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1.
Accumulation of radiolabelled naphthalene-1-acetic acid (1-NAA), 2,4-dichlorophenoxyacetic acid (2,4-D), and indole-3-acetic acid (IAA) has been measured in suspension-cultured tobacco (Nicotiana tabacum) cells. In this paper is presented a simple methodology allowing activities of the auxin influx and efflux carriers to be monitored independently by measuring the cellular accumulation of [3H]NAA and [14C]2,4-D. We have shown that 1-NAA enters cells by passive diffusion and has its accumulation level controlled by the efflux carrier. By contrast, 2,4-D uptake is mostly ensured by the influx carrier and this auxin is not secreted by the efflux carrier. Both auxin carriers contribute to IAA accumulation. The kinetic parameters and specificity of each carrier have been determined and new information concerning interactions with naphthylphthalamic acid, pyrenoylbenzoic acid, and naphthalene-2-acetic acid are provided. The relative contributions of diffusion and carrier-mediated influx and efflux to the membrane transport of 2,4-D, 1-NAA, and IAA have been quantified, and the data indicate that plant cells are able to modulate over a large range their auxin content by modifying the activity of each carrier.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- 1-NAA
naphthalene-1-acetic acid
- 2-NAA
naphthalene-2-acetic acid
- NPA
N-1-naphthylphthalamic acid
- PBA
2-(1-pyrenoyl)benzoic acid
- Vm
maximum transport capacity of the carrier
In honour of Professor Dieter Klämbt's 65th birthdayThe authors thank Drs. A.E. Geissler and G.F. Katekar (CSIRO, Canberra City, Australia) for providing auxin efflux carrier inhibitors CPD, CPP, and PBA, and Dr. H. Barbier-Brygoo (Institut des Sciences Végétales, CNRS, Gif-sur-Yvette, France) for helpful discussions. This work was supported by funds from the Centre National de la Recherche Scientifique (UPR0040). 相似文献
2.
Targeting of auxin carriers to the plasma membrane: differential effects of brefeldin A on the traffic of auxin uptake and efflux carriers 总被引:1,自引:1,他引:0
Monensin and brefeldin A (BFA), inhibitors of Golgi-mediated protein secretion, rapidly perturb the transport catalytic activity
of specific plasma membrane-associated efflux carriers for indole-3-acetic acid (IAA) and inhibit polar transport of IAA.
To determine if these responses result solely from perturbation of the efflux carrier or whether specific auxin uptake carrier
function is also affected, the influence of BFA on the cellular transport of a range of auxins with contrasting affinities
for specific auxin uptake and efflux carriers was investigated in zucchini (Cucurbita pepo L.) hypocotyl tissue. In-flight addition of BFA (3 · 10−5 mol · dm−3) caused a rapid (lag < 10 min) and substantial (fourfold) increase in the rate of [1-14C]IAA net uptake by zucchini hypocotyl tissue. In the presence of the specific auxin efflux carrier inhibitor N-1-naphthylphthalamic acid (NPA; 3 · 10−6 mol · dm−3), BFA slightly reduced the rate of [1-14C]IAA net uptake. Stimulation of [1-14C]IAA net uptake by BFA was concentration-dependent. In the absence of BFA, net uptake of [1-14C]IAA exhibited the characteristic biphasic response to increasing concentrations of competing cold IAA but in the presence
of BFA, [1-14C]IAA uptake decreased smoothly with increase in concentration of competing unlabelled IAA, indicating a loss of auxin efflux
carrier activity but retention of functional uptake carriers. The half-time for mediated efflux of [1-14C]IAA from preloaded zucchini tissue was substantially increased by BFA (t1/2 = 51 min, controls; 107 min, BFA-treated). Treatment with BFA and/or NPA did not significantly affect the net uptake by,
or efflux from, zucchini tissue of [1-14C]2,4-dichlorophenoxyacetic acid ([1-14C]2,4-D), a substrate for the auxin uptake carrier but not the auxin efflux carrier. Uptake of [1-14C]2,4-D declined smoothly with increasing concentrations of competing unlabelled IAA whether or not BFA was included in the
uptake medium, confirming the failure of BFA to perturb auxin uptake carrier function. Transport of 1-[4-3H]naphthaleneacetic acid (1-NAA) exhibited little response to BFA or NPA, confirming that it is only a weakly transported
substrate for the efflux carrier in zucchini cells.
Received: 12 November 1997 / Accepted: 27 January 1998 相似文献
3.
Zhuang X Jiang J Li J Ma Q Xu Y Xue Y Xu Z Chong K 《The Plant journal : for cell and molecular biology》2006,48(4):581-591
Development and organogenesis in both dicot and monocot plants are highly dependent on polar auxin transport (PAT), which requires the proper asymmetric localization of both auxin influx and efflux carriers. In the model dicot plant Arabidopsis thaliana, the trafficking and localization of auxin efflux facilitators such as PIN-FORMED1 (PIN1) are mediated by GNOM, a guanine-nucleotide exchange factor (GEF) for the ADP-ribosylation factor (ARF) family of small GTPases, but molecular regulators of the auxin influx facilitators remain unknown. Here, we show that over-expression of OsAGAP, an ARF-GTPase-activating protein (ARF-GAP) in rice, impaired PAT and interfered with both primary and lateral root development. The lateral root phenotype could be rescued by the membrane-permeable auxin 1-naphthyl acetic acid, but not by indole 3-acetic acid (IAA) or by 2,4-dichloro-phenoxyacetic acid, which require influx facilitators to enter the cells. OsAGAP-over-expressing plants had alterations in vesicle trafficking and localization of the presumptive A. thaliana auxin-influx carrier AUX1, but not in the localization of the auxin efflux facilitators. Together, our data suggest that OsAGAP has a specific role in regulating vesicle trafficking pathways such as the auxin influx pathway, which in turn controls auxin-dependent root growth in plants. 相似文献
4.
The pH-driven accumulation of [3H]indolyl-3-acetic acid (IAA) has been found to occur in membrane vesicles of lupin (Lupinus albus L.) hypocotyls. Most of this association of auxin with membranes is very sensitive to osmotic shock, high concentrations of permeable weak acids, incubation at 20° C for 20 min and to some ionophores. Long incubation times also depress the ability to accumulate radioactive IAA but this ability can be partially restored by a treatment that presumably reconstitutes the pH gradient across the membranes. Two specific inhibitors of auxin transport, N-1-naphtylphthalamic acid and 2,3,5-triiodobenzoic acid, stimulate net IAA uptake with an optimum at about 10-6 M (pH 5.0). At least two auxin carriers appear to be present in the lupin membrane vesicles. An uptake carrier seems to be saturated at 10-7 M IAA in the presence of N-1-naphtylphthalamic acid, but higher IAA concentrations are needed to saturate an efflux carrier. The uptake carrier also shows a high affinity for IAA and 2,4-dichlorophenoxyacetic acid and a low affinity for 1-naphthylacetic acid.Abbreviations CCCP
carbonylcyanide m-chlorophenylhydrazone
- 2,4-D
2,4-dichlorophenoxyacetic acid
- IAA
indolyl-3-acetic acid
- NAA
naphthalene-1-acetic acid
- NIG
nigeriein
- NPA
N-1-naphthylphthalamic acid
- TIBA
2,3,5-triiodobenzoic acid
- VAL
valinomycin 相似文献
5.
The 1-N-naphthylphthalamic acid (NPA)-binding protein is a putative negative regulator of polar auxin transport that has been shown
to block auxin efflux from both whole plant tissues and microsomal membrane vesicles. We previously showed that NPA is hydrolyzed
by plasma-membrane amidohydrolases that co-localize with tyrosine, proline, and tryptophan-specific aminopeptidases (APs)
in the cotyledonary node, hypocotyl-root transition zone and root distal elongation zone of Arabidopsisthaliana (L.) Heynh. seedlings. Moreover, amino acyl-β-naphthylamide (aa-NA) conjugates resembling NPA in structure have NPA-like
inhibitory activity on growth, suggesting a possible role of APs in NPA action. Here we report that the same aa-NA conjugates
and the AP inhibitor bestatin also block auxin efflux from seedling tissue. Bestatin and, to a lesser extent, some aa-NA conjugates
were more effective inhibitors of low-affinity specific [3H]NPA-binding than were the flavonoids quercetin and kaempferol but had no effect on high-affinity binding. Since the APs
are inhibited by flavonoids, we compared the localization of endogenous flavonoids and APs in seedling tissue. A correlation
between AP and flavonoid localization was found in 5- to 6-d-old seedlings. Evidence that these flavonoids regulate auxin
accumulation in vivo was obtained using the flavonoid-deficient mutant, tt4. In whole-seedling [14C]indole-3-acetic acid transport studies, the pattern of auxin distribution in the tt4 mutant was shown to be altered. The defect appeared to be in auxin accumulation, as a considerable amount of auxin escaped
from the roots. Treatment of the tt4 mutant with the missing intermediate naringenin restored normal auxin distribution and accumulation by the root. These results
implicate APs and endogenous flavonoids in the regulation of auxin efflux.
Received: 2 December 1999 / Accepted: 16 January 2000 相似文献
6.
Stieger PA Reinhardt D Kuhlemeier C 《The Plant journal : for cell and molecular biology》2002,32(4):509-517
Auxin is of vital importance in virtually every aspect of plant growth and development, yet, even after almost a century of intense study, major gaps in our knowledge of its synthesis, distribution, perception, and signal transduction remain. One unique property of auxin is its polar transport, which in many well-documented cases is a critical part of its mode of action. Auxin is actively transported through the action of both influx and efflux carriers. Inhibition of polar transport by the efflux inhibitor N-1-naphthylphthalamic acid (NPA) causes a complete cessation of leaf initiation, a defect that can be reversed by local application of the auxin, indole-3-acetic acid (IAA), to the responsive zone of the shoot apical meristem. In this study, we address the role of the auxin influx carrier in the positioning and outgrowth of leaf primordia at the shoot apical meristem of tomato. By using a combination of transport inhibitors and synthetic auxins, we demonstrate that interference with auxin influx has little effect on organ formation as such, but prevents proper localization of leaf primordia. These results suggest the existence of functional auxin concentration gradients in the shoot apical meristem that are actively set up and maintained by the action of efflux and influx carriers. We propose a model in which efflux carriers control auxin delivery to the shoot apical meristem, whereas influx and efflux carriers regulate auxin distribution within the meristem. 相似文献
7.
Carrier-mediated uptake of indole-3-acetic acid (IAA) by microsomal vesicles from Cucurbita pepo L. hypocotyls was strongly inhibited by 2,4-dichlorophenoxyacetic acid (2,4-D; i
50= 0.3 M) but only weakly by 1-naphthylacetic acid (NAA). The fully ionised auxin indol-3-yl methanesulphonic acid also inhibited (i
50=3 M). The same affinity ranking of these auxins for the uptake carrier, an electroimpelled auxin anion-H+ symport, is demonstrable in hypocotyl segments. The specificity of the auxin-anion eflux carrier was tested by the ability of different nonradioactive auxins to compete with [3H]IAA and reduce the stimulation of net radioactive uptake by N-1-naphthylphthalamic acid (NPA), a noncompetitive inhibitor of this carrier. By this criterion, NAA and IAA had comparable affinities, with 2,4-D interaction more weakly. Stimulation of [3H]IAA uptake by NAA, as a result of competition for the efflux carrier, could also be demonstrated when a suitable concentration of 2,4-D was used selectively to inhibit the uptake carrier. However, when [3H]NAA was used, no stimulation of its association with vesicles by NPA, 2,3,5-triiodobenzoic acid, or nonradioactive NAA was found. In hypocotyl segments, [3H]NAA net uptake was much less sensitive to NPA stimulation than was [14C]IAA uptake. The apparent contradictions concerning NAA could be explained by carrier-mediated auxin efflux making a smaller relative contribution to the overall transport of NAA than of IAA. The relationship between carrier specificity as manifested in vitro and the specificity of polar auxin transport is discussed.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- IAA
indole-3-acetic acid
- ION3
mixture of 4 M carbonylcyanide m-chlorophenylhydrazone, nigericin and valinomycin
- IMS
indol-3-yl methanesulphonic acid
- NAA
1-naphthylacetic aci
- NPA
N-1-naphthylphthalamic acid 相似文献
8.
Hosek P Kubes M Lanková M Dobrev PI Klíma P Kohoutová M Petrásek J Hoyerová K Jirina M Zazímalová E 《Journal of experimental botany》2012,63(10):3815-3827
The molecular basis of cellular auxin transport is still not fully understood. Although a number of carriers have been identified and proved to be involved in auxin transport, their regulation and possible activity of as yet unknown transporters remain unclear. Nevertheless, using single-cell-based systems it is possible to track the course of auxin accumulation inside cells and to specify and quantify some auxin transport parameters. The synthetic auxins 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthalene-1-acetic acid (NAA) are generally considered to be suitable tools for auxin transport studies because they are transported specifically via either auxin influx or efflux carriers, respectively. Our results indicate that NAA can be metabolized rapidly in tobacco BY-2 cells. The predominant metabolite has been identified as NAA glucosyl ester and it is shown that all NAA metabolites were retained inside the cells. This implies that the transport efficiency of auxin efflux transporters is higher than previously assumed. By contrast, the metabolism of 2,4-D remained fairly weak. Moreover, using data on the accumulation of 2,4-D measured in the presence of auxin transport inhibitors, it is shown that 2,4-D is also transported by efflux carriers. These results suggest that 2,4-D is a promising tool for determining both auxin influx and efflux activities. Based on the accumulation data, a mathematical model of 2,4-D transport at a single-cell level is proposed. Optimization of the model provides estimates of crucial transport parameters and, together with its validation by successfully predicting the course of 2,4-D accumulation, it confirms the consistency of the present concept of cellular auxin transport. 相似文献
9.
Short-Lived and Phosphorylated Proteins Contribute to
Carrier-Mediated Efflux, but Not to Influx, of Auxin in
Suspension-Cultured Tobacco Cells 总被引:9,自引:1,他引:8
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Auxin is transported across the plasma membrane of plant cells by diffusion and by two carriers operating in opposite directions, the influx and efflux carriers. Both carriers most likely play an important role in controlling auxin concentration and distribution in plants but little is known regarding their regulation. We describe the influence of modifications of the transmembrane pH gradient and the effect of agents interfering with protein synthesis, protein traffic, and protein phosphorylation on the activity of the auxin carriers in suspension-cultured tobacco (Nicotiana tabacum L.) cells. Carrier-mediated influx and efflux were monitored independently by measuring the accumulation of [14C]2,4-dichlorophenoxyacetic acid and [3H]naphthylacetic acid, respectively. The activity of the influx carrier decreased on increasing external pH and on decreasing internal pH, whereas that of the efflux carrier was only impaired on internal acidification. The efflux carrier activity was inhibited by cycloheximide, brefeldin A, and the protein kinase inhibitors staurosporine and K252a, as shown by the increased capability of treated cells to accumulate [3H]naphthylacetic acid. Kinetics and reversibility of the effect of brefeldin A were consistent with one or several components of the efflux system being turned over at the plasma membrane with a half-time of less than 10 min. Inhibition of efflux by protein kinase inhibitors suggested that protein phosphorylation was essential to sustain the activity of the efflux carrier. On the contrary, the pharmacological agents used in this study failed to inhibit [14C]2,4-dichlorophenoxyacetic acid accumulation, suggesting that rapidly turned-over proteins or proteins activated by phosphorylation are not essential to carrier-mediated auxin influx. Our data support the idea that the efflux carrier in plants constitutes a complex system regulated at multiple levels, in marked contrast with the influx carrier. Physiological implications of the kinetic features of this regulation are discussed. 相似文献
10.
Binding of fusicoccin (FC) to microsomal preparations of corn (Zea mays L.) coleoptiles is enhanced after incubation of the tissue with indole-3-acetic acid (IAA). Treatment of the kinetic data according to Scatchard shows that the enhancement is a consequence of an increase in the number of high-affinity FC-binding sites without changes of their KD. The minimal effective concentration of IAA is 10-7 M; above 10-5 M the effect declines. The stimulation is insensitive to protein-synthesis inhibitors (cycloheximide and puromycin). The same effect is observed with the synthetic auxins 2,4-dichlorophenoxyacetic acid and naphtalene-1-acetic acid while it is abolished by the auxin antagonists naphtalene-2-acetic acid and p-chlorophenoxyisobutyric acid. Since the above effect is only observed with intact tissue and not after incubation of IAA with microsomal preparations, a direct interaction of IAA with the FC-binding sites is ruled out and an alternative mechanism must be sought.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- FC
fusicoccin
- [3H]FC
3H-labeled dihydrofusicoccin
- IAA
indole-3-acetic acid
- 1-NAA
naphtalene-1-acetic acid
- 2-NAA
naphtalene-2-acetic acid
- PCIB
p-chlorophenoxyisobutyric acid 相似文献
11.
Analogues of auxin modifying growth and development of some monocot and dicot plants 总被引:1,自引:0,他引:1
The dependence of morphogenetic processes in the formation of vegetative and generative organs in spring oilseed rape and
barley on exogenously applied physiological analogues of auxin: 2,4-D (2,4-dichlorphenoxyacetic acid), NAA (naphthalene-1-acetic
acid), TA-12 (1-[2-chloroethoxycarbonyl-methyl]-4-naphthalenesulfonic acid calcium salt) and TA-14 (1-[2-dimethylaminoethoxicarbonylmethyl]naphtalene
chlormethylate) were investigated. The experiments were performed with hypocotyl tissue cultures of oilseed rape and barley
microspores in vitro. The auxin analogues applied revealed differences of morphogenetic competence in dedifferentiation-redifferentiation processes
that occurred in oilseed rape cultures. TA-12 and TA-14 applied together with NAA and BA (6-benzylaminopurine) caused more
intensive callus growth in comparison with 2,4-D. Rhizogenesis was induced when 2,4-D was substituted by TA-12. Compound TA-14,
unlike TA-12, facilitated the appearance and development of cotyledons in callus tissues. Hower the compounds TA-12 and TA-14
have no positive effect in monocot plant — barly anther culture for callogenesis and regeneration in comparison to indole-3-acetic
acid (IAA). TA-14 and TA-12 showed similar but not identical auxin properties and demonstrated high efficiency as modifiers
of rape-dicot plant growth and morphogenesis. 相似文献
12.
Inoculation and nitrate alter phytohormone levels in soybean roots: differences between a supernodulating mutant and the wild type 总被引:9,自引:0,他引:9
The levels of different cytokinins, indole-3-acetic acid (IAA) and abscisic acid (ABA) in roots of Glycine max [L.] Merr. cv. Bragg and its supernodulating mutant nts382 were compared for the first time. Forty-eight hours after inoculation with Bradyrhizobium, quantitative and qualitative differences were found in the root's endogenous hormone status between cultivar Bragg and the
mutant nts382. The six quantified cytokinins, ranking similarly in each genotype, were present at higher concentrations (30–196% on average
for isopentenyl adenosine and dihydrozeatin riboside, respectively) in mutant roots. By contrast, the ABA content was 2-fold
higher in Bragg, while the basal levels of IAA [0.53 μmol (g DW)−1, on average] were similar in both genotypes. In 1 mM NO3
−-fed Bragg roots 48 h post-inoculation, IAA, ABA and the cytokinins isopentenyl adenine, and isopentenyl adenosine quantitatively
increased with respect to uninoculated controls. However, only the two cytokinins increased in the mutant. High NO3
− (8 mM) markedly reduced root auxin concentration, and neither genotypic differences nor the inoculation-induced increase
in auxin concentration in Bragg was observed under these conditions. Cytokinins and ABA, on the other hand, were little affected
by 8 mM NO3
−. Root IAA/cytokinin and ABA/cytokinin ratios were always higher in Bragg relative to the mutant, and responded to inoculation
(mainly in Bragg) and nitrate (both genotypes). The overall results are consistent with the auxin-burst-control hypothesis
for the explanation of autoregulation and supernodulation in soybean. However, they are still inconclusive with respect to
the inhibitory effect of NO3
−.
Received: 16 April 1999 / Accepted: 13 December 1999 相似文献
13.
14.
Alain Delbarre Philippe Muller Viviane Imhoff Jean-Louis Morgat Hélène Barbier-Brygoo 《Planta》1994,195(2):159-167
Uptake and metabolism of exogenous naphthalene-1-acetic acid (NAA) and indole-3-acetic acid (IAA) have been studied in tobacco (Nicotiana tabacum L. cv. Xanthi) mesophyll protoplasts. Both auxins entered protoplasts by diffusion under the action of the transmembrane pH gradient without any detectable participation of an influx carrier. Molecules were accumulated by an anion-trapping mechanism and most of them were metabolized within hours, essentially as glucose-ester and amino-acid conjugates. Protoplasts were equipped with a functional auxin-efflux carrier as evidenced by the inhibitory effect of naphthylphtalamic acid on IAA efflux. Basically, similar mechanisms of NAA and IAA uptake occurred in protoplasts. However, the two auxins differed in their levels of accumulation, due to different membrane-transport characteristics, and the nature of the metabolites produced. This shows the need to estimate the accumulation and the metabolism of auxins when analyzing their effects in a given cell system. The internal auxin concentration could be modulated by changing the transmembrane pH gradient, giving an interesting perspective for discriminating between the effects of intra- and extracellular auxin on physiological processes.Abbreviations BA
benzoic acid
- Ci/Ce
accumulation ratio of auxin
- IAAasp
N-[3-indolylacetyl]-dl-aspartic acid
- NAA
naphthalene-1-acetic acid
- NAAasp
N-[1-naphthylacetyl]-l-aspartic acid
- NPA
N-1-naphthylphthalamic acid
The authors thank Dr. M. Caboche (I.N.R.A, Versailles, France) for his generous gifts of some amide derivatives of 1-NAA, Mr. P. Varennes and Dr. B. Das (I.C.S.N., C.N.R.S., Gif-sur-Yvette, France) for recording and interpreting the mass spectra of NAA glucose ester, and Prof. P. Manigault (Institut des Sciences Végétales, Gif-sur-Yvette) for microscopy measurements of protoplast dimensions. This work was supported by funds from the C.N.R.S, I.N.R.A, and E.E.C. 相似文献
15.
Parry G Delbarre A Marchant A Swarup R Napier R Perrot-Rechenmann C Bennett MJ 《The Plant journal : for cell and molecular biology》2001,25(4):399-406
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. 相似文献
16.
17.
Anions modify the response of guard-cell anion channels to auxin 总被引:4,自引:0,他引:4
The anion channel in the guard-cell plasma membrane of Vicia faba, GCAC1, possesses recognition sites for the plant growth hormone auxin at the extracellular mouth of the channel (Marten et al. 1991, Nature 353:759-762). Using the patch-clamp technique we could demonstrate that auxins induced