hormone level in the feeding site. Our data also indicate a role of local auxin peaks in nematode attraction towards the root. PMID:27312670

  20. Function of type-2 Arabidopsis hemoglobin in the auxin-mediated formation of embryogenic cells during morphogenesis

    DEFF Research Database (Denmark)

    Elhiti, Mohamed; Hebelstrup, Kim; Wang, Aiming;


    Suppression of the Arabidopsis GLB2, a type-2 nonsymbiotic hemoglobin, enhances somatic embryogenesis by increasing auxin production. In the glb2 knock-out line (GLB2 -/-) polarization of PIN1 proteins and auxin maxima occurred at the base of the cotyledons of the zygotic explants, which are the ...

  1. Can Surface Flux Transport Account for the Weak Polar Field in Cycle 23? (United States)

    Jiang, Jie; Cameron, Robert H.; Schmitt, Dieter; Schüssler, Manfred


    To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations.

  2. Can surface flux transport account for the weak polar field in cycle 23?

    CERN Document Server

    Jiang, Jie; Schmitt, Dieter; Schuessler, Manfred


    To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations.

  3. Double ferromagnetic metal/semiconductor schottky barrier confined quasi-ballistic transport channel as spin polarizer

    Institute of Scientific and Technical Information of China (English)

    Wen Wu


    Spin polarizer is one of the most important devices for the newly developing field of spintronics, which may revolute the popular information techniques. Here we present a phenomenal model for a novel spin polarizer, which utilizes two back to back ferromagnetic metal/semiconductor Schottky barriers to define a semiconductor transport channel whose length is less than the spin decoherence length of the host semiconductor. Along this channel, conducting electrons move diffusively in momentum space while they keep ballistic motion in spin space. Across the channel, electrons suffer a spin dependent tunneling, which establishes spin polarization along the channel.

  4. Polarization correction for ionization loss in a galactic cosmic ray transport code (HZETRN) (United States)

    Shinn, Judy L.; Farhat, Hamidullah; Badavi, Francis F.; Wilson, John W.


    An approximate polarization correction for ionization loss suggested by Sternheimer has been implemented in the galactic cosmic ray transport code (HZETRN) developed at the Langley Research Center. Sample calculations made for the aluminum shield and liquid hydrogen shield show no more than a plus or minus 2 percent change in the linear energy transfer (LET) distribution for flux compared with those without polarization correction. This very small change is expected because the effect of polarization correction on the reduction in stopping power of ions with energies above 2 GeV/amu is suppressed by the decrease in galactic cosmic ray ion flux at such high energies.

  5. Spin-Polarized Transport through Parallel Double Quantum Dots Coupled to Ferromagnetic Leads

    Institute of Scientific and Technical Information of China (English)

    HOU Tao; WU Shao-Quan; BI Ai-Hua; YANG Fu-Bin; SUN Wei-Li


    We theoretically study the spin-polarized transport phenomena of the parallel double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. The Hamiltonian is solved by means of the equation-of-motion approach. We analyse the transmission probability of this system in both the equilibrium and nonequilibrium cases, and our results reveal that the transport properties show some noticeable characteristics depending upon both the spin-polarized strength p and the value of the magnetic flux Ф. Moreover, in the parallel configuration, the position of the Kondo peak shifts while it remains unchanged for the antiparallel configuration. These effects might have some potential applications in spintronics.

  6. Shoot-supplied ammonium targets the root auxin influx carrier AUX1 and inhibits lateral root emergence in Arabidopsis

    KAUST Repository

    Li, Baohai


    Deposition of ammonium (NH4 +) from the atmosphere is a substantial environmental problem. While toxicity resulting from root exposure to NH4 + is well studied, little is known about how shoot-supplied ammonium (SSA) affects root growth. In this study, we show that SSA significantly affects lateral root (LR) development. We show that SSA inhibits lateral root primordium (LRP) emergence, but not LRP initiation, resulting in significantly impaired LR number. We show that the inhibition is independent of abscisic acid (ABA) signalling and sucrose uptake in shoots but relates to the auxin response in roots. Expression analyses of an auxin-responsive reporter, DR5:GUS, and direct assays of auxin transport demonstrated that SSA inhibits root acropetal (rootward) auxin transport while not affecting basipetal (shootward) transport or auxin sensitivity of root cells. Mutant analyses indicated that the auxin influx carrier AUX1, but not the auxin efflux carriers PIN-FORMED (PIN)1 or PIN2, is required for this inhibition of LRP emergence and the observed auxin response. We found that AUX1 expression was modulated by SSA in vascular tissues rather than LR cap cells in roots. Taken together, our results suggest that SSA inhibits LRP emergence in Arabidopsis by interfering with AUX1-dependent auxin transport from shoot to root. © 2011 Blackwell Publishing Ltd.

  7. Auxin and ABA act as central regulators of developmental networks associated with paradormancy in Canada thistle (Cirsium arvense)

    KAUST Repository

    Anderson, James V.


    Abstract Dormancy in underground vegetative buds of Canada thistle, an herbaceous perennial weed, allows escape from current control methods and contributes to its invasive nature. In this study, ∼65 % of root sections obtained from greenhouse propagated Canada thistle produced new vegetative shoots by 14 days post-sectioning. RNA samples obtained from sectioned roots incubated 0, 24, 48, and 72 h at 25°C under 16:8 h light-dark conditions were used to construct four MID-tagged cDNA libraries. Analysis of in silico data obtained using Roche 454 GS-FLX pyrosequencing technologies identified molecular networks associated with paradormancy release in underground vegetative buds of Canada thistle. Sequencing of two replicate plates produced ∼2.5 million ESTs with an average read length of 362 bases. These ESTs assembled into 67358 unique sequences (21777 contigs and 45581 singlets) and annotation against the Arabidopsis database identified 15232 unigenes. Among the 15232 unigenes, we identified processes enriched with transcripts involved in plant hormone signaling networks. To follow-up on these results, we examined hormone profiles in roots, which identified changes in abscisic acid (ABA) and ABA metabolites, auxins, and cytokinins post-sectioning. Transcriptome and hormone profiling data suggest that interaction between auxin- and ABA-signaling regulate paradormancy maintenance and release in underground adventitious buds of Canada thistle. Our proposed model shows that sectioning-induced changes in polar auxin transport alters ABA metabolism and signaling, which further impacts gibberellic acid signaling involving interactions between ABA and FUSCA3. Here we report that reduced auxin and ABA-signaling, in conjunction with increased cytokinin biosynthesis post-sectioning supports a model where interactions among hormones drives molecular networks leading to cell division, differentiation, and vegetative outgrowth. ©Springer-Verlag (outside the USA) 2012.

  8. Spin-polarized quantum transport properties through flexible phosphorene (United States)

    Chen, Mingyan; Yu, Zhizhou; Xie, Yiqun; Wang, Yin


    We report a first-principles study on the tunnel magnetoresistance (TMR) and spin-injection efficiency (SIE) through phosphorene with nickel electrodes under the mechanical tension and bending on the phosphorene region. Both the TMR and SIE are largely improved under these mechanical deformations. For the uniaxial tension (ɛy) varying from 0% to 15% applied along the armchair transport (y-)direction of the phosphorene, the TMR ratio is enhanced with a maximum of 107% at ɛy = 10%, while the SIE increases monotonously from 8% up to 43% with the increasing of the strain. Under the out-of-plane bending, the TMR overall increases from 7% to 50% within the bending ratio of 0%-3.9%, and meanwhile the SIE is largely improved to around 70%, as compared to that (30%) of the flat phosphorene. Such behaviors of the TMR and SIE are mainly affected by the transmission of spin-up electrons in the parallel configuration, which is highly dependent on the applied mechanical tension and bending. Our results indicate that the phosphorene based tunnel junctions have promising applications in flexible electronics.

  9. Ectopic KNOX Expression Affects Plant Development by Altering Tissue Cell Polarity and Identity[OPEN (United States)

    Rebocho, Alexandra B.


    Plant development involves two polarity types: tissue cell (asymmetries within cells are coordinated across tissues) and regional (identities vary spatially across tissues) polarity. Both appear altered in the barley (Hordeum vulgare) Hooded mutant, in which ectopic expression of the KNOTTED1-like Homeobox (KNOX) gene, BKn3, causes inverted polarity of differentiated hairs and ectopic flowers, in addition to wing-shaped outgrowths. These lemma-specific effects allow the spatiotemporal analysis of events following ectopic BKn3 expression, determining the relationship between KNOXs, polarity, and shape. We show that tissue cell polarity, based on localization of the auxin transporter SISTER OF PINFORMED1 (SoPIN1), dynamically reorients as ectopic BKn3 expression increases. Concurrently, ectopic expression of the auxin importer LIKE AUX1 and boundary gene NO APICAL MERISTEM is activated. The polarity of hairs reflects SoPIN1 patterns, suggesting that tissue cell polarity underpins oriented cell differentiation. Wing cell files reveal an anisotropic growth pattern, and computational modeling shows how polarity guiding growth can account for this pattern and wing emergence. The inverted ectopic flower orientation does not correlate with SoPIN1, suggesting that this form of regional polarity is not controlled by tissue cell polarity. Overall, the results suggest that KNOXs trigger different morphogenetic effects through interplay between tissue cell polarity, identity, and growth. PMID:27553356

  10. Ectopic KNOX Expression Affects Plant Development by Altering Tissue Cell Polarity and Identity. (United States)

    Richardson, Annis Elizabeth; Rebocho, Alexandra B; Coen, Enrico S


    Plant development involves two polarity types: tissue cell (asymmetries within cells are coordinated across tissues) and regional (identities vary spatially across tissues) polarity. Both appear altered in the barley (Hordeum vulgare) Hooded mutant, in which ectopic expression of the KNOTTED1-like Homeobox (KNOX) gene, BKn3, causes inverted polarity of differentiated hairs and ectopic flowers, in addition to wing-shaped outgrowths. These lemma-specific effects allow the spatiotemporal analysis of events following ectopic BKn3 expression, determining the relationship between KNOXs, polarity, and shape. We show that tissue cell polarity, based on localization of the auxin transporter SISTER OF PINFORMED1 (SoPIN1), dynamically reorients as ectopic BKn3 expression increases. Concurrently, ectopic expression of the auxin importer LIKE AUX1 and boundary gene NO APICAL MERISTEM is activated. The polarity of hairs reflects SoPIN1 patterns, suggesting that tissue cell polarity underpins oriented cell differentiation. Wing cell files reveal an anisotropic growth pattern, and computational modeling shows how polarity guiding growth can account for this pattern and wing emergence. The inverted ectopic flower orientation does not correlate with SoPIN1, suggesting that this form of regional polarity is not controlled by tissue cell polarity. Overall, the results suggest that KNOXs trigger different morphogenetic effects through interplay between tissue cell polarity, identity, and growth.

  11. 7-Rhamnosylated Flavonols Modulate Homeostasis of the Plant Hormone Auxin and Affect Plant Development. (United States)

    Kuhn, Benjamin M; Errafi, Sanae; Bucher, Rahel; Dobrev, Petre; Geisler, Markus; Bigler, Laurent; Zažímalová, Eva; Ringli, Christoph


    Flavonols are a group of secondary metabolites that affect diverse cellular processes. They are considered putative negative regulators of the transport of the phytohormone auxin, by which they influence auxin distribution and concomitantly take part in the control of plant organ development. Flavonols are accumulating in a large number of glycosidic forms. Whether these have distinct functions and diverse cellular targets is not well understood. The rol1-2 mutant of Arabidopsis thaliana is characterized by a modified flavonol glycosylation profile that is inducing changes in auxin transport and growth defects in shoot tissues. To determine whether specific flavonol glycosides are responsible for these phenotypes, a suppressor screen was performed on the rol1-2 mutant, resulting in the identification of an allelic series of UGT89C1, a gene encoding a flavonol 7-O-rhamnosyltransferase. A detailed analysis revealed that interfering with flavonol rhamnosylation increases the concentration of auxin precursors and auxin metabolites, whereas auxin transport is not affected. This finding provides an additional level of complexity to the possible ways by which flavonols influence auxin distribution and suggests that flavonol glycosides play an important role in regulating plant development.

  12. Plant development, auxin, and the subsystem incompleteness theorem. (United States)

    Niklas, Karl J; Kutschera, Ulrich


    Plant morphogenesis (the process whereby form develops) requires signal cross-talking among all levels of organization to coordinate the operation of metabolic and genomic subsystems operating in a larger network of subsystems. Each subsystem can be rendered as a logic circuit supervising the operation of one or more signal-activated system. This approach simplifies complex morphogenetic phenomena and allows for their aggregation into diagrams of progressively larger networks. This technique is illustrated here by rendering two logic circuits and signal-activated subsystems, one for auxin (IAA) polar/lateral intercellular transport and another for IAA-mediated cell wall loosening. For each of these phenomena, a circuit/subsystem diagram highlights missing components (either in the logic circuit or in the subsystem it supervises) that must be identified experimentally if each of these basic plant phenomena is to be fully understood. We also illustrate the "subsystem incompleteness theorem," which states that no subsystem is operationally self-sufficient. Indeed, a whole-organism perspective is required to understand even the most simple morphogenetic process, because, when isolated, every biological signal-activated subsystem is morphogenetically ineffective.

  13. Synergistic action of auxin and ethylene on root elongation inhibition is caused by a reduction of epidermal cell length. (United States)

    Alarcón, M Victoria; Lloret, Pedro G; Salguero, Julio


    Auxin and ethylene have been largely reported to reduce root elongation in maize primary root. However the effects of auxin are greater than those caused by ethylene. Although auxin stimulates ethylene biosynthesis through the specific increase of ACC synthase, the auxin inhibitory effect on root elongation is not mediated by the auxin-induced increase of ethylene production. Recently it has been demonstrated that root inhibition by the application of the synthetic auxin NAA (1-naphtalenacetic acid) is increased if combined with the ethylene precursor ACC (1-aminocyclopropane-1-carboxilic acid) when both compounds are applied at very low concentrations.   Root elongation is basically the result of two processes: a) cell divisions in the meristem where meristematic cells continuously generate new cells and b) subsequently polarized growth by elongation along the root axis as cells leave the meristem and enter the root elongation zone. Our results indicate that exogenous auxin reduced both root elongation and epidermal cell length. In a different way, ethylene at very low concentrations only inhibited root elongation without affecting significantly epidermal cell length. However, these concentrations of ethylene increased the inhibitory effect of auxin on root elongation and cell length. Consequently the results support the hypothesis that ethylene acts synergistically with auxin in the regulation of root elongation and that inhibition by both hormones is due, at least partially, to the reduction of cell length in the epidermal layer.

  14. Patterns of auxin and abscisic acid movement in the tips of gravistimulated primary roots of maize (United States)

    Young, L. M.; Evans, M. L.


    Because both abscisic acid (ABA) and auxin (IAA) have been suggested as possible chemical mediators of differential growth during root gravitropism, we compared with redistribution of label from applied 3H-IAA and 3H-ABA during maize root gravitropism and examined the relative basipetal movement of 3H-IAA and 3H-ABA applied to the caps of vertical roots. Lateral movement of 3H-ABA across the tips of vertical roots was non-polar and about 2-fold greater than lateral movement of 3H-IAA (also non-polar). The greater movement of ABA was not due to enhanced uptake since the uptake of 3H-IAA was greater than that of 3H-ABA. Basipetal movement of label from 3H-IAA or 3H-ABA applied to the root cap was determined by measuring radioactivity in successive 1 mm sections behind the tip 90 minutes after application. ABA remained largely in the first mm (point of application) whereas IAA was concentrated in the region 2-4 mm from the tip with substantial levels found 7-8 mm from the tip. Pretreatment with inhibitors of polar auxin transport decreased both gravicurvature and the basipetal movement of IAA. When roots were placed horizontally, the movement of 3H-IAA from top to bottom across the cap was enhanced relative to movement from bottom to top whereas the pattern of movement of label from 3H-ABA was unaffected. These results are consistent with the hypothesis that IAA plays a role in root gravitropism but contrary to the idea that gravi-induced asymmetric distribution of ABA contributes to the response.

  15. Glucose and auxin signaling interaction in controlling Arabidopsis thaliana seedlings root growth and development.

    Directory of Open Access Journals (Sweden)

    Bhuwaneshwar S Mishra

    Full Text Available BACKGROUND: Plant root growth and development is highly plastic and can adapt to many environmental conditions. Sugar signaling has been shown to affect root growth and development by interacting with phytohormones such as gibberellins, cytokinin and abscisic acid. Auxin signaling and transport has been earlier shown to be controlling plant root length, number of lateral roots, root hair and root growth direction. PRINCIPAL FINDINGS: Increasing concentration of glucose not only controls root length, root hair and number of lateral roots but can also modulate root growth direction. Since root growth and development is also controlled by auxin, whole genome transcript profiling was done to find out the extent of interaction between glucose and auxin response pathways. Glucose alone could transcriptionally regulate 376 (62% genes out of 604 genes affected by IAA. Presence of glucose could also modulate the extent of regulation 2 fold or more of almost 63% genes induced or repressed by IAA. Interestingly, glucose could affect induction or repression of IAA affected genes (35% even if glucose alone had no significant effect on the transcription of these genes itself. Glucose could affect auxin biosynthetic YUCCA genes family members, auxin transporter PIN proteins, receptor TIR1 and members of a number of gene families including AUX/IAA, GH3 and SAUR involved in auxin signaling. Arabidopsis auxin receptor tir1 and response mutants, axr2, axr3 and slr1 not only display a defect in glucose induced change in root length, root hair elongation and lateral root production but also accentuate glucose induced increase in root growth randomization from vertical suggesting glucose effects on plant root growth and development are mediated by auxin signaling components. CONCLUSION: Our findings implicate an important role of the glucose interacting with auxin signaling and transport machinery to control seedling root growth and development in changing nutrient

  16. Structural Biology of Nuclear Auxin Action. (United States)

    Dinesh, Dhurvas Chandrasekaran; Villalobos, Luz Irina A Calderón; Abel, Steffen


    Auxin coordinates plant development largely via hierarchical control of gene expression. During the past decades, the study of early auxin genes paired with the power of Arabidopsis genetics have unraveled key nuclear components and molecular interactions that perceive the hormone and activate primary response genes. Recent research in the realm of structural biology allowed unprecedented insight into: (i) the recognition of auxin-responsive DNA elements by auxin transcription factors; (ii) the inactivation of those auxin response factors by early auxin-inducible repressors; and (iii) the activation of target genes by auxin-triggered repressor degradation. The biophysical studies reviewed here provide an impetus for elucidating the molecular determinants of the intricate interactions between core components of the nuclear auxin response module.

  17. Role of auxin during intercellular infection of Discaria trinervis by Frankia

    Directory of Open Access Journals (Sweden)

    Leandro eImanishi


    Full Text Available Nitrogen-fixing nodules induced by Frankia in the actinorhizal plant Discaria trinervis result from a primitive intercellular root invasion pathway that does not involve root hair deformation and infection threads. Here, we analyzed the role of auxin in this intercellular infection pathway at the molecular level and compared it with our previous work in the intracellular infected actinorhizal plant Casuarina glauca. Immunolocalisation experiments showed that auxin accumulated in Frankia-infected cells in both systems. We then characterized the expression of auxin transporters in D. trinervis nodules. No activation of the heterologous CgAUX1 promoter was detected in infected cells in D. trinervis. These results were confirmed with the endogenous D. trinervis gene, DtAUX1. However, DtAUX1 was expressed in the nodule meristem. Consistently, transgenic D. trinervis plants containing the auxin response marker DR5:VENUS showed expression of the reporter gene in the meristem. Immunolocalisation experiments using an antibody against the auxin efflux carrier PIN1, revealed the presence of this transporter in the plasma membrane of infected cells. Finally, we used in silico cellular models to analyse auxin fluxes in D. trinervis nodules. Our results point to the existence of divergent roles of auxin in intercellularly- and intracellularly-infected actinorhizal plants, an ancestral infection pathways leading to root nodule symbioses.

  18. Role of auxin during intercellular infection of Discaria trinervis by Frankia (United States)

    Imanishi, Leandro; Perrine-Walker, Francine M.; Ndour, Adama; Vayssières, Alice; Conejero, Genevieve; Lucas, Mikaël; Champion, Antony; Laplaze, Laurent; Wall, Luis; Svistoonoff, Sergio


    Nitrogen-fixing nodules induced by Frankia in the actinorhizal plant Discaria trinervis result from a primitive intercellular root invasion pathway that does not involve root hair deformation and infection threads. Here, we analyzed the role of auxin in this intercellular infection pathway at the molecular level and compared it with our previous work in the intracellular infected actinorhizal plant Casuarina glauca. Immunolocalisation experiments showed that auxin accumulated in Frankia-infected cells in both systems. We then characterized the expression of auxin transporters in D. trinervis nodules. No activation of the heterologous CgAUX1 promoter was detected in infected cells in D. trinervis. These results were confirmed with the endogenous D. trinervis gene, DtAUX1. However, DtAUX1 was expressed in the nodule meristem. Consistently, transgenic D. trinervis plants containing the auxin response marker DR5:VENUS showed expression of the reporter gene in the meristem. Immunolocalisation experiments using an antibody against the auxin efflux carrier PIN1, revealed the presence of this transporter in the plasma membrane of infected cells. Finally, we used in silico cellular models to analyse auxin fluxes in D. trinervis nodules. Our results point to the existence of divergent roles of auxin in intercellularly- and intracellularly-infected actinorhizal plants, an ancestral infection pathways leading to root nodule symbioses. PMID:25191330

  19. Modeling halotropism: a key role for root tip architecture and reflux loop remodeling in redistributing auxin (United States)

    van den Berg, Thea; Korver, Ruud A.; Testerink, Christa


    A key characteristic of plant development is its plasticity in response to various and dynamically changing environmental conditions. Tropisms contribute to this flexibility by allowing plant organs to grow from or towards environmental cues. Halotropism is a recently described tropism in which plant roots bend away from salt. During halotropism, as in most other tropisms, directional growth is generated through an asymmetric auxin distribution that generates differences in growth rate and hence induces bending. Here, we develop a detailed model of auxin transport in the Arabidopsis root tip and combine this with experiments to investigate the processes generating auxin asymmetry during halotropism. Our model points to the key role of root tip architecture in allowing the decrease in PIN2 at the salt-exposed side of the root to result in a re-routing of auxin to the opposite side. In addition, our model demonstrates how feedback of auxin on the auxin transporter AUX1 amplifies this auxin asymmetry, while a salt-induced transient increase in PIN1 levels increases the speed at which this occurs. Using AUX1-GFP imaging and pin1 mutants, we experimentally confirmed these model predictions, thus expanding our knowledge of the cellular basis of halotropism. PMID:27510970

  20. Inter-regulation of the unfolded protein response and auxin signaling. (United States)

    Chen, Yani; Aung, Kyaw; Rolčík, Jakub; Walicki, Kathryn; Friml, Jiří; Brandizzi, Federica


    The unfolded protein response (UPR) is a signaling network triggered by overload of protein-folding demand in the endoplasmic reticulum (ER), a condition termed ER stress. The UPR is critical for growth and development; nonetheless, connections between the UPR and other cellular regulatory processes remain largely unknown. Here, we identify a link between the UPR and the phytohormone auxin, a master regulator of plant physiology. We show that ER stress triggers down-regulation of auxin receptors and transporters in Arabidopsis thaliana. We also demonstrate that an Arabidopsis mutant of a conserved ER stress sensor IRE1 exhibits defects in the auxin response and levels. These data not only support that the plant IRE1 is required for auxin homeostasis, they also reveal a species-specific feature of IRE1 in multicellular eukaryotes. Furthermore, by establishing that UPR activation is reduced in mutants of ER-localized auxin transporters, including PIN5, we define a long-neglected biological significance of ER-based auxin regulation. We further examine the functional relationship of IRE1 and PIN5 by showing that an ire1 pin5 triple mutant enhances defects of UPR activation and auxin homeostasis in ire1 or pin5. Our results imply that the plant UPR has evolved a hormone-dependent strategy for coordinating ER function with physiological processes.

  1. Modeling halotropism: a key role for root tip architecture and reflux loop remodeling in redistributing auxin. (United States)

    van den Berg, Thea; Korver, Ruud A; Testerink, Christa; Ten Tusscher, Kirsten H W J


    A key characteristic of plant development is its plasticity in response to various and dynamically changing environmental conditions. Tropisms contribute to this flexibility by allowing plant organs to grow from or towards environmental cues. Halotropism is a recently described tropism in which plant roots bend away from salt. During halotropism, as in most other tropisms, directional growth is generated through an asymmetric auxin distribution that generates differences in growth rate and hence induces bending. Here, we develop a detailed model of auxin transport in the Arabidopsis root tip and combine this with experiments to investigate the processes generating auxin asymmetry during halotropism. Our model points to the key role of root tip architecture in allowing the decrease in PIN2 at the salt-exposed side of the root to result in a re-routing of auxin to the opposite side. In addition, our model demonstrates how feedback of auxin on the auxin transporter AUX1 amplifies this auxin asymmetry, while a salt-induced transient increase in PIN1 levels increases the speed at which this occurs. Using AUX1-GFP imaging and pin1 mutants, we experimentally confirmed these model predictions, thus expanding our knowledge of the cellular basis of halotropism.

  2. Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts

    DEFF Research Database (Denmark)

    Hu, C.-M.; Nitta, Junsaku; Jensen, Ane


    Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spi...... orientations. Spin dephasing and spin precession effects are studied by temperature and 2DEG channel length dependent measurements. Interdigital-ferromagnetic contacts suppress unwanted effects due to ferromagnetic microstrip inhomogeneities by averaging....


    Experiments have been conducted to investigate a two-stage effect of auxin on abscission. The two stages were demonstrated on greenhouse-grown Black...the second stage - the stage which is stimulated by auxin . Similar experiments were performed with petioles of various lengths and ages. The...implications of these results indicate possible sites of auxin action on leaf abscission. (Author)

  4. Self-organization and advective transport in the cell polarity formation for asymmetric cell division. (United States)

    Seirin Lee, Sungrim; Shibata, Tatsuo


    Anterior-Posterior (AP) polarity formation of cell membrane proteins plays a crucial role in determining cell asymmetry, which depends not only on the several genetic process but also biochemical and biophysical interactions. The mechanism of AP formation of Caenorhabditis elegans embryo is characterized into the three processes: (i) membrane association and dissociation of posterior and anterior proteins, (ii) diffusion into the membrane and cytosol, and (iii) active cortical and cytoplasmic flows induced by the contraction of the acto-myosin cortex. We explored the mechanism of symmetry breaking and AP polarity formation using self-recruitment model of posterior proteins. We found that the AP polarity pattern is established over wide range in the total mass of polarity proteins and the diffusion ratio in the cytosol to the membrane. We also showed that the advective transport in both membrane and cytosol during the establishment phase affects optimal time interval of establishment and positioning of the posterior domain, and plays a role to increase the robustness in the AP polarity formation by reducing the number of posterior domains for the sensitivity of initial conditions. We also demonstrated that a proper ratio of the total mass to cell size robustly regulate the length scale of the posterior domain.

  5. Endothelial Barrier and Polarized Transportation%内皮屏障与极性运输

    Institute of Scientific and Technical Information of China (English)

    李海韵; 吉尚戎


    极化细胞的极性分布和功能行使,需要不同机制相互协作,改变胞内蛋白的运输和分布,并对环境变化做出极性应激.内皮细胞(endothelial cells,ECs)是一类具有极性特征的单层特化上皮细胞,在结构和功能上形成面向血液的顶端区域(apical membrane domain)和面向下方平滑肌细胞的基底侧区域(basolateral membrane domain).内皮功能障碍和细胞极性丢失,与心血管疾病及癌症的发生紧密相关.在炎症和免疫应答中,内皮细胞通过胞内蛋白的持续分选维持极性,协助血液中大分子跨过内皮屏障完成生理功能,同时,对血液或组织中的生理变化做出极性应答.%The polarized distribution of functions in polarized cells requires the coordinated interaction of multiple mechanisms,such as intracellular protein trafficking,asymmetry distribution and polarized responds to extracellular changes.Endothelial cells (ECs) are monolayer of specialized epithelia with polarity,showing structurally and functionally distinct apical domain orienting toward blood and basolateral domain facing smooth muscle cells.Endothelial dysfunction and defects in polarity are closely associated with cardiovascular disease and cancer.In inflammation and immune response,endothelial cells maintain their polarization through continual intracellular protein sorting,facilitate the transcellular transport of macromolecules in blood across endothelial barrier and show polarized responds to physiological change in blood or interstitial fluid.

  6. The Arabidopsis bZIP11 transcription factor links low-energy signalling to auxin-mediated control of primary root growth. (United States)

    Weiste, Christoph; Pedrotti, Lorenzo; Selvanayagam, Jebasingh; Muralidhara, Prathibha; Fröschel, Christian; Novák, Ondřej; Ljung, Karin; Hanson, Johannes; Dröge-Laser, Wolfgang


    Plants have to tightly control their energy homeostasis to ensure survival and fitness under constantly changing environmental conditions. Thus, it is stringently required that energy-consuming stress-adaptation and growth-related processes are dynamically tuned according to the prevailing energy availability. The evolutionary conserved SUCROSE NON-FERMENTING1 RELATED KINASES1 (SnRK1) and the downstream group C/S1 basic leucine zipper (bZIP) transcription factors (TFs) are well-characterised central players in plants' low-energy management. Nevertheless, mechanistic insights into plant growth control under energy deprived conditions remains largely elusive. In this work, we disclose the novel function of the low-energy activated group S1 bZIP11-related TFs as regulators of auxin-mediated primary root growth. Whereas transgenic gain-of-function approaches of these bZIPs interfere with the activity of the root apical meristem and result in root growth repression, root growth of loss-of-function plants show a pronounced insensitivity to low-energy conditions. Based on ensuing molecular and biochemical analyses, we propose a mechanistic model, in which bZIP11-related TFs gain control over the root meristem by directly activating IAA3/SHY2 transcription. IAA3/SHY2 is a pivotal negative regulator of root growth, which has been demonstrated to efficiently repress transcription of major auxin transport facilitators of the PIN-FORMED (PIN) gene family, thereby restricting polar auxin transport to the root tip and in consequence auxin-driven primary root growth. Taken together, our results disclose the central low-energy activated SnRK1-C/S1-bZIP signalling module as gateway to integrate information on the plant's energy status into root meristem control, thereby balancing plant growth and cellular energy resources.

  7. Spin transport at the international linear collider and its impact on the measurement of polarization

    Energy Technology Data Exchange (ETDEWEB)

    Beckmann, Moritz


    At the planned International Linear Collider (ILC), the longitudinal beam polarization needs to be determined with an unprecedented precision. For that purpose, the beam delivery systems (BDS) are equipped with two laser Compton polarimeters each, which are foreseen to achieve a systematic uncertainty of {<=} 0.25 %. The polarimeters are located 1.6 km upstream and 150 m downstream of the e{sup +}e{sup -} interaction point (IP). The average luminosity-weighted longitudinal polarization P{sup lumi}{sub z}, which is the decisive quantity for the experiments, has to be determined from these measurements with the best possible precision. Therefore, a detailed understanding of the spin transport in the BDS is mandatory to estimate how precise the longitudinal polarization at the IP is known from the polarimeter measurements. The envisaged precision for the propagation of the measurement value is {<=} 0.1 %. This thesis scrutinizes the spin transport in view of the achievable precision. A detailed beamline simulation for the BDS has been developed, including the simulation of the beam-beam collisions at the IP. The following factors which might limit the achievable precision is investigated: a variation of the beam parameters, the beam alignment precision at the polarimeters and the IP, the bunch rotation at the IP, the detector magnets, the beam-beam collisions, the emission of synchrotron radiation and misalignments of the beamline elements. In absence of collisions, a precision of 0.085% on the propagation of the measured longitudinal polarization has been found achievable. This result however depends mainly on the presumed precisions for the parallel alignment of the beam at the polarimeters and for the alignment of polarization vector. In presence of collisions, the measurement at the downstream polarimeter depends strongly on the intensity of the collision and the size of the polarimeter laser spot. Therefore, a more detailed study of the laser-bunch interaction is

  8. Dynamics of auxin movement in the gravistimulated leaf-sheath pulvinus of oat (Avena sativa) (United States)

    Brock, Thomas C.; Kapen, E. H.; Ghosheh, Najati S.; Kaufman, Peter B.


    The role of auxin redistribution in the graviresponse of the leaf-sheath pulvinus of oat was evaluated using H-3-indole-3-acetic acid (H-3-IAA) preloaded into isolated pulvini. Results obtained reveal that, while lateral transport of auxin occurs following gravistimulation, it is not necessary for a graviresponse. Localized changes in tissue responsiveness or the conversion of conjugated hormone to free hormone may suffice to drive the graviresponse.

  9. Mechanistic Framework for Establishment, Maintenance, and Alteration of Cell Polarity in Plants

    Directory of Open Access Journals (Sweden)

    Pankaj Dhonukshe


    Full Text Available Cell polarity establishment, maintenance, and alteration are central to the developmental and response programs of nearly all organisms and are often implicated in abnormalities ranging from patterning defects to cancer. By residing at the distinct plasma membrane domains polar cargoes mark the identities of those domains, and execute localized functions. Polar cargoes are recruited to the specialized membrane domains by directional secretion and/or directional endocytic recycling. In plants, auxin efflux carrier PIN proteins display polar localizations in various cell types and play major roles in directional cell-to-cell transport of signaling molecule auxin that is vital for plant patterning and response programs. Recent advanced microscopy studies applied to single cells in intact plants reveal subcellular PIN dynamics. They uncover the PIN polarity generation mechanism and identified important roles of AGC kinases for polar PIN localization. AGC kinase family members PINOID, WAG1, and WAG2, belonging to the AGC-3 subclass predominantly influence the polar localization of PINs. The emerging mechanism for AGC-3 kinases action suggests that kinases phosphorylate PINs mainly at the plasma membrane after initial symmetric PIN secretion for eventual PIN internalization and PIN sorting into distinct ARF-GEF-regulated polar recycling pathways. Thus phosphorylation status directs PIN translocation to different cell sides. Based on these findings a mechanistic framework evolves that suggests existence of cell side-specific recycling pathways in plants and implicates AGC3 kinases for differential PIN recruitment among them for eventual PIN polarity establishment, maintenance, and alteration.

  10. miRNA-mediated auxin signalling repression during Vat-mediated aphid resistance in Cucumis melo. (United States)

    Sattar, Sampurna; Addo-Quaye, Charles; Thompson, Gary A


    Resistance to Aphis gossypii in melon is attributed to the presence of the single dominant R gene virus aphid transmission (Vat), which is biologically expressed as antibiosis, antixenosis and tolerance. However, the mechanism of resistance is poorly understood at the molecular level. Aphid-induced transcriptional changes, including differentially expressed miRNA profiles that correspond to resistance interaction have been reported in melon. The potential regulatory roles of miRNAs in Vat-mediated aphid resistance were further revealed by identifying the specific miRNA degradation targets. A total of 70 miRNA:target pairs, including 28 novel miRNA:target pairs, for the differentially expressed miRNAs were identified: 11 were associated with phytohormone regulation, including six miRNAs that potentially regulate auxin interactions. A model for a redundant regulatory system of miRNA-mediated auxin insensitivity is proposed that incorporates auxin perception, auxin modification and auxin-regulated transcription. Chemically inhibiting the transport inhibitor response-1 (TIR-1) auxin receptor in susceptible melon tissues provides in vivo support for the model of auxin-mediated impacts on A. gossypii resistance.

  11. The effects of auxin and strigolactones on tuber initiation and stolon architecture in potato. (United States)

    Roumeliotis, Efstathios; Kloosterman, Bjorn; Oortwijn, Marian; Kohlen, Wouter; Bouwmeester, Harro J; Visser, Richard G F; Bachem, Christian W B


    Various transcriptional networks and plant hormones have been implicated in controlling different aspects of potato tuber formation. Due to its broad impact on many plant developmental processes, a role for auxin in tuber initiation has been suggested but never fully resolved. Here, auxin concentrations were measured throughout the plant prior to and during the process of tuber formation. Auxin levels increase dramatically in the stolon prior to tuberization and remain relatively high during subsequent tuber growth, suggesting a promoting role for auxin in tuber formation. Furthermore, in vitro tuberization experiments showed higher levels of tuber formation from axillary buds of explants where the auxin source (stolon tip) had been removed. This phenotype could be rescued by application of auxin on the ablated stolon tips. In addition, a synthetic strigolactone analogue applied on the basal part of the stolon resulted in fewer tubers. The experiments indicate that a system for the production and directional transport of auxin exists in stolons and acts synergistically with strigolactones to control the outgrowth of the axillary stolon buds, similar to the control of above-ground shoot branching.

  12. Auxins as Signals in Arbuscular Mycorrhiza Formation (United States)

    Güther, Mike


    Plant hormones such as auxin derivatives are likely signals during the establishment of an arbuscular mycorrhizal (AM) symbiosis. Although reports on auxin levels during AM in different plant species are contradictory, the contribution of auxins to the establishment of an AM symbiosis might be an important factor especially for the development of lateral roots which are the preferred infection sites for the fungi. In addition to evidence that different auxins could be elevated after colonization with AM fungi, there are also overlapping gene expression patterns between auxin-treated and AM-inoculated roots that provide further clues on auxin-triggered colonization events. Using an auxin-inducible promoter-reporter system it was shown that the reporter was strongly induced in AM colonized roots, although co-localization with AM fungi was not observed. Our data are discussed in frame of a model together with other plant hormones which might be involved in the AM colonization processes. PMID:19704695

  13. Studies of the Production and Transport of Highly Polarized Ultracold Neutrons for the UCNA Experiment (United States)

    Holley, A. T.


    The goal of the UCNA experiment is to determine the angular correlation between the electron momentum and the neutron spin (the beta-asymmetry) in neutron decay using polarized ultracold neutrons (UCN). The experimental strategy is to transport UCN into a decay volume through a 7T static magnetic field using the magnetic potential to polarize the UCN. The initial UCN spin can then be reversed via an rf adiabatic spin-flipper in a 1T field region whose gradient is tailored to optimize the adiabatic spin-flipper's performance. The spin-flipper, which also allows in situ measurement of the UCN depolarization rate, is a resonant `bird-cage' cavity capable of producing rf fields in excess of 5G at 30Mhz. In order to minimize the UCN depolarization rate, UCN guides are constructed of diamond-like carbon films on quartz tubing, a technology which has been demonstrated to produce less than 3x10-3 depolarizations per bounce. The performance of this system will be described, and compared to expectations from detailed Monte Carlo transport models. The implications for high precision measurements of polarized ultracold neutrons will also be discussed.

  14. Theoretical and experimental evidence indicates that there is no detectable auxin gradient in the angiosperm female gametophyte. (United States)

    Lituiev, Dmytro S; Krohn, Nádia G; Müller, Bruno; Jackson, David; Hellriegel, Barbara; Dresselhaus, Thomas; Grossniklaus, Ueli


    The plant life cycle alternates between a diploid sporophytic and a haploid gametophytic generation. The female gametophyte (FG) of flowering plants is typically formed through three syncytial mitoses, followed by cellularisation that forms seven cells belonging to four cell types. The specification of cell fates in the FG has been suggested to depend on positional information provided by an intrinsic auxin concentration gradient. The goal of this study was to develop mathematical models that explain the formation of this gradient in a syncytium. Two factors were proposed to contribute to the maintenance of the auxin gradient in Arabidopsis FGs: polar influx at early stages and localised auxin synthesis at later stages. However, no gradient could be generated using classical, one-dimensional theoretical models under these assumptions. Thus, we tested other hypotheses, including spatial confinement by the large central vacuole, background efflux and localised degradation, and investigated the robustness of cell specification under different parameters and assumptions. None of the models led to the generation of an auxin gradient that was steep enough to allow sufficiently robust patterning. This led us to re-examine the response to an auxin gradient in developing FGs using various auxin reporters, including a novel degron-based reporter system. In agreement with the predictions of our models, auxin responses were not detectable within the FG of Arabidopsis or maize, suggesting that the effects of manipulating auxin production and response on cell fate determination might be indirect.

  15. Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots. (United States)

    Wang, Shengyin; Ren, Xiaoyan; Huang, Bingru; Wang, Ge; Zhou, Peng; An, Yuan


    The objective of this study was to investigate Al(3+)-induced IAA transport, distribution, and the relation of these two processes to Al(3+)-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L(-1) IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress significantly decreased the IAA concentration in apical buds and root tips. The distribution of IAA fluorescence signals in root tips was disturbed, and the IAA transportation from shoot base to root tip was inhibited. The highest intensity of fluorescence signals was detected in the apical meristematic zone. Exogenous application of IAA markedly alleviated the Al(3+)-induced inhibition of root growth by increasing IAA accumulation and recovering the damaged cell structure in root tips. In addition, Al(3+) stress up-regulated expression of AUX1 and PIN2 genes. These results indicate that Al(3+)-induced reduction of root growth could be associated with the inhibitions of IAA synthesis in apical buds and IAA transportation in roots, as well as the imbalance of IAA distribution in root tips.

  16. Spin Polarized Transport in an AC-Driven Quantum Curved Nanowire

    Directory of Open Access Journals (Sweden)

    Walid A. Zein


    Full Text Available Using the effective-mass approximation method, and Floquet theory, we study the spin transport characteristics through a curved quantum nanowire. The spin polarization, P, and the tunneling magnetoresistance, TMR, are deduced under the effect of microwave and infrared radiations of wide range of frequencies. The results show an oscillatory behavior of both the spin polarization and the tunneling magnetoresistance. This is due to Fano-type resonance and the interplay between the strength of spin-orbit coupling and the photons in the subbands of the one-dimensional nanowire. The present results show that this investigation is very important, and the present device might be used to be a sensor for small strain in semiconductor nanostructures and photodetector.

  17. Ferritin polarization and iron transport across monolayer epithelial barriers in mammals

    Directory of Open Access Journals (Sweden)

    Esther G. Meyron-Holtz


    Full Text Available Epithelial barriers are found in many tissues such as the intestine, kidney and brain where they separate the external environment from the body or a specific compartment from its periphery. Due to the tight junctions that connect epithelial barrier-cells (EBCs, the transport of compounds takes place nearly exclusively across the apical or basolateral membrane, the cell-body and the opposite membrane of the polarized EBC, and is regulated on numerous levels including barrier-specific adapted trafficking-machineries.Iron is an essential element but toxic at excess. Therefore, all iron-requiring organisms tightly regulate iron concentrations on systemic and cellular levels. In contrast to most cell types that control just their own iron homeostasis, EBCs also regulate homeostasis of the compartment they enclose or the body as a whole. Iron is transported across EBCs by specialized transporters such as the transferrin receptor and ferroportin. Recently, the iron storage protein ferritin was also attributed a role in the regulation of systemic iron homeostasis and we gathered evidence from the literature and original data that ferritin is polarized in EBC, suggesting also a role for ferritin in iron trafficking across EBCs.

  18. The effect of carbon monoxide integrating nitric oxide through auxin signal in Arabidopsis to modulate iron deficiency

    Directory of Open Access Journals (Sweden)

    Liming eYang


    Full Text Available Carbon monoxide (CO and nitric oxide (NO are essential modulators that regulate the plant response to iron deficiency (-Fe. Auxin is a phytohormone that plays important roles in plant growth and development. We report here that in Arabidopsis –Fe enhanced heme oxygenase-dependent CO generation and auxin transport through redistribution of PIN1 protein, which subsequently increased NO accumulation; NO signaling regulated the activity of ferric chelate reductase (FCR and the expression of Fe-uptake genes including basic helix-loop-helix transcription factor (FIT and the ferric reduction oxidase 2 (FRO2. Over-expression of HY1 encoding heme oxygenase, or treatment with CO donor enhanced basipetal auxin transport, FCR activity, and the expressions of FIT and FRO2 under –Fe. Such effects were compromised in the mutant aux1-7 impaired in auxin transport or in the mutant noa1 or nia1/nia2 defective in NO biosynthesis. -Fe failed to promote auxin transport and FCR activity in hy1 mutant; such inability was reversed in the double mutant of hy1/yucca1 with elevated auxin production, or in hy1/cue1 mutant with NO over-accumulation. Taken together, our results suggest that CO modulates NO signaling through auxin to cope with Fe deficiency in Arabidopsis.

  19. Repression of the Auxin Response Pathway Increases Arabidopsis Susceptibility to Necrotrophic Fungi

    Institute of Scientific and Technical Information of China (English)

    Francisco Llorente; Paul Muskett; Andrea Sánchez-Vallet; Gemma López; Brisa Ramos; Clara Sánchez-Rodríguez; Lucia Jordá; Jane Parker; Antonio Molina


    In plants, resistance to necrotrophic pathogens depends on the interplay between different hormone systems, such as those regulated by salicylic acid (SA), jasmonic acid (JA), ethylene, and abscisic acid. Repression of auxin signaling by the SA pathway was recently shown to contribute to antibacterial resistance. Here, we demonstrate that Arabidopsis auxin signaling mutants axrl, axr2, and axr6 that have defects in the auxin-stimulated SCF (Skpl-Cullin-F-box) ubiquitination pathway exhibit increased susceptibility to the necrotrophic fungi Plectosphaerella cucumerina and Botrytis cinerea. Also, stabilization of the auxin transcriptional repressor AXR3 that is normally targeted for removal by the SCF-ubiquitin/proteasome machinery occurs upon P. cucumerina infection. Pharmacological inhibition of auxin transport or proteasome function each compromise necrotroph resistance of wild-type plants to a similar extent as in non-treated auxin response mutants. These results suggest that auxin signaling is important for resistance to the necrotrophic fungi P. cucumerina and B. cinerea. SGTlb (one of two Arabidopsis SGT1 genes encoding HSP90/HSC70 co-chaperones) promotes the functions of SCF E3-ubiquitin ligase complexes in auxin and JA responses and resistance conditioned by certain Resistance (R) genes to biotrophic pathogens. We find that sgtlb mutants are as resistant to P. cucumerina as wild-type plants. Conversely, auxin/SCF signaling mutants are uncompromised in RPP4-triggered resistance to the obligate biotrophic oomycete, Hyaloperonospora parasitica. Thus, the predominant action of SGTlb in R gene-conditioned resistance to oomycetes appears to be at a site other than assisting SCF E3-ubiquitin ligases. However, genetic additivity of sgtlb axr1 double mutants in susceptibility to H. parasitica suggests that SCF-mediated ubiquitination contributes to limiting biotrophic pathogen colonization once plant-pathogen compatibility is established.

  20. A Simple Auxin Transcriptional Response System Regulates Multiple Morphogenetic Processes in the Liverwort Marchantia polymorpha. (United States)

    Flores-Sandoval, Eduardo; Eklund, D Magnus; Bowman, John L


    In land plants comparative genomics has revealed that members of basal lineages share a common set of transcription factors with the derived flowering plants, despite sharing few homologous structures. The plant hormone auxin has been implicated in many facets of development in both basal and derived lineages of land plants. We functionally characterized the auxin transcriptional response machinery in the liverwort Marchantia polymorpha, a member of the basal lineage of extant land plants. All components known from flowering plant systems are present in M. polymorpha, but they exist as single orthologs: a single MpTOPLESS (TPL) corepressor, a single MpTRANSPORT inhibitor response 1 auxin receptor, single orthologs of each class of auxin response factor (ARF; MpARF1, MpARF2, MpARF3), and a single negative regulator auxin/indole-3-acetic acid (MpIAA). Phylogenetic analyses suggest this simple system is the ancestral condition for land plants. We experimentally demonstrate that these genes act in an auxin response pathway--chimeric fusions of the MpTPL corepressor with heterodimerization domains of MpARF1, MpARF2, or their negative regulator, MpIAA, generate auxin insensitive plants that lack the capacity to pattern and transition into mature stages of development. Our results indicate auxin mediated transcriptional regulation acts as a facilitator of branching, differentiation and growth, rather than acting to determine or specify tissues during the haploid stage of the M. polymorpha life cycle. We hypothesize that the ancestral role of auxin is to modulate a balance of differentiated and pluri- or totipotent cell states, whose fates are determined by interactions with combinations of unrelated transcription factors.

  1. Multi-scale characean experimental system: from electrophysiology of membrane transporters to cell-to-cell connectivity, cytoplasmic streaming and auxin metabolism.

    Directory of Open Access Journals (Sweden)

    Mary Jane Beilby


    Full Text Available The morphology of characean algae could be mistaken for a higher plant: stem-like axes with leaf-like branchlets anchored in the soil by root-like rhizoids. However, all of these structures are made up of giant multinucleate cells separated by multicellular nodal complexes. The excised internodal cells survive long enough for the nodes to give rise to new thallus. The size of the internodes and their thick cytoplasmic layer minimize impalement injury and allow specific micro-electrode placement. The cell structure can be manipulated by centrifugation, perfusion of cell contents or creation of cytoplasmic droplets, allowing access to both vacuolar and cytoplasmic compartments and both sides of the cell membranes. Thousands of electrical measurements on intact or altered cells and cytoplasmic droplets laid down basis to modern plant electrophysiology. Furthermore, the giant internodal cells and whole thalli facilitate research into many other plant properties. As nutrients have to be transported from rhizoids to growing parts of the thallus and hormonal signals need to pass from cell to cell, Characeae possess very fast cytoplasmic streaming. The mechanism was resolved in the characean model. Plasmodesmata between the internodal cells and nodal complexes facilitate transport of ions, nutrients and photosynthates across the nodes. The internal structure was found to be similar to those of higher plants. Recent experiments suggest a strong circadian influence on metabolic pathways producing indole-3-acetic acid (IAA and serotonin/melatonin. The review will discuss the impact of the characean models arising from fragments of cells, single cells, cell-to-cell transport or whole thalli on understanding of plant evolution and physiology.

  2. Multi-Scale Characean Experimental System: From Electrophysiology of Membrane Transporters to Cell-to-Cell Connectivity, Cytoplasmic Streaming and Auxin Metabolism. (United States)

    Beilby, Mary J


    The morphology of characean algae could be mistaken for a higher plant: stem-like axes with leaf-like branchlets anchored in the soil by root-like rhizoids. However, all of these structures are made up of giant multinucleate cells separated by multicellular nodal complexes. The excised internodal cells survive long enough for the nodes to give rise to new thallus. The size of the internodes and their thick cytoplasmic layer minimize impalement injury and allow specific micro-electrode placement. The cell structure can be manipulated by centrifugation, perfusion of cell contents or creation of cytoplasmic droplets, allowing access to both vacuolar and cytoplasmic compartments and both sides of the cell membranes. Thousands of electrical measurements on intact or altered cells and cytoplasmic droplets laid down basis to modern plant electrophysiology. Furthermore, the giant internodal cells and whole thalli facilitate research into many other plant properties. As nutrients have to be transported from rhizoids to growing parts of the thallus and hormonal signals need to pass from cell to cell, Characeae possess very fast cytoplasmic streaming. The mechanism was resolved in the characean model. Plasmodesmata between the internodal cells and nodal complexes facilitate transport of ions, nutrients and photosynthates across the nodes. The internal structure was found to be similar to those of higher plants. Recent experiments suggest a strong circadian influence on metabolic pathways producing indole-3-acetic acid (IAA) and serotonin/melatonin. The review will discuss the impact of the characean models arising from fragments of cells, single cells, cell-to-cell transport or whole thalli on understanding of plant evolution and physiology.

  3. Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots


    Shengyin Wang; Xiaoyan Ren; Bingru Huang; Ge Wang; Peng Zhou; Yuan An


    The objective of this study was to investigate Al3+-induced IAA transport, distribution, and the relation of these two processes to Al3+-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L−1 IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress signi...

  4. A Polar Discrete Ordinate Radiation Transport Method for 2D ALE Meshes in HYDRA (United States)

    Chang, Britton; Marinak, Marty; Weber, Chris; Peterson, Luc


    The Polar Discrete Ordinate Radiation Transport Method in HYDRA has been extended to handle general 2D r-z meshes. Previously the method was only for orthogonal 2D meshes. The new method can be employed with the ALE methodology for managing mesh motion that is used to simulate Rayleigh-Taylor and Richtmyer-Meshkov instabilities on NIF capsule implosions. The results of an examination of this kind will be compared to those obtained by the corresponding diffusion method. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

  5. Spin-polarized quantum transport through an Aharonov-Bohm quantum-dot-ring

    Institute of Scientific and Technical Information of China (English)

    Wang Jian-Ming; Wang Rui; Liang Jiu-Qing


    In this paper the quantum transport through an Aharonov-Bohm (AB) quantum-dot-ring with two dot-array arms described by a single-band tight-binding Hamiltonian is investigated in the presence of additional magnetic fields applied to the dot-array arms to produce spin flip of electrons. A far richer interference pattern than that in the charge transport alone is found. Besides the usual AB oscillation the tunable spin polarization of the current by the magnetic flux is a new observation and is seen to be particularly useful in technical applications. The spectrum of transmission probability is modulated by the quantum dot numbers on the up-arc and down-arc of the ring, which, however, does not affect the period of the AB oscillation.

  6. Nonequilibrium spin-polarized thermal transport in ferromagnetic-quantum dot-metal system (United States)

    Xu, Li; Li, Zhi-Jian; Niu, Pengbin; Nie, Yi-Hang


    We use nonequilibrium Green function to analyze the nonequilibrium spin-polarized thermal transport through the ferromagnetic-quantum dot-metal system, in which a quantum dot (QD) is coupled to the ferromagnetic and metal electrodes with the voltage bias and the temperature shift. The differential thermoelectric conductance L (θ) is always zero and has no relation with the temperature shift when ε is equal to the Fermi level. The positive and negative values of L (θ) manifest the thermoelectric characteristic of electron-like (or hole-like) carrier when the temperature shift is nonzero. The electrostatic potential U becomes spin-dependent, and makes the dot level renormalization when the ferromagnetic-quantum dot-metal system is driven by the voltage bias and the temperature shift. We define that the spin polarization of the currents between the spin current Is and the electric current Ic is denoted as Is /Ic. The spin polarization Is /Ic shows novel and unique physical phenomenon when the voltage bias and the temperature shift are changed in the nonequilibrium state. Another interesting phenomenon is that we can obtain the pure spin current and a zero point of the thermocurrent Ith by adjusting the voltage bias and the temperature shift.

  7. An ABC transporter B family protein, ABCB19, is required for cytoplasmic streaming and gravitropism of the inflorescence stems. (United States)

    Okamoto, Keishi; Ueda, Haruko; Shimada, Tomoo; Tamura, Kentaro; Koumoto, Yasuko; Tasaka, Masao; Morita, Miyo Terao; Hara-Nishimura, Ikuko


    A significant feature of plant cells is the extensive motility of organelles and the cytosol, which was originally defined as cytoplasmic streaming. We suggested previously that a three-way interaction between plant-specific motor proteins myosin XIs, actin filaments, and the endoplasmic reticulum (ER) was responsible for cytoplasmic streaming. (1) Currently, however, there are no reports of molecular components for cytoplasmic streaming other than the actin-myosin-cytoskeleton and ER-related proteins. In the present study, we found that elongated cells of inflorescence stems of Arabidopsis thaliana exhibit vigorous cytoplasmic streaming. Statistical analysis showed that the maximal velocity of plastid movements is 7.26 µm/s, which is much faster than the previously reported velocities of organelles. Surprisingly, the maximal velocity of streaming in the inflorescence stem cells was significantly reduced to 1.11 µm/s in an Arabidopsis mutant, abcb19-101, which lacks ATP BINDING CASSETTE SUBFAMILY B19 (ABCB19) that mediates the polar transport of the phytohormone auxin together with PIN-FORMED (PIN) proteins. Polar auxin transport establishes the auxin concentration gradient essential for plant development and tropisms. Deficiency of ABCB19 activity eventually caused enhanced gravitropic responses of the inflorescence stems and abnormally flexed inflorescence stems. These results suggest that ABCB19-mediated auxin transport plays a role not only in tropism regulation, but also in cytoplasmic streaming.

  8. Lattice-gas model for active vesicle transport by molecular motors with opposite polarities (United States)

    Muhuri, Sudipto; Pagonabarraga, Ignacio


    We introduce a multispecies lattice-gas model for motor protein driven collective cargo transport on cellular filaments. We use this model to describe and analyze the collective motion of interacting vesicle cargos being carried by oppositely directed molecular motors, moving on a single biofilament. Building on a totally asymmetric exclusion process to characterize the motion of the interacting cargos, we allow for mass exchange with the environment, input, and output at filament boundaries and focus on the role of interconversion rates and how they affect the directionality of the net cargo transport. We quantify the effect of the various different competing processes in terms of nonequilibrium phase diagrams. The interplay of interconversion rates, which allow for flux reversal and evaporation-deposition processes, introduces qualitatively unique features in the phase diagrams. We observe regimes of three-phase coexistence, the possibility of phase re-entrance, and a significant flexibility in how the different phase boundaries shift in response to changes in control parameters. The moving steady-state solutions of this model allows for different possibilities for the spatial distribution of cargo vesicles, ranging from homogeneous distribution of vesicles to polarized distributions, characterized by inhomogeneities or shocks. Current reversals due to internal regulation emerge naturally within the framework of this model. We believe that this minimal model will clarify the understanding of many features of collective vesicle transport, apart from serving as the basis for building more exact quantitative models for vesicle transport relevant to various in vivo situations.

  9. The glucosinolate breakdown product indole-3-carbinol acts as an auxin antagonist in roots of Arabidopsis thaliana. (United States)

    Katz, Ella; Nisani, Sophia; Yadav, Brijesh S; Woldemariam, Melkamu G; Shai, Ben; Obolski, Uri; Ehrlich, Marcelo; Shani, Eilon; Jander, Georg; Chamovitz, Daniel A


    The glucosinolate breakdown product indole-3-carbinol functions in cruciferous vegetables as a protective agent against foraging insects. While the toxic and deterrent effects of glucosinolate breakdown on herbivores and pathogens have been studied extensively, the secondary responses that are induced in the plant by indole-3-carbinol remain relatively uninvestigated. Here we examined the hypothesis that indole-3-carbinol plays a role in influencing plant growth and development by manipulating auxin signaling. We show that indole-3-carbinol rapidly and reversibly inhibits root elongation in a dose-dependent manner, and that this inhibition is accompanied by a loss of auxin activity in the root meristem. A direct interaction between indole-3-carbinol and the auxin perception machinery was suggested, as application of indole-3-carbinol rescues auxin-induced root phenotypes. In vitro and yeast-based protein interaction studies showed that indole-3-carbinol perturbs the auxin-dependent interaction of Transport Inhibitor Response (TIR1) with auxin/3-indoleacetic acid (Aux/IAAs) proteins, further supporting the possibility that indole-3-carbinol acts as an auxin antagonist. The results indicate that chemicals whose production is induced by herbivory, such as indole-3-carbinol, function not only to repel herbivores, but also as signaling molecules that directly compete with auxin to fine tune plant growth and development.

  10. Role of Auxin in orchid development. (United States)

    Darling-Novak, Stacey; Luna, Lila J; Gamage, Roshan N


    Auxin's capacity to regulate aspects of plant development has been well characterized in model plant systems. In contrast, orchids have received considerably less attention, but the realization that many orchid species are endangered has led to culture-based propagation studies which have unveiled some functions for auxin in this system. This mini-review summarizes the many auxin-mediated developmental responses in orchids that are consistent with model systems; however, it also brings to the forefront auxin responses that are unique to orchid development, namely protocorm formation and ovary/ovule maturation. With regard to shoot establishment, we also assess auxin's involvement in orchid germination, PLB formation, and somatic embryogenesis. Further, it makes evident that auxin flow during germination of the undifferentiated, but mature, orchid embryo mirrors late embryogenesis of typical angiosperms. Also discussed is the use of orchid protocorms in future phytohormone studies to better understand the mechanisms behind meristem formation and organogenesis.

  11. Numerical study of the auroral particle transport in the polar upper atmosphere

    Institute of Scientific and Technical Information of China (English)


    Starting from the Boltzmann equation and with some reasonable assumptions, a one-dimensional transport equation of charged energetic particles is derived by taking account of major interactions with neutral species in the upper atmosphere, including the processes of elastic scattering, the excitation, the ionization and the secondary electron production. The transport equation is numerically solved, for a simplified atmosphere consisting only of nitrogen molecules (N2), to obtain the variations of incident electron fluxes as a function of altitude, energy and pitch angle. The model results can describe fairly the transport characteristics of pre-cipitating auroral electron spectra in the polar upper atmosphere; meanwhile the N2 ionization rates calculated from the modeled differential flux spectra also exhibit good agreements with existing empirical models in terms of several key parameters. Taking the energy flux spectra of precipitating electrons observed by FAST satellite flying over EISCAT site on May 15, 1997 as model inputs, the model-calculated ionization rate profile of neutral atmosphere consists reasonably with that recon-structed from electron density measurements by the radar.

  12. Reciprocity relation for the vector radiative transport equation and its application to diffuse optical tomography with polarized light

    CERN Document Server

    Tricoli, Ugo; Da Silva, Anabela; Markel, Vadim A


    We derive a reciprocity relation for vector radiative transport equation (vRTE) that describes propagation of polarized light in multiple-scattering media. We then show how this result, together with translational invariance of a plane-parallel sample, can be used to compute efficiently the sensitivity kernel of diffuse optical tomography (DOT) by Monte Carlo simulations. Numerical examples of polarization-selective sensitivity kernels thus computed are given.

  13. The Allelochemical MDCA Inhibits Lignification and Affects Auxin Homeostasis1[OPEN (United States)

    Steenackers, Ward; Corneillie, Sander; Van de Wouwer, Dorien; Zažímalová, Eva


    The phenylpropanoid 3,4-(methylenedioxy)cinnamic acid (MDCA) is a plant-derived compound first extracted from roots of Asparagus officinalis and further characterized as an allelochemical. Later on, MDCA was identified as an efficient inhibitor of 4-COUMARATE-CoA LIGASE (4CL), a key enzyme of the general phenylpropanoid pathway. By blocking 4CL, MDCA affects the biosynthesis of many important metabolites, which might explain its phytotoxicity. To decipher the molecular basis of the allelochemical activity of MDCA, we evaluated the effect of this compound on Arabidopsis thaliana seedlings. Metabolic profiling revealed that MDCA is converted in planta into piperonylic acid (PA), an inhibitor of CINNAMATE-4-HYDROXYLASE (C4H), the enzyme directly upstream of 4CL. The inhibition of C4H was also reflected in the phenolic profile of MDCA-treated plants. Treatment of in vitro grown plants resulted in an inhibition of primary root growth and a proliferation of lateral and adventitious roots. These observed growth defects were not the consequence of lignin perturbation, but rather the result of disturbing auxin homeostasis. Based on DII-VENUS quantification and direct measurement of cellular auxin transport, we concluded that MDCA disturbs auxin gradients by interfering with auxin efflux. In addition, mass spectrometry was used to show that MDCA triggers auxin biosynthesis, conjugation, and catabolism. A similar shift in auxin homeostasis was found in the c4h mutant ref3-2, indicating that MDCA triggers a cross talk between the phenylpropanoid and auxin biosynthetic pathways independent from the observed auxin efflux inhibition. Altogether, our data provide, to our knowledge, a novel molecular explanation for the phytotoxic properties of MDCA. PMID:27506238

  14. PHABULOSA Mediates an Auxin Signaling Loop to Regulate Vascular Patterning in Arabidopsis. (United States)

    Müller, Christina Joy; Valdés, Ana Elisa; Wang, Guodong; Ramachandran, Prashanth; Beste, Lisa; Uddenberg, Daniel; Carlsbecker, Annelie


    Plant vascular tissues, xylem and phloem, differentiate in distinct patterns from procambial cells as an integral transport system for water, sugars, and signaling molecules. Procambium formation is promoted by high auxin levels activating class III homeodomain leucine zipper (HD-ZIP III) transcription factors (TFs). In the root of Arabidopsis (Arabidopsis thaliana), HD-ZIP III TFs dose-dependently govern the patterning of the xylem axis, with higher levels promoting metaxylem cell identity in the central axis and lower levels promoting protoxylem at its flanks. It is unclear, however, by what mechanisms the HD-ZIP III TFs control xylem axis patterning. Here, we present data suggesting that an important mechanism is their ability to moderate the auxin response. We found that changes in HD-ZIP III TF levels affect the expression of genes encoding core auxin response molecules. We show that one of the HD-ZIP III TFs, PHABULOSA, directly binds the promoter of both MONOPTEROS (MP)/AUXIN RESPONSE FACTOR5, a key factor in vascular formation, and IAA20, encoding an auxin/indole acetic acid protein that is stable in the presence of auxin and able to interact with and repress MP activity. The double mutant of IAA20 and its closest homolog IAA30 forms ectopic protoxylem, while overexpression of IAA30 causes discontinuous protoxylem and occasional ectopic metaxylem, similar to a weak loss-of-function mp mutant. Our results provide evidence that HD-ZIP III TFs directly affect the auxin response and mediate a feed-forward loop formed by MP and IAA20 that may focus and stabilize the auxin response during vascular patterning and the differentiation of xylem cell types.

  15. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction (United States)

    Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, J.-Q.


    We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  16. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    Directory of Open Access Journals (Sweden)

    Chao Zhang


    Full Text Available We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  17. Magnetometry and transport data complement polarized neutron reflectometry in magnetic depth profiling

    Energy Technology Data Exchange (ETDEWEB)

    Wang Yi; He Xi; Mukherjee, T.; Binek, Ch. [Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, Jorgenson Hall, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Fitzsimmons, M. R. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Sahoo, S. [Seagate Technology, Minneapolis, Minnesota 55435 (United States)


    Exchange coupled magnetic hard layer/soft layer thin films show a variety of complex magnetization reversal mechanisms depending on the hierarchy of interaction strengths within and between the films. Magnetization reversal can include uniform rotation, soft layer biasing, as well as exchange spring behavior. We investigate the magnetization reversal of a CoPt/Permalloy/Ta/Permalloy heterostructure. Here, Stoner-Wohlfarth-type uniform magnetization rotation of the virtually free Permalloy layer and exchange spring behavior of the strongly pinned Permalloy layer are found in the same sample. We investigate the complex magnetization reversal by polarized neutron reflectometry, magnetometry, and magneto-transport. The synergy of combining these experimental methods together with theoretical modeling is key to obtain the complete quantitative depth resolved information of the magnetization reversal processes for a multilayer of mesoscopic thickness.

  18. Development of perturbation Monte Carlo methods for polarized light transport in a discrete particle scattering model. (United States)

    Nguyen, Jennifer; Hayakawa, Carole K; Mourant, Judith R; Venugopalan, Vasan; Spanier, Jerome


    We present a polarization-sensitive, transport-rigorous perturbation Monte Carlo (pMC) method to model the impact of optical property changes on reflectance measurements within a discrete particle scattering model. The model consists of three log-normally distributed populations of Mie scatterers that approximate biologically relevant cervical tissue properties. Our method provides reflectance estimates for perturbations across wavelength and/or scattering model parameters. We test our pMC model performance by perturbing across number densities and mean particle radii, and compare pMC reflectance estimates with those obtained from conventional Monte Carlo simulations. These tests allow us to explore different factors that control pMC performance and to evaluate the gains in computational efficiency that our pMC method provides.

  19. Spin-polarized transport in a normal/ferromagnetic/normal zigzag graphene nanoribbon junction

    Institute of Scientific and Technical Information of China (English)

    Tian Hong-Yu; Wang Jun


    We investigate the spin-dependent electron transport in single and double normal/ferromagnetic/normal zigzag graphene nanoribbon (NG/FG/NG) junctions.The ferromagnetism in the FG region originates from the spontaneous magnetization of the zigzag graphene nanoribbon.It is shown that when the zigzag-chain number of the ribbon is even and only a single transverse mode is actived,the single NG/FG/NG junction can act as a spin polarizer and/or a spin analyzer because of the valley selection rule and the spin-exchange field in the FG,while the double NG/FG/NG/FG/NG junction exhibits a quantum switching effect,in which the on and the off states switch rapidly by varying the cross angle between two FG magnetizations.Our findings may shed light on the application of magnetized graphene nanoribbons to spintronics devices.

  20. Sublimation and transport of water from the north residual polar cap on Mars (United States)

    Haberle, Robert M.; Jakosky, Bruce M.


    The possible role of the north residual cap in the current Martian water cycle was examined using models to assess the ability of the cap to supply water to the atmosphere and the ability of the atmospheric circulation to transport it out of the polar regions to low northern latitudes. Results indicate that rather extreme circumstances would be required for the cap to provide all of the observed increase in atmospheric water, such as a combination of high surface winds, low cap emissivities, or substantial evaporation from dark material. But even if these conditions could be met, the high-latitude circulation is too localized in scale to move much water vapor out of the polar environment. Both the present calculations and the data from the Viking's Mars Atmospheric Water Detection Experiment show that about two thirds of the water appearing in the Martian northern hemisphere during summer must be supplied by other sources. It is suggested that the additional source is water desorbing from the nonpolar regolith.

  1. Gravitropism: lateral thinking in auxin transport. (United States)

    Moore, Ian


    Plant stems and roots orient themselves with respect to directional illumination and gravity by differential growth on either side of the organ. A model formulated in the 1930s proposed that tropic growth curvature arose from growth hormone redistribution. Studies with Arabidopsis are beginning to reveal the mechanism.

  2. Research Progresses on Auxin Response Factors

    Institute of Scientific and Technical Information of China (English)

    Hai-Bin Wei; Bai-Ming Cui; Yan-Li Ren; Juan-Hua Li; Wei-Bin Liao; Nan-Fei Xu; Ming Peng


    Auxin response factors (ARFs), a family of transcription factors, have been discovered recently. The ARFs bind specifically to the auxin response elements (AuxREs) within promoters of primary auxin responsive genes and function as activators or repressors. The ARFs contain three domains, namely a conserved Nterminal DNA-binding domain, a non-conserved middle region, and a conserved C-terminal dirnerization domain. The ARFs can form a protein complex with auxin/indoleacetic acid through homodimerization or heterodimerization. The particular protein-protein interaction may play a key role in modulating the expression of early auxin responsive genes. The identification of ARF mutations in Arabidopsis helps to demonstrate/dissect the function of ARFs in the normal growth and development of plants. Phylogenetic analysis also reveals some interesting protein evolution points in the ARF family.

  3. NCP1/AtMOB1A Plays Key Roles in Auxin-Mediated Arabidopsis Development. (United States)

    Cui, Xiaona; Guo, Zhiai; Song, Lizhen; Wang, Yanli; Cheng, Youfa


    MOB1 protein is a core component of the Hippo signaling pathway in animals where it is involved in controlling tissue growth and tumor suppression. Plant MOB1 proteins display high sequence homology to animal MOB1 proteins, but little is known regarding their role in plant growth and development. Herein we report the critical roles of Arabidopsis MOB1 (AtMOB1A) in auxin-mediated development in Arabidopsis. We found that loss-of-function mutations in AtMOB1A completely eliminated the formation of cotyledons when combined with mutations in PINOID (PID), which encodes a Ser/Thr protein kinase that participates in auxin signaling and transport. We showed that atmob1a was fully rescued by its Drosophila counterpart, suggesting functional conservation. The atmob1a pid double mutants phenocopied several well-characterized mutant combinations that are defective in auxin biosynthesis or transport. Moreover, we demonstrated that atmob1a greatly enhanced several other known auxin mutants, suggesting that AtMOB1A plays a key role in auxin-mediated plant development. The atmob1a single mutant displayed defects in early embryogenesis and had shorter root and smaller flowers than wild type plants. AtMOB1A is uniformly expressed in embryos and suspensor cells during embryogenesis, consistent with its role in embryo development. AtMOB1A protein is localized to nucleus, cytoplasm, and associated to plasma membrane, suggesting that it plays roles in these subcellular localizations. Furthermore, we showed that disruption of AtMOB1A led to a reduced sensitivity to exogenous auxin. Our results demonstrated that AtMOB1A plays an important role in Arabidopsis development by promoting auxin signaling.

  4. Potential spin-polarized transport in gold-doped armchair graphene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Pankaj, E-mail: [Nanomaterials Research Group, ABV-Indian Institute of Information Technology and Management (IIITM), Gwalior 474015, MP (India); Dhar, Subhra [Nanomaterials Research Group, ABV-Indian Institute of Information Technology and Management (IIITM), Gwalior 474015, MP (India); Jaiswal, Neeraj K. [Discipline of Physics, PDPM-Indian Institute of Information Technology, Design and Manufacturing (IIITDM), Jabalpur 482005 (India)


    Based on NEGF-DFT computations, systematic investigation of electronic, magnetic and transport properties of AGNRs are done by employing Au through different doping mechanisms. Remarkable Au–AGNR bonding is observed in case of substitution due to the presence of impurity at the edges. Both substitution and adsorption of Au on AGNR surface induce significant changes in the electronic spin transport of the sp{sup 2} hybridized carbon sheets. AGNRs are semiconducting with lower total energy for the FM configuration, and the I–V characteristics reveal semiconductor to metal transition of Au-doped AGNR. The spin injection is voltage controlled in all the investigated Au-doped AGNRs. - Highlights: • Edge Au-substitution promotes semiconductor–metal transition in AGNR. • NDR due to bias-dependent transmission in Au-substituted AGNRs. • Voltage controlled spin injection in all investigated Au-doped AGNRs. • Strong spin polarization occurs at 0.5 V in Au-hole adsorbed AGNRs.

  5. Composite structure of auxin response elements. (United States)

    Ulmasov, T; Liu, Z B; Hagen, G; Guilfoyle, T J


    The auxin-responsive soybean GH3 gene promoter is composed of multiple auxin response elements (AuxREs), and each AuxRE contributes incrementally to the strong auxin inducibility to the promoter. Two independent AuxREs of 25 bp (D1) and 32 bp (D4) contain the sequence TGTCTC. Results presented here show that the TGTCTC element in D1 and D4 is required but not sufficient for auxin inducibility in carrot protoplast transient expression assays. Additional nucleotides upstream of TGTCTC are also required for auxin inducibility. These upstream sequences showed constitutive activity and no auxin inducibility when part or all of the TGTCTC element was mutated or deleted. In D1, the constitutive element overlaps the 5' portion of TGTCTC; in D4, the constitutive element is separated from TGTCTC. An 11-bp element in D1, CCTCGTGTCTC, conferred auxin inducibility to a minimal cauliflower mosaic virus 35S promoter in transgenic tobacco seedlings as well as in carrot protoplasts (i.e., transient expression assays). Both constitutive elements bound specifically to plant nuclear proteins, and the constitutive element in D1 bound to a recombinant soybean basic leucine zipper transcription factor with G-box specificity. To demonstrate further the composite nature of AuxREs and the ability of the TGTCTC element to confer auxin inducibility, we created a novel AuxRE by placing a yeast GAL4 DNA binding site adjacent to the TGTCTC element. Expression of a GAL4-c-Rel transactivator in the presence of this novel AuxRE resulted in auxin-inducible expression. Our results indicate that at least some AuxREs have a composite structure consisting of a constitutive element adjacent to a conserved TGTCTC element that confers auxin inducibility.

  6. Halogenated auxins affect microtubules and root elongation in Lactuca sativa (United States)

    Zhang, N.; Hasenstein, K. H.


    We studied the effect of 4,4,4-trifluoro-3-(indole-3-)butyric acid (TFIBA), a recently described root growth stimulator, and 5,6-dichloro-indole-3-acetic acid (DCIAA) on growth and microtubule (MT) organization in roots of Lactuca sativa L. DCIAA and indole-3-butyric acid (IBA) inhibited root elongation and depolymerized MTs in the cortex of the elongation zone, inhibited the elongation of stele cells, and promoted xylem maturation. Both auxins caused the plane of cell division to shift from anticlinal to periclinal. In contrast, TFIBA (100 micromolar) promoted elongation of primary roots by 40% and stimulated the elongation of lateral roots, even in the presence of IBA, the microtubular inhibitors oryzalin and taxol, or the auxin transport inhibitor naphthylphthalamic acid. However, TFIBA inhibited the formation of lateral root primordia. Immunostaining showed that TFIBA stabilized MTs orientation perpendicular to the root axis, doubled the cortical cell length, but delayed xylem maturation. The data indicate that the auxin-induced inhibition of elongation and swelling of roots results from reoriented phragmoplasts, the destabilization of MTs in elongating cells, and promotion of vessel formation. In contrast, TFIBA induced promotion of root elongation by enhancing cell length, prolonging transverse MT orientation, delaying cell and xylem maturation.

  7. Small-molecule auxin inhibitors that target YUCCA are powerful tools for studying auxin function. (United States)

    Kakei, Yusuke; Yamazaki, Chiaki; Suzuki, Masashi; Nakamura, Ayako; Sato, Akiko; Ishida, Yosuke; Kikuchi, Rie; Higashi, Shouichi; Kokudo, Yumiko; Ishii, Takahiro; Soeno, Kazuo; Shimada, Yukihisa


    Auxin is essential for plant growth and development, this makes it difficult to study the biological function of auxin using auxin-deficient mutants. Chemical genetics have the potential to overcome this difficulty by temporally reducing the auxin function using inhibitors. Recently, the indole-3-pyruvate (IPyA) pathway was suggested to be a major biosynthesis pathway in Arabidopsis thaliana L. for indole-3-acetic acid (IAA), the most common member of the auxin family. In this pathway, YUCCA, a flavin-containing monooxygenase (YUC), catalyzes the last step of conversion from IPyA to IAA. In this study, we screened effective inhibitors, 4-biphenylboronic acid (BBo) and 4-phenoxyphenylboronic acid (PPBo), which target YUC. These compounds inhibited the activity of recombinant YUC in vitro, reduced endogenous IAA content, and inhibited primary root elongation and lateral root formation in wild-type Arabidopsis seedlings. Co-treatment with IAA reduced the inhibitory effects. Kinetic studies of BBo and PPBo showed that they are competitive inhibitors of the substrate IPyA. Inhibition constants (Ki ) of BBo and PPBo were 67 and 56 nm, respectively. In addition, PPBo did not interfere with the auxin response of auxin-marker genes when it was co-treated with IAA, suggesting that PPBo is not an inhibitor of auxin sensing or signaling. We propose that these compounds are a class of auxin biosynthesis inhibitors that target YUC. These small molecules are powerful tools for the chemical genetic analysis of auxin function.

  8. POPCORN functions in the auxin pathway to regulate embryonic body plan and meristem organization in Arabidopsis. (United States)

    Xiang, Daoquan; Yang, Hui; Venglat, Prakash; Cao, Yongguo; Wen, Rui; Ren, Maozhi; Stone, Sandra; Wang, Edwin; Wang, Hong; Xiao, Wei; Weijers, Dolf; Berleth, Thomas; Laux, Thomas; Selvaraj, Gopalan; Datla, Raju


    The shoot and root apical meristems (SAM and RAM) formed during embryogenesis are crucial for postembryonic plant development. We report the identification of POPCORN (PCN), a gene required for embryo development and meristem organization in Arabidopsis thaliana. Map-based cloning revealed that PCN encodes a WD-40 protein expressed both during embryo development and postembryonically in the SAM and RAM. The two pcn alleles identified in this study are temperature sensitive, showing defective embryo development when grown at 22°C that is rescued when grown at 29°C. In pcn mutants, meristem-specific expression of WUSCHEL (WUS), CLAVATA3, and WUSCHEL-RELATED HOMEOBOX5 is not maintained; SHOOTMERISTEMLESS, BODENLOS (BDL) and MONOPTEROS (MP) are misexpressed. Several findings link PCN to auxin signaling and meristem function: ectopic expression of DR5(rev):green fluorescent protein (GFP), pBDL:BDL-GFP, and pMP:MP-β-glucuronidase in the meristem; altered polarity and expression of pPIN1:PIN1-GFP in the apical domain of the developing embryo; and resistance to auxin in the pcn mutants. The bdl mutation rescued embryo lethality of pcn, suggesting that improper auxin response is involved in pcn defects. Furthermore, WUS, PINFORMED1, PINOID, and TOPLESS are dosage sensitive in pcn, suggesting functional interaction. Together, our results suggest that PCN functions in the auxin pathway, integrating auxin signaling in the organization and maintenance of the SAM and RAM.

  9. Functionally different PIN proteins control auxin flux during bulbil development in Agave tequilana. (United States)

    Abraham Juárez, María Jazmín; Hernández Cárdenas, Rocío; Santoyo Villa, José Natzul; O'Connor, Devin; Sluis, Aaron; Hake, Sarah; Ordaz-Ortiz, José; Terry, Leon; Simpson, June


    In Agave tequilana, reproductive failure or inadequate flower development stimulates the formation of vegetative bulbils at the bracteoles, ensuring survival in a hostile environment. Little is known about the signals that trigger this probably unique phenomenon in agave species. Here we report that auxin plays a central role in bulbil development and show that the localization of PIN1-related proteins is consistent with altered auxin transport during this process. Analysis of agave transcriptome data led to the identification of the A. tequilana orthologue of PIN1 (denoted AtqPIN1) and a second closely related gene from a distinct clade reported as 'Sister of PIN1' (denoted AtqSoPIN1). Quantitative real-time reverse transcription-PCR (RT-qPCR) analysis showed different patterns of expression for each gene during bulbil formation, and heterologous expression of the A. tequilana PIN1 and SoPIN1 genes in Arabidopsis thaliana confirmed functional differences between these genes. Although no free auxin was detected in induced pedicel samples, changes in the levels of auxin precursors were observed. Taken as a whole, the data support the model that AtqPIN1 and AtqSoPIN1 have co-ordinated but distinct functions in relation to auxin transport during the initial stages of bulbil formation.

  10. Adenosine Diphosphate Ribosylation Factor-GTPaseActivating Protein Stimulates the Transport of AUX1Endosome, Which Relies on Actin Cytoskeletal Organization in Rice Root DevelopmentF

    Institute of Scientific and Technical Information of China (English)

    Cheng Du; Yunyuan XU; Yingdian Wang; Kang Chong


    Polar auxin transport,which depends on polarized subcellular distribution of AUXIN RESISTANT 1/LIKE AUX1 (AUX1/LAX) influx carriers and PIN-FORMED (PIN) efflux carriers,mediates various processes of plant growth and development.Endosomal recycling of PIN1 is mediated by an adenosine diphosphate (ADP)ribosylation factor (ARF)-GTPase exchange factor protein,GNOM.However,the mediation of auxin influx carrier recycling is poorly understood.Here,we report that overexpression of OsAGAP,an ARF-GTPase-activating protein in rice,stimulates vesicle transport from the plasma membrane to the Golgi apparatus in protoplasts and transgenic plants and induces the accumulation of early endosomes and AUX1.AUX1 endosomes could partially colocalize with FM4-64 labeled early endosome after actin disruption.Furthermore,OsAGAP is involved in actin cytoskeletal organization,and its overexpression tends to reduce the thickness and bundling of actin filaments.Fluorescence recovery after photobleaching analysis revealed exocytosis of the AUX1 recycling endosome was not affected in the OsAGAP overexpression cells,and was only slightly promoted when the actin filaments were completely disrupted by Lat B.Thus,we propose that AUX1 accumulation in the OsAGAP overexpression and actin disrupted cells may be due to the fact that endocytosis of the auxin influx carrier AUX1 early endosome was greatly promoted by actin cytoskeleton disruption.

  11. Spin-polarized transport through single-molecule magnet Mn6 complexes

    KAUST Repository

    Cremades, Eduard


    The coherent transport properties of a device, constructed by sandwiching a Mn6 single-molecule magnet between two gold surfaces, are studied theoretically by using the non-equilibrium Green\\'s function approach combined with density functional theory. Two spin states of such Mn6 complexes are explored, namely the ferromagnetically coupled configuration of the six MnIII cations, leading to the S = 12 ground state, and the low S = 4 spin state. For voltages up to 1 volt the S = 12 ground state shows a current one order of magnitude larger than that of the S = 4 state. Furthermore this is almost completely spin-polarized, since the Mn6 frontier molecular orbitals for S = 12 belong to the same spin manifold. As such the high-anisotropy Mn6 molecule appears as a promising candidate for implementing, at the single molecular level, both spin-switches and low-temperature spin-valves. © 2013 The Royal Society of Chemistry.

  12. Kinetic Space Weather: Toward a Global Hybrid Model of the Polar Ionosphere-Lower Magnetosphere Plasma Transport (United States)

    Horwitz, James L.


    During the indicated period of performance, we had a number of publications concerned with kinetic polar ionosphere-lower magnetosphere plasma transport. For the IUGG 1991-4 Quadrennial Report, we reviewed aspects of U.S. accomplishments concerned with polar plasma transport, among other issues. In another review, we examined the computer simulations of multiple-scale processes in space plasmas, including polar plasma outflow and transport. We also examined specifically multiscale processes in ionospheric outflows. We developed a Generalized Semi-Kinetic(GSK) model for the topside-lower magnetosphere which explored the synergistic action of wave heating and electric potentials in the formation of auroral Ion conics, in particular the "pressure cooker" mechanism. We extended the GSK model all the way down to 120 km and applied this code to illustrate the response of the ionosphere- magnetosphere to soft-electron precipitation and convection-driven frictional ion heating, respectively. Later, the convection-driven heating work was extended to a paper for the Journal of Geophysical Research. In addition to the above full published papers, we also presented the first developments of the coupled fluid-semikinetic model for polar plasma transport during this period. The results from a steady-state treatment were presented, with the second presentation being concerned with the effects of photo-electrons on the polar wind, and the first garnering an outstanding student paper award from the American Geophysical Union. We presented the first results from a time-dependent version of this coupled fluid-semikinetic model.

  13. Neutron Radiation Affects the Expression of Genes Involved in the Response to Auxin, Senescence and Oxidative Stress in Arabidopsis (United States)

    Fortunati, A.; Tassone, P.; Migliaccio, F.


    Researches were conducted on the effect of neutron radiation on the expression of genes auxin activated or connected with the process of senescence in Arabidopsis plants. The research was done by applying the real-time polymerase chain reaction (PCR) technique. The results indicated that the auxin response factors (ARFs) genes are clearly downregulated, whereas the indolacetic acid-induced (Aux/IAAs) genes in some cases were upregulated. By contrast in the mutants for auxin transport aux1 and eir1 the ARFs genes were upregulated. In addition, both in the wildtype and mutants, some already known genes activated by stress and senescence were significantly upregulated. On the basis of these researches we conclude that the process of senescence induced by irradiation is, at least in part, controlled by the physiology of the hormone auxin.

  14. The role of Phe82 and Phe351 in auxin-induced substrate perception by TIR1 ubiquitin ligase: a novel insight from molecular dynamics simulations.

    Directory of Open Access Journals (Sweden)

    Ge-Fei Hao

    Full Text Available It is well known that Auxin plays a key role in controlling many aspects of plant growth and development. Crystal structures of Transport inhibitor response 1 (TIR1, a true receptor of auxin, were very recently determined for TIR1 alone and in complexes with auxin and different synthetic analogues and an Auxin/Indole-3-Acetic Acid (Aux/IAA substrate peptide. However, the dynamic conformational changes of the key residues of TIR1 that take place during the auxin and substrate perception by TIR1 and the detailed mechanism of these changes are still unclear. In the present study, various computational techniques were integrated to uncover the detailed molecular mechanism of the auxin and Aux/IAA perception process; these simulations included molecular dynamics (MD simulations on complexes and the free enzyme, the molecular mechanics Poisson Boltzmann surface area (MM-PBSA calculations, normal mode analysis, and hydrogen bond energy (HBE calculations. The computational simulation results provided a reasonable explanation for the structure-activity relationships of auxin and its synthetic analogues in view of energy. In addition, a more detailed model for auxin and Aux/IAA perception was also proposed, indicating that Phe82 and Phe351 played a pivotal role in Aux/IAA perception. Upon auxin binding, Phe82 underwent conformational changes to accommodate the subsequent binding of Aux/IAA. As a result, auxin enhances the TIR1-Aux/IAA interactions by acting as a "molecular glue". Besides, Phe351 acts as a "fastener" to further improve the substrate binding. The structural and mechanistic insights obtained from the present study will provide valuable clues for the future design of promising auxin analogues.

  15. Auxin level and regeneration of Begonia leaves. (United States)

    Heide, O M


    As previously found, both the level of ether-extractable auxin (presumably indole-3-acetic acid) and the root-forming ability of B.xcheimantha leaves are increased under long-day conditions by high temperature, whereas the capacity for adventitious bud formation is reduced. However, this relation is present under relatively high light intensity only. Under the low light intensities in late fall neither auxin level nor regeneration ability were significantly affected by temperature.Dark treatment of detached leaves for 2 to 16 days greatly counteracted the inhibitory effect of high temperature on bud formation and reduced both the auxin level and the root-forming ability of the leaves.The great seasonal changes in the regeneration ability of Begonia leaves seem to be the result of a complex interaction of temperature, day-length, and daily light energy on the level of endogenous auxin and other growth regulators.

  16. Transport of Spin-Polarized Current Through a Mesoscopic Ring with Two Leads Induced by Aharonov-Bohm and Aharonov-Casher Phases

    Institute of Scientific and Technical Information of China (English)

    GAO Ying-Fang; ZHANG Yong-Ping; LIANG Jiu-Qing


    @@ We study the transport of spin-polarized current induced by the Aharonov-Bohm and Aharonov-Casher phases in a mesoscopic ring with two leads in the presence of a cylindrically symmetric electric field and the magnetic flux at the centre of the same ring. An exact solution for the quantum transport is obtained. It is shown that the transport spin-polarized current and its polarizability can be controlled by the electric field and the magnetic flux as well.

  17. Auxin asymmetry during gravitropism by tomato hypocotyls (United States)

    Harrison, M. A.; Pickard, B. G.


    Gravitropic asymmetry of auxin was observed in hypocotyls of tomato (Lycopersicon esculentum Mill.) soon after horizontal placement: the ratio of apically supplied [3H]IAA collected from the lower sides to that from the upper sides was about 1.4 between 5 and 10 minutes. This was adequately early to account for the beginning of curvature. The auxin asymmetry ratio rose to about 2.5 between 20 and 25 minutes, and to 3.5 during the main phase of curvature. This compares reasonably well with the roughly 3.9 ratio for elongation on the lower side to elongation on the upper side that is the basis for the curvature. These data extend evidence that the Went-Cholodny theory for the mediation of tropisms is valid for dicot stems. Also consistent with the theory, an auxin asymmetry ratio of 2.5 was observed when wrong-way gravitropic curvature developed following application of a high level of auxin. In addition to reversing the asymmetry of elongation, the large supplement of auxin resulted in lower net elongation. Previous data established that ethylene is not involved in this decrease of growth as a function of increasing level of auxin.

  18. The acropetal effects of indole-3-acetic acid in isolated shoot segments of Acer pseudoplatanus L. II. Possible regulation by a vectorial fieid of auxin waves

    Directory of Open Access Journals (Sweden)

    Jacek A. Adamczyk


    Full Text Available The acropetal effects of auxin on elongation of axillary buds and on modulation of the wave-like pattern of basipetal efflux of natural auxin to agar from Acer pseudoplatanus L. shoots were studied. When synthetic IAA was applied to cut surfaces of one of two branches the elongation growth of buds situated on the opposite branch was retarded, suggesting regulation independent of the direct action of the molecules of the applied IAA. Oscillations in basipetal transport of natural auxin along the stem segments were observed corroborating the results of other authors using different tree species. Apical application of synthetic IAA for 1 hour to the lateral branch caused a phase shift of the wave-like pattern of basipetal efflux of natural auxin, when the stem segment above the treated branch was sectioned. The same effect was observed evoked by the laterally growing branch which is interpreted as an effect of natural auxin produced by the actively growing shoot. These modulations could be propagated acropetally at a rate excluding direct action of auxin molecules at the sites of measurement. The results seem to corroborate the hypothesis suggesting that auxin is involved in acropetal regulation of shoot apex growth through its effect upon modulation of the vectorial field which arises when the auxin-waves translocate in cambium.

  19. Characterization of the growth and auxin physiology of roots of the tomato mutant, diageotropica (United States)

    Muday, G. K.; Lomax, T. L.; Rayle, D. L.


    Roots of the tomato (Lycopersicon esculentum, Mill.) mutant (diageotropica (dgt) exhibit an altered phenotype. These roots are agravitropic and lack lateral roots. Relative to wild-type (VFN8) roots, dgt roots are less sensitive to growth inhibition by exogenously applied IAA and auxin transport inhibitors (phytotropins), and the roots exhibit a reduction in maximal growth inhibition in response to ethylene. However, IAA transport through roots, binding of the phytotropin, tritiated naphthylphthalamic acid ([3H]NPA), to root microsomal membranes, NPA-sensitive IAA uptake by root segments, and uptake of [3H]NPA into root segments are all similar in mutant and wild-type roots. We speculate that the reduced sensitivity of dgt root growth to auxin-transport inhibitors and ethylene is an indirect result of the reduction in sensitivity to auxin in this single gene, recessive mutant. We conclude that dgt roots, like dgt shoots, exhibit abnormalities indicating they have a defect associated with or affecting a primary site of auxin perception or action.

  20. Mechanism of Auxin Interaction with Auxin Binding Protein (ABP1): A Molecular Dynamics Simulation Study (United States)

    Bertoša, Branimir; Kojić-Prodić, Biserka; Wade, Rebecca C.; Tomić, Sanja


    Auxin Binding Protein 1 (ABP1) is ubiquitous in green plants. It binds the phytohormone auxin with high specificity and affinity, but its role in auxin-induced processes is unknown. To understand the proposed receptor function of ABP1 we carried out a detailed molecular modeling study. Molecular dynamics simulations showed that ABP1 can adopt two conformations differing primarily in the position of the C-terminus and that one of them is stabilized by auxin binding. This is in agreement with experimental evidence that auxin induces changes at the ABP1 C-terminus. Simulations of ligand egress from ABP1 revealed three main routes by which an auxin molecule can enter or leave the ABP1 binding site. Assuming the previously proposed orientation of ABP1 to plant cell membranes, one of the routes leads to the membrane and the other two to ABP1's aqueous surroundings. A network of hydrogen-bonded water molecules leading from the bulk water to the zinc-coordinated ligands in the ABP1 binding site was formed in all simulations. Water entrance into the zinc coordination sphere occurred simultaneously with auxin egress. These results suggest that the hydrogen-bonded water molecules may assist in protonation and deprotonation of auxin molecules and their egress from the ABP1 binding site. PMID:17766341

  1. SCFTIR1/AFB-auxin signalling regulates PIN vacuolar trafficking and auxin fluxes during root gravitropism

    NARCIS (Netherlands)

    Baster, P.; Robert, S.; Kleine-Vehn, J.; Vanneste, S.; Kania, U.; Grunewald, W.; Rybel, de B.P.M.; Beeckman, T.; Friml, J.


    The distribution of the phytohormone auxin regulates many aspects of plant development including growth response to gravity. Gravitropic root curvature involves coordinated and asymmetric cell elongation between the lower and upper side of the root, mediated by differential cellular auxin levels. Th

  2. Flow field design and optimization based on the mass transport polarization regulation in a flow-through type vanadium flow battery (United States)

    Zheng, Qiong; Xing, Feng; Li, Xianfeng; Ning, Guiling; Zhang, Huamin


    Vanadium flow battery holds great promise for use in large scale energy storage applications. However, the power density is relatively low, leading to significant increase in the system cost. Apart from the kinetic and electronic conductivity improvement, the mass transport enhancement is also necessary to further increase the power density and reduce the system cost. To better understand the mass transport limitations, in the research, the space-varying and time-varying characteristic of the mass transport polarization is investigated based on the analysis of the flow velocity and reactant concentration in the bulk electrolyte by modeling. The result demonstrates that the varying characteristic of mass transport polarization is more obvious at high SoC or high current densities. To soften the adverse impact of the mass transport polarization, a new rectangular plug flow battery with a plug flow and short flow path is designed and optimized based on the mass transport polarization regulation (reducing the mass transport polarization and improving its uniformity of distribution). The regulation strategy of mass transport polarization is practical for the performance improvement in VFBs, especially for high power density VFBs. The findings in the research are also applicable for other flow batteries and instructive for practical use.

  3. Effect of polarization roughness scattering (PRS) on two-dimensional electron transport of MgZnO/ZnO heterostructures (United States)

    Wang, Ping; Guo, Lixin; Song, Zhenjie; Yang, Yintang; Shang, Tao; Li, Jing; Huang, Feng; Zheng, Qinghong


    Quantum transport properties of two-dimensional electron gas (2DEG) in undoped MgZnO/ZnO heterostructures with polarization charge effect have been investigated theoretically. Polarization roughness scattering (PRS) combining polarization charge and interface roughness scattering was proposed as a new scattering mechanism. It was found that the carriers confined in the heterostructures (HSs) would be scattered from polarization charges when they were moving along the in-plane and PRS played a very important role for the low-temperature electron mobility when the electron density Ns exceeded 1.0e11 cm-2, especially in a higher electron density region. With PRS, the experimental data on the density dependence of 2DEG mobility in the MgZnO/ZnO HSs under study can be well reproduced. The study indicates that the improved processing techniques providing a smooth interface and a good separation between the 2DEG electrons and the polarization charges should be significant for the quantum device’s performance.

  4. A Testing Ground for Polarized Maser Transport: Multi-Epoch Analysis of a π/2 Electric Vector Rotation (United States)

    Tobin, Taylor; Kemball, Athol J.


    The near circumstellar environment (NCSE) around Asymptotic Giant Branch (AGB) stars is chaotic, exhibiting shocks, turbulence, velocity gradients, and a potentially dynamically significant magnetic field (Vlemmings et al. 2005). Very Long Baseline Interferometry (VLBI) of masers emanating from these environments can provide sub-milliarcsecond angular resolution of the NCSE (Kemball 2002). Solidifying the origin of the polarization in these masers may be the key to understanding the magnitude and behavior of these stars' magnetic fields (eg. Goldreich et al. 1973; Elitzur 1996). However, other theories of polarized maser transport do not rely heavily on the magnetic field; some are more dependent on anisotropic pumping (Elitzur 1996; Watson 2009) or anisotropic resonant scattering (Asensio Ramos et al. 2005; Houde 2014). One optimal test of these theories is their ability to account for a π/2 rotation of the Electric Vector Position Angle (EVPA) observed in some maser features. The profile of linear polarization across such a feature varies with the generating mechanism. In this study, we utilize multi-epoch observations of ν=1, J=1-0 SiO maser emission around TX Cam (Diamond & Kemball 2003; Kemball et al. 2009; Gonidakis et al. 2010) to analyze a single feature with a π/2 rotation that persisted for five epochs and compare it to the behavior expected according to various theories of maser polarization. In addition, we analyze the low levels of circular polarization - now achievable due to recent improvements in millimeter-wavelength circular polarization reduction (Kemball & Richter 2011) - and compare their correlation with other parameters to further test these polarization generation theories.

  5. Cell-Cell Communication in Yeast Using Auxin Biosynthesis and Auxin Responsive CRISPR Transcription Factors. (United States)

    Khakhar, Arjun; Bolten, Nicholas J; Nemhauser, Jennifer; Klavins, Eric


    An engineering framework for synthetic multicellular systems requires a programmable means of cell-cell communication. Such a communication system would enable complex behaviors, such as pattern formation, division of labor in synthetic microbial communities, and improved modularity in synthetic circuits. However, it remains challenging to build synthetic cellular communication systems in eukaryotes due to a lack of molecular modules that are orthogonal to the host machinery, easy to reconfigure, and scalable. Here, we present a novel cell-to-cell communication system in Saccharomyces cerevisiae (yeast) based on CRISPR transcription factors and the plant hormone auxin that exhibits several of these features. Specifically, we engineered a sender strain of yeast that converts indole-3-acetamide (IAM) into auxin via the enzyme iaaH from Agrobacterium tumefaciens. To sense auxin and regulate transcription in a receiver strain, we engineered a reconfigurable library of auxin-degradable CRISPR transcription factors (ADCTFs). Auxin-induced degradation is achieved through fusion of an auxin-sensitive degron (from IAA corepressors) to the CRISPR TF and coexpression with an auxin F-box protein. Mirroring the tunability of auxin perception in plants, our family of ADCTFs exhibits a broad range of auxin sensitivities. We characterized the kinetics and steady-state behavior of the sender and receiver independently as well as in cocultures where both cell types were exposed to IAM. In the presence of IAM, auxin is produced by the sender cell and triggers deactivation of reporter expression in the receiver cell. The result is an orthogonal, rewireable, tunable, and, arguably, scalable cell-cell communication system for yeast and other eukaryotic cells.

  6. Mutant analysis in Arabidopsis provides insight into the molecular mode of action of the auxinic herbicide dicamba.

    Directory of Open Access Journals (Sweden)

    Cynthia Gleason

    Full Text Available Herbicides that mimic the natural auxin indole-3-acetic acid are widely used in weed control. One common auxin-like herbicide is dicamba, but despite its wide use, plant gene responses to dicamba have never been extensively studied. To further understand dicamba's mode of action, we utilized Arabidopsis auxin-insensitive mutants and compared their sensitivity to dicamba and the widely-studied auxinic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D. The mutant axr4-2, which has disrupted auxin transport into cells, was resistant to 2,4-D but susceptible to dicamba. By comparing dicamba resistance in auxin signalling F-box receptor mutants (tir1-1, afb1, afb2, afb3, and afb5, only tir1-1 and afb5 were resistant to dicamba, and this resistance was additive in the double tir1-1/afb5 mutant. Interestingly, tir1-1 but not afb5 was resistant to 2,4-D. Whole genome analysis of dicamba-induced gene expression showed that 10 hours after application, dicamba stimulated many stress-responsive and signalling genes, including those involved in biosynthesis or signalling of auxin, ethylene, and abscisic acid (ABA, with TIR1 and AFB5 required for the dicamba-responsiveness of some genes. Research into dicamba-regulated gene expression and the selectivity of auxin receptors has provided molecular insight into dicamba-regulated signalling and could help in the development of novel herbicide resistance in crop plants.

  7. Carbohydrate Stress Affecting Fruitlet Abscission and Expression of Genes Related to Auxin Signal Transduction Pathway in Litchi

    Directory of Open Access Journals (Sweden)

    Wang-Jin Lu


    Full Text Available Auxin, a vital plant hormone, regulates a variety of physiological and developmental processes. It is involved in fruit abscission through transcriptional regulation of many auxin-related genes, including early auxin responsive genes (i.e., auxin/indole-3-acetic acid (AUX/IAA, Gretchen Hagen3 (GH3 and small auxin upregulated (SAUR and auxin response factors (ARF, which have been well characterized in many plants. In this study, totally five auxin-related genes, including one AUX/IAA (LcAUX/IAA1, one GH3 (LcGH3.1, one SAUR (LcSAUR1 and two ARFs (LcARF1 and LcARF2, were isolated and characterized from litchi fruit. LcAUX/IAA1, LcGH3.1, LcSAUR1, LcARF1 and LcARF2 contain open reading frames (ORFs encoding polypeptides of 203, 613, 142, 792 and 832 amino acids, respectively, with their corresponding molecular weights of 22.67, 69.20, 11.40, 88.20 and 93.16 kDa. Expression of these genes was investigated under the treatment of girdling plus defoliation which aggravated litchi fruitlet abscission due to the blockage of carbohydrates transport and the reduction of endogenous IAA content. Results showed that transcript levels of LcAUX/IAA1, LcGH3.1 and LcSAUR1 mRNAs were increased after the treatment in abscission zone (AZ and other tissues, in contrast to the decreasing accumulation of LcARF1 mRNA, suggesting that LcAUX/IAA1, LcSAUR1 and LcARF1 may play more important roles in abscission. Our results provide new insight into the process of fruitlet abscission induced by carbohydrate stress and broaden our understanding of the auxin signal transduction pathway in this process at the molecular level.

  8. Effect of Porosity and Concentration Polarization on Electrolyte Diffusive Transport Parameters through Ceramic Membranes with Similar Nanopore Size

    Directory of Open Access Journals (Sweden)

    Virginia Romero


    Full Text Available Diffusive transport through nanoporous alumina membranes (NPAMs produced by the two-step anodization method, with similar pore size but different porosity, is studied by analyzing membrane potential measured with NaCl solutions at different concentrations. Donnan exclusion of co-ions at the solution/membrane interface seem to exert a certain control on the diffusive transport of ions through NPAMs with low porosity, which might be reduced by coating the membrane surface with appropriated materials, as it is the case of SiO2. Our results also show the effect of concentration polarization at the membrane surface on ionic transport numbers (or diffusion coefficients for low-porosity and high electrolyte affinity membranes, which could mask values of those characteristic electrochemical parameters.

  9. Molecular cloning and characterization of the genes encoding an auxin efflux carrier and the auxin influx carriers associated with the adventitious root formation in mango (Mangifera indica L.) cotyledon segments. (United States)

    Li, Yun-He; Zou, Ming-Hong; Feng, Bi-Hong; Huang, Xia; Zhang, Zhi; Sun, Guang-Ming


    Polar auxin transport (PAT) plays an important role in the adventitious root formation of mango cotyledon segments, but the molecular mechanism remains unclear. In this study, we cloned a gene encoding an auxin efflux carrier (designated as MiPIN1), and we cloned four genes encoding auxin influx carriers (designated as MiAUX1, MiAUX2, MiAUX3 and MiAUX4). The results of a phylogenetic tree analysis indicated that MiPIN1 and the MiAUXs belong to plant PIN and AUXs/LAXs groups. Quantitative real-time PCR indicated that the expression of MiPIN1 and the MiAUXs was lowest at 0 days but sharply increased on and after day 4. During the root formation in the mango cotyledon segments, the MiPIN1 expression in the distal cut surface (DCS) was always higher than the expression in the proximal cut surface (PCS) whereas the expression of the MiAUXs in the PCS was usually higher than in the DCS. This expression pattern might be result in the PAT from the DCS to the PCS, which is essential for the adventitious root formation in the PCS. Our previous study indicated that a pre-treatment of embryos with indole-3-butyric acid (IBA) significantly promoted adventitious rooting in PCS whereas a pre-treatment with 2,3,5-triiodobenzoic acid (TIBA) completely inhibited this rooting. In this study, however, IBA and TIBA pre-treatments slightly changed the expression of MiPIN1. In contrast, while the MiAUX3 and MiAUX4 expression levels were significantly up-regulated by the IBA pre-treatment, the expression levels were down-regulated by the TIBA pre-treatment. These findings imply that MiAUX3 and MiAUX4 are more sensitive to the IBA and TIBA treatments and that they might play important roles during adventitious root formation in mango cotyledon segments.

  10. On Polar Magnetic Field Reversal and Surface Flux Transport During Solar Cycle 24

    CERN Document Server

    Sun, Xudong; Liu, Yang; Zhao, Junwei


    As each solar cycle progresses, remnant magnetic flux from active regions (ARs) migrates poleward to cancel the old-cycle polar field. We describe this polarity reversal process during Cycle 24 using four years (2010.33--2014.33) of line-of-sight magnetic field measurements from the Helioseismic and Magnetic Imager. The total flux associated with ARs reached maximum in the north in 2011, more than two years earlier than the south; the maximum is significantly weaker than Cycle 23. The process of polar field reversal is relatively slow, north-south asymmetric, and episodic. We estimate that the global axial dipole changed sign in October 2013; the northern and southern polar fields (mean above 60$^\\circ$ latitude) reversed in November 2012 and March 2014, respectively, about 16 months apart. Notably, the poleward surges of flux in each hemisphere alternated in polarity, giving rise to multiple reversals in the north. We show that the surges of the trailing sunspot polarity tend to correspond to normal mean AR ...

  11. Effects of ethylene on the kinetics of curvature and auxin redistribution in gravistimulated roots of Zea mays (United States)

    Lee, J. S.; Evans, M. L.


    We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus.

  12. The promoting effects of alginate oligosaccharides on root development in Oryza sativa L. mediated by auxin signaling. (United States)

    Zhang, Yunhong; Yin, Heng; Zhao, Xiaoming; Wang, Wenxia; Du, Yuguang; He, Ailing; Sun, Kegang


    Alginate oligosaccharides (AOS), which are marine oligosaccharides, are involved in regulating plant root growth, but the promotion mechanism for AOS remains unclear. Here, AOS (10-80 mg/L) induced the expression of auxin-related gene (OsYUCCA1, OsYUCCA5, OsIAA11 and OsPIN1) in rice (Oryza sativa L.) tissues to accelerate auxin biosynthesis and transport, and reduced indole-3-acetic acid (IAA) oxidase activity in rice roots. These changes resulted in the increase of 37.8% in IAA concentration in rice roots, thereby inducing the expression of root development-related genes, promoting root growth in a dose-dependent manner, which were inhibited by auxin transport inhibitor 2,3,5-triiodo benzoic acid (TIBA) and calcium-chelating agent ethylene glycol bis (2-aminoethyl) tetraacetic acid (EGTA). AOS also induced calcium signaling generation in rice roots. Those results indicated that auxin mediated AOS regulation of root development, and calcium signaling may act mainly in the upstream of auxin in the regulation of AOS on rice root development.

  13. DASH transcription factor impacts Medicago truncatula seed size by its action on embryo morphogenesis and auxin homeostasis. (United States)

    Noguero, Mélanie; Le Signor, Christine; Vernoud, Vanessa; Bandyopadhyay, Kaustav; Sanchez, Myriam; Fu, Chunxiang; Torres-Jerez, Ivone; Wen, Jiangqi; Mysore, Kirankumar S; Gallardo, Karine; Udvardi, Michael; Thompson, Richard; Verdier, Jerome


    The endosperm plays a pivotal role in the integration between component tissues of molecular signals controlling seed development. It has been shown to participate in the regulation of embryo morphogenesis and ultimately seed size determination. However, the molecular mechanisms that modulate seed size are still poorly understood especially in legumes. DASH (DOF Acting in Seed embryogenesis and Hormone accumulation) is a DOF transcription factor (TF) expressed during embryogenesis in the chalazal endosperm of the Medicago truncatula seed. Phenotypic characterization of three independent dash mutant alleles revealed a role for this TF in the prevention of early seed abortion and the determination of final seed size. Strong loss-of-function alleles cause severe defects in endosperm development and lead to embryo growth arrest at the globular stage. Transcriptomic analysis of dash pods versus wild-type (WT) pods revealed major transcriptional changes and highlighted genes that are involved in auxin transport and perception as mainly under-expressed in dash mutant pods. Interestingly, the exogenous application of auxin alleviated the seed-lethal phenotype, whereas hormonal dosage revealed a much higher auxin content in dash pods compared with WT. Together these results suggested that auxin transport/signaling may be affected in the dash mutant and that aberrant auxin distribution may contribute to the defect in embryogenesis resulting in the final seed size phenotype.

  14. Auxin regulates SNARE-dependent vacuolar morphology restricting cell size. (United States)

    Löfke, Christian; Dünser, Kai; Scheuring, David; Kleine-Vehn, Jürgen


    The control of cellular growth is central to multicellular patterning. In plants, the encapsulating cell wall literally binds neighbouring cells to each other and limits cellular sliding/migration. In contrast to its developmental importance, growth regulation is poorly understood in plants. Here, we reveal that the phytohormone auxin impacts on the shape of the biggest plant organelle, the vacuole. TIR1/AFBs-dependent auxin signalling posttranslationally controls the protein abundance of vacuolar SNARE components. Genetic and pharmacological interference with the auxin effect on vacuolar SNAREs interrelates with auxin-resistant vacuolar morphogenesis and cell size regulation. Vacuolar SNARE VTI11 is strictly required for auxin-reliant vacuolar morphogenesis and loss of function renders cells largely insensitive to auxin-dependent growth inhibition. Our data suggests that the adaptation of SNARE-dependent vacuolar morphogenesis allows auxin to limit cellular expansion, contributing to root organ growth rates.

  15. Rational design of an auxin antagonist of the SCF(TIR1) auxin receptor complex. (United States)

    Hayashi, Ken-ichiro; Neve, Joshua; Hirose, Masakazu; Kuboki, Atsuhito; Shimada, Yukihisa; Kepinski, Stefan; Nozaki, Hiroshi


    The plant hormone auxin is a master regulator of plant growth and development. By regulating rates of cell division and elongation and triggering specific patterning events, indole 3-acetic acid (IAA) regulates almost every aspect of plant development. The perception of auxin involves the formation of a ternary complex consisting of an F-box protein of the TIR1/AFB family of auxin receptors, the auxin molecule, and a member the Aux/IAA family of co-repressor proteins. In this study, we identified a potent auxin antagonist, α-(phenylethyl-2-oxo)-IAA, as a lead compound for TIR1/AFB receptors by in silico virtual screening. This molecule was used as the basis for the development of a more potent TIR1 antagonist, auxinole (α-[2,4-dimethylphenylethyl-2-oxo]-IAA), using a structure-based drug design approach. Auxinole binds TIR1 to block the formation of the TIR1-IAA-Aux/IAA complex and so inhibits auxin-responsive gene expression. Molecular docking analysis indicates that the phenyl ring in auxinole would strongly interact with Phe82 of TIR1, a residue that is crucial for Aux/IAA recognition. Consistent with this predicted mode of action, auxinole competitively inhibits various auxin responses in planta. Additionally, auxinole blocks auxin responses of the moss Physcomitrella patens, suggesting activity over a broad range of species. Our works not only substantiates the utility of chemical tools for plant biology but also demonstrates a new class of small molecule inhibitor of protein-protein interactions common to mechanisms of perception of other plant hormones, such as jasmonate, gibberellin, and abscisic acid.

  16. Sugar demand, not auxin, is the initial regulator of apical dominance. (United States)

    Mason, Michael G; Ross, John J; Babst, Benjamin A; Wienclaw, Brittany N; Beveridge, Christine A


    For almost a century the plant hormone auxin has been central to theories on apical dominance, whereby the growing shoot tip suppresses the growth of the axillary buds below. According to the classic model, the auxin indole-3-acetic acid is produced in the shoot tip and transported down the stem, where it inhibits bud growth. We report here that the initiation of bud growth after shoot tip loss cannot be dependent on apical auxin supply because we observe bud release up to 24 h before changes in auxin content in the adjacent stem. After the loss of the shoot tip, sugars are rapidly redistributed over large distances and accumulate in axillary buds within a timeframe that correlates with bud release. Moreover, artificially increasing sucrose levels in plants represses the expression of BRANCHED1 (BRC1), the key transcriptional regulator responsible for maintaining bud dormancy, and results in rapid bud release. An enhancement in sugar supply is both necessary and sufficient for suppressed buds to be released from apical dominance. Our data support a theory of apical dominance whereby the shoot tip's strong demand for sugars inhibits axillary bud outgrowth by limiting the amount of sugar translocated to those buds.

  17. The Clubroot Pathogen (Plasmodiophora brassicae Influences Auxin Signaling to Regulate Auxin Homeostasis in Arabidopsis

    Directory of Open Access Journals (Sweden)

    Linda Jahn


    Full Text Available The clubroot disease, caused by the obligate biotrophic protist Plasmodiophora brassicae, affects cruciferous crops worldwide. It is characterized by root swellings as symptoms, which are dependent on the alteration of auxin and cytokinin metabolism. Here, we describe that two different classes of auxin receptors, the TIR family and the auxin binding protein 1 (ABP1 in Arabidopsis thaliana are transcriptionally upregulated upon gall formation. Mutations in the TIR family resulted in more susceptible reactions to the root pathogen. As target genes for the different pathways we have investigated the transcriptional regulation of selected transcriptional repressors (Aux/IAA and transcription factors (ARF. As the TIR pathway controls auxin homeostasis via the upregulation of some auxin conjugate synthetases (GH3, the expression of selected GH3 genes was also investigated, showing in most cases upregulation. A double gh3 mutant showed also slightly higher susceptibility to P. brassicae infection, while all tested single mutants did not show any alteration in the clubroot phenotype. As targets for the ABP1-induced cell elongation the effect of potassium channel blockers on clubroot formation was investigated. Treatment with tetraethylammonium (TEA resulted in less severe clubroot symptoms. This research provides evidence for the involvement of two auxin signaling pathways in Arabidopsis needed for the establishment of the root galls by P. brassicae.

  18. Auxin signaling modules regulate maize inflorescence architecture. (United States)

    Galli, Mary; Liu, Qiujie; Moss, Britney L; Malcomber, Simon; Li, Wei; Gaines, Craig; Federici, Silvia; Roshkovan, Jessica; Meeley, Robert; Nemhauser, Jennifer L; Gallavotti, Andrea


    In plants, small groups of pluripotent stem cells called axillary meristems are required for the formation of the branches and flowers that eventually establish shoot architecture and drive reproductive success. To ensure the proper formation of new axillary meristems, the specification of boundary regions is required for coordinating their development. We have identified two maize genes, BARREN INFLORESCENCE1 and BARREN INFLORESCENCE4 (BIF1 and BIF4), that regulate the early steps required for inflorescence formation. BIF1 and BIF4 encode AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) proteins, which are key components of the auxin hormone signaling pathway that is essential for organogenesis. Here we show that BIF1 and BIF4 are integral to auxin signaling modules that dynamically regulate the expression of BARREN STALK1 (BA1), a basic helix-loop-helix (bHLH) transcriptional regulator necessary for axillary meristem formation that shows a striking boundary expression pattern. These findings suggest that auxin signaling directly controls boundary domains during axillary meristem formation and define a fundamental mechanism that regulates inflorescence architecture in one of the most widely grown crop species.

  19. Spin-polarized transport in hydrogen-passivated graphene and silicene nanoribbons with magnetic transition-metal substituents. (United States)

    García-Fuente, A; Gallego, L J; Vega, A


    We present a systematic theoretical study of the electronic transport in hydrogen passivated zigzag graphene and silicene nanoribbons with between zero and four neighboring H atoms on one edge replaced by magnetic transition metals (Fe, Co, and Ni). The calculations were performed using equilibrium transport and density-functional theory with the generalized gradient approximation to exchange and correlation. We considered the magnetic moments of the two edges aligned both ferromagnetically (Ferro-F form) and antiferromagnetically (Ferro-A form). The Ferro-A graphene-based ribbons were all semiconducting and would support moderate spin-polarized currents of either sign by applying positive or negative gate voltages. The Ferro-F graphene-based ribbons were all metallic; the most interesting for possible spintronic applications being that with a single Ni atom, in which strong spin-filtering at low bias resulted from a deep trough in the transmission of one spin component around the Fermi level. By contrast, in the Si-based analog this trough was split, partially eliminating the polarization of the current. This splitting was found to be related to the buckled structure of the Si-based nanoribbon, which has its origin in its preference for sp(3)-like hybridization.

  20. Understanding the charge transport and polarities in organic donor-acceptor mixed-stack crystals: molecular insights from the super-exchange couplings. (United States)

    Geng, Hua; Zheng, Xiaoyan; Shuai, Zhigang; Zhu, Lingyun; Yi, Yuanping


    Charge transport and polarity in organic D-A mixed-stack crystals are examined in terms of super-exchange electronic couplings. When the super-exchange coupling is dominated by the interaction between donor HOMO and acceptor LUMO, ambipolar transport is achieved. Otherwise, involvement of other bridge orbitals can lead to unbalanced, even to unipolar transport in a special case that the HOMO-LUMO interaction vanishes.

  1. Polar Processes in a 50-year Simulation of Stratospheric Chemistry and Transport (United States)

    Kawa, S.R.; Douglass, A. R.; Patrick, L. C.; Allen, D. R.; Randall, C. E.


    The unique chemical, dynamical, and microphysical processes that occur in the winter polar lower stratosphere are expected to interact strongly with changing climate and trace gas abundances. Significant changes in ozone have been observed and prediction of future ozone and climate interactions depends on modeling these processes successfully. We have conducted an off-line model simulation of the stratosphere for trace gas conditions representative of 1975-2025 using meteorology from the NASA finite-volume general circulation model. The objective of this simulation is to examine the sensitivity of stratospheric ozone and chemical change to varying meteorology and trace gas inputs. This presentation will examine the dependence of ozone and related processes in polar regions on the climatological and trace gas changes in the model. The model past performance is base-lined against available observations, and a future ozone recovery scenario is forecast. Overall the model ozone simulation is quite realistic, but initial analysis of the detailed evolution of some observable processes suggests systematic shortcomings in our description of the polar chemical rates and/or mechanisms. Model sensitivities, strengths, and weaknesses will be discussed with implications for uncertainty and confidence in coupled climate chemistry predictions.

  2. Transport versus energetic particle precipitation: Northern polar stratospheric NOx and ozone in January-March 2012 (United States)

    Päivärinta, S.-M.; Verronen, P. T.; Funke, B.; Gardini, A.; Seppälä, A.; Andersson, M. E.


    In early 2012, a strong sudden stratospheric warming (SSW) took place, accompanied by several medium-scale solar proton events (SPEs). Here we use a chemistry transport model (CTM) in order to assess the relative contributions of (1) intensified downward transport of odd nitrogen (NOx) and (2) in situ production of NOx by protons, on stratospheric NOx and ozone during January-March 2012. The CTM is constrained by an upper boundary condition for reactive nitrogen (NOy) species, based on satellite observations from Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board Envisat, and includes a new parameterization of the SPE-caused effects on NOy and odd hydrogen (HOx) species. We found that the amount of NOx increases due to both transport and in situ production effects, the intensified descent of NOx dominating the middle and upper stratospheric impact. The model results indicate NOx enhancements of 120-3300% (5-48 ppbv) between 38 and 50 km, caused by the transport of mesosphere/lower thermosphere NOx down to the stratosphere following the SSW. The SPEs increase NOx by up to 820-1200% (14-21 ppbv) at 33 to 50 km. The effect on the stratospheric ozone is larger following the downward transport of NOx than during and after the SPEs. The model predicts ozone losses of up to 17% and 9% at around 40 km due to transport and SPE effects, respectively.

  3. Arabidopsis TWISTED DWARF1 functionally interacts with Auxin Exporter ABCB1 on the root plasma membrane

    DEFF Research Database (Denmark)

    Wang, Bangjun; Bailly, Aurélien; Zwiewka, Marta


    . In planta bioluminescence resonance energy transfer analysis was used to verify specific ABC transporter B1 (ABCB1)-TWD1 interaction. Our data support a model in which TWD1 promotes lateral ABCB-mediated auxin efflux via protein-protein interaction at the plasma membrane, minimizing reflux from the root...

  4. Auxin and ethylene response interactions during Arabidopsis root hair development dissected by auxin influx modulators. (United States)

    Rahman, Abidur; Hosokawa, Satoko; Oono, Yutaka; Amakawa, Taisaku; Goto, Nobuharu; Tsurumi, Seiji


    The plant hormones auxin and ethylene have been shown to play important roles during root hair development. However, cross talk between auxin and ethylene makes it difficult to understand the independent role of either hormone. To dissect their respective roles, we examined the effects of two compounds, chromosaponin I (CSI) and 1-naphthoxyacetic acid (1-NOA), on the root hair developmental process in wild-type Arabidopsis, ethylene-insensitive mutant ein2-1, and auxin influx mutants aux1-7, aux1-22, and double mutant aux1-7 ein2. Beta-glucuronidase (GUS) expression analysis in the BA-GUS transgenic line, consisting of auxin-responsive domains of PS-IAA4/5 promoter and GUS reporter, revealed that 1-NOA and CSI act as auxin uptake inhibitors in Arabidopsis roots. The frequency of root hairs in ein2-1 roots was greatly reduced in the presence of CSI or 1-NOA, suggesting that endogenous auxin plays a critical role for the root hair initiation in the absence of an ethylene response. All of these mutants showed a reduction in root hair length, however, the root hair length could be restored with a variable concentration of 1-naphthaleneacetic acid (NAA). NAA (10 nM) restored the root hair length of aux1 mutants to wild-type level, whereas 100 nM NAA was needed for ein2-1 and aux1-7 ein2 mutants. Our results suggest that insensitivity in ethylene response affects the auxin-driven root hair elongation. CSI exhibited a similar effect to 1-NOA, reducing root hair growth and the number of root hair-bearing cells in wild-type and ein2-1 roots, while stimulating these traits in aux1-7and aux1-7ein2 roots, confirming that CSI is a unique modulator of AUX1.

  5. L-Cysteine inhibits root elongation through auxin/PLETHORA and SCR/SHR pathway in Arabidopsis thaliana. (United States)

    Wang, Zhen; Mao, Jie-Li; Zhao, Ying-Jun; Li, Chuan-You; Xiang, Cheng-Bin


    L-Cysteine plays a prominent role in sulfur metabolism of plants. However, its role in root development is largely unknown. Here, we report that L-cysteine reduces primary root growth in a dosage-dependent manner. Elevating cellular L-cysteine level by exposing Arabidopsis thaliana seedlings to high L-cysteine, buthionine sulphoximine, or O-acetylserine leads to altered auxin maximum in root tips, the expression of quiescent center cell marker as well as the decrease of the auxin carriers PIN1, PIN2, PIN3, and PIN7 of primary roots. We also show that high L-cysteine significantly reduces the protein level of two sets of stem cell specific transcription factors PLETHORA1/2 and SCR/SHR. However, L-cysteine does not downregulate the transcript level of PINs, PLTs, or SCR/SHR, suggesting that an uncharacterized post-transcriptional mechanism may regulate the accumulation of PIN, PLT, and SCR/SHR proteins and auxin transport in the root tips. These results suggest that endogenous L-cysteine level acts to maintain root stem cell niche by regulating basal- and auxin-induced expression of PLT1/2 and SCR/SHR. L-Cysteine may serve as a link between sulfate assimilation and auxin in regulating root growth.

  6. Transport-limited water splitting at ion-selective interfaces during concentration polarization

    CERN Document Server

    Nielsen, Christoffer P


    We present an analytical model of salt- and water-ion transport across an ion-selective interface based on an assumption of local equilibrium of the water-dissociation reaction. The model yields current-voltage characteristics and curves of water-ion current versus salt-ion current, which are in qualitative agreement with experimental results published in the literature. The analytical results are furthermore in agreement with direct numerical simulations. As part of the analysis, we find approximate solutions to the classical problem of pure salt transport across an ion-selective interface. These solutions provide closed-form expressions for the current-voltage characteristics, which include the overlimiting current due to the development of an extended space charge region. Finally, we discuss how the addition of an acid or a base affects the transport properties of the system and thus provide predictions accessible to further experimental tests of the model.

  7. General circulation driven by baroclinic forcing due to cloud layer heating: Significance of planetary rotation and polar eddy heat transport (United States)

    Yamamoto, Masaru; Takahashi, Masaaki


    A high significance of planetary rotation and poleward eddy heat fluxes is determined for general circulation driven by baroclinic forcing due to cloud layer heating. In a high-resolution simplified Venus general circulation model, a planetary-scale mixed Rossby-gravity wave with meridional winds across the poles produces strong poleward heat flux and indirect circulation. This strong poleward heat transport induces downward momentum transport of indirect cells in the regions of weak high-latitude jets. It also reduces the meridional temperature gradient and vertical shear of the high-latitude jets in accordance with the thermal wind relation below the cloud layer. In contrast, strong equatorial superrotation and midlatitude jets form in the cloud layer in the absence of polar indirect cells in an experiment involving Titan's rotation. Both the strong midlatitude jet and meridional temperature gradient are maintained in the situation that eddy horizontal heat fluxes are weak. The presence or absence of strong poleward eddy heat flux is one of the important factors determining the slow or fast superrotation state in the cloud layer through the downward angular momentum transport and the thermal wind relation. For fast Earth rotation, a weak global-scale Hadley circulation of the low-density upper atmosphere maintains equatorial superrotation and midlatitude jets above the cloud layer, whereas multiple meridional circulations suppress the zonal wind speed below the cloud layer.

  8. Contact-Free Mapping of Electronic Transport Phenomena of Polar Domains in SrMnO3 Films (United States)

    Schaab, J.; Krug, I. P.; Doǧanay, H.; Hackl, J.; Gottlob, D. M.; Khan, M. I.; Nemšák, S.; Maurel, L.; Langenberg, E.; Algarabel, P. A.; Pardo, J. A.; Schneider, C. M.; Meier, D.


    High-resolution mapping of electronic transport phenomena plays an increasingly important role for the characterization of ferroic domains and their functionality. At present, spatially resolved electronic transport data are commonly gained from local two-point measurements, collected in line-by-line scans with a conducting nanosized probe. Here, we introduce an innovative experimental approach based on low-energy electron microscopy. As a model case, we study polar domains of varying conductance in strained SrMnO3 . By a direct comparison with conductive atomic force and electrostatic force microscopy, we reveal that the applied low-energy electron-microscopy experiment can be considered as an inverse I (V ) measurement, providing access to the local electronic conductance with nanoscale resolution and short data-acquisition times in the order of 10 - 102 ms . Low-energy electrons thus hold yet unexplored application opportunities as a minimal-invasive probe for local electronic transport phenomena, opening a promising route towards spatially resolved, high-throughput sampling at the nanoscale.

  9. Investigation of Carbohydrate Metabolism and Transport in Castor Bean Seedlings by Cyclic JCross Polarization Imaging and Spectroscopy (United States)

    Heidenreich, M.; Köckenberger, W.; Kimmich, R.; Chandrakumar, N.; Bowtell, R.


    NMR experiments using13C-labeled compounds offer the possibility of noninvasive monitoring of carbohydrate transport and metabolism in living plants, but are usually hampered by the low sensitivity of the13C nucleus. The problem of low sensitivity can be overcome by using the cyclicJcross polarization (CYCLCROP) technique, which allows the indirect detection of13C nuclei coupled to1H nuclei with the high NMR sensitivity of protons. We report here on methods for imaging and spectroscopy based on the CYCLCROP technique, and their use in the firstin vivoNMR study of carbohydrate transport and metabolism in castor bean seedlings (Ricinus communis L.). Comprehensive acquisition strategies for the various NMR methods are given, including the procedure for setting up the experiments. In addition, a full analysis of the effect of relaxation on the signals generated from smallJ-coupled spin systems by the CYCLCROP sequence is given, and the high sensitivity of the sequence is demonstrated. In thein vivostudy of six-day-old castor bean seedlings, we were able to measure the uptake of labeled hexoses, supplied in solution to the cotyledons, and their conversion to sucrose, as well as the transport of this sucrose in the vascular bundles. Images of the actual distribution of labeled sucrose in the hypocotyl of the seedling have also been obtained. The resulting data show some evidence for a preferential incorporation of labeled fructose in the process of sucrose synthesis, which decreases with the time of incubation.

  10. Transport-limited water splitting at ion-selective interfaces during concentration polarization

    DEFF Research Database (Denmark)

    Nielsen, Christoffer Peder; Bruus, Henrik


    We present an analytical model of salt- and water-ion transport across an ion-selective interface based on an assumption of local equilibrium of the water-dissociation reaction. The model yields current-voltage characteristics and curves of water-ion current versus salt-ion current, which are in ...

  11. Gravitropism in higher plant shoots. V - Changing sensitivity to auxin (United States)

    Salisbury, Frank B.; Gillespie, Linda; Rorabaugh, Patricia


    The relationship in plants between the sensitivity to auxin and differential growth and bending was investigated experimentally. Decapitated and marked sunflower hypocotyl sections were immersed in buffered auxin solutions of different concentrations (0, 10 to the -8th, or 0.001 molar) and were photographed at 1/2 hr intervals; the negatives were analyzed with a digitizer/computer to evaluate surface-length changes in terms of Michaelis-Menten enzyme kinetics. It was found that bending decreased with increasing concentration of auxin. Increasing the auxin concentration inhibits the elongation growth of lower surfaces but promotes upper-surface growth, indicating that the lower surfaces have a greater Km sensitivity to applied auxin than the upper surfaces. At optimum auxin levels (maximum growth), the growth of bottom surfaces exceeded that of top surfaces, indicating that bottom tissues had a greater Vmax sensitivity.

  12. The Sensitivity of Arctic Ozone Loss to Polar Stratospheric Cloud Volume and Chlorine and Bromine Loading in a Chemistry and Transport Model (United States)

    Douglass, A. R.; Stolarski, R. S.; Strahan, S. E.; Polansky, B. C.


    The sensitivity of Arctic ozone loss to polar stratospheric cloud volume (V(sub PSC)) and chlorine and bromine loading is explored using chemistry and transport models (CTMs). A simulation using multi-decadal output from a general circulation model (GCM) in the Goddard Space Flight Center (GSFC) CTM complements one recycling a single year s GCM output in the Global Modeling Initiative (GMI) CTM. Winter polar ozone loss in the GSFC CTM depends on equivalent effective stratospheric chlorine (EESC) and polar vortex characteristics (temperatures, descent, isolation, polar stratospheric cloud amount). Polar ozone loss in the GMI CTM depends only on changes in EESC as the dynamics repeat annually. The GSFC CTM simulation reproduces a linear relationship between ozone loss and Vpsc derived from observations for 1992 - 2003 which holds for EESC within approx.85% of its maximum (approx.1990 - 2020). The GMI simulation shows that ozone loss varies linearly with EESC for constant, high V(sub PSC).

  13. Field-assisted spin-polarized electron transport through a single quantum well with spin-orbit coupling

    Institute of Scientific and Technical Information of China (English)

    Ding Xiu-Huan; Zhang Cun-Xi; Wang Rui; Zhou Yun-Qing; Kong Ling-Min


    We have investigated theoretically the field-driven electron transport through a single-quantum-well semiconductor heterostructure with spin-orbit coupling.The splitting of the asymmetric Fano-type resonance peaks due to the Dresselhaus spin-orbit coupling is found to be highly sensitive to the direction of the incident electron.The splitting of the Fano-type resonance induces the spin-polarization dependent electron current.The location and the line shape of the Fano-type resonance can be controlled by adjusting the energy and the direction of the incident electron,the oscillation frequency,and the amplitude of the external field.These interesting features may be used to devise tunable spin filters and realize pure spin transmission currents.

  14. Auxin-Oxylipin Crosstalk: Relationship of Antagonists

    Institute of Scientific and Technical Information of China (English)

    Maik Hoffmann; Mathias Hentrich; Stephan Pollmann


    Phytohormones regulate a wide array of developmental processes throughout the life cycle of plants. Herein, the various plant hormones may interact additively, synergistically, or antagonistically. By their cooperation they create a delicate regulatory network whose net output largely depends on the action of specific phytohormone combinations rather than on the independent activities of separate hormones. While most classical studies of plant hormonal control have focused mainly on the action of single hormones or on the synergistic interaction of hormones in regulating various developmental processes, recent work is beginning to shed light on the crosstalk of nominally antagonistic plant hormones, such as gibberellins and auxins with oxylipins or abscisic acid. In this review, we summarize our current understanding of how two of the first sight antagonistic plant hormones, i.e. auxins and oxylipins,interact in controlling plant responses and development.

  15. A one dimensional model study of the mechanism of halogen liberation and vertical transport in the polar troposphere

    Directory of Open Access Journals (Sweden)

    E. Lehrer


    Full Text Available Sudden depletions of tropospheric ozone during spring were reported from the Arctic and also from Antarctic coastal sites. Field studies showed that those depletion events are caused by reactive halogen species, especially bromine compounds. However the source and seasonal variation of reactive halogen species is still not completely understood. There are several indications that the halogen mobilisation from the sea ice surface of the polar oceans may be the most important source for the necessary halogens. Here we present a one dimensional model study aimed at determining the primary source of reactive halogens. The model includes gas phase and heterogeneous bromine and chlorine chemistry as well as vertical transport between the surface and the top of the boundary layer. The autocatalytic Br release by photochemical processes (bromine explosion and subsequent rapid bromine catalysed ozone depletion is well reproduced in the model and the major source of reactive bromine appears to be the sea ice surface. The sea salt aerosol alone is not sufficient to yield the high levels of reactive bromine in the gas phase necessary for fast ozone depletion. However, the aerosol efficiently 'recycles' less reactive bromine species (e.g. HBr and feeds them back into the ozone destruction cycle. Isolation of the boundary layer air from the free troposphere by a strong temperature inversion was found to be critical for boundary layer ozone depletion to happen. The combination of strong surface inversions and presence of sunlight occurs only during polar spring.

  16. Effect of metallation, substituents and inter/intra-molecular polarization on electronic couplings for hole transport in stacked porphyrin dyads. (United States)

    Hernández-Fernández, F; Pavanello, M; Visscher, L


    We carried out a systematic study of the hole transport properties for a series of symmetrically stacked porphyrin dimers. In the first part of this study, we evaluated the sensitivity of electronic couplings to orbital relaxation due to molecular ionization and intermolecular interactions for a series of halogenated porphyrins. The effect of polarization was estimated by comparing electronic couplings from fragment orbital density functional theory (FODFT) and frozen density embedding electron transfer (FDE-CT). For the dimers considered, the effect of polarization was estimated to be less than 20%, in line with previous studies on different molecular dimers. Thus, we decided to employ a computationally cheaper FODFT method to continue our study of the effect of metals and substituents on the electronic couplings for hole transfer. We find that, compared to the non-metallated porphyrins, Ni, Fe and Pt significantly reduce the coupling, while Zn, Ti, Cd and Pd increase it. The effect of substituents was studied on a series of meso-substituted porphyrins (meso-tetrapyridineporphyrin, meso-tetraphenylporphyrin and derivatives) for which we could relate a reduction of the coupling to steric effects that reduce the overlap between the frontier orbitals of the monomers.

  17. The circadian clock regulates auxin signaling and responses in Arabidopsis.

    Directory of Open Access Journals (Sweden)

    Michael F Covington


    Full Text Available The circadian clock plays a pervasive role in the temporal regulation of plant physiology, environmental responsiveness, and development. In contrast, the phytohormone auxin plays a similarly far-reaching role in the spatial regulation of plant growth and development. Went and Thimann noted 70 years ago that plant sensitivity to auxin varied according to the time of day, an observation that they could not explain. Here we present work that explains this puzzle, demonstrating that the circadian clock regulates auxin signal transduction. Using genome-wide transcriptional profiling, we found many auxin-induced genes are under clock regulation. We verified that endogenous auxin signaling is clock regulated with a luciferase-based assay. Exogenous auxin has only modest effects on the plant clock, but the clock controls plant sensitivity to applied auxin. Notably, we found both transcriptional and growth responses to exogenous auxin are gated by the clock. Thus the circadian clock regulates some, and perhaps all, auxin responses. Consequently, many aspects of plant physiology not previously thought to be under circadian control may show time-of-day-specific sensitivity, with likely important consequences for plant growth and environmental responses.

  18. Hairy roots are more sensitive to auxin than normal roots (United States)

    Shen, Wen Hui; Petit, Annik; Guern, Jean; Tempé, Jacques


    Responses to auxin of Lotus corniculatus root tips or protoplasts transformed by Agrobacterium rhizogenes strains 15834 and 8196 were compared to those of their normal counterparts. Three different types of experiments were performed, involving long-term, medium-term, or short-term responses to a synthetic auxin, 1-naphthaleneacetic acid. Root tip elongation, proton excretion by root tips, and transmembrane electrical potential difference of root protoplasts were measured as a function of exogenous auxin concentration. The sensitivity of hairy root tips or protoplasts to exogenous auxin was found to be 100-1000 times higher than that of untransformed material. PMID:16593928

  19. AUXIN AND GROWTH OF EXCISED ROOTS OF Bryophyllum calycinum. (United States)

    Robbins, W J; Hervey, A


    Exogenous auxin (alpha-naphthalene acetic acid, indole acetic acid, or 2,4-dichlorophenoxyacetic acid) was essential for the growth of single excised root tips of Bryophyllum calycinum in 50 ml of a mineral salt-sucrose medium supplemented with vitamins. Large inocula with a dry weight of 2.0 mg or more grew with no auxin added to the medium. Evidence for the synthesis of auxin by the excised roots grown from the larger inocula is presented. Leaching of auxin from single root tips cultivated in 15 or 50 ml of basal medium is considered to account for their failure to grow.

  20. Transport-limited water splitting at ion-selective interfaces during concentration polarization


    Nielsen, Christoffer Peder; Bruus, Henrik


    We present an analytical model of salt- and water-ion transport across an ion-selective interface based on an assumption of local equilibrium of the water-dissociation reaction. The model yields current-voltage characteristics and curves of water-ion current versus salt-ion current, which are in qualitative agreement with experimental results published in the literature. The analytical results are furthermore in agreement with direct numerical simulations. As part of the analysis, we find app...

  1. Ethylene Inhibits Root Elongation during Alkaline Stress through AUXIN1 and Associated Changes in Auxin Accumulation. (United States)

    Li, Juan; Xu, Heng-Hao; Liu, Wen-Cheng; Zhang, Xiao-Wei; Lu, Ying-Tang


    Soil alkalinity causes major reductions in yield and quality of crops worldwide. The plant root is the first organ sensing soil alkalinity, which results in shorter primary roots. However, the mechanism underlying alkaline stress-mediated inhibition of root elongation remains to be further elucidated. Here, we report that alkaline conditions inhibit primary root elongation of Arabidopsis (Arabidopsis thaliana) seedlings by reducing cell division potential in the meristem zones and that ethylene signaling affects this process. The ethylene perception antagonist silver (Ag(+)) alleviated the inhibition of root elongation by alkaline stress. Moreover, the ethylene signaling mutants ethylene response1-3 (etr1-3), ethylene insensitive2 (ein2), and ein3-1 showed less reduction in root length under alkaline conditions, indicating a reduced sensitivity to alkalinity. Ethylene biosynthesis also was found to play a role in alkaline stress-mediated root inhibition; the ethylene overproducer1-1 mutant, which overproduces ethylene because of increased stability of 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHASE5, was hypersensitive to alkaline stress. In addition, the ethylene biosynthesis inhibitor cobalt (Co(2+)) suppressed alkaline stress-mediated inhibition of root elongation. We further found that alkaline stress caused an increase in auxin levels by promoting expression of auxin biosynthesis-related genes, but the increase in auxin levels was reduced in the roots of the etr1-3 and ein3-1 mutants and in Ag(+)/Co(2+)-treated wild-type plants. Additional genetic and physiological data showed that AUXIN1 (AUX1) was involved in alkaline stress-mediated inhibition of root elongation. Taken together, our results reveal that ethylene modulates alkaline stress-mediated inhibition of root growth by increasing auxin accumulation by stimulating the expression of AUX1 and auxin biosynthesis-related genes.

  2. A theoretical model for ROP localisation by auxin in Arabidopsis root hair cells.

    Directory of Open Access Journals (Sweden)

    Robert J H Payne

    Full Text Available Local activation of Rho GTPases is important for many functions including cell polarity, morphology, movement, and growth. Although a number of molecules affecting Rho-of-Plants small GTPase (ROP signalling are known, it remains unclear how ROP activity becomes spatially organised. Arabidopsis root hair cells produce patches of ROP at consistent and predictable subcellular locations, where root hair growth subsequently occurs.We present a mathematical model to show how interaction of the plant hormone auxin with ROPs could spontaneously lead to localised patches of active ROP via a Turing or Turing-like mechanism. Our results suggest that correct positioning of the ROP patch depends on the cell length, low diffusion of active ROP, a gradient in auxin concentration, and ROP levels. Our theory provides a unique explanation linking the molecular biology to the root hair phenotypes of multiple mutants and transgenic lines, including OX-ROP, CA-rop, aux1, axr3, tip1, eto1, etr1, and the triple mutant aux1 ein2 gnom(eb.We show how interactions between Rho GTPases (in this case ROPs and regulatory molecules (in this case auxin could produce characteristic subcellular patterning that subsequently affects cell shape. This has important implications for research on the morphogenesis of plants and other eukaryotes. Our results also illustrate how gradient-regulated Turing systems provide a particularly robust and flexible mechanism for pattern formation.

  3. ROP GTPase-mediated auxin signaling regulates pavement cell interdigitation in Arabidopsis thaliana

    Institute of Scientific and Technical Information of China (English)

    Deshu Lin; Huibo Ren; Ying Fu


    In multicel ular plant organs, cel shape formation depends on molecular switches to transduce developmental or environmental signals and to coordinate cel‐to‐cel communi-cation. Plants have a specific subfamily of the Rho GTPase family, usual y cal ed Rho of Plants (ROP), which serve as a critical signal transducer involved in many cel ular processes. In the last decade, important advances in the ROP‐mediated regulation of plant cel morphogenesis have been made by using Arabidopsis thaliana leaf and cotyledon pavement cel s. Especial y, the auxin‐ROP signaling networks have been demonstrated to control interdigitated growth of pavement cel s to form jigsaw‐puzzle shapes. Here, we review findings related to the discovery of this novel auxin‐signaling mecha-nism at the cel surface. This signaling pathway is to a large extent independent of the wel‐known Transport Inhibitor Response (TIR)–Auxin Signaling F‐Box (AFB) pathway, and instead requires Auxin Binding Protein 1 (ABP1) interaction with the plasma membrane‐localized, transmembrane kinase (TMK) receptor‐like kinase to regulate ROP proteins. Once activated, ROP influences cytoskeletal organization and inhibits endocytosis of the auxin transporter PIN1. The present review focuses on ROP signaling and its self‐organizing feature al owing ROP proteins to serve as a bustling signal decoder and integrator for plant cel morphogenesis.

  4. Sequential induction of auxin efflux and influx carriers regulates lateral root emergence. (United States)

    Péret, Benjamin; Middleton, Alistair M; French, Andrew P; Larrieu, Antoine; Bishopp, Anthony; Njo, Maria; Wells, Darren M; Porco, Silvana; Mellor, Nathan; Band, Leah R; Casimiro, Ilda; Kleine-Vehn, Jürgen; Vanneste, Steffen; Sairanen, Ilkka; Mallet, Romain; Sandberg, Göran; Ljung, Karin; Beeckman, Tom; Benkova, Eva; Friml, Jiří; Kramer, Eric; King, John R; De Smet, Ive; Pridmore, Tony; Owen, Markus; Bennett, Malcolm J


    In Arabidopsis, lateral roots originate from pericycle cells deep within the primary root. New lateral root primordia (LRP) have to emerge through several overlaying tissues. Here, we report that auxin produced in new LRP is transported towards the outer tissues where it triggers cell separation by inducing both the auxin influx carrier LAX3 and cell-wall enzymes. LAX3 is expressed in just two cell files overlaying new LRP. To understand how this striking pattern of LAX3 expression is regulated, we developed a mathematical model that captures the network regulating its expression and auxin transport within realistic three-dimensional cell and tissue geometries. Our model revealed that, for the LAX3 spatial expression to be robust to natural variations in root tissue geometry, an efflux carrier is required--later identified to be PIN3. To prevent LAX3 from being transiently expressed in multiple cell files, PIN3 and LAX3 must be induced consecutively, which we later demonstrated to be the case. Our study exemplifies how mathematical models can be used to direct experiments to elucidate complex developmental processes.

  5. Implementation of Outstanding Electronic Transport in Polar Covalent Boron Nitride Atomic Chains: another Extraordinary Odd-Even Behaviour. (United States)

    Xu, Xiaodong; Li, Weiqi; Liu, Linhua; Feng, Jikang; Jiang, Yongyuan; Tian, Wei Quan


    A theoretical investigation of the unique electronic transport properties of the junctions composed of boron nitride atomic chains bridging symmetric graphene electrodes with point-contacts is executed through non-equilibrium Green's function technique in combination with density functional theory. Compared with carbon atomic chains, the boron nitride atomic chains have an alternative arrangement of polar covalent B-N bonds and different contacts coupling electrodes, showing some unusual properties in functional atomic electronic devices. Remarkably, they have an extraordinary odd-even behavior of conductivity with the length increase. The rectification character and negative differential resistance of nonlinear current-voltage characteristics can be achieved by manipulating the type of contacts between boron nitride atomic chains bridges and electrodes. The junctions with asymmetric contacts have an intrinsic rectification, caused by stronger coupling in the C-N contact than the C-B contact. On the other hand, for symmetric contact junctions, it is confirmed that the transport properties of the junctions primarily depend on the nature of contacts. The junctions with symmetric C-N contacts have higher conductivity than their C-B contacts counterparts. Furthermore, the negative differential resistances of the junctions with only C-N contacts is very conspicuous and can be achieved at lower bias.

  6. Piezoelectric polarization and quantum size effects on the vertical transport in AlGaN/GaN resonant tunneling diodes (United States)

    H, Dakhlaoui; S, Almansour


    In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-Al x Ga(1-x)N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current-voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, Al x Ga(1-x)N width, and the aluminum concentration x Al. The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current-voltage (I-V) characteristic strongly depends on aluminum concentration x Al. It is shown that the peak-to-valley ratio (PVR) increases with x Al value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors. Project supported by the Deanship of Scientific Research of University of Dammam (Grant No. 2014137).

  7. Concentration Dependent Speciation and Mass Transport Properties of Switchable Polarity Solvents

    Energy Technology Data Exchange (ETDEWEB)

    Aaron D. Wilson; Christopher J. Orme


    Tertiary amine switchable polarity solvents (SPS) consisting of predominantly water, tertiary amine, and tertiary ammonium and bicarbonate ions were produced at various concentrations for three different amines: N,N-dimethylcyclohexylamine, N,N-dimethyloctylamine, and 1 cyclohexylpiperidine. For all concentrations, physical properties were measured including viscosity, molecular diffusion coefficients, freezing point depression, and density. Based on these measurements a variation on the Mark Houwink equation was developed to predict the viscosity of any tertiary amine SPS as a function of concentration using the amine’s molecular mass. The observed physical properties allowed the identification of solution state speciation of non-osmotic SPS, where the amine to carbonic acid ratio is significantly greater than one. These results indicate that at most concentrations the stoichiometric excess amine is involved in solvating a proton with two amines. The physical properties of osmotic SPS have consistent concentration dependence behavior over a wide range of concentrations; this consistence suggests osmotic pressures based on low concentrations freezing point studies can be reliably extrapolated to higher concentrations.

  8. A Note on the Radiative and Collisional Branching Ratios in Polarized Radiation Transport with Coherent Scattering (United States)

    Casini, R.; del Pino Alemán, T.; Manso Sainz, R.


    We discuss the implementation of physically meaningful branching ratios between the CRD and partial redistribution contributions to the emissivity of a polarized multi-term atom in the presence of both inelastic and elastic collisions. Our derivation is based on a recent theoretical formulation of partially coherent scattering, and it relies on a heuristic diagrammatic analysis of the various radiative and collisional processes to determine the proper form of the branching ratios. The expression we obtain for the emissivity is {\\boldsymbol{\\varepsilon }}=[{{\\boldsymbol{\\varepsilon }}}(1)-{{\\boldsymbol{\\varepsilon }}}{{f}.{{s}}.}(2)]+{{\\boldsymbol{\\varepsilon }}}(2), where {{\\boldsymbol{\\varepsilon }}}(1) and {{\\boldsymbol{\\varepsilon }}}(2) are the emissivity terms for the redistributed and partially coherent radiation, respectively, and where “f.s.” implies that the corresponding term must be evaluated assuming a flat-spectrum average of the incident radiation. This result is shown to be in agreement with prior literature on the subject in the limit of the unpolarized multi-level atom.

  9. Methods comparison, transport and distribution of polar herbicides in the Baltic Sea. (United States)

    Skeff, Wael; Orlikowska, Anna; Schulz-Bull, Detlef E


    Two LC-MS/MS methods including different sample preparation and quantitative processes showed a good agreement for analysis of the herbicides MCPA, mecoprop, isoproturon, bentazon and chloridazon, and the metabolite chloridazon-methyl-desphenyl (CMD) in estuarine waters. Due to different sensitivity of the methods only one could be used to analyze marine samples. The transport of these compounds to the Baltic Sea via ten German estuaries and their distribution between coastal water and sediments was studied. The results showed that all selected compounds can be transported to the Baltic Sea (0.9-747ng/L). Chloridazon, bentazon, isoproturon and CMD were detected (0.9-8.9ng/L) in the coastal waters and chloridazon and isorproturon in the sediments (5-136pg/g d.w.). Levels of contaminants in the sediments could be influenced by the total organic carbon content. Concentrations observed in the Baltic Sea are most likely not high enough to cause acute effects, but long term effect studies are strongly recommended.

  10. Influence of the electric polarization on carrier transport and recombinaton dynamics in ZnO-based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, Matthias


    The present thesis deals with the influence of the electric polarization on properties of free carriers in ZnO-based semiconductor heterostructures. Thereby especially transport properties of free carriers as well as their recombination dynamics are studied. The thesis treats four main topics. The first main topic lies on the phsical properties of the applied materials, here the connection of the band gap and the lattice constant of thin Mg{sub x}Zn{sub 1-x}O films and their magnesium content is described. Furthermore the morphology of such films is discussed. Different substrates and deposition conditions are thereby detailedly considered. The second main topic treats the properties of undoped and phosphorus doped thin ZnO and Mg{sub x}Zn{sub 1-x}O films. The structural, transport, and luminescence properties are here compared and conclusions drawn on the growth conditions. In the third main topic quantum effects on ZnO/Mg{sub x}Zn{sub 1-x}O interfaces are treated. Hereby especially the influence of the electric polarization is considered. The presence of a two-dimensional electron gas is proved, and the necessary conditions for the generation of the so-called confined Stark effect are explained. Especially the growth-relevant parameters are considered. The fourth main topic represent coupling phenomena in ZnO/BaTiO{sub 3} heterostructures. Thereby first the experimentally observed properties of different heterostructures are shown, which were grown on different substrates. Here structural and transport properties hold the spotlight. A model for the description of the formation of space-charge zones in such heterostructures is introduced and applied for the description of the experimental results. The usefulness of the ferroelectric properties of the material BaTiO{sub 3} in combination with semiconducting ZnO were studied. For this ferroelectric field effect transistors were fabricated under application of both materials. The principle suitedness of the

  11. The role of auxin and cytokinin signalling in specifying the root architecture of Arabidopsis thaliana

    KAUST Repository

    Muraro, Daniele


    Auxin and cytokinin are key hormonal signals that control the cellular architecture of the primary root and the initiation of new lateral root organs in the plant Arabidopsis thaliana. Both developmental processes are regulated by cross-talk between these hormones and their signalling pathways. In this paper, sub-cellular and multi-cellular mathematical models are developed to investigate how interactions between auxin and cytokinin influence the size and location of regions of division and differentiation within the primary root, and describe how their cross-regulation may cause periodic branching of lateral roots. We show how their joint activity may influence tissue-specific oscillations in gene expression, as shown in Moreno-Risueno et al. (2010) and commented upon in Traas and Vernoux (2010), and we propose mechanisms that may generate synchronisation of such periodic behaviours inside a cell and with its neighbours. Using a multi-cellular model, we also analyse the roles of cytokinin and auxin in specifying the three main regions of the primary root (elongation, transition and division zones), our simulation results being in good agreement with independent experimental observations. We then use our model to generate testable predictions concerning the effect of varying the concentrations of the auxin efflux transporters on the sizes of the different root regions. In particular, we predict that over-expression of the transporters will generate a longer root with a longer elongation zone and a smaller division zone than that of a wild type root. This root will contain fewer cells than its wild type counterpart. We conclude that our model can provide a useful tool for investigating the response of cell division and elongation to perturbations in hormonal signalling. © 2012 Elsevier Ltd.

  12. Spin- and valley-polarized transport in a monolayer of MoS2 (United States)

    Krstajić, P. M.; Vasilopoulos, P.; Tahir, M.


    We investigate dc and ac transport in a monolayer of MoS2 in the presence of an effective mass asymmetry, a momentum-dependent term, and an out-of plane or in-plane Zeeman term. Analytical results are presented for both dc and ac conductivities in the framework of linear response theory. We show that the spin-Hall conductivity exhibits a strong dependence on the strength of the spin-orbit interaction while both spin- and valley-Hall conductivities show a very weak dependence on the temperature. The sum of the well separated spin-up and spin-down components of the diffusive dc longitudinal conductivity is linear in the electron concentration though the Fermi level is a nonmonotonic function of it. Further, we evaluate the power absorption spectrum and assess its dependence on the spin and valley degrees of freedom as well as on the scattering which is essential at low frequencies.

  13. The Use of Auxin Quantification for Understanding Clonal Tree Propagation

    Directory of Open Access Journals (Sweden)

    Carlos A. Stuepp


    Full Text Available Qualitative and quantitative hormone analyses have been essential for understanding the metabolic, physiological, and morphological processes that are influenced by plant hormones. Auxins are key hormones in the control of many aspects of plant growth and development and their endogenous levels are considered critical in the process of adventitious root induction. Exogenous auxins are used extensively in the clonal propagation of tree species by cuttings or tissue culture. Understanding of auxin effects has advanced with the development of increasingly accurate methods for auxin quantification. However, auxin analysis has been challenging because auxins typically occur at low concentrations, while compounds that interfere with their detection often occur at high concentrations, in plant tissues. Interference from other compounds has been addressed by extensive purification of plant extracts prior to auxin analysis, although this means that quantification methods have been limited by their expense. This review explores the extraction, purification, and quantification of auxins and the application of these techniques in developing improved methods for the clonal propagation of forestry trees.

  14. A proteomics study of auxin effects in Arabidopsis thaliana

    Institute of Scientific and Technical Information of China (English)

    Meiqing Xing; Hongwei Xue


    Many phytohormones regulate plant growth and development through modulating protein degradation.In this study,a proteome study based on multidimensional non-gel shotgun approach was performed to analyze the auxin-induced protein degradation via ubiquitinproteasome pathway of Arabidopsis thaliana,with the emphasis to study the overall protein changes after auxin treatment (1 nM or 1 μM indole-3-acetic acid for 6,12,or 24 h).More than a thousand proteins were detected by using label-free shotgun method,and 386 increased proteins and 370 decreased ones were identified after indole-3-acetic acid treatment.By using the auxin receptor-deficient mutant,tir1-1,as control,comparative analysis revealed that 69 and 79 proteins were significantly decreased and increased,respectively.Detailed analysis showed that among the altered proteins,some were previously reported to be associated with auxin regulation and others are potentially involved in mediating the auxin effects on specific cellular and physiological processes by regulating photosynthesis,chloroplast development,cytoskeleton,and intracellular signaling.Our results demonstrated that label-free shotgun proteomics is a powerful tool for large-scale protein identification and the analysis of the proteomic profiling of auxin-regulated biological processes will provide informative clues of underlying mechanisms of auxin effects.These results will help to expand the understanding of how auxin regulates plant growth and development via protein degradation.

  15. The role of auxin in cell specification during arabidopsis embryogenesis

    NARCIS (Netherlands)

    Lokerse, A.S.


    Auxin is a structurally simple molecule, yet it elicits many different responses in plants. In Chapter 1 we have reviewed how specificity in the output of auxin signaling could be generated by distinct regulation and the unique properties of the members of the Aux/IAA and ARF transcription factor fa

  16. Effect of asymmetric auxin application on Helianthus hypocotyl curvature (United States)

    Migliaccio, F.; Rayle, D. L.


    Indole-3-acetic acid was applied asymmetrically to the hypocotyls of sunflower (Helianthus annuus L.) seedlings. After 5 hours on a clinostat, auxin gradients as small as 1 to 1.3 produced substantial (more than 60 degrees) hypocotyl curvature. This result suggests the asymmetric growth underlying hypocotyl gravitropism can be explained by lateral auxin redistribution.

  17. Expression of gibberellin 20-oxidase1 (AtGA20ox1) in Arabidopsis seedlings with altered auxin status is regulated at multiple levels. (United States)

    Desgagné-Penix, Isabel; Sponsel, Valerie M


    Bioactive gibberellins (GAs) affect many biological processes including germination, stem growth, transition to flowering, and fruit development. The location, timing, and level of bioactive GA are finely tuned to ensure that optimal growth and development occur. The balance between GA biosynthesis and deactivation is controlled by external factors such as light and by internal factors that include auxin. The role of auxin transport inhibitors (ATIs) and auxins on GA homeostasis in intact light-grown Arabidopsis thaliana (L.) Heynh. seedlings was investigated. Two ATIs, 1-N-naphthylthalamic acid (NPA) and 1-naphthoxyacetic acid (NOA) caused elevated expression of the GA biosynthetic enzyme AtGA20-oxidase1 (AtGA20ox1) in shoot but not in root tissues, and only at certain developmental stages. It was investigated whether enhanced AtGA20ox1 gene expression was a consequence of altered flow through the GA biosynthetic pathway, or was due to impaired GA signalling that can lead to enhanced AtGA20ox1 expression and accumulation of a DELLA protein, Repressor of ga1-3 (RGA). Both ATIs promoted accumulation of GFP-fused RGA in shoots and roots, and this increase was counteracted by the application of GA(4). These results suggest that in ATI-treated seedlings the impediment to DELLA protein degradation may be a deficiency of bioactive GA at sites of GA response. It is proposed that the four different levels of AtGA20ox1 regulation observed here are imposed in a strict hierarchy: spatial (organ-, tissue-, cell-specific) > developmental > metabolic > auxin regulation. Thus results show that, in intact auxin- and auxin transport inhibitor-treated light-grown Arabidopsis seedlings, three other levels of regulation supersede the effects of auxin on AtGA20ox1.

  18. The transport of indole-3-acetic Acid in boron- and calcium-deficient sunflower hypocotyl segments. (United States)

    Tang, P M; Dela Fuente, R K


    Transfer of sunflower (Helianthus annuus L. cv Russian Mammoth) seedlings from complete nutrient solution to solutions deficient in either boron or calcium resulted in a steady decline in the rate of auxin transport, compared to seedlings that remained in the complete solution. In seedlings transferred to solutions deficient in both B and Ca, the decline in auxin transport was greater than seedlings deficient in only one element. The transfer of B- or Ca-deficient seedlings back to the complete solution prevented further decline in auxin transport, but auxin transport did not increase to the same level as seedlings maintained in complete solution. The significant reduction in auxin transport during the early stages of B or Ca deficiency was not related to (a) reduced growth rate of the hypocotyl, (b) increased acropetal movement of auxin, or (c) lack of respiratory substrates in the hypocotyl. In addition, no difference was found in the water-extractable total and ionic Ca in B-deficient and control nondeficient hypocotyls, indicating a direct effect of B on auxin transport, rather than indirectly by affecting Ca absorption. The rate of auxin transport in hypocotyls deficient in either B or Ca, was inversely correlated with K(+) leakage and rate of respiration. The data presented strongly support the view that there are separate sites for B and Ca in the basipetal transport of the plant hormone indoleacetic acid.

  19. Oligogalacturonide-auxin antagonism does not require posttranscriptional gene silencing or stabilization of auxin response repressors in Arabidopsis. (United States)

    Savatin, Daniel V; Ferrari, Simone; Sicilia, Francesca; De Lorenzo, Giulia


    α-1-4-Linked oligogalacturonides (OGs) derived from plant cell walls are a class of damage-associated molecular patterns and well-known elicitors of the plant immune response. Early transcript changes induced by OGs largely overlap those induced by flg22, a peptide derived from bacterial flagellin, a well-characterized microbe-associated molecular pattern, although responses diverge over time. OGs also regulate growth and development of plant cells and organs, due to an auxin-antagonistic activity. The molecular basis of this antagonism is still unknown. Here we show that, in Arabidopsis (Arabidopsis thaliana), OGs inhibit adventitious root formation induced by auxin in leaf explants as well as the expression of several auxin-responsive genes. Genetic, biochemical, and pharmacological experiments indicate that inhibition of auxin responses by OGs does not require ethylene, jasmonic acid, and salicylic acid signaling and is independent of RESPIRATORY BURST OXIDASE HOMOLOGUE D-mediated reactive oxygen species production. Free indole-3-acetic acid levels are not noticeably altered by OGs. Notably, OG- as well as flg22-auxin antagonism does not involve any of the following mechanisms: (1) stabilization of auxin-response repressors; (2) decreased levels of auxin receptor transcripts through the action of microRNAs. Our results suggest that OGs and flg22 antagonize auxin responses independently of Aux/Indole-3-Acetic Acid repressor stabilization and of posttranscriptional gene silencing.

  20. Polar delivery in plants; commonalities and differences to animal epithelial cells. (United States)

    Kania, Urszula; Fendrych, Matyaš; Friml, Jiři


    Although plant and animal cells use a similar core mechanism to deliver proteins to the plasma membrane, their different lifestyle, body organization and specific cell structures resulted in the acquisition of regulatory mechanisms that vary in the two kingdoms. In particular, cell polarity regulators do not seem to be conserved, because genes encoding key components are absent in plant genomes. In plants, the broad knowledge on polarity derives from the study of auxin transporters, the PIN-FORMED proteins, in the model plant Arabidopsis thaliana. In animals, much information is provided from the study of polarity in epithelial cells that exhibit basolateral and luminal apical polarities, separated by tight junctions. In this review, we summarize the similarities and differences of the polarization mechanisms between plants and animals and survey the main genetic approaches that have been used to characterize new genes involved in polarity establishment in plants, including the frequently used forward and reverse genetics screens as well as a novel chemical genetics approach that is expected to overcome the limitation of classical genetics methods.

  1. Interactions of auxinic compounds on a Ca2+ signaling and root growth in Arabidopsis thaliana (United States)

    Auxinic-like compounds have been widely used as weed control agents. Over the years, the mode of action of auxinic herbicides have been elucidated, but most studies thus far have focused on their effects on later stages of plant growth. Here, we show that some select auxins and auxinic-like herbicid...

  2. Correlations between gravitropic curvature and auxin movement across gravistimulated roots of Zea mays (United States)

    Young, L. M.; Evans, M. L.; Hertel, R.


    We compared the kinetics of auxin redistribution across the caps of primary roots of 2-day-old maize (Zea mays, cv Merit) seedlings with the time course of gravitropic curvature. [3H] indoleacetic acid was applied to one side of the cap in an agar donor and radioactivity moving across the cap was collected in an agar receiver applied to the opposite side. Upon gravistimulation the roots first curved upward slightly, then returned to the horizontal and began curving downward, reaching a final angle of about 67 degrees. Movement of label across the caps of gravistimulated roots was asymmetric with preferential downward movement (ratio downward/upward = ca. 1.6, radioactivity collected during the 90 min following beginning of gravistimulation). There was a close correlation between the development of asymmetric auxin movement across the root cap and the rate of curvature, with both values increasing to a maximum and then declining as the roots approached the final angle of curvature. In roots preadapted to gravity (alternate brief stimulation on opposite flanks over a period of 1 hour) the initial phase of upward curvature was eliminated and downward bending began earlier than for controls. The correlation between asymmetric auxin movement and the kinetics of curvature also held in comparisons between control and preadapted roots. Both downward auxin transport asymmetry and downward curvature occurred earlier in preadapted roots than in controls. These findings are consistent with suggestions that the root cap is not only the site of perception but also the location of the initial redistribution of effectors that ultimately leads to curvature.

  3. Intraflagellar transport is required for polarized recycling of the TCR/CD3 complex to the immune synapse. (United States)

    Finetti, Francesca; Paccani, Silvia Rossi; Riparbelli, Maria Giovanna; Giacomello, Emiliana; Perinetti, Giuseppe; Pazour, Gregory J; Rosenbaum, Joel L; Baldari, Cosima T


    Most eukaryotic cells have a primary cilium which functions as a sensory organelle. Cilia are assembled by intraflagellar transport (IFT), a process mediated by multimeric IFT particles and molecular motors. Here we show that lymphoid and myeloid cells, which lack primary cilia, express IFT proteins. IFT20, an IFT component essential for ciliary assembly, was found to colocalize with both the microtubule organizing centre (MTOC) and Golgi and post-Golgi compartments in T-lymphocytes. In antigen-specific conjugates, IFT20 translocated to the immune synapse. IFT20 knockdown resulted in impaired T-cell receptor/CD3 (TCR/CD3) clustering and signalling at the immune synapse, due to defective polarized recycling. Moreover, IFT20 was required for the inducible assembly of a complex with other IFT components (IFT57 and IFT88) and the TCR. The results identify IFT20 as a new regulator of immune synapse assembly in T cells and provide the first evidence to implicate IFT in membrane trafficking in cells lacking primary cilia, thereby introducing a new perspective on IFT function beyond its role in ciliogenesis.

  4. Auxin modulates the enhanced development of root hairs in Arabidopsis thaliana (L.) Heynh. under elevated CO(2). (United States)

    Niu, Yaofang; Jin, Chongwei; Jin, Gulei; Zhou, Qingyan; Lin, Xianyong; Tang, Caixian; Zhang, Yongsong


    Root hairs may play a critical role in nutrient acquisition of plants grown under elevated CO(2) . This study investigated how elevated CO(2) enhanced the development of root hairs in Arabidopsis thaliana (L.) Heynh. The plants under elevated CO(2) (800 µL L(-1)) had denser and longer root hairs, and more H-positioned cells in root epidermis than those under ambient CO(2) (350 µL L(-1)). The elevated CO(2) increased auxin production in roots. Under elevated CO(2) , application of either 1-naphthoxyacetic acid (1-NOA) or N-1-naphthylphthalamic acid (NPA) blocked the enhanced development of root hairs. The opposite was true when the plants under ambient CO(2) were treated with 1-naphthylacetic acid (NAA), an auxin analogue. Furthermore, the elevated CO(2) did not enhance the development of root hairs in auxin-response mutants, axr1-3, and auxin-transporter mutants, axr4-1, aux1-7 and pin1-1. Both elevated CO(2) and NAA application increased expressions of caprice, triptychon and rho-related protein from plants 2, and decreased expressions of werewolf, GLABRA2, GLABRA3 and the transparent testa glabra 1, genes related to root-hair development, while 1-NOA and NPA application had an opposite effect. Our study suggests that elevated CO(2) enhanced the development of root hairs in Arabidopsis via the well-characterized auxin signalling and transport that modulate the initiation of root hairs and the expression of its specific genes.

  5. L-Cysteine inhibits root elongation through auxin/PLETHORA and SCR/SHR pathway in Arabidopsis thaliana

    Institute of Scientific and Technical Information of China (English)

    Zhen Wang; Jie-Li Mao; Ying-Jun Zhao; Chuan-You Li; Cheng-Bin Xiang


    L‐Cysteine plays a prominent role in sulfur metabo-lism of plants. However, its role in root development is largely unknown. Here, we report that L‐cysteine reduces primary root growth in a dosage‐dependent manner. Elevating cel ular L‐cysteine level by exposing Arabidopsis thaliana seedlings to high L‐cysteine, buthionine sulphoximine, or O‐acetylserine leads to altered auxin maximum in root tips, the expression of quiescent center cel marker as wel as the decrease of the auxin carriers PIN1, PIN2, PIN3, and PIN7 of primary roots. We also show that high L‐cysteine significantly reduces the protein level of two sets of stem cel specific transcription factors PLETHORA1/2 and SCR/SHR. However, L‐cysteine does not downregulate the transcript level of PINs, PLTs, or SCR/SHR, suggesting that an uncharacterized post‐transcriptional mech-anism may regulate the accumulation of PIN, PLT, and SCR/SHR proteins and auxin transport in the root tips. These results suggest that endogenous L‐cysteine level acts to maintain root stem cel niche by regulating basal‐and auxin‐induced expression of PLT1/2 and SCR/SHR. L‐Cysteine may serve as a link between sulfate assimilation and auxin in regulating root growth.

  6. The role of auxin in temperature regulated hypocotyl elongation

    Energy Technology Data Exchange (ETDEWEB)

    Estelle, Mark [Univ. of California, San Diego, CA (United States)


    The major goal of this project was to determine how auxin mediates the response of Arabidopsis seedlings to increased ambient temperature. Previous studies have shown that the response is due, in part, to increased auxin biosynthesis via the IPA auxin biosynthetic pathway. This effect is related to increased transcription of genes that encode enzymes in this pathway. However, during the last year we have shown that transcription of key auxin regulated genes increases within minutes of a shift to elevated temperature. This response is probably to rapid to be explained by changes in the levels of auxin biosynthetic enzymes. Interestingly, we have recently discovered that temperature shift is associated with a rapid increase in the level of the auxin co-receptor TIR1. This change appears is the result of increased stability of the protein. At the same time, we have discovered that stability of TIR1 is dependent on the chaperone HSP9o and its co-chaperone SGT1. By using the specific HSP90 inhibitor GDA, we show that HSP90 is required for the temperature dependent change in TIR1 levels. We have also shown that HSP90 and SGT1 interact directly with TIR1. Our results also lead us to propose a new model in which the plant responds rapidly to changes in ambient temperature by directly regulating the TIR1/AFB receptor system, thus modulating the auxin signaling pathway.

  7. MicroRNA directs mRNA cleavage of the transcription factor NAC1 to downregulate auxin signals for arabidopsis lateral root development. (United States)

    Guo, Hui-Shan; Xie, Qi; Fei, Ji-Feng; Chua, Nam-Hai


    Although several plant microRNAs (miRNAs) have been shown to play a role in plant development, no phenotype has yet been associated with a reduction or loss of expression of any plant miRNA. Arabidopsis thaliana miR164 was predicted to target five NAM/ATAF/CUC (NAC) domain-encoding mRNAs, including NAC1, which transduces auxin signals for lateral root emergence. Here, we show that miR164 guides the cleavage of endogenous and transgenic NAC1 mRNA, producing 3'-specific fragments. Cleavage was blocked by NAC1 mutations that disrupt base pairing with miR164. Compared with wild-type plants, Arabidopsis mir164a and mir164b mutant plants expressed less miR164 and more NAC1 mRNA and produced more lateral roots. These mutant phenotypes can be complemented by expression of the appropriate MIR164a and MIR164b genomic sequences. By contrast, inducible expression of miR164 in wild-type plants led to decreased NAC1 mRNA levels and reduced lateral root emergence. Auxin induction of miR164 was mirrored by an increase in the NAC1 mRNA 3' fragment, which was not observed in the auxin-insensitive mutants auxin resistant1 (axr1-12), axr2-1, and transport inhibitor response1. Moreover, the cleavage-resistant form of NAC1 mRNA was unaffected by auxin treatment. Our results indicate that auxin induction of miR164 provides a homeostatic mechanism to clear NAC1 mRNA to downregulate auxin signals.

  8. Spin polarized transports through a narrow-gap semiconductor wire with ferromagnetic contacts formed on InAlAs step-graded buffer layers


    Akabori, M; Yamada, S.


    We investigated the transport properties of ferromagnetic/semiconductor hybrid structures utilizing an InAs/In_Al_As modulation-doped heterostructures formed on a GaAs (001) substrate with In_xAl_As step-graded buffer layers. We used NiFe as ferromagnetic electrodes for injection/detection of spin-polarized electrons, which were formed on side walls of the semiconductor mesa to contact electron channel directly. We measured magneto-transport properties of the samples with current flow between...

  9. Advances in Research of Auxin Signaling in the Root Tip%植物根尖生长素信号研究进展

    Institute of Scientific and Technical Information of China (English)

    沈燕霞; 倪君


    Auxin signaling regulates many aspects of plant development. In this article, we gave a brief review of advances in research of auxin signaling in the root tip. We summarized recent progress from three aspects, auxin transport and distribution in root tip, the influences of auxin signaling in root tip cell identities, and auxin signaling in the quiescent center. In addition, we provided prospective views of this field in the end of this article.%生长素信号调控植物生长发育的各个方面.该文综述了生长素信号在植物根尖的研究进展概况,从生长素在根尖的运输与分布、生长素信号对根尖细胞命运的影响及静止中心细胞的生长素信号研究三个方面进行了阐述,并对未来该领域的研究方向进行了展望.

  10. YUCCA auxin biosynthetic genes are required for Arabidopsis shade avoidance

    Directory of Open Access Journals (Sweden)

    Patricia Müller-Moulé


    Full Text Available Plants respond to neighbor shade by increasing stem and petiole elongation. Shade, sensed by phytochrome photoreceptors, causes stabilization of PHYTOCHROME INTERACTING FACTOR proteins and subsequent induction of YUCCA auxin biosynthetic genes. To investigate the role of YUCCA genes in phytochrome-mediated elongation, we examined auxin signaling kinetics after an end-of-day far-red (EOD-FR light treatment, and found that an auxin responsive reporter is rapidly induced within 2 hours of far-red exposure. YUCCA2, 5, 8, and 9 are all induced with similar kinetics suggesting that they could act redundantly to control shade-mediated elongation. To test this hypothesis we constructed a yucca2, 5, 8, 9 quadruple mutant and found that the hypocotyl and petiole EOD-FR and shade avoidance responses are completely disrupted. This work shows that YUCCA auxin biosynthetic genes are essential for detectable shade avoidance and that YUCCA genes are important for petiole shade avoidance.

  11. Plant cells use auxin efflux to explore geometry. (United States)

    Zaban, Beatrix; Liu, Wenwen; Jiang, Xingyu; Nick, Peter


    Cell movement is the central mechanism for animal morphogenesis. Plant cell development rather relies on flexible alignment of cell axis adjusting cellular differentiation to directional cues. As central input, vectorial fields of mechanical stress and gradients of the phytohormone auxin have been discussed. In tissue contexts, mechanical and chemical signals will always act in concert; experimentally it is difficult to dissect their individual roles. We have designed a novel approach, based on cells, where directionality has been eliminated by removal of the cell wall. We impose a new axis using a microfluidic set-up to generate auxin gradients. Rectangular microvessels are integrated orthogonally with the gradient. Cells in these microvessels align their new axis with microvessel geometry before touching the wall. Auxin efflux is necessary for this touch-independent geometry exploration and we suggest a model, where auxin gradients can be used to align cell axis in tissues with minimized mechanical tensions.

  12. YUCCA auxin biosynthetic genes are required for Arabidopsis shade avoidance (United States)

    Müller-Moulé, Patricia; Nozue, Kazunari; Pytlak, Melissa L.; Palmer, Christine M.; Covington, Michael F.; Wallace, Andreah D.; Harmer, Stacey L.


    Plants respond to neighbor shade by increasing stem and petiole elongation. Shade, sensed by phytochrome photoreceptors, causes stabilization of PHYTOCHROME INTERACTING FACTOR proteins and subsequent induction of YUCCA auxin biosynthetic genes. To investigate the role of YUCCA genes in phytochrome-mediated elongation, we examined auxin signaling kinetics after an end-of-day far-red (EOD-FR) light treatment, and found that an auxin responsive reporter is rapidly induced within 2 hours of far-red exposure. YUCCA2, 5, 8, and 9 are all induced with similar kinetics suggesting that they could act redundantly to control shade-mediated elongation. To test this hypothesis we constructed a yucca2, 5, 8, 9 quadruple mutant and found that the hypocotyl and petiole EOD-FR and shade avoidance responses are completely disrupted. This work shows that YUCCA auxin biosynthetic genes are essential for detectable shade avoidance and that YUCCA genes are important for petiole shade avoidance. PMID:27761349

  13. Synthesis of some useful tritium labelled auxins

    Energy Technology Data Exchange (ETDEWEB)

    Buchman, O.; Pri-Bar, I.; Shimoni, M.; Azran, J. (Israel Atomic Energy Commission, Beersheba (Israel). Nuclear Research Center-Negev)


    The synthesis of six useful auxins labelled with tritium is described. The following compounds were prepared: 3-indoleacetic acid-5-[sup 3]H (28.9 Ci-1.07 TBq/mmol), 3-indolebutyric acid-5-[sup 3]H (7.3 Ci-270 GBq/mmol), 1-naphthylacetic acid-4-[sup 3]H (27.6 Ci-1.02 TBq/mmol), 2,4-dichloropheno-xyacetic acid-5-[sup 3]H (18.5 Ci-685 GBq/mmol), 2(2,4-dichlorophenoxy-5-[sup 3]H) -propionic acid (20.7 Ci-766 GBq/mmol), 2(2,4-dichlorophenoxy)-propionic acid-3-[sup 3]H (0.39 Ci-14.4 GMq/mmol), and 4-chlorophenoxyacetic acid-2-[sup 3]H (13.3 Ci-492 GBq/mmol). (author).

  14. High temperature promotes auxin-mediated hypocotyl elongation in Arabidopsis


    Gray, William M; Östin, Anders; Sandberg, Göran; Romano, Charles P.; Estelle, Mark


    Physiological studies with excised stem segments have implicated the plant hormone indole-3-acetic acid (IAA or auxin) in the regulation of cell elongation. Supporting evidence from intact plants has been somewhat more difficult to obtain, however. Here, we report the identification and characterization of an auxin-mediated cell elongation growth response in Arabidopsis thaliana. When grown in the light at high temperature (29°C), Arabidopsis seedlings exhibit dramatic hypocotyl elongation co...

  15. Hairy roots are more sensitive to auxin than normal roots


    Shen, Wen Hui; Petit, Annik; Guern, Jean; Tempé, Jacques


    Responses to auxin of Lotus corniculatus root tips or protoplasts transformed by Agrobacterium rhizogenes strains 15834 and 8196 were compared to those of their normal counterparts. Three different types of experiments were performed, involving long-term, medium-term, or short-term responses to a synthetic auxin, 1-naphthaleneacetic acid. Root tip elongation, proton excretion by root tips, and transmembrane electrical potential difference of root protoplasts were measured as a function of exo...

  16. Charge transfer and polarization for chloride ions bound in ClC transport proteins: natural bond orbital and energy decomposition analyses. (United States)

    Church, Jonathan; Pezeshki, Soroosh; Davis, Christal; Lin, Hai


    ClC transport proteins show a distinct "broken-helix" architecture, in which certain α-helices are oriented with their N-terminal ends pointed toward the binding sites where the chloride ions are held extensively by the backbone amide nitrogen atoms from the helices. To understand the effectiveness of such binding structures, we carried out natural bond orbital analysis and energy decomposition analysis employing truncated active-site model systems for the bound chloride ions along the translocation pore of the EcClC proteins. Our results indicated that the chloride ions are stabilized in such a binding environment by electrostatic, polarization, and charge-transfer interactions with the backbone and a few side chains. Up to ~25% of the formal charges of the chloride ions were found smeared out to the surroundings primarily via charge transfer from the chloride's lone pair n(Cl) orbitals to the protein's antibonding σ*(N-H) or σ*(O-H) orbitals; those σ* orbitals are localized at the polar N-H and O-H bonds in the chloride's first solvation shells formed by the backbone amide groups and the side chains of residues Ser107, Arg147, Glu148, and Tyr445. Polarizations by the chloride ions were dominated by the redistribution of charge densities among the π orbitals and lone pair orbitals of the protein atoms, in particular the atoms of the backbone peptide links and of the side chains of Arg147, Glu148, and Tyr445. The substantial amounts of electron density involved in charge transfer and in polarization were consistent with the large energetic contributions by the two processes revealed by the energy decomposition analysis. The significant polarization and charge-transfer effects may have impacts on the mechanisms and dynamics of the chloride transport by the ClC proteins.

  17. Nitric Oxide-Mediated Maize Root Apex Responses to Nitrate are Regulated by Auxin and Strigolactones

    Directory of Open Access Journals (Sweden)

    Alessandro eManoli


    Full Text Available Nitrate (NO3- is a key element for crop production but its levels in agricultural soils are limited. Plants have developed mechanisms to cope with these NO3- fluctuations based on sensing nitrate at the root apex. Particularly, the transition zone (TZ of root apex has been suggested as a signalling-response zone. This study dissects cellular and molecular mechanisms underlying NO3- resupply effects on primary root growth in maize, confirming nitric oxide (NO as a putative modulator. Nitrate restoration induced primary root elongation within the first 2 h, corresponding to a stimulation of cell elongation at the basal border of the TZ. Xyloglucans (XGs immunolocalization together with Brefeldin A applications demonstrated that nitrate resupply induces XG accumulation. This effect was blocked by cPTIO (NO scavenger. Transcriptional analysis of ZmXET1 confirmed the stimulatory effect of nitrate on XGs accumulation in cells of the TZ. Immunolocalization analyses revealed a positive effect of nitrate resupply on auxin and PIN1 accumulation, but a transcriptional regulation of auxin biosynthesis/transport/signalling genes was excluded. Short-term nitrate treatment repressed the transcription of genes involved in strigolactones (SLs biosynthesis and transport, mainly in the TZ. Enhancement of carotenoid cleavage dioxygenases (CCDs transcription in presence of cPTIO indicated endogenous NO as a negative modulator of CCDs activity. Finally, treatment with the SLs-biosynthesis inhibitor (TIS108 restored the root growth in the nitrate-starved seedlings. Present report suggests that the NO-mediated root apex responses to nitrate are accomplished in cells of the TZ via integrative actions of auxin, NO and SLs.

  18. Nitric Oxide-Mediated Maize Root Apex Responses to Nitrate are Regulated by Auxin and Strigolactones. (United States)

    Manoli, Alessandro; Trevisan, Sara; Voigt, Boris; Yokawa, Ken; Baluška, František; Quaggiotti, Silvia


    Nitrate (NO3 (-)) is a key element for crop production but its levels in agricultural soils are limited. Plants have developed mechanisms to cope with these NO3 (-) fluctuations based on sensing nitrate at the root apex. Particularly, the transition zone (TZ) of root apex has been suggested as a signaling-response zone. This study dissects cellular and molecular mechanisms underlying NO3 (-) resupply effects on primary root (PR) growth in maize, confirming nitric oxide (NO) as a putative modulator. Nitrate restoration induced PR elongation within the first 2 h, corresponding to a stimulation of cell elongation at the basal border of the TZ. Xyloglucans (XGs) immunolocalization together with Brefeldin A applications demonstrated that nitrate resupply induces XG accumulation. This effect was blocked by cPTIO (NO scavenger). Transcriptional analysis of ZmXET1 confirmed the stimulatory effect of nitrate on XGs accumulation in cells of the TZ. Immunolocalization analyses revealed a positive effect of nitrate resupply on auxin and PIN1 accumulation, but a transcriptional regulation of auxin biosynthesis/transport/signaling genes was excluded. Short-term nitrate treatment repressed the transcription of genes involved in strigolactones (SLs) biosynthesis and transport, mainly in the TZ. Enhancement of carotenoid cleavage dioxygenases (CCDs) transcription in presence of cPTIO indicated endogenous NO as a negative modulator of CCDs activity. Finally, treatment with the SLs-biosynthesis inhibitor (TIS108) restored the root growth in the nitrate-starved seedlings. Present report suggests that the NO-mediated root apex responses to nitrate are accomplished in cells of the TZ via integrative actions of auxin, NO and SLs.

  19. Overlap of proteome changes in Medicago truncatula in response to auxin and Sinorhizobium meliloti. (United States)

    van Noorden, Giel E; Kerim, Tursun; Goffard, Nicolas; Wiblin, Robert; Pellerone, Flavia I; Rolfe, Barry G; Mathesius, Ulrike


    We used proteome analysis to identify proteins induced during nodule initiation and in response to auxin in Medicago truncatula. From previous experiments, which found a positive correlation between auxin levels and nodule numbers in the M. truncatula supernodulation mutant sunn (supernumerary nodules), we hypothesized (1) that auxin mediates protein changes during nodulation and (2) that auxin responses might differ between the wild type and the supernodulating sunn mutant during nodule initiation. Increased expression of the auxin response gene GH3:beta-glucuronidase was found during nodule initiation in M. truncatula, similar to treatment of roots with auxin. We then used difference gel electrophoresis and tandem mass spectrometry to compare proteomes of wild-type and sunn mutant roots after 24 h of treatment with Sinorhizobium meliloti, auxin, or a control. We identified 131 of 270 proteins responding to treatment with S. meliloti and/or auxin, and 39 of 89 proteins differentially displayed between the wild type and sunn. The majority of proteins changed similarly in response to auxin and S. meliloti after 24 h in both genotypes, supporting hypothesis 1. Proteins differentially accumulated between untreated wild-type and sunn roots also showed changes in auxin response, consistent with altered auxin levels in sunn. However, differences between the genotypes after S. meliloti inoculation were largely not due to differential auxin responses. The role of the identified candidate proteins in nodule initiation and the requirement for their induction by auxin could be tested in future functional studies.

  20. Pure spin polarized transport based on Rashba spin-orbit interaction through the Aharonov-Bohm interferometer embodied four-quantum-dot ring

    Institute of Scientific and Technical Information of China (English)

    Wu Li-Jun; Han Yu


    The spin-polarized linear conductance spectrum and current-voltage characteristics in a four-quantum-dot ring embodied into Aharonov-Bohm (AB) interferometer are investigated theoretically by considering a local Rashba spin-orbit interaction.It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π,and that Hubbard U cannot influence the electron transport properties in this case.When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength,the electronic spin polarization can reach a maximum value.Furthermore,by adjusting the bias voltages applied to the leads,the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations.Based on the numerical results,such a model can be applied to the design of a spin filter device.

  1. Production, formation, and transport of high-brightness atomic hydrogen beam studies for the relativistic heavy ion collider polarized source upgrade

    Energy Technology Data Exchange (ETDEWEB)

    Kolmogorov, A., E-mail:; Stupishin, N. [Budker Institute of Nuclear Physics, Novosibirsk (Russian Federation); Atoian, G.; Ritter, J.; Zelenski, A. [Brookhaven National Laboratory, Upton, New York 11973 (United States); Davydenko, V.; Ivanov, A. [Budker Institute of Nuclear Physics, Novosibirsk (Russian Federation); Novosibirsk State University, Novosibirsk (Russian Federation)


    The RHIC polarized H{sup −} ion source had been successfully upgraded to higher intensity and polarization by using a very high brightness fast atomic beam source developed at BINP, Novosibirsk. In this source the proton beam is extracted by a four-grid multi-aperture ion optical system and neutralized in the H{sub 2} gas cell downstream from the grids. The proton beam is extracted from plasma emitter with a low transverse ion temperature of ∼0.2 eV which is formed by plasma jet expansion from the arc plasma generator. The multi-hole grids are spherically shaped to produce “geometrical” beam focusing. Proton beam formation and transport of atomic beam were experimentally studied at test bench.

  2. Tomato fruit development in the auxin-resistant dgt mutant is induced by pollination but not by auxin treatment. (United States)

    Mignolli, Francesco; Mariotti, Lorenzo; Lombardi, Lara; Vidoz, María Laura; Ceccarelli, Nello; Picciarelli, Piero


    In tomato (Solanum lycopersicum Mill.), auxin is believed to play a pivotal role in controlling fruit-set and early ovary growth. In this paper we investigated the effect of the reduced auxin sensitivity exhibited by the diageotropica (dgt) tomato mutant on ovary growth during early stage of fruit development. Here we show that in hand-pollinated ovaries fruit-set was not affected by the dgt lesion while fruit growth was reduced. This reduction was associated with a smaller cell size of mesocarp cells, with a lower mean C values and with a lower gene expression of the expansin gene LeExp2. When a synthetic auxin (4-CPA, chlorophenoxyacetic acid) was applied to the flowers of wild type plants, parthenocarpic ovary growth was induced. On the contrary, auxin application to the flowers of dgt plants failed to induce parthenocarpy. Hand-pollinated ovaries of dgt contained higher levels of IAA compared to wild type and this was not associated with high transcript levels of genes encoding a key regulatory enzyme of IAA biosynthesis (ToFZYs) but with lower expression levels of GH3, a gene involved in the conjugation of IAA to amino acids. The expression of diverse Aux/IAA genes and SAUR (small auxin up-regulated RNA) was also altered in the dgt ovaries. The dgt lesion does not seem to affect specific Aux/IAA genes in terms of transcript occurrence but rather in terms of relative levels of expression. Transcript levels of Aux/IAA genes were up regulated in auxin-treated ovaries of wild-type but not in dgt. Together, our results suggest that dgt ovary cells are not able to sense and/or transduce the external auxin signal, whereas pollinated dgt ovary cells are able to detect the IAA present in fertilized ovules promoting fruit development.

  3. Bicarbonate utilization and pH polarity. The response of photosynthetic electron transport to carbon limitation in Potamogeton lucens leaves

    NARCIS (Netherlands)

    van Ginkel, LC; Prins, HBA


    By the process of pH polarity, several submersed angiosperms can use bicarbonate as carbon source for photosynthesis. Under conditions of relatively high light intensity and low CO2 availability, the pH of the apoplast and unstirred layer becomes acid at one side of the leaf and alkaline at the othe

  4. Effects of auxins and cytokinins on tomato callus from anthers

    Directory of Open Access Journals (Sweden)

    Janina H. Rogozińska


    Full Text Available An investigation was carried out on growth substance requirements of tomato callus derived from anthers for culture in vitro. Linsmaier and Skoog (1965 medium was used with various levels of auxins (IAA and NAA and cytokinins (K and BAP. The results show that cytokinin is an absolute requirement for callus growth irrespective of the auxin level. The optimum concentration of auxin in combination with cytokinin was found to be 5 μM of NAA or 25 μM of IAA, with 5 μM of K or BAP. Callus growth on media with NAA and cytokinin was superior to that on IAA, amounting to 6.05 g per piece on medium with 5 μM of NAA and BAP. Tissues grown on this medium have the highest water content. At the onset of culture the tissue is characterized by weak growth and attains its maximal increase in fresh weight after 6 weeks.

  5. The role of auxin in shaping shoot architecture. (United States)

    Gallavotti, Andrea


    The variety of plant architectures observed in nature is predominantly determined by vegetative and reproductive branching patterns, the positioning of lateral organs, and differential stem elongation. Branches, lateral organs, and stems are the final products of the activity of meristems, groups of stem cells whose function is genetically determined and environmentally influenced. Several decades of studies in different plant species have shed light on the essential role of the hormone auxin in plant growth and development. Auxin influences stem elongation and regulates the formation, activity, and fate of meristems, and has therefore been recognized as a major hormone shaping plant architecture. Increasing our knowledge of the molecular mechanisms that regulate auxin function is necessary to understand how different plant species integrate a genetically determined developmental programme, the establishment of a body plan, with constant inputs from the surrounding environment. This information will allow us to develop the molecular tools needed to modify plant architecture in several crop species and in rapidly changing environments.

  6. Influence of adsorbed polar molecules on the electronic transport in a composite material Li(1.1)V3O8-PMMA for lithium batteries. (United States)

    Badot, J C; Ligneel, E; Dubrunfaut, O; Gaubicher, J; Guyomard, D; Lestriez, B


    The broadband dielectric spectroscopy (BDS) technique (40 to 10(10) Hz) is used here to measure the electronic transport across all observed size scales of a Li(1.1)V(3)O(8)-polymer-gel composite material for lithium batteries. Different electrical relaxations are evidenced, resulting from the polarizations at the different scales of the architecture: (i) atomic lattice (small-polaron hopping), (ii) particles, (iii) clusters of particles, and finally (iv) sample-current collector interface. A very good agreement with dc-conductivity measurements on a single macro-crystal [M. Onoda and I. Amemiya, J. Phys.: Condens. Matter, 2003, 15, 3079.] shows that the BDS technique does allow probing the bulk (intrinsic) electrical properties of a material in the form of a network of particles separated by boundaries in a composite. Moreover, this study highlights a lowering of the surface electronic conductivity of Li(1.1)V(3)O(8) particles upon adsorption of polar ethylene carbonate (EC) and propylene carbonate (PC) that trap surface polarons. This result is meaningful as EC and PC are typical constituents of a liquid electrolyte of lithium batteries. It is thus suggested that interactions between active material particles and the liquid electrolyte play a role in the electronic transport within composite electrodes used in a lithium battery.

  7. Seek and Ye Shall [eventually] Find: The End of the Search for the Auxin Receptor

    Institute of Scientific and Technical Information of China (English)

    Lawrence HOBBIE


    The mechanism by which the plant hormone auxin regulates gene expression has been shown to involve regulated degradation, through the ubiquitin-proteasome pathway, of transcriptional repressor proteins. However, the key first component in this pathway, the receptor that binds auxin and initiates auxin signaling, has remained a mystery. Two recent papers identify the F-box protein TIR1, part of the complex that attaches ubiquitin to its targets, as an auxin receptor. This breakthrough reveals a new mode of signal transduction and lays the groundwork for a more complete understanding of auxin physiology.

  8. Comprehensive RNA-Seq Analysis on the Regulation of Tomato Ripening by Exogenous Auxin.

    Directory of Open Access Journals (Sweden)

    Jiayin Li

    Full Text Available Auxin has been shown to modulate the fruit ripening process. However, the molecular mechanisms underlying auxin regulation of fruit ripening are still not clear. Illumina RNA sequencing was performed on mature green cherry tomato fruit 1 and 7 days after auxin treatment, with untreated fruit as a control. The results showed that exogenous auxin maintained system 1 ethylene synthesis and delayed the onset of system 2 ethylene synthesis and the ripening process. At the molecular level, genes associated with stress resistance were significantly up-regulated, but genes related to carotenoid metabolism, cell degradation and energy metabolism were strongly down-regulated by exogenous auxin. Furthermore, genes encoding DNA demethylases were inhibited by auxin, whereas genes encoding cytosine-5 DNA methyltransferases were induced, which contributed to the maintenance of high methylation levels in the nucleus and thus inhibited the ripening process. Additionally, exogenous auxin altered the expression patterns of ethylene and auxin signaling-related genes that were induced or repressed in the normal ripening process, suggesting significant crosstalk between these two hormones during tomato ripening. The present work is the first comprehensive transcriptome analysis of auxin-treated tomato fruit during ripening. Our results provide comprehensive insights into the effects of auxin on the tomato ripening process and the mechanism of crosstalk between auxin and ethylene.

  9. Development of the Poplar-Laccaria bicolor Ectomycorrhiza Modifies Root Auxin Metabolism, Signaling, and Response. (United States)

    Vayssières, Alice; Pěnčík, Ales; Felten, Judith; Kohler, Annegret; Ljung, Karin; Martin, Francis; Legué, Valérie


    Root systems of host trees are known to establish ectomycorrhizae (ECM) interactions with rhizospheric fungi. This mutualistic association leads to dramatic developmental modifications in root architecture, with the formation of numerous short and swollen lateral roots ensheathed by a fungal mantle. Knowing that auxin plays a crucial role in root development, we investigated how auxin metabolism, signaling, and response are affected in poplar (Populus spp.)-Laccaria bicolor ECM roots. The plant-fungus interaction leads to the arrest of lateral root growth with simultaneous attenuation of the synthetic auxin response element DR5. Measurement of auxin-related metabolites in the free-living partners revealed that the mycelium of L. bicolor produces high concentrations of the auxin indole-3-acetic acid (IAA). Metabolic profiling showed an accumulation of IAA and changes in the indol-3-pyruvic acid-dependent IAA biosynthesis and IAA conjugation and degradation pathways during ECM formation. The global analysis of auxin response gene expression and the regulation of AUXIN SIGNALING F-BOX PROTEIN5, AUXIN/IAA, and AUXIN RESPONSE FACTOR expression in ECM roots suggested that symbiosis-dependent auxin signaling is activated during the colonization by L. bicolor. Taking all this evidence into account, we propose a model in which auxin signaling plays a crucial role in the modification of root growth during ECM formation.

  10. The influence of firn air transport processes and radiocarbon production on gas records from polar firn and ice

    DEFF Research Database (Denmark)

    Buizert, Christo

    does not vanish completely in the lock-in zone, as is commonly assumed. Six state-of-the-art firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1 Gaussian distribution. We present the first intercomparison study of firn air models, where we...... introduce diagnostic scenarios designed to probe speciffc aspects of the model physics. Our results show that there are major di erences in the way the models handle advective transport, and that dffusive fractionation of isotopes in the firn is poorly constrained by the models....... and storage. Understanding of these processes is essential for a correct interpretation of ice core gas records. In this work we focus on transport processes in the porous firn layer prior to bubble trapping, and in situ cosmogenic radiocarbon ( 14 C) production in ice. First, we present a review of firn air...

  11. Regulation of auxin responses in tomato fruit development

    NARCIS (Netherlands)

    Jong, M. de


    The transformation from an ovary to a rapidly growing fruit includes molecular, biochemical and structural changes that must be tightly coordinated. Depending on the phase of fruit development, the temporal and spatial organization of these changes is mediated by phytohormones, such as auxin, gibber

  12. Gene expression profiles of auxin metabolism in maturing apple fruit (United States)

    Variation exists among apple genotypes in fruit maturation and ripening patterns that influences at-harvest fruit firmness and postharvest storability. Based on the results from our previous large-scale transcriptome profiling on apple fruit maturation and well-documented auxin-ethylene crosstalk, t...

  13. Effect of ferroelectric polarization switching on the electronic transport properties of La0.8Ca0.2MnO3 film (United States)

    Xie, Qiyun; Zhai, Zhangyin; Wu, Xiaoshan; Gao, Ju


    La0.8Ca0.2MnO3 thin film grown on 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-PT) substrate has shown very interesting transport properties, which is modulated by the ferroelectric polarization switching in the substrate. The ferroelectric poling reduces the in-plane strain by about 0.135% with the applied piezovoltage of 500 V to PMN-PT substrate. The resistance is lowered and the metal-insulator transition temperature (Tp) is increased due to the reduced in-plane strain. Moreover, it is shown that the ferroelectric field effect competes strongly with the strain effect especially when the temperature is lowered below Tp in our film.

  14. Gravitropism in higher plant shoots. VI. Changing sensitivity to auxin in gravistimulated soybean hypocotyls (United States)

    Rorabaugh, P. A.; Salisbury, F. B.


    Although the Cholodny-Went model of auxin redistribution has been used to explain the transduction phase of gravitropism for over 60 years, problems are apparent, especially with dicot stems. An alternative to an auxin gradient is a physiological gradient in which lower tissues of a horizontal stem become more sensitive than upper tissues to auxin already present. Changes in tissue sensitivity to auxin were tested by immersing marked Glycine max Merrill (soybean) hypocotyl sections in buffered auxin solutions (0, 10(-8) to 10(-2) molar indoleacetic acid) and observing bending and growth of upper and lower surfaces. The two surfaces of horizontal hypocotyl sections responded differently to the same applied auxin stimulus; hypocotyls bent up (lower half grew more) in buffer alone or in low auxin levels, but bent down (upper half grew more) in high auxin. Dose-response curves were evaluated with Michaelis-Menten kinetics, with auxin-receptor binding analogous to enzyme-substrate binding. Vmax for the lower half was usually greater than that for the upper half, which could indicate more binding sites in the lower half. Km of the upper half was always greater than that of the lower half (unmeasurably low), which could indicate that upper-half binding sites had a much lower affinity for auxin than lower-half sites. Dose-response curves were also obtained for sections scrubbed' (cuticle abraded) on top or bottom before immersion in auxin, and gravitropic memory' experiments of L. Brauner and A. Hagar (1958 Planta 51: 115-147) were duplicated. [1-14C]Indoleacetic acid penetration was equal into the two halves, and endogenous plus exogenously supplied (not radiolabeled) free auxin in the two halves (by gas chromatography-selected ion monitoring-mass spectrometry) was also equal. Thus, differential growth occurred without free auxin redistribution, contrary to Cholodny-Went but in agreement with a sensitivity model.

  15. Auxinic herbicides, mechanisms of action, and weed resistance: A look into recent plant science advances

    Directory of Open Access Journals (Sweden)

    Pedro Jacob Christoffoleti


    Full Text Available Auxin governs dynamic cellular processes involved at several stages of plant growth and development. In this review, we discuss the mechanisms employed by auxin in light of recent scientific advances, with a focus on synthetic auxins as herbicides and synthetic auxin resistance mechanisms. Two auxin receptors were reported. The plasma membrane receptor ABP1 (Auxin Binding Protein 1 alters the structure and arrangement of actin filaments and microtubules, leading to plant epinasty and reducing peroxisomes and mitochondria mobility in the cell environment. The second auxin receptor is the gene transcription pathway regulated by the SCFTir/AFB ubiquitination complex, which destroys transcription repressor proteins that interrupt Auxin Response Factor (ARF activation. As a result mRNA related with Abscisic Acid (ABA and ethylene are transcribed, producing high quantities of theses hormones. Their associated action leads to high production of Reactive Oxygen Species (ROS, leading to tissue and plant death. Recently, another ubiquitination pathway which is described as a new auxin signaling route is the F-box protein S-Phase Kinase-Associated Protein 2A (SKP2A. It is active in cell division regulation and there is evidence that auxin herbicides can deregulate the SKP2A pathway, which leads to severe defects in plant development. In this discussion, we propose that SFCSKP2A auxin binding site alteration could be a new auxinic herbicide resistance mechanism, a concept which may contribute to the current progress in plant biology in its quest to clarify the many questions that still surround auxin herbicide mechanisms of action and the mechanisms of weed resistance.

  16. Transcription factor WRKY46 modulates the development of Arabidopsis lateral roots in osmotic/salt stress conditions via regulation of ABA signaling and auxin homeostasis. (United States)

    Ding, Zhong Jie; Yan, Jing Ying; Li, Chun Xiao; Li, Gui Xin; Wu, Yun Rong; Zheng, Shao Jian


    The development of lateral roots (LR) is known to be severely inhibited by salt or osmotic stress. However, the molecular mechanisms underlying LR development in osmotic/salt stress conditions are poorly understood. Here we show that the gene encoding the WRKY transcription factor WRKY46 (WRKY46) is expressed throughout lateral root primordia (LRP) during early LR development and that expression is subsequently restricted to the stele of the mature LR. In osmotic/salt stress conditions, lack of WRKY46 (in loss-of-function wrky46 mutants) significantly reduces, while overexpression of WRKY46 enhances, LR development. We also show that exogenous auxin largely restores LR development in wrky46 mutants, and that the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) inhibits LR development in both wild-type (WT; Col-0) and in a line overexpressing WRKY46 (OV46). Subsequent analysis of abscisic acid (ABA)-related mutants indicated that WRKY46 expression is down-regulated by ABA signaling, and up-regulated by an ABA-independent signal induced by osmotic/salt stress. Next, we show that expression of the DR5:GUS auxin response reporter is reduced in roots of wrky46 mutants, and that both wrky46 mutants and OV46 display altered root levels of free indole-3-acetic acid (IAA) and IAA conjugates. Subsequent RT-qPCR and ChIP-qPCR experiments indicated that WRKY46 directly regulates the expression of ABI4 and of genes regulating auxin conjugation. Finally, analysis of wrky46 abi4 double mutant plants confirms that ABI4 acts downstream of WRKY46. In summary, our results demonstrate that WRKY46 contributes to the feedforward inhibition of osmotic/salt stress-dependent LR inhibition via regulation of ABA signaling and auxin homeostasis.

  17. An Integrative Analysis of the Effects of Auxin on Jasmonic Acid Biosynthesis in Arabidopsis thaliana

    Institute of Scientific and Technical Information of China (English)

    Jun Liu; Xiu-Jie Wang


    Auxin and jasmonic acid (JA) are two plant phytohormones that both participate in the regulation of many developmental processes. Jasmonic acid also plays important roles in plant stress response reactions.Although extensive investigations have been undertaken to study the biological functions of auxin and JA,little attention has been paid to the cross-talk between their regulated pathways. In the few available reports examining the effects of auxin on the expression of JA or JA-responsive genes, both synergetic and antagonistic results have been found. To further investigate the relationship between auxin and JA, we adopted an integrative method that combines microarray expression data with pathway information to study the behavior of the JA biosynthesis pathway under auxin treatment. Our results showed an overall downregulation of genes involved in JA biosynthesis, providing the first report of a relationship between auxin and the JA synthesis pathway in Arabidopsis seedlings.

  18. ARF-Aux/IAA interactions through domain III/IV are not strictly required for auxin-responsive gene expression



    Auxin response factors (ARFs), together with auxin/indole acetic acid proteins (Aux/IAAs), are transcription factors that play key roles in regulating auxin-responsive transcription in plants. Current models for auxin signaling predict that auxin response is dependent on ARF-Aux/IAA interactions mediated by the related protein-protein interaction domain (i.e., referred to as the CTD) found in the ARF and Aux/IAA C-terminal regions. When auxin concentrations in a cell are low, ARF activators r...

  19. Studies on water transport through the sweet cherry fruit surface. 10. Evidence for polar pathways across the exocarp. (United States)

    Weichert, Holger; Knoche, Moritz


    Water uptake through the fruit surface is considered as an important factor in cracking of sweet cherry (Prunus avium L.) fruit. Uptake may occur by diffusion and/or viscous flow along a polar pathway. To establish the mechanism of water uptake, the effects of viscosity and molecular weight of selected osmotica on water uptake into detached sweet cherry fruit were investigated. In addition we investigated the effect of temperature on penetration of 2-(1-naphthyl)[1-(14)C]acetic acid ([(14)C]NAA; pK(a) = 4.2) as a molecular probe in the non-dissociated (pH 2.2) and dissociated (pH 6.2) forms. Rates of water uptake were linearly related to the inverse viscosity of gum arabic solutions (range of concentrations and dynamic viscosities 10-300 g L(-1) and 1.3 x 10(-3) to 115.9 x 10(-3) Pa s, respectively). When fruit was incubated in solutions of osmotica of differing molecular weight that were isotonic to the fruit's water potential, water uptake depended on the molecular weight of the osmoticum [range 58-6000 for NaCl to poly(ethylene glycol) 6000 (PEG 6000)]. There was no uptake from PEG 6000 solutions, but rates of water uptake increased as the molecular weight of the osmotica decreased. Apparent water potentials of sweet cherry fruit, determined by incubating fruit in concentration series of selected osmotica, increased as the molecular weight of the osmotica increased up to 1500 and remained constant between 1500 and 6000. Reflection coefficients (sigma) estimated from this relationship were closely related to hydrodynamic radii (r) of the osmotica [sigma = 1.0(+/-0.0) - [10.9(+/-0.9) x 10(-11)][r(-1) (m(-1))], R(2) = 0.97, P < 0.0001]. The permeability of the sweet cherry fruit exocarp to NAA (pK(a) = 4.2) and temperature dependence of NAA permeability (P(d)) as indexed by the energy of activation (E(a), temperature range 5-35 degrees C) were significantly higher for the non-dissociated NAA (pH 2.2, P(d) = 10.2(+/-0.8) x 10(-8) m s(-1), E(a) = 67.0 +/- 1.7 kJ mol

  20. How auxin and cytokinin phytohormones modulate root microbe interactions

    Directory of Open Access Journals (Sweden)

    Stéphane Boivin


    Full Text Available A large range of microorganisms can associate with plants, resulting in neutral, friendly or hostile interactions. The ability of plants to recognize compatible and incompatible microorganisms and to limit or promote their colonization is therefore crucial for their survival. Elaborated communication networks determine the degree of association between the host plant and the invading microorganism. Central to these regulations of plant microbe interactions, phytohormones modulate microorganism plant associations and coordinate cellular and metabolic responses associated to the progression of microorganisms across different plant tissues. We review here hormonal regulations, focusing on auxin and cytokinin phytohormones, involved in the interactions between plant roots and soil microorganisms, including bacteria and fungi associations, either beneficial (symbiotic or detrimental (pathogenic. The aim is to highlight similarities and differences in cytokinin/auxin functions amongst various compatible versus incompatible associations.

  1. Voltage transients elicited by sudden step-up of auxin (United States)

    Pickard, B. G.


    It is hypothesized (i) that the molecular mechanism for the reception of friction and flexure and the mechanism by which auxin enhances ethylene production have in common a release of free calcium into the cytosol, (ii) that elevated cytosolic calcium initiates vesicle exocytosis, and (iii) that the vesicles release a factor or set of factors which depolarizes the plasmalemma and promotes ethylene synthesis. One consequence of such exocytosis should be small, extracellularly observable voltage transients. Transients, ranging in size up to 600 microvolts and possessing risetimes (10-90%) of approximately 200 ms, are known to be elicited in etiolated stems of Pisum sativum L. by friction and are here shown to be elicited by sudden increase of auxin concentration and also by a Ca2+ ionophore.

  2. Lateral root development in Arabidopsis: fifty shades of auxin. (United States)

    Lavenus, Julien; Goh, Tatsuaki; Roberts, Ianto; Guyomarc'h, Soazig; Lucas, Mikaël; De Smet, Ive; Fukaki, Hidehiro; Beeckman, Tom; Bennett, Malcolm; Laplaze, Laurent


    The developmental plasticity of the root system represents a key adaptive trait enabling plants to cope with abiotic stresses such as drought and is therefore important in the current context of global changes. Root branching through lateral root formation is an important component of the adaptability of the root system to its environment. Our understanding of the mechanisms controlling lateral root development has progressed tremendously in recent years through research in the model plant Arabidopsis thaliana (Arabidopsis). These studies have revealed that the phytohormone auxin acts as a common integrator to many endogenous and environmental signals regulating lateral root formation. Here, we review what has been learnt about the myriad roles of auxin during lateral root formation in Arabidopsis.

  3. The diageotropica gene differentially affects auxin and cytokinin responses throughout development in tomato. (United States)

    Coenen, C; Lomax, T L


    The interactions between the plant hormones auxin and cytokinin throughout plant development are complex, and genetic investigations of the interdependency of auxin and cytokinin signaling have been limited. We have characterized the cytokinin sensitivity of the auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) in a range of auxin- and cytokinin-regulated responses. Intact, etiolated dgt seedlings showed cross-resistance to cytokinin with respect to root elongation, but cytokinin effects on hypocotyl growth and ethylene synthesis in these seedlings were not impaired by the dgt mutation. Seven-week-old, green wild-type and dgt plants were also equally sensitive to cytokinin with respect to shoot growth and hypocotyl and internode elongation. The effects of cytokinin and the dgt mutation on these processes appeared additive. In tissue culture organ regeneration from dgt hypocotyl explants showed reduced sensitivity to auxin but normal sensitivity to cytokinin, and the effects of cytokinin and the mutation were again additive. However, although callus induction from dgt hypocotyl explants required auxin and cytokinin, dgt calli did not show the typical concentration-dependent stimulation of growth by either auxin or cytokinin observed in wild-type cells. Cross-resistance of the dgt mutant to cytokinin thus was found to be limited to a small subset of auxin- and cytokinin-regulated growth processes affected by the dgt mutation, indicating that auxin and cytokinin regulate plant growth through both shared and separate signaling pathways.

  4. Functional characterization of PaLAX1, a putative auxin permease, in heterologous plant systems. (United States)

    Hoyerová, Klára; Perry, Lucie; Hand, Paul; Lanková, Martina; Kocábek, Tomás; May, Sean; Kottová, Jana; Paces, Jan; Napier, Richard; Zazímalová, Eva


    We have isolated the cDNA of the gene PaLAX1 from a wild cherry tree (Prunus avium). The gene and its product are highly similar in sequences to both the cDNAs and the corresponding protein products of AUX/LAX-type genes, coding for putative auxin influx carriers. We have prepared and characterized transformed Nicotiana tabacum and Arabidopsis thaliana plants carrying the gene PaLAX1. We have proved that constitutive overexpression of PaLAX1 is accompanied by changes in the content and distribution of free indole-3-acetic acid, the major endogenous auxin. The increase in free indole-3-acetic acid content in transgenic plants resulted in various phenotype changes, typical for the auxin-overproducing plants. The uptake of synthetic auxin, 2,4-dichlorophenoxyacetic acid, was 3 times higher in transgenic lines compared to the wild-type lines and the treatment with the auxin uptake inhibitor 1-naphthoxyacetic acid reverted the changes caused by the expression of PaLAX1. Moreover, the agravitropic response could be restored by expression of PaLAX1 in the mutant aux1 plants, which are deficient in auxin influx carrier activity. Based on our data, we have concluded that the product of the gene PaLAX1 promotes the uptake of auxin into cells, and, as a putative auxin influx carrier, it affects the content and distribution of free endogenous auxin in transgenic plants.

  5. The role of SEUSS in auxin response and floral organ patterning. (United States)

    Pfluger, Jennifer; Zambryski, Patricia


    Genetic and physiological analyses implicate auxin flux in patterning, initiation and growth of floral organs. Within the Arabidopsis flower, the ETTIN/ARF3 transcription factor responds to auxin to effect perianth organ number and reproductive organ differentiation. This work describes a modifier of ettin that causes filamentous, mispositioned outer whorl organs and reduced numbers of malformed stamens in the double mutant. The modifier was discovered to be a new allele of the seuss (seu) mutant. SEU encodes a novel protein that is predicted to transcriptionally co-repress the AGAMOUS floral organ identity gene. The effects of seu on ett are shown to be independent of the SEU-AG pathway. Furthermore, morphological, physiological and genetic evidence implicate SEU in auxin-regulated growth and development. seu has a pleiotropic phenotype that includes reductions in several classic auxin responses such as apical dominance, lateral root initiation, sensitivity to exogenous auxin and activation of the DR5 auxin response reporter. seu displays a synergistic interaction with the auxin response mutant pinoid, producing flowers with few outer whorl organs. Collectively, these data suggest that SEU is a novel factor affecting auxin response. A model is proposed in which SEU functions jointly with ETT in auxin response to promote floral organ patterning and growth.

  6. Investigating a Potential Auxin-Related Mode of Hormetic/Inhibitory Action of the Phytotoxin Parthenin. (United States)

    Belz, Regina G


    Parthenin is a metabolite of Parthenium hysterophorus and is believed to contribute to the weed's invasiveness via allelopathy. Despite the potential of parthenin to suppress competitors, low doses stimulate plant growth. This biphasic action was hypothesized to be auxin-like and, therefore, an auxin-related mode of parthenin action was investigated using two approaches: joint action experiments with Lactuca sativa, and dose-response experiments with auxin/antiauxin-resistant Arabidopsis thaliana genotypes. The joint action approach comprised binary mixtures of subinhibitory doses of the auxin 3-indoleacetic acid (IAA) mixed with parthenin or one of three reference compounds [indole-3-butyric acid (IBA), 2,3,5-triiodobenzoic acid (TIBA), 2-(p-chlorophenoxy)-2-methylpropionic acid (PCIB)]. The reference compounds significantly interacted with IAA at all doses, but parthenin interacted only at low doses indicating that parthenin hormesis may be auxin-related, in contrast to its inhibitory action. The genetic approach investigated the response of four auxin/antiauxin-resistant mutants and a wildtype to parthenin or two reference compounds (IAA, PCIB). The responses of mutant plants to the reference compounds confirmed previous reports, but differed from the responses observed for parthenin. Parthenin stimulated and inhibited all mutants independent of resistance. This provided no indication for an auxin-related action of parthenin. Therefore, the hypothesis of an auxin-related inhibitory action of parthenin was rejected in two independent experimental approaches, while the hypothesis of an auxin-related stimulatory effect could not be rejected.

  7. In vitro auxin binding to cellular membranes of cucumber fruits. (United States)

    Narayanan, K R; Mudge, K W; Poovaiah, B W


    Specific binding of 1-naphthaleneacetic acid (NAA) to crude membrane preparations from cucumber (Cucumis sativus L.) was demonstrated. This in vitro binding had a pH optimum of 3.75 and an equilibrium dissociation constant of 10 to 20 micromolar with 1250 picomoles binding sites per gram fresh weight. The NAA-binding sites were pronase sensitive. The supernatant from the fruit partially inhibited the in vitro NAA binding to fruit membranes. NAA, 2-naphthoxyacetic acid, 3-indoleacetic acid, 2-4-dichlorophenoxyacetic acid, and 2,3,5-triiodobenzoic acid, which are reported to be very good inducers of parthenocarpy in cucumber, showed a high degree of specific binding to cucumber fruit membranes. In comparison, 2-naphthaleneacetic acid and indolepropionic acid, which are reported to be very weak auxins in corn coleoptile, pea stem, and strawberry fruit growth bioassays, did not bind efficiently to cucumber fruit membranes. In vitro binding studies with fruit membranes suggest that auxin stimulated fruit growth may be mediated by membrane-associated, auxin-binding protein(s).

  8. Concentration polarization effects on the macromolecular transport in the presence of non-uniform magnetic field: A numerical study using a lumen-wall model

    Energy Technology Data Exchange (ETDEWEB)

    Mohammadpourfard, M., E-mail: [Department of Mechanical Engineering, Azarbaijan Shahid Madani University, Tabriz 53751-71379 (Iran, Islamic Republic of); Aminfar, H., E-mail: [Faculty of Mechanical Engineering, University of Tabriz, Tabriz (Iran, Islamic Republic of); Khajeh, K., E-mail: [Faculty of Mechanical Engineering, University of Tabriz, Tabriz (Iran, Islamic Republic of)


    In this paper, the concentration polarization phenomena in a two dimensional tube under steady state conditions containing ferrofluid (blood and 4 vol% Fe{sub 3}O{sub 4}) is reported in the presence of non-uniform magnetic field. Lumen-wall model has been used for solving the mass transport equation. Hemodynamics parameters such as flow rate, viscosity, wall shear stress (WSS) and the macromolecules surface concentration which accumulate on the blood vessel wall, influenced the formation and progression of atherosclerosis disease. Effective parameters on the low density lipoprotein (LDL) surface concentration (LSC) such as: the wall filtration velocity, inlet Reynolds number and WSS under applied non-uniform magnetic field have been examined. Numerical solution of governing equations of the flow field have been obtained by using the single-phase model and the control volume technique. Magnetic field is generated by an electric current going through a thin and straight wire oriented perpendicular to the tube. Results show WSS in the vicinity of magnetic field source increased and LSC decreased along the wall. - Highlights: • In this paper the concentration polarization phenomena of blood flow is reported in the presence of non-uniform magnetic field. • In presence of non-uniform magnetic field LSC will decrease along the wall due to the increasing the velocity gradients near the magnetic source. • When non-uniform magnetic field intensity increases, LSC along the wall becomes lower. • Non-uniform magnetic field can affects the flow more in low Reynolds numbers.

  9. Relative importance of horizontal and vertical transports to the formation of ionospheric storm-enhanced density and polar tongue of ionization (United States)

    Liu, Jing; Wang, Wenbin; Burns, Alan; Solomon, Stanley C.; Zhang, Shunrong; Zhang, Yongliang; Huang, Chaosong


    There are still uncertainties regarding the formation mechanisms for storm-enhanced density (SED) in the high and subauroral latitude ionosphere. In this work, we deploy the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) and GPS total electron content (TEC) observations to identify the principle mechanisms for SED and the tongue of ionization (TOI) through term-by-term analysis of the ion continuity equation and also identify the advantages and deficiencies of the TIEGCM in capturing high-latitude and subauroral latitude ionospheric fine structures for the two geomagnetic storm events occurring on 17 March 2013 and 2015. Our results show that in the topside ionosphere, upward E × B ion drifts are most important in SED formation and are offset by antisunward neutral winds and downward ambipolar diffusion effects. In the bottomside F region ionosphere, neutral winds play a major role in generating SEDs. SED signature in TEC is mainly caused by upward E × B ion drifts that lift the ionosphere to higher altitudes where chemical recombination is slower. Horizontal E × B ion drifts play an essential role in transporting plasma from the dayside convection throat region to the polar cap to form TOIs. Inconsistencies between model results and GPS TEC data were found: (1) GPS relative TEC difference between storm time and quiet time has "holes" in the dayside ion convection entrance region, which do not appear in the model results. (2) The model tends to overestimate electron density enhancements in the polar region. Possible causes for these inconsistencies are discussed in this article.

  10. Physiological asymmetry in etiolated pea epicotyls: relation to patterns of auxin distribution and phototropic behavior (United States)

    Kuhn, H.; Galston, A. W.


    Etiolated pea seedlings require transformation of Pr phytochrome to Pfr before they display optimal phototropic response to unilateral blue light. This study investigates the possible role of auxin transport in explaining these phenomena. Labeled [2-14C]IAA applied to the intact terminal buds of dark-grown and red light-treated pea seedlings was measured 210 min later on the shaded and illuminated sides of the epicotyl as a function of direction and duration of irradiation with blue light. Totally darkened epicotyls show an asymmetry in distribution of radioactivity in the upper growth zone of the epicotyl, in favor of the side under the concave part of the apical hook. Red light, which greatly potentiates curvature toward subsequent unilateral blue light, lowers this asymmetry. Blue light directed to the epicotyl of red-pretreated plants in a plane parallel to the hook and from the side bearing the convex portion of the hook induces positive phototropic curvature as well as a surplus of radioactivity on the illuminated side of the upper epicotyl and on the shaded side of the lower growth zone of the epicotyl. Light directed to the side bearing the concave part of the hook also causes an accumulation of counts in the upper part of the lighted side but produces neither curvature of the epicotyl nor accumulation of counts in the lower shaded side. Because of this built-in physiological asymmetry in the growth zone just below the apical hook, it is difficult to explain the effects of red and blue light on curvature in terms of patterns of auxin distribution alone.

  11. A new multi-gas constrained model of trace gas non-homogeneous transport in firn: evaluation and behaviour at eleven polar sites

    Directory of Open Access Journals (Sweden)

    E. Witrant


    Full Text Available Insoluble trace gases are trapped in polar ice at the firn-ice transition, at approximately 50 to 100 m below the surface, depending primarily on the site temperature and snow accumulation. Models of trace gas transport in polar firn are used to relate firn air and ice core records of trace gases to their atmospheric history. We propose a new model based on the following contributions. First, the firn air transport model is revised in a poromechanics framework with emphasis on the non-homogeneous properties and the treatment of gravitational settling. We then derive a nonlinear least square multi-gas optimisation scheme to calculate the effective firn diffusivity (automatic diffusivity tuning. The improvements gained by the multi-gas approach are investigated (up to ten gases for a single site are included in the optimisation process. We apply the model to four Arctic (Devon Island, NEEM, North GRIP, Summit and seven Antarctic (DE08, Berkner Island, Siple Dome, Dronning Maud Land, South Pole, Dome C, Vostok sites and calculate their respective depth-dependent diffusivity profiles. Among these different sites, a relationship is inferred between the snow accumulation rate and an increasing thickness of the lock-in zone defined from the isotopic composition of molecular nitrogen in firn air (denoted δ15N. It is associated with a reduced diffusivity value and an increased ratio of advective to diffusive flux in deep firn, which is particularly important at high accumulation rate sites. This has implications for the understanding of δ15N of N2 records in ice cores, in relation with past variations of the snow accumulation rate. As the snow accumulation rate is clearly a primary control on the thickness of the lock-in zone, our new approach that allows for the estimation of the lock-in zone width as a function of accumulation may lead to a better constraint on the age difference between the ice and entrapped gases.

  12. Metals and Rare Earth Elements in polar aerosol as specific markers of natural and anthropogenic aerosol sources areas and atmospheric transport processes (United States)

    Giardi, Fabio; Becagli, Silvia; Caiazzo, Laura; Cappelletti, David; Grotti, Marco; Malandrino, Mery; Salzano, Roberto; Severi, Mirko; Traversi, Rita; Udisti, Roberto


    Metals and Rare Earth Elements (REEs) in the aerosol have conservative properties from the formation to the deposition and can be useful to identify and quantify their natural and anthropic sources and to study the atmospheric transport processes. In spite of their importance relatively little is known about metals and especially REEs in the Artic atmosphere due to their low concentration in such environment. The present work reports the first attempt to determine and interpret the behaviour of metals and REEs in polar aerosol at high temporal resolution. Daily PM10 samples of arctic atmospheric particulate were collected on Teflon filters, during six spring-summer campaigns, since 2010, in the laboratory of Gruvebadet in Ny Ålesund (78°56' N, 11°56' E, Svalbard Islands, Norway). Chemical analyses were carried out through Inductively Coupled Plasma Mass Spectrometer provided with a desolvation nebulizer inlet system, allowing to reduce isobaric interferences and thus to quantify trace and ultra-trace metals in very low concentration in the Arctic aerosol samples. The results are useful in order to study sources areas, transport processes and depositional effects of natural and anthropic atmospheric particulate reaching the Arctic from southern industrialized areas; moreover, the observed seasonal trends give information about the different impact of natural and anthropic emissions driven by phenomena such as the Arctic Haze and the melting of the snow. In particular Rare Earth Elements (often in the ppt range) can be considered as soil's fingerprints of the particulate source areas and their determination, together with air-mass backtrajectory analysis, allow to identify dust source areas for the arctic mineral aerosol.

  13. Theoretical Analysis of Thermal Transport in Graphene Supported on Hexagonal Boron Nitride: The Importance of Strong Adhesion Due to π -Bond Polarization (United States)

    Pak, Alexander J.; Hwang, Gyeong S.


    One important attribute of graphene that makes it attractive for high-performance electronics is its inherently large thermal conductivity (κ ) for the purposes of thermal management. Using a combined density-functional theory and classical molecular-dynamics approach, we predict that the κ of graphene supported on hexagonal boron nitride (h -BN) can be as large as 90% of the κ of suspended graphene, in contrast to the significant suppression of κ (more than 70% reduction) on amorphous silica. Interestingly, we find that this enhanced thermal transport is largely attributed to increased lifetimes of the in-plane acoustic phonon modes, which is a notable contrast from the dominant contribution of out-of-plane acoustic modes in suspended graphene. This behavior is possible due to the charge polarization throughout graphene that induces strong interlayer adhesion between graphene and h -BN. These findings highlight the potential benefit of layered dielectric substrates such as h -BN for graphene-based thermal management, in addition to their electronic advantages. Furthermore, our study brings attention to the importance of understanding the interlayer interactions of graphene with layered dielectric materials which may offer an alternative technological platform for substrates in electronics.

  14. Auxin-induced growth of Avena coleoptiles involves two mechanisms with different pH optima (United States)

    Cleland, R. E.


    Although rapid auxin-induced growth of coleoptile sections can persist for at least 18 hours, acid-induced growth lasts for a much shorter period of time. Three theories have been proposed to explain this difference in persistence. To distinguish between these theories, the pH dependence for auxin-induced growth of oat (Avena sativa L.) coleoptiles has been determined early and late in the elongation process. Coleoptile sections from which the outer epidermis was removed to facilitate buffer entry were incubated, with or without 10 micromolar indoleacetic acid, in 20 millimolar buffers at pH 4.5 to 7.0 to maintain a fixed wall pH. During the first 1 to 2 hours after addition of auxin, elongation occurs by acid-induced extension (i.e. the pH optimum is <5 and the elongation varies inversely with the solution pH). Auxin causes no additional elongation because the buffers prevent further changes in wall pH. After 60 to 90 minutes, a second mechanism of auxin-induced growth, whose pH optimum is 5.5 to 6.0, predominates. It is proposed that rapid growth responses to changes in auxin concentration are mediated by auxin-induced changes in wall pH, whereas the prolonged, steady-state growth rate is controlled by a second, auxin-mediated process whose pH optimum is less acidic.

  15. A novel sensor to map auxin response and distribution at high spatio-temporal resolution. (United States)

    Brunoud, Géraldine; Wells, Darren M; Oliva, Marina; Larrieu, Antoine; Mirabet, Vincent; Burrow, Amy H; Beeckman, Tom; Kepinski, Stefan; Traas, Jan; Bennett, Malcolm J; Vernoux, Teva


    Auxin is a key plant morphogenetic signal but tools to analyse dynamically its distribution and signalling during development are still limited. Auxin perception directly triggers the degradation of Aux/IAA repressor proteins. Here we describe a novel Aux/IAA-based auxin signalling sensor termed DII-VENUS that was engineered in the model plant Arabidopsis thaliana. The VENUS fast maturing form of yellow fluorescent protein was fused in-frame to the Aux/IAA auxin-interaction domain (termed domain II; DII) and expressed under a constitutive promoter. We initially show that DII-VENUS abundance is dependent on auxin, its TIR1/AFBs co-receptors and proteasome activities. Next, we demonstrate that DII-VENUS provides a map of relative auxin distribution at cellular resolution in different tissues. DII-VENUS is also rapidly degraded in response to auxin and we used it to visualize dynamic changes in cellular auxin distribution successfully during two developmental responses, the root gravitropic response and lateral organ production at the shoot apex. Our results illustrate the value of developing response input sensors such as DII-VENUS to provide high-resolution spatio-temporal information about hormone distribution and response during plant growth and development.

  16. A noncanonical auxin-sensing mechanism is required for organ morphogenesis in arabidopsis

    NARCIS (Netherlands)

    Simonini, Sara; Deb, Joyita; Moubayidin, Laila; Stephenson, Pauline; Valluru, Manoj; Freire-Rios, Alejandra; Sorefan, Karim; Weijers, Dolf; Friml, Jiří; Østergaard, Lars


    Tissue patterning in multicellular organisms is the output of precise spatio–temporal regulation of gene expression coupled with changes in hormone dynamics. In plants, the hormone auxin regulates growth and development at every stage of a plant’s life cycle. Auxin signaling occurs through bindin

  17. Auxin-induced growth of Avena coleoptiles involves two mechanisms with different pH optima (United States)

    Cleland, R. E.


    Although rapid auxin-induced growth of coleoptile sections can persist for at least 18 hours, acid-induced growth lasts for a much shorter period of time. Three theories have been proposed to explain this difference in persistence. To distinguish between these theories, the pH dependence for auxin-induced growth of oat (Avena sativa L.) coleoptiles has been determined early and late in the elongation process. Coleoptile sections from which the outer epidermis was removed to facilitate buffer entry were incubated, with or without 10 micromolar indoleacetic acid, in 20 millimolar buffers at pH 4.5 to 7.0 to maintain a fixed wall pH. During the first 1 to 2 hours after addition of auxin, elongation occurs by acid-induced extension (i.e. the pH optimum is Auxin causes no additional elongation because the buffers prevent further changes in wall pH. After 60 to 90 minutes, a second mechanism of auxin-induced growth, whose pH optimum is 5.5 to 6.0, predominates. It is proposed that rapid growth responses to changes in auxin concentration are mediated by auxin-induced changes in wall pH, whereas the prolonged, steady-state growth rate is controlled by a second, auxin-mediated process whose pH optimum is less acidic.

  18. Maximizing adhesion of auxin solutions to stem cuttings using sodium cellulose glycolate (United States)

    Auxin solutions prepared with sodium cellulose glycolate (SCG; a thickening agent, also known as sodium carboxymethylcellulose) and applied to stem cuttings using a basal quick-dip extend the duration of exposure of cuttings to the auxin and have previously been shown to increase root number and/or ...

  19. Auxins and gibberellins in embryonic shoots of Scots pine in relation to flower sex differentiation



    Flower sex differentiation in Scots pine is correlated with endogenous balance of auxins to gibberellins. Male flower primordia initiation is connected with high amounts of gibberellins whereas the initiation of female ones is associated with a high level of auxins and a low content of gibberellins.

  20. Auxins and gibberellins in embryonic shoots of Scots pine in relation to flower sex differentiation

    Directory of Open Access Journals (Sweden)

    H. Kulikowska


    Full Text Available Flower sex differentiation in Scots pine is correlated with endogenous balance of auxins to gibberellins. Male flower primordia initiation is connected with high amounts of gibberellins whereas the initiation of female ones is associated with a high level of auxins and a low content of gibberellins.

  1. Arabidopsis NAC1 transduces auxin signal downstream of TIR1 to promote lateral root development. (United States)

    Xie, Q; Frugis, G; Colgan, D; Chua, N H


    Auxin plays a key role in lateral root formation, but the signaling pathway for this process is poorly understood. We show here that NAC1, a new member of the NAC family, is induced by auxin and mediates auxin signaling to promote lateral root development. NAC1 is a transcription activator consisting of an N-terminal conserved NAC-domain that binds to DNA and a C-terminal activation domain. This factor activates the expression of two downstream auxin-responsive genes, DBP and AIR3. Transgenic plants expressing sense or antisense NAC1 cDNA show an increase or reduction of lateral roots, respectively. Finally, TIR1-induced lateral root development is blocked by expression of antisense NAC1 cDNA, and NAC1 overexpression can restore lateral root formation in the auxin-response mutant tir1, indicating that NAC1 acts downstream of TIR1.

  2. Isolation of transcription factors binding auxin response elements using a yeast one-hybrid system

    Institute of Scientific and Technical Information of China (English)

    齐眉; 黄美娟; 陈凡


    Plant hormones play an important role during higher plant embryogenesis. Auxin is central to the development of vascular tissues, formation of lateral and adventitious roots, control of apical dominance, and tropic responses. Auxin response element (AuxRE), present in the promoters of many auxin-induced genes, can confer auxin responsiveness. Using carrot somatic embryo under specific developmental phase, a cDNA expression library was constructed. Several plasmids were recombined containing the tetramer of AuxRE as a bait. After screening by a yeast one-hy- brid system, one positive clone was confirmed and characterized. Electrophoretic mobility shift assay showed that AxRF1 protein expressed in yeast cell could bind AuxRE in vitro. It suggests that AxRF1 participates in regulation of the expression of auxin responsive gene during carrot somatic embryogenesis.

  3. Expression characteristics of GFP driven by NAC1 promoter and its responses to auxin and gibberellin

    Institute of Scientific and Technical Information of China (English)

    WANG Youhua; DUAN Liusheng; LU Mengzhu; LI Zhaohu; WANG Minjie; ZHAI Zhixi


    A 1050 bp fragment upstream transcription start site of a transcription factor gene NAC1 in Arabidopsis thaliana was amplified and cloned into plasmid pRD420 to construct a green fluorescent protein(GFP) fusion system under the control of NAC1 promoter. Plasmids were introduced into tobacco by Agrobacterium mediated method to regenerate plants with NAC1-GFP gene, and expression pattern of NAC1-GFP and its responses to auxin and gibberellin (GA) were observed. GFP was found to accumulate specifically in root, and was detected after treatment of auxin, N-1-Naphthylphthalamic acid (NPA, an auxin antagonist) or GA3. It was indicated that the expression of GFP driven by NAC1 promoter was induced not only by auxin but also by GAs, suggesting that NAC1 mediated both the auxin signaling and the GAs signaling involved in lateral roots development.

  4. Arabidopsis AIP1-2 restricted by WER-mediated patterning modulates planar polarity. (United States)

    Kiefer, Christian S; Claes, Andrea R; Nzayisenga, Jean-Claude; Pietra, Stefano; Stanislas, Thomas; Hüser, Anke; Ikeda, Yoshihisa; Grebe, Markus


    The coordination of cell polarity within the plane of the tissue layer (planar polarity) is crucial for the development of diverse multicellular organisms. Small Rac/Rho-family GTPases and the actin cytoskeleton contribute to planar polarity formation at sites of polarity establishment in animals and plants. Yet, upstream pathways coordinating planar polarity differ strikingly between kingdoms. In the root of Arabidopsis thaliana, a concentration gradient of the phytohormone auxin coordinates polar recruitment of Rho-of-plant (ROP) to sites of polar epidermal hair initiation. However, little is known about cytoskeletal components and interactions that contribute to this planar polarity or about their relation to the patterning machinery. Here, we show that ACTIN7 (ACT7) represents a main actin isoform required for planar polarity of root hair positioning, interacting with the negative modulator ACTIN-INTERACTING PROTEIN1-2 (AIP1-2). ACT7, AIP1-2 and their genetic interaction are required for coordinated planar polarity of ROP downstream of ethylene signalling. Strikingly, AIP1-2 displays hair cell file-enriched expression, restricted by WEREWOLF (WER)-dependent patterning and modified by ethylene and auxin action. Hence, our findings reveal AIP1-2, expressed under control of the WER-dependent patterning machinery and the ethylene signalling pathway, as a modulator of actin-mediated planar polarity.

  5. UGT74D1 is a novel auxin glycosyltransferase from Arabidopsis thaliana.

    Directory of Open Access Journals (Sweden)

    Shang-Hui Jin

    Full Text Available Auxin is one type of phytohormones that plays important roles in nearly all aspects of plant growth and developmental processes. The glycosylation of auxins is considered to be an essential mechanism to control the level of active auxins. Thus, the identification of auxin glycosyltransferases is of great significance for further understanding the auxin regulation. In this study, we biochemically screened the group L of Arabidopsis thaliana glycosyltransferase superfamily for enzymatic activity toward auxins. UGT74D1 was identified to be a novel auxin glycosyltransferase. Through HPLC and LC-MS analysis of reaction products in vitro by testing eight substrates including auxins and other compounds, we found that UGT74D1 had a strong glucosylating activity toward indole-3-butyric acid [IBA], indole-3-propionic acid [IPA], indole-3-acetic acid [IAA] and naphthaleneacetic acid [NAA], catalyzing them to form corresponding glucose esters. Biochemical characterization showed that this enzyme had a maximum activity in HEPES buffer at pH 6.0 and 37°C. In addition, the enzymatic activity analysis of crude protein and the IBA metabolite analysis from transgenic Arabidopsis plants overexpressing UGT74D1 gene were also carried out. Experimental results indicated that over-production of the UGT74D1 in plants indeed led to increased level of the glucose conjugate of IBA. Moreover, UGT74D1 overexpression lines displayed curling leaf phenotype, suggesting a physiological role of UGT74D1 in affecting the activity of auxins. Our current data provide a new target gene for further genetic studies to understand the auxin regulation by glycosylation in plants.

  6. Mutation of Arabidopsis CATALASE2 results in hyponastic leaves by changes of auxin levels. (United States)

    Gao, Xiang; Yuan, Hong-Mei; Hu, Ye-Qin; Li, Jing; Lu, Ying-Tang


    Auxin and H2 O2 play vital roles in plant development and environmental responses; however, it is unclear whether and how H2 O2 modulates auxin levels. Here, we investigate this question using cat2-1 mutant, which exhibits reduced catalase activity and accumulates high levels of H2 O2 under photorespiratory conditions. At a light intensity of 150 μmol m(-2) s(-1) , the mutant exhibited up-curled leaves that have increased H2 O2 contents and decreased auxin levels. At low light intensities (30 μmol m(-2) s(-1)), the leaves of the mutant were normal, but exhibited reduced H2 O2 contents and elevated auxin levels. These findings suggest that H2 O2 modulates auxin levels. When auxin was directly applied to cat2-1 leaves, the up-curled leaves curled downwards. In addition, transformation of cat2-1 plants with pCAT2:iaaM, which increases auxin levels, rescued the hyponastic leaf phenotype. Using qRT-PCR, we demonstrated that the transcription of auxin synthesis-related genes and of genes that regulate leaf curvature is suppressed in cat2-1. Furthermore, application of glutathione rescued the up-curled leaves of cat2-1 and increased auxin levels, but did not change H2 O2 levels. Thus, the hyponastic leaves of cat2-1 reveal crosstalk between H2 O2 and auxin signalling that is mediated by changes in glutathione redox status.

  7. A new multi-gas constrained model of trace gas non-homogeneous transport in firn: evaluation and behavior at eleven polar sites

    Directory of Open Access Journals (Sweden)

    E. Witrant


    Full Text Available Insoluble trace gases are trapped in polar ice at the firn-ice transition, at approximately 50 to 100 m below the surface, depending primarily on the site temperature and snow accumulation. Due to the different time scales for snow accumulation versus diffusion of gases through the snowpack, age differences between gases and the ice in which they are "trapped" can be large; e.g. several thousand years in central Antarctica (a low snow accumulation area. Models of trace gas diffusion in polar firn are used to relate firn air and ice core records of trace gases to their atmospheric history. We propose a new diffusion model based on the following contributions. First, the airflow transport model is revised in a poromechanics framework with specific emphasis on the non-homogeneous properties (convective layer, depth-dependent diffusivity and lock-in zone and an almost-stagnant behavior described by Darcy's law (gravity effect. We then derive a non-linear least square multi-gas optimization scheme to calculate the effective firn diffusivity (automatic diffusivity tuning. The improvements associated with the additional constraints gained by the multi-gas approach are investigated (up to eleven gases for a single site are included in the optimization process. The model is applied to measured data from four Arctic (Devon Island, NEEM, North GRIP, Summit and seven Antarctic (DE08, Berkner Island, Siple Dome, Dronning Maud Land, South Pole, Dome C, Vostok sites and the depth-dependent diffusivity profiles are calculated. Among these different sites, a relationship between an increasing thickness of the lock-in zone defined from the isotopic composition of molecular nitrogen in firn air (denoted δ15N and the snow accumulation rate is obtained, in accordance with observations. It is associated with reduced diffusivity depth-gradients in deep firn, which decreases gas density depth-gradients, at high accumulation rate sites. This has implications

  8. Tricho- and atrichoblast cell files show distinct PIN2 auxin efflux carrier exploitations and are jointly required for defined auxin-dependent root organ growth. (United States)

    Löfke, Christian; Scheuring, David; Dünser, Kai; Schöller, Maria; Luschnig, Christian; Kleine-Vehn, Jürgen


    The phytohormone auxin is a vital growth regulator in plants. In the root epidermis auxin steers root organ growth. However, the mechanisms that allow adjacent tissues to integrate growth are largely unknown. Here, the focus is on neighbouring epidermal root tissues to assess the integration of auxin-related growth responses. The pharmacologic, genetic, and live-cell imaging approaches reveal that PIN2 auxin efflux carriers are differentially controlled in tricho- and atrichoblast cells. PIN2 proteins show lower abundance at the plasma membrane of trichoblast cells, despite showing higher rates of intracellular trafficking in these cells. The data suggest that PIN2 proteins display distinct cell-type-dependent trafficking rates to the lytic vacuole for degradation. Based on this insight, it is hypothesized that auxin-dependent processes are distinct in tricho- and atrichoblast cells. Moreover, genetic interference with epidermal patterning supports this assumption and suggests that tricho- and atrichoblasts have distinct importance for auxin-sensitive root growth and gravitropic responses.

  9. Wall to membrane linkers, stretch activated channels, and the detection of tension, voltage, temperature, auxin, and pH (United States)

    Pickard, B. G.


    Introduction. The higher plant is a heterogeneous, mechanically prestressed structure continually subject to shifting forces. When a cell grows in a plant at gravitropic equilibrium, it must create localized maxima of shear in walls of neighboring cells. Such mechanical stress and strain are likely detected in a variety of ways. However, tension-sensitive ion channels are of particular interest because it appears that they are elaborately evolved for sensory function. We hypothesize that 1) the patchy patterns of high shear are focused via wall-to-membrane linkers onto the plasma membrane, where 2) they are translated by mechanosensory cation channels into corresponding patterns of high cytosolic Ca2+, which 3) initiate local enhancement of wall expansion. Further, we hypothesize that the local promotion of enhancement is achieved at least in part by local intensification of auxin transport across the plasma membrane. By implication, when an organ is asymmetrically pressed, rubbed, or bent or when it is displaced in the gravitational field, the net asymmetry of shear stress occurring across the organ would lead to asymmetric redistribution of auxin and corrective asymmetric growth. We shall describe a representative mechanosensitive Ca(2+) -selective cation channel (MCaC) with susceptibilities to xenobiotics implicating it as a force transducer in thigmo- and gravitropism. Then, we shall consider whether a putative wall-to-membrane linker (WML) could be a key feature of the molecular architecture permitting the stress distributed in the wall system to be focused on the channels.

  10. Auxin Is Rapidly Induced by Herbivore Attack and Regulates a Subset of Systemic, Jasmonate-Dependent Defenses1[OPEN (United States)

    Machado, Ricardo A. R.; Robert, Christelle A. M.; Arce, Carla C. M.; Ferrieri, Abigail P.; Jimenez-Aleman, Guillermo H.


    Plant responses to herbivore attack are regulated by phytohormonal networks. To date, the role of the auxin indole-3-acetic acid (IAA) in this context is not well understood. We quantified and manipulated the spatiotemporal patterns of IAA accumulation in herbivore-attacked Nicotiana attenuata plants to unravel its role in the regulation of plant secondary metabolism. We found that IAA is strongly, rapidly, and specifically induced by herbivore attack. IAA is elicited by herbivore oral secretions and fatty acid conjugate elicitors and is accompanied by a rapid transcriptional increase of auxin biosynthetic YUCCA-like genes. IAA accumulation starts 30 to 60 s after local induction and peaks within 5 min after induction, thereby preceding the jasmonate (JA) burst. IAA accumulation does not require JA signaling and spreads rapidly from the wound site to systemic tissues. Complementation and transport inhibition experiments reveal that IAA is required for the herbivore-specific, JA-dependent accumulation of anthocyanins and phenolamides in the stems. In contrast, IAA does not affect the accumulation of nicotine or 7-hydroxygeranyllinalool diterpene glycosides in the same tissue. Taken together, our results uncover IAA as a rapid and specific signal that regulates a subset of systemic, JA-dependent secondary metabolites in herbivore-attacked plants. PMID:27485882

  11. Constitutive expression of pathogen-inducible OsWRKY31 enhances disease resistance and affects root growth and auxin response in transgenic rice plants

    Institute of Scientific and Technical Information of China (English)

    Juan Zhang; Youliang Peng; Zejian Guo


    WRKY transcription factors have many regulatory roles in response to biotic and abiotic stresses. In this study, we isolated a rice WRKY gene (OsWRKY31) that is induced by the rice blast fungus Magnaporthe grisea and auxin. This gene encodes a polypeptide of 211 amino-acid residues and belongs to a subgroup of the rice WRKY gene family that probably originated after the divergence of monocot and dicot plants. OsWRKY31 was found to be localized to the nucleus of onion epidermis cells to transiently express OsWRKY31-eGFP fusion protein. Analysis of 0sWRKY31 and its mutants fused with a Cal4 DNA-binding domain indicated that OsWRKY31 has transactivation activity in yeast. Overexpression of the OsWRKY31 gene was found to enhance resistance against infection with M. grisea, and the transgenic lines exhibited reduced lateral root formation and elongation compared with wild-type and RNAi plants. The lines with overexpression showed constitutive expression of many defense-related genes, such as PBZ1 and OsSci2, as well as early auxin-response genes, such as OsIAA4 and OsCrll genes. Furthermore, the plants with overexpression were less sensitive to exogenously supplied IBA, NAA and 2,4-D at high concentrations, suggesting that overexpression of the OsWRKY31 gene might alter the auxin response or transport. These results also suggest that OsWRKY31 might be a common component in the signal transduction pathways of the auxin response and the defense response in rice.

  12. The role of pre-symbiotic auxin signaling in ectendomycorrhiza formation between the desert truffle Terfezia boudieri and Helianthemum sessiliflorum. (United States)

    Turgeman, Tidhar; Lubinsky, Olga; Roth-Bejerano, Nurit; Kagan-Zur, Varda; Kapulnik, Yoram; Koltai, Hinanit; Zaady, Eli; Ben-Shabat, Shimon; Guy, Ofer; Lewinsohn, Efraim; Sitrit, Yaron


    The ectendomycorrhizal fungus Terfezia boudieri is known to secrete auxin. While some of the effects of fungal auxin on the plant root system have been described, a comprehensive understanding is still lacking. A dual culture system to study pre mycorrhizal signal exchange revealed previously unrecognized root-fungus interaction mediated by the fungal auxin. The secreted fungal auxin induced negative taproot gravitropism, attenuated taproot growth rate, and inhibited initial host development. Auxin also induced expression of Arabidopsis carriers AUX1 and PIN1, both of which are involved in the gravitropic response. Exogenous application of auxin led to a root phenotype, which fully mimicked that induced by ectomycorrhizal fungi. Co-cultivation of Arabidopsis auxin receptor mutants tir1-1, tir1-1 afb2-3, tir1-1 afb1-3 afb2-3, and tir1-1 afb2-3 afb3-4 with Terfezia confirmed that auxin induces the observed root phenotype. The finding that auxin both induces taproot deviation from the gravity axis and coordinates growth rate is new. We propose a model in which the fungal auxin induces horizontal root development, as well as the coordination of growth rates between partners, along with the known auxin effect on lateral root induction that increases the availability of accessible sites for colonization at the soil plane of fungal spore abundance. Thus, the newly observed responses described here of the root to Terfezia contribute to a successful encounter between symbionts.

  13. Polarization versus Temperature in Pyridinium Ionic Liquids

    DEFF Research Database (Denmark)

    Chaban, V. V.; Prezhdo, O. V.


    Electronic polarization and charge transfer effects play a crucial role in thermodynamic, structural, and transport properties of room-temperature ionic liquids (RTILs). These nonadditive interactions constitute a useful tool for tuning physical chemical behavior of RTILs. Polarization and charge...

  14. Auxin, ethylene and light in gravitropic growth: new insights (United States)

    Edelmann, Hg; Sabovljevic, A.; Njio, G.; Roth, U.

    The regulation mechanism of gravitropic differential plant growth is commonly divided into three sequential processes: the perception of the gravistimulus (generally attributed to amyloplast sedimentation), the transduction of the perceived signal (of which very little is known), and the adequate differential growth response (generally attributed to asymmetric auxin redistribution). The detailled mechanism is still unresolved and remains to be elucidated in significant parts. Employing 2D SDS-PAGE /Q-TOF amongst other methods and strategies we studied the effect of different auxins on gravitropism of coleoptiles and hypocotyls. We also analyzed the effects of light and ethylene (synthesis and perception) on gravitropic growth of primary shoots and roots and analyzed the protein pattern with respect to the observed physiological effects. In coleoptiles, under the applied experimental conditions the effect of 2,4-dichlorophenoxy acetic acid (2,4 D) on gravitropism differed from the effect of indolylacetic acid (IAA), which was similar to the one observed in sunflower hypocotyls. In roots, the relevance of ethylene for gravitropic differential growth and the capacity to evade mechanical barriers during horizontal gravistimulation was analyzed in detail. A special focus was addressed on the physiological significance of the root cap. We will show that the relevance of ethylene for gravitropism has hitherto been misjudged. Further new findings and their implications for the regulation mechanism of gravitropism will be presented and discussed. Kramer et al., (2003) J. Ex. Bot. 54, (393), 2723-2732 Edelmann, H.G., (2002) J. Ex. Bot. 53, (375), 1825-1828

  15. The Arabidopsis gene DIG6 encodes a large 60S subunit nuclear export GTPase 1 that is involved in ribosome biogenesis and affects multiple auxin-regulated development processes

    KAUST Repository

    Zhao, Huayan


    The circularly permuted GTPase large subunit GTPase 1 (LSG1) is involved in the maturation step of the 60S ribosome and is essential for cell viability in yeast. Here, an Arabidopsis mutant dig6 (drought inhibited growth of lateral roots) was isolated. The mutant exhibited multiple auxin-related phenotypes, which included reduced lateral root number, altered leaf veins, and shorter roots. Genetic mapping combined with next-generation DNA sequencing identified that the mutation occurred in AtLSG1-2. This gene was highly expressed in regions of auxin accumulation. Ribosome profiling revealed that a loss of function of AtLSG1-2 led to decreased levels of monosomes, further demonstrating its role in ribosome biogenesis. Quantitative proteomics showed that the expression of certain proteins involved in ribosome biogenesis was differentially regulated, indicating that ribosome biogenesis processes were impaired in the mutant. Further investigations showed that an AtLSG1-2 deficiency caused the alteration of auxin distribution, response, and transport in plants. It is concluded that AtLSG1-2 is integral to ribosome biogenesis, consequently affecting auxin homeostasis and plant development.

  16. Auxin induces cell proliferation in an experimental model of mammalian renal tubular epithelial cells. (United States)

    Cernaro, Valeria; Medici, Maria Antonietta; Leonello, Giuseppa; Buemi, Antoine; Kohnke, Franz Heinrich; Villari, Antonino; Santoro, Domenico; Buemi, Michele


    Indole-3-acetic acid is the main auxin produced by plants and plays a key role in the plant growth and development. This hormone is also present in humans where it is considered as a uremic toxin deriving from tryptophan metabolism. However, beyond this peculiar aspect, the involvement of auxin in human pathophysiology has not been further investigated. Since it is a growth hormone, we evaluated its proliferative properties in an in vitro model of mammalian renal tubular epithelial cells. We employed an experimental model of renal tubular epithelial cells belonging to the LLC-PK1 cell line that is derived from the kidney of healthy male pig. Growth effects of auxin against LLC-PK1 cell lines were determined by a rapid colorimetric assay. Increasing concentrations of auxin (to give a final concentration from 1 to 1000 ng/mL) were added and microplates were incubated for 72 h. Each auxin concentration was assayed in four wells and repeated four times. Cell proliferation significantly increased, compared to control cells, 72 h after addition of auxin to cultured LLC-PK1 cells. Statistically significant values were observed when 100 ng/mL (p auxin influences cell growth not only in plants, where its role is well documented, but also in mammalian cell lines. This observation opens new scenarios in the field of tissue regeneration and may stimulate a novel line of research aiming at investigating whether this hormone really influences human physiology and pathophysiology and in particular, kidney regeneration.

  17. An auxin-responsive endogenous peptide regulates root development in Arabidopsis. (United States)

    Yang, Fengxi; Song, Yu; Yang, Hao; Liu, Zhibin; Zhu, Genfa; Yang, Yi


    Auxin plays critical roles in root formation and development. The components involved in this process, however, are not well understood. Here, we newly identified a peptide encoding gene, auxin-responsive endogenous polypeptide 1 (AREP1), which is induced by auxin, and mediates root development in Arabidopsis. Expression of AREP1 was specific to the cotyledon and to root and shoot meristem tissues. Amounts of AREP1 transcripts and AREP1-green fluorescent protein fusion proteins were elevated in response to indoleacetic acid treatment. Suppression of AREP1 through RNAi silencing resulted in reduction of primary root length, increase of lateral root number, and expansion of adventitious roots, compared to the observations in wild-type plants in the presence of auxin. By contrast, transgenic plants overexpressing AREP1 showed enhanced growth of the primary root under auxin treatment. Additionally, root morphology, including lateral root number and adventitious roots, differed greatly between transgenic and wild-type plants. Further analysis indicated that the expression of auxin-responsive genes, such as IAA3, IAA7, IAA17, GH3.2, GH3.3, and SAUR-AC1, was significantly higher in AREP1 RNAi plants, and was slightly lower in AREP1 overexpressing plants than in wild-type plants. These results suggest that the novel endogenous peptide AREP1 plays an important role in the process of auxin-mediated root development.

  18. Spin transport in undoped InGaAs/AlGaAs multiple quantum well studied via spin photocurrent excited by circularly polarized light. (United States)

    Zhu, Laipan; Liu, Yu; Huang, Wei; Qin, Xudong; Li, Yuan; Wu, Qing; Chen, Yonghai


    The spin diffusion and drift at different excitation wavelengths and different temperatures have been studied in undoped InGaAs/AlGaAs multiple quantum well (MQW). The spin polarization was created by optical spin orientation using circularly polarized light, and the reciprocal spin Hall effect was employed to measure the spin polarization current. We measured the ratio of the spin diffusion coefficient to the mobility of spin-polarized carriers. From the wavelength dependence of the ratio, we found that the spin diffusion and drift of holes became as important as electrons in this undoped MQW, and the ratio for light holes was much smaller than that for heavy holes at room temperature. From the temperature dependence of the ratio, the correction factors for the common Einstein relationship for spin-polarized electrons and heavy holes were firstly obtained to be 93 and 286, respectively.

  19. Galactose inhibits auxin-induced growth of Avena coleoptiles by two mechanisms (United States)

    Cheung, S. P.; Cleland, R. E.


    Galactose inhibits auxin-induced growth of Avena coleoptiles by at least two mechanisms. First, it inhibits auxin-induced H(+)-excretion needed for the initiation of rapid elongation. Galactose cannot be doing so by directly interfering with the ATPase since fusicoccin-induced H(+)-excretion is not affected. Secondly, galactose inhibits long-term auxin-induced growth, even in an acidic (pH 4.5) solution. This may be due to an inhibition of cell wall synthesis. However, galactose does not reduce the capacity of walls to be loosened by H+, given exogenously or excreted in response to fusicoccin.

  20. The Solanum lycopersicum AUXIN RESPONSE FACTOR 7 (SlARF7) mediates cross-talk between auxin and gibberellin signalling during tomato fruit set and development (United States)

    de Jong, Maaike; Wolters-Arts, Mieke; García-Martínez, José L.; Mariani, Celestina; Vriezen, Wim H.


    Transgenic tomato plants (Solanum lycopersicum L.) with reduced mRNA levels of AUXIN RESPONSE FACTOR 7 (SlARF7) form parthenocarpic fruits with morphological characteristics that seem to be the result of both increased auxin and gibberellin (GA) responses during fruit growth. This paper presents a more detailed analysis of these transgenic lines. Gene expression analysis of auxin-responsive genes show that SlARF7 may regulate only part of the auxin signalling pathway involved in tomato fruit set and development. Also, part of the GA signalling pathway was affected by the reduced levels of SlARF7 mRNA, as morphological and molecular analyses display similarities between GA-induced fruits and fruits formed by the RNAi SlARF7 lines. Nevertheless, the levels of GAs were strongly reduced compared with that in seeded fruits. These findings indicate that SlARF7 acts as a modifier of both auxin and gibberellin responses during tomato fruit set and development. PMID:20937732

  1. A genomics approach to understanding the role of auxin in apple (Malus x domestica fruit size control

    Directory of Open Access Journals (Sweden)

    Devoghalaere Fanny


    Full Text Available Abstract Background Auxin is an important phytohormone for fleshy fruit development, having been shown to be involved in the initial signal for fertilisation, fruit size through the control of cell division and cell expansion, and ripening related events. There is considerable knowledge of auxin-related genes, mostly from work in model species. With the apple genome now available, it is possible to carry out genomics studies on auxin-related genes to identify genes that may play roles in specific stages of apple fruit development. Results High amounts of auxin in the seed compared with the fruit cortex were observed in 'Royal Gala' apples, with amounts increasing through fruit development. Injection of exogenous auxin into developing apples at the start of cell expansion caused an increase in cell size. An expression analysis screen of auxin-related genes involved in auxin reception, homeostasis, and transcriptional regulation showed complex patterns of expression in each class of gene. Two mapping populations were phenotyped for fruit size over multiple seasons, and multiple quantitative trait loci (QTLs were observed. One QTL mapped to a region containing an Auxin Response Factor (ARF106. This gene is expressed during cell division and cell expansion stages, consistent with a potential role in the control of fruit size. Conclusions The application of exogenous auxin to apples increased cell expansion, suggesting that endogenous auxin concentrations are at least one of the limiting factors controlling fruit size. The expression analysis of ARF106 linked to a strong QTL for fruit weight suggests that the auxin signal regulating fruit size could partially be modulated through the function of this gene. One class of gene (GH3 removes free auxin by conjugation to amino acids. The lower expression of these GH3 genes during rapid fruit expansion is consistent with the apple maximising auxin concentrations at this point.

  2. Transcriptome analysis of the rhizosphere bacterium Azospirillum brasilense reveals an extensive auxin response. (United States)

    Van Puyvelde, Sandra; Cloots, Lore; Engelen, Kristof; Das, Frederik; Marchal, Kathleen; Vanderleyden, Jos; Spaepen, Stijn


    The rhizosphere bacterium Azospirillum brasilense produces the auxin indole-3-acetic acid (IAA) through the indole-3-pyruvate pathway. As we previously demonstrated that transcription of the indole-3-pyruvate decarboxylase (ipdC) gene is positively regulated by IAA, produced by A. brasilense itself or added exogenously, we performed a microarray analysis to study the overall effects of IAA on the transcriptome of A. brasilense. The transcriptomes of A. brasilense wild-type and the ipdC knockout mutant, both cultured in the absence and presence of exogenously added IAA, were compared.Interfering with the IAA biosynthesis/homeostasis in A. brasilense through inactivation of the ipdC gene or IAA addition results in much broader transcriptional changes than anticipated. Based on the multitude of changes observed by comparing the different transcriptomes, we can conclude that IAA is a signaling molecule in A. brasilense. It appears that the bacterium, when exposed to IAA, adapts itself to the plant rhizosphere, by changing its arsenal of transport proteins and cell surface proteins. A striking example of adaptation to IAA exposure, as happens in the rhizosphere, is the upregulation of a type VI secretion system (T6SS) in the presence of IAA. The T6SS is described as specifically involved in bacterium-eukaryotic host interactions. Additionally, many transcription factors show an altered regulation as well, indicating that the regulatory machinery of the bacterium is changing.

  3. Homologues of the Arabidopsis thaliana SHI/STY/LRP1 genes control auxin biosynthesis and affect growth and development in the moss Physcomitrella patens. (United States)

    Eklund, D Magnus; Thelander, Mattias; Landberg, Katarina; Ståldal, Veronika; Nilsson, Anders; Johansson, Monika; Valsecchi, Isabel; Pederson, Eric R A; Kowalczyk, Mariusz; Ljung, Karin; Ronne, Hans; Sundberg, Eva


    The plant hormone auxin plays fundamental roles in vascular plants. Although exogenous auxin also stimulates developmental transitions and growth in non-vascular plants, the effects of manipulating endogenous auxin levels have thus far not been reported. Here, we have altered the levels and sites of auxin production and accumulation in the moss Physcomitrella patens by changing the expression level of homologues of the Arabidopsis SHI/STY family proteins, which are positive regulators of auxin biosynthesis genes. Constitutive expression of PpSHI1 resulted in elevated auxin levels, increased and ectopic expression of the auxin response reporter GmGH3pro:GUS, and in an increased caulonema/chloronema ratio, an effect also induced by exogenous auxin application. In addition, we observed premature ageing and necrosis in cells ectopically expressing PpSHI1. Knockout of either of the two PpSHI genes resulted in reduced auxin levels and auxin biosynthesis rates in leafy shoots, reduced internode elongation, delayed ageing, a decreased caulonema/chloronema ratio and an increased number of axillary hairs, which constitute potential auxin biosynthesis sites. Some of the identified auxin functions appear to be analogous in vascular and non-vascular plants. Furthermore, the spatiotemporal expression of the PpSHI genes and GmGH3pro:GUS strongly overlap, suggesting that local auxin biosynthesis is important for the regulation of auxin peak formation in non-vascular plants.

  4. TCP15 modulates cytokinin and auxin responses during gynoecium development in Arabidopsis. (United States)

    Lucero, Leandro E; Uberti-Manassero, Nora G; Arce, Agustín L; Colombatti, Francisco; Alemano, Sergio G; Gonzalez, Daniel H


    We studied the role of Arabidopsis thaliana TCP15, a member of the TEOSINTE BRANCHED1-CYCLOIDEA-PCF (TCP) transcription factor family, in gynoecium development. Plants that express TCP15 from the 35S CaMV promoter (35S:TCP15) develop flowers with defects in carpel fusion and a reduced number of stigmatic papillae. In contrast, the expression of TCP15 fused to a repressor domain from its own promoter causes the development of outgrowths topped with stigmatic papillae from the replum. 35S:TCP15 plants show lower levels of the auxin indoleacetic acid and reduced expression of the auxin reporter DR5 and the auxin biosynthesis genes YUCCA1 and YUCCA4, suggesting that TCP15 is a repressor of auxin biosynthesis. Treatment of plants with cytokinin enhances the developmental effects of expressing TCP15 or its repressor form. In addition, treatment of a knock-out double mutant in TCP15 and the related gene TCP14 with cytokinin causes replum enlargement, increased development of outgrowths, and the induction of the auxin biosynthesis genes YUCCA1 and YUCCA4. A comparison of the phenotypes observed after cytokinin treatment of plants with altered expression levels of TCP15 and auxin biosynthesis genes suggests that TCP15 modulates gynoecium development by influencing auxin homeostasis. We propose that the correct development of the different tissues of the gynoecium requires a balance between auxin levels and cytokinin responses, and that TCP15 participates in a feedback loop that helps to adjust this balance.

  5. GH3-mediated auxin homeostasis links growth regulation with stress adaptation response in Arabidopsis. (United States)

    Park, Jung-Eun; Park, Ju-Young; Kim, Youn-Sung; Staswick, Paul E; Jeon, Jin; Yun, Ju; Kim, Sun-Young; Kim, Jungmook; Lee, Yong-Hwan; Park, Chung-Mo


    Plants constantly monitor environmental fluctuations to optimize their growth and metabolism. One example is adaptive growth occurring in response to biotic and abiotic stresses. Here, we demonstrate that GH3-mediated auxin homeostasis is an essential constituent of the complex network of auxin actions that regulates stress adaptation responses in Arabidopsis. Endogenous auxin pool is regulated, at least in part, through negative feedback by a group of auxin-inducible GH3 genes encoding auxin-conjugating enzymes. An Arabidopsis mutant, wes1-D, in which a GH3 gene WES1 is activated by nearby insertion of the (35)S enhancer, exhibited auxin-deficient traits, including reduced growth and altered leaf shape. Interestingly, WES1 is also induced by various stress conditions as well as by salicylic acid and abscisic acid. Accordingly, wes1-D was resistant to both biotic and abiotic stresses, and stress-responsive genes, such as pathogenesis-related genes and CBF genes, were upregulated in this mutant. In contrast, a T-DNA insertional mutant showed reduced stress resistance. We therefore propose that GH3-mediated growth suppression directs reallocation of metabolic resources to resistance establishment and represents the fitness costs of induced resistance.

  6. Low temperature inhibits root growth by reducing auxin accumulation via ARR1/12. (United States)

    Zhu, Jiang; Zhang, Kun-Xiao; Wang, Wen-Shu; Gong, Wen; Liu, Wen-Cheng; Chen, Hong-Guo; Xu, Heng-Hao; Lu, Ying-Tang


    Plants exhibit reduced root growth when exposed to low temperature; however, how low temperature modulates root growth remains to be understood. Our study demonstrated that low temperature reduces both meristem size and cell number, repressing the division potential of meristematic cells by reducing auxin accumulation, possibly through the repressed expression of PIN1/3/7 and auxin biosynthesis-related genes, although the experiments with exogenous auxin application also suggest the involvement of other factor(s). In addition, we verified that ARABIDOPSIS RESPONSE REGULATOR 1 (ARR1) and ARR12 are involved in low temperature-mediated inhibition of root growth by showing that the roots of arr1-3 arr12-1 seedlings were less sensitive than wild-type roots to low temperature, in terms of changes in root length and meristem cell number. Furthermore, low temperature reduced the levels of PIN1/3 transcripts and the auxin level to a lesser extent in arr1-3 arr12-1 roots than in wild-type roots, suggesting that cytokinin signaling is involved in the low-temperature-mediated reduction of auxin accumulation. Taken together, our data suggest that low temperature inhibits root growth by reducing auxin accumulation via ARR1/12.

  7. Modulation of auxin content in Arabidopsis confers improved drought stress resistance. (United States)

    Shi, Haitao; Chen, Li; Ye, Tiantian; Liu, Xiaodong; Ding, Kejian; Chan, Zhulong


    Auxin is a well-known plant phytohormone that is involved in multiple plant growth processes and stress responses. In this study, auxin response was significantly modulated under drought stress condition. The iaaM-OX transgenic lines with higher endogenous indole-3-acetic acid (IAA) level and IAA pre-treated wild type (WT) plants exhibited enhanced drought stress resistance, while the yuc1yuc2yuc6 triple mutants with lower endogenous IAA level showed decreased stress resistance in comparison to non-treated WT plants. Additionally, endogenous and exogenous auxin positively modulated the expression levels of multiple abiotic stress-related genes (RAB18, RD22, RD29A, RD29B, DREB2A, and DREB2B), and positively affected reactive oxygen species (ROS) metabolism and underlying antioxidant enzyme activities. Moreover, auxin significantly modulated some carbon metabolites including amino acids, organic acids, sugars, sugar alcohols and aromatic amines. Notably, endogenous and exogenous auxin positively modulated root architecture especially the lateral root number. Taken together, this study demonstrated that auxin might participate in the positive regulation of drought stress resistance, through regulation of root architecture, ABA-responsive genes expression, ROS metabolism, and metabolic homeostasis, at least partially.

  8. Arabidopsis PLC2 is involved in auxin-modulated reproductive development. (United States)

    Li, Lin; He, Yuqing; Wang, Yarui; Zhao, Shujuan; Chen, Xi; Ye, Tiantian; Wu, Yuxuan; Wu, Yan


    Phospholipase C (PLC) is an enzyme that plays crucial roles in various signal transduction pathways in mammalian cells. However, the role of PLC in plant development is poorly understood. Here we report involvement of PLC2 in auxin-mediated reproductive development in Arabidopsis. Disruption of PLC2 led to sterility, indicating a significant role for PLC2 in reproductive development. Development of both male and female gametophytes was severely perturbed in plc2 mutants. Moreover, elevated auxin levels were observed in plc2 floral tissues, suggesting that the infertility of plc2 plants may be associated with increased auxin concentrations in the reproductive organs. We show that expression levels of the auxin reporters DR5:GUS and DR5:GFP were elevated in plc2 anthers and ovules. In addition, we found that expression of the auxin biosynthetic YUCCA genes was increased in plc2 plants. We conclude that PLC2 is involved in auxin biosynthesis and signaling, thus modulating development of both male and female gametophytes in Arabidopsis.

  9. Auxin-dependent compositional change in Mediator in ARF7- and ARF19-mediated transcription. (United States)

    Ito, Jun; Fukaki, Hidehiro; Onoda, Makoto; Li, Lin; Li, Chuanyou; Tasaka, Masao; Furutani, Masahiko


    Mediator is a multiprotein complex that integrates the signals from transcription factors binding to the promoter and transmits them to achieve gene transcription. The subunits of Mediator complex reside in four modules: the head, middle, tail, and dissociable CDK8 kinase module (CKM). The head, middle, and tail modules form the core Mediator complex, and the association of CKM can modify the function of Mediator in transcription. Here, we show genetic and biochemical evidence that CKM-associated Mediator transmits auxin-dependent transcriptional repression in lateral root (LR) formation. The AUXIN/INDOLE 3-ACETIC ACID 14 (Aux/IAA14) transcriptional repressor inhibits the transcriptional activity of its binding partners AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 by making a complex with the CKM-associated Mediator. In addition, TOPLESS (TPL), a transcriptional corepressor, forms a bridge between IAA14 and the CKM component MED13 through the physical interaction. ChIP assays show that auxin induces the dissociation of MED13 but not the tail module component MED25 from the ARF7 binding region upstream of its target gene. These findings indicate that auxin-induced degradation of IAA14 changes the module composition of Mediator interacting with ARF7 and ARF19 in the upstream region of their target genes involved in LR formation. We suggest that this regulation leads to a quick switch of signal transmission from ARFs to target gene expression in response to auxin.

  10. Negative feedback regulation of auxin signaling by ATHB8/ACL5-BUD2 transcription module. (United States)

    Baima, Simona; Forte, Valentina; Possenti, Marco; Peñalosa, Andrés; Leoni, Guido; Salvi, Sergio; Felici, Barbara; Ruberti, Ida; Morelli, Giorgio


    The role of auxin as main regulator of vascular differentiation is well established, and a direct correlation between the rate of xylem differentiation and the amount of auxin reaching the (pro)cambial cells has been proposed. It has been suggested that thermospermine produced by ACAULIS5 (ACL5) and bushy and dwarf2 (BUD2) is one of the factors downstream to auxin contributing to the regulation of this process in Arabidopsis. Here, we provide an in-depth characterization of the mechanism through which ACL5 modulates xylem differentiation. We show that an increased level of ACL5 slows down xylem differentiation by negatively affecting the expression of homeodomain-leucine zipper (HD-ZIP) III and key auxin signaling genes. This mechanism involves the positive regulation of thermospermine biosynthesis by the HD-ZIP III protein Arabidopsis thaliana homeobox8 tightly controlling the expression of ACL5 and BUD2. In addition, we show that the HD-ZIP III protein REVOLUTA contributes to the increased leaf vascularization and long hypocotyl phenotype of acl5 likely by a direct regulation of auxin signaling genes such as like auxin resistant2 (LAX2) and LAX3. We propose that proper formation and differentiation of xylem depend on a balance between positive and negative feedback loops operating through HD-ZIP III genes.

  11. An auxin-responsive endogenous peptide regulates root development in Arabidopsis

    Institute of Scientific and Technical Information of China (English)

    Fengxi Yang; Yu Song; Hao Yang; Zhibin Liu; Genfa Zhu; Yi Yang


    Auxin plays critical roles in root formation and development. The components involved in this process, however, are not well understood. Here, we newly identified a peptide encoding gene, auxin-responsive endogenous polypeptide 1 (AREP1), which is induced by auxin, and mediates root development in Arabidopsis. Expression of AREP1 was specific to the cotyledon and to root and shoot meristem tissues. Amounts of AREP1 transcripts and AREP1-green fluorescent protein fusion proteins were elevated in response to indoleacetic acid treatment. Suppression of AREP1 through RNAi silencing resulted in reduction of primary root length, increase of lateral root number, and expansion of adventitious roots, compared to the observations in wild-type plants in the presence of auxin. By contrast, transgenic plants overexpressing AREP1 showed enhanced growth of the primary root under auxin treatment. Additionally, rootmorphology, including lateral root number and adventitious roots, differed greatly between transgenic and wildtype plants. Further analysis indicated that the expression of auxin-responsive genes, such as IAA3, IAA7, IAA17, GH3.2, GH3.3, and SAUR-AC1, was significantly higher in AREP1 RNAi plants, and was slightly lower in AREP1 overexpressing plants than in wildtype plants. These results suggest that the novel endogenous peptide AREP1 plays an important role in the process of auxinmediated root development.

  12. Oligomerization of SCFTIR1 Is Essential for Aux/IAA Degradation and Auxin Signaling in Arabidopsis. (United States)

    Dezfulian, Mohammad H; Jalili, Espanta; Roberto, Don Karl A; Moss, Britney L; Khoo, Kerry; Nemhauser, Jennifer L; Crosby, William L


    The phytohormone auxin is a key regulator of plant growth and development. Molecular studies in Arabidopsis have shown that auxin perception and signaling is mediated via TIR1/AFB-Aux/IAA co-receptors that assemble as part of the SCFTIR1/AFB E3 ubiquitin-ligase complex and direct the auxin-regulated degradation of Aux/IAA transcriptional repressors. Despite the importance of auxin signaling, little is known about the functional regulation of the TIR1/AFB receptor family. Here we show that TIR1 can oligomerize in planta via a set of spatially clustered amino acid residues. While none of the residues identified reside in the interaction interface of the TIR1-Aux/IAA degron, they nonetheless regulate the binding of TIR1 to Aux/IAA substrate proteins and their subsequent degradation in vivo as an essential aspect of auxin signaling. We propose oligomerization of TIR1 as a novel regulatory mechanism in the regulation of auxin-mediated plant patterning and development.

  13. The outer epidermis of Avena and maize coleoptiles is not a unique target for auxin in elongation growth (United States)

    Cleland, R. E.


    A controversy exists as to whether or not the outer epidermis in coleoptiles is a unique target for auxin in elongation growth. The following evidence indicates that the outer epidermis is not the only auxin-responsive cell layer in either Avena sativa L. or Zea mays L. coleoptiles. Coleoptile sections from which the epidermis has been removed by peeling elongate in response to auxin. The magnitude of the response is similar to that of intact sections provided the incubation solution contains both auxin and sucrose. The amount of elongation is independent of the amount of epidermis removed. Sections of oat coleoptiles from which the epidermis has been removed from one side are nearly straight after 22 h in auxin and sucrose, despite extensive growth of the sections. These data indicate that the outer epidermis is not a unique target for auxin in elongation growth, at least in Avena and maize coleoptiles.

  14. 生长素对水稻根系生长发育调控的研究进展%Advances on Molecular Mechanism of Auxin in Rice Root

    Institute of Scientific and Technical Information of China (English)

    康书静; 钱前; 朱丽


    水稻根系是非常重要的吸收营养和水分的器官,其生长与发育受多个植物激素协同调控。本文综述了生长素对水稻根形态建成调控的分子遗传学研究进展,影响生长素合成的YUCCA基因是通过控制生长素在植株体内的浓度来改变根的形态。而生长素运输主要通过调控生长素输出载体PIN和生长素输入载体AUXI的极性分布,影响侧根和不定根的发育,以及根的向重性。此外,TIR1、Aux/IAA与ARF互作在生长素信号转导中起重要的调控作用。其他激素可以通过信号转导途径影响生长素的分布,调控根系统的建成。但目前水稻相关基因的克隆进展缓慢,对生长素调控网络认识还不够清晰。因此,更为深入的研究水稻生长素相关基因将对理解水稻根系发育的分子机制具有重要意义。%Rice root is the main organ for nutrient and water absorption, its growth and development are regulated by several plant hormones collaboratively. Of which,auxin is the extensively studied. In this paper, the author elucidate the development process and molecular mechanism of rice root architecture by analyzing the regulating genes that have been cloned. Comprehensive analysis re-veals that the root shape is altered by auxin biosynthesis genes that regulate auxin concentration. Auxin transport regulate the devel-opment of lateral root and crown root through controlling auxin influx and efflux. Auxin signal transduction, which affects the root sys-tem, is regulated by TIR1、Aux/IAA and ARF. Besides the distrubition of auxin is influenced by acting with other plant hormones. However,these cloned root shape genes in rice is still insufficient, and the outline of molecular regulation network of auxin is not clear. Therefore,it is important to further understand molecular mechanism of auxin in rice root by screening and collecting rice auxin mutants with root mutations.

  15. Apoplastic reactive oxygen species transiently decrease auxin signaling and cause stress-induced morphogenic response in Arabidopsis. (United States)

    Blomster, Tiina; Salojärvi, Jarkko; Sipari, Nina; Brosché, Mikael; Ahlfors, Reetta; Keinänen, Markku; Overmyer, Kirk; Kangasjärvi, Jaakko


    Reactive oxygen species (ROS) are ubiquitous signaling molecules in plant stress and development. To gain further insight into the plant transcriptional response to apoplastic ROS, the phytotoxic atmospheric pollutant ozone was used as a model ROS inducer in Arabidopsis (Arabidopsis thaliana) and gene expression was analyzed with microarrays. In contrast to the increase in signaling via the stress hormones salicylic acid, abscisic acid, jasmonic acid (JA), and ethylene, ROS treatment caused auxin signaling to be transiently suppressed, which was confirmed with a DR5-uidA auxin reporter construct. Transcriptomic data revealed that various aspects of auxin homeostasis and signaling were modified by apoplastic ROS. Furthermore, a detailed analysis of auxin signaling showed that transcripts of several auxin receptors and Auxin/Indole-3-Acetic Acid (Aux/IAA) transcriptional repressors were reduced in response to apoplastic ROS. The ROS-derived changes in the expression of auxin signaling genes partially overlapped with abiotic stress, pathogen responses, and salicylic acid signaling. Several mechanisms known to suppress auxin signaling during biotic stress were excluded, indicating that ROS regulated auxin responses via a novel mechanism. Using mutants defective in various auxin (axr1, nit1, aux1, tir1 afb2, iaa28-1, iaa28-2) and JA (axr1, coi1-16) responses, ROS-induced cell death was found to be regulated by JA but not by auxin. Chronic ROS treatment resulted in altered leaf morphology, a stress response known as "stress-induced morphogenic response." Altered leaf shape of tir1 afb2 suggests that auxin was a negative regulator of stress-induced morphogenic response in the rosette.

  16. Thermoperiodic control of hypocotyl elongation depends on auxin-induced ethylene signaling that controls downstream PHYTOCHROME INTERACTING FACTOR3 activity. (United States)

    Bours, Ralph; Kohlen, Wouter; Bouwmeester, Harro J; van der Krol, Alexander


    We show that antiphase light-temperature cycles (negative day-night temperature difference [-DIF]) inhibit hypocotyl growth in Arabidopsis (Arabidopsis thaliana). This is caused by reduced cell elongation during the cold photoperiod. Cell elongation in the basal part of the hypocotyl under -DIF was restored by both 1-aminocyclopropane-1-carboxylic acid (ACC; ethylene precursor) and auxin, indicating limited auxin and ethylene signaling under -DIF. Both auxin biosynthesis and auxin signaling were reduced during -DIF. In addition, expression of several ACC Synthase was reduced under -DIF but could be restored by auxin application. In contrast, the reduced hypocotyl elongation of ethylene biosynthesis and signaling mutants could not be complemented by auxin, indicating that auxin functions upstream of ethylene. The PHYTOCHROME INTERACTING FACTORS (PIFs) PIF3, PIF4, and PIF5 were previously shown to be important regulators of hypocotyl elongation. We now show that, in contrast to pif4 and pif5 mutants, the reduced hypocotyl length in pif3 cannot be rescued by either ACC or auxin. In line with this, treatment with ethylene or auxin inhibitors reduced hypocotyl elongation in PIF4 overexpressor (PIF4ox) and PIF5ox but not PIF3ox plants. PIF3 promoter activity was strongly reduced under -DIF but could be restored by auxin application in an ACC Synthase-dependent manner. Combined, these results show that PIF3 regulates hypocotyl length downstream, whereas PIF4 and PIF5 regulate hypocotyl length upstream of an auxin and ethylene cascade. We show that, under -DIF, lower auxin biosynthesis activity limits the signaling in this pathway, resulting in low activity of PIF3 and short hypocotyls.

  17. Auxin-binding pocket of ABP1 is crucial for its gain-of-function cellular and developmental roles. (United States)

    Grones, Peter; Chen, Xu; Simon, Sibu; Kaufmann, Walter A; De Rycke, Riet; Nodzyński, Tomasz; Zažímalová, Eva; Friml, Jiří


    The plant hormone auxin is a key regulator of plant growth and development. Auxin levels are sensed and interpreted by distinct receptor systems that activate a broad range of cellular responses. The Auxin-Binding Protein1 (ABP1) that has been identified based on its ability to bind auxin with high affinity is a prime candidate for the extracellular receptor responsible for mediating a range of auxin effects, in particular, the fast non-transcriptional ones. Contradictory genetic studies suggested prominent or no importance of ABP1 in many developmental processes. However, how crucial the role of auxin binding to ABP1 is for its functions has not been addressed. Here, we show that the auxin-binding pocket of ABP1 is essential for its gain-of-function cellular and developmental roles. In total, 16 different abp1 mutants were prepared that possessed substitutions in the metal core or in the hydrophobic amino acids of the auxin-binding pocket as well as neutral mutations. Their analysis revealed that an intact auxin-binding pocket is a prerequisite for ABP1 to activate downstream components of the ABP1 signalling pathway, such as Rho of Plants (ROPs) and to mediate the clathrin association with membranes for endocytosis regulation. In planta analyses demonstrated the importance of the auxin binding pocket for all known ABP1-mediated postembryonic developmental processes, including morphology of leaf epidermal cells, root growth and root meristem activity, and vascular tissue differentiation. Taken together, these findings suggest that auxin binding to ABP1 is central to its function, supporting the role of ABP1 as auxin receptor.

  18. APORT: a program for the area-based apportionment of county variables to cells of a polar grid. [Airborne pollutant transport models

    Energy Technology Data Exchange (ETDEWEB)

    Fields, D.E.; Little, C.A.


    The APORT computer code was developed to apportion variables tabulated for polygon-structured civil districts onto cells of a polar grid. The apportionment is based on fractional overlap between the polygon and the grid cells. Centering the origin of the polar system at a pollutant source site yields results that are very useful for assessing and interpreting the effects of airborne pollutant dissemination. The APOPLT graphics code, which uses the same data set as APORT, provides a convenient visual display of the polygon structure and the extent of the polar grid. The APORT/APOPLT methodology was verified by application to county summaries of cattle population for counties surrounding the Oyster Creek, New Jersey, nuclear power plant. These numerical results, which were obtained using approximately 2-min computer time on an IBM System 360/91 computer, compare favorably to results of manual computations in both speed and accuracy.

  19. Transport of calcium in seedlings and cuttings of mung bean

    Energy Technology Data Exchange (ETDEWEB)

    Broadbent, W.


    At germination, a very small proportion of stored calcium is mobilized to the axis in the absence of exogenous supplies of calcium. There is no evidence for transport in phloem since exported calcium does not enter the seedling root. /sup 45/Calcium is not redistributed when applied to cotyledons at germination of leaves of seedlings. A subsequent large addition of unlabelled calcium promotes a small redistribution from leaves. Triiodobenzoic acid (TIBA), applied to leaves, leads to a small reduction in calcium accumulation but does not effect redistribution. Auxin is without effect and auxin plus TIBA promotes accumulation. These results are discussed in relation to possible extracellular binding sites for calcium.

  20. Functional Characterization of PaLAX1, a Putative Auxin Permease, in Heterologous Plant Systems1[W][OA (United States)

    Hoyerová, Klára; Perry, Lucie; Hand, Paul; Laňková, Martina; Kocábek, Tomáš; May, Sean; Kottová, Jana; Pačes, Jan; Napier, Richard; Zažímalová, Eva


    We have isolated the cDNA of the gene PaLAX1 from a wild cherry tree (Prunus avium). The gene and its product are highly similar in sequences to both the cDNAs and the corresponding protein products of AUX/LAX-type genes, coding for putative auxin influx carriers. We have prepared and characterized transformed Nicotiana tabacum and Arabidopsis thaliana plants carrying the gene PaLAX1. We have proved that constitutive overexpression of PaLAX1 is accompanied by changes in the content and distribution of free indole-3-acetic acid, the major endogenous auxin. The increase in free indole-3-acetic acid content in transgenic plants resulted in various phenotype changes, typical for the auxin-overproducing plants. The uptake of synthetic auxin, 2,4-dichlorophenoxyacetic acid, was 3 times higher in transgenic lines compared to the wild-type lines and the treatment with the auxin uptake inhibitor 1-naphthoxyacetic acid reverted the changes caused by the expression of PaLAX1. Moreover, the agravitropic response could be restored by expression of PaLAX1 in the mutant aux1 plants, which are deficient in auxin influx carrier activity. Based on our data, we have concluded that the product of the gene PaLAX1 promotes the uptake of auxin into cells, and, as a putative auxin influx carrier, it affects the content and distribution of free endogenous auxin in transgenic plants. PMID:18184737

  1. Polarization, political

    NARCIS (Netherlands)

    M. Wojcieszak


    Polarization has been studied in three different forms: on a social, group, and individual level. This entry first focuses on the undisputed phenomenon of elite polarization (i.e., increasing adherence of policy positions among the elites) and also outlines different approaches to assessing mass pol

  2. Polar Codes (United States)


    QPSK Gaussian channels . .......................................................................... 39 vi 1. INTRODUCTION Forward error correction (FEC...Capacity of BSC. 7 Figure 5. Capacity of AWGN channel . 8 4. INTRODUCTION TO POLAR CODES Polar codes were introduced by E. Arikan in [1]. This paper...Under authority of C. A. Wilgenbusch, Head ISR Division EXECUTIVE SUMMARY This report describes the results of the project “More reliable wireless

  3. YUCCA6 over-expression demonstrates auxin function in delaying leaf senescence in Arabidopsis thaliana

    KAUST Repository

    Kim, Jeong Im


    The Arabidopsis thaliana YUCCA family of flavin monooxygenase proteins catalyses a rate-limiting step in de novo auxin biosynthesis. A YUCCA6 activation mutant, yuc6-1D, has been shown to contain an elevated free IAA level and to display typical high-auxin phenotypes. It is reported here that Arabidopsis plants over-expressing YUCCA6, such as the yuc6-1D activation mutant and 35S:YUC6 transgenic plants, displayed dramatic longevity. In addition, plants over-expressing YUCCA6 exhibited classical, delayed dark-induced and hormone-induced senescence in assays using detached rosette leaves. However, plants over-expressing an allele of YUCCA6, that carries mutations in the NADPH cofactor binding site, exhibited neither delayed leaf senescence phenotypes nor phenotypes typical of auxin overproduction. When the level of free IAA was reduced in yuc6-1D by conjugation to lysine, yuc6-1D leaves senesced at a rate similar to the wild-type leaves. Dark-induced senescence in detached leaves was accompanied by a decrease in their free IAA content, by the reduced expression of auxin biosynthesis enzymes such as YUCCA1 and YUCCA6 that increase cellular free IAA levels, and by the increased expression of auxin-conjugating enzymes encoded by the GH3 genes that reduce the cellular free auxin levels. Reduced transcript abundances of SAG12, NAC1, and NAC6 during senescence in yuc6-1D compared with the wild type suggested that auxin delays senescence by directly or indirectly regulating the expression of senescence-associated genes. 2011 The Author(s).

  4. Molecular regulation of somatic embryogenesis in potato: an auxin led perspective. (United States)

    Sharma, Sanjeev Kumar; Millam, Steve; Hedley, Peter E; McNicol, Jim; Bryan, Glenn J


    Potato internodal segments (INS) treated with the auxin 2,4-dichlorophenoxyacetic acid can be induced to develop somatic embryos upon their transfer to an auxin-free medium, while the continuous presence of auxin in the medium suppresses the progression of embryogenically-induced somatic cells to embryos. We have employed these contrasting pathways, in combination with potato microarrays representing circa 10,000 genes, to profile global gene expression patterns during the progression of somatic embryogenesis in potato. The induction phase, characterised by the presence of auxin, was analysed by the direct comparison of RNA isolated from freshly excised (0 days) and embryogenically induced (14 days) INS explants. RNAs from embryo-forming (withdrawal of auxin after 14 days) and embryo-inhibitory (continuous presence of auxin) conditions, isolated over a range of time-points until the emergence of somatic embryos, were compared in a loop design to identify auxin responsive genes putatively involved in the process of somatic embryogenesis. A total of 402 transcripts were found to be showing significant differential expression patterns during somatic embryogenesis 'induction' phase, 524 during 'embryo-transition' phase, while 44 transcripts were common to both phases. Functional classification of these transcripts, using Gene Ontology vocabularies (molecular and biological), revealed that a significant proportion of transcripts were involved in processes which are more relevant to somatic embryogenesis such as apoptosis, development, reproduction, stress and signal transduction. This is the first study profiling global gene expression patterns during true somatic embryogenesis initiated from mature and completely differentiated explants and has enabled the description of stage-specific expression patterns of a large number of genes during potato somatic embryogenesis (PSE). The significance of the key identified genes during critical stages of somatic embryogenesis is

  5. Polarization holography

    DEFF Research Database (Denmark)

    Nikolova, L.; Ramanujam, P.S.

    Current research into holography is concerned with applications in optically storing, retrieving, and processing information. Polarization holography has many unique properties compared to conventional holography. It gives results in high efficiency, achromaticity, and special polarization...... properties. This books reviews the research carried out in this field over the last 15 years. The authors provide basic concepts in polarization and the propa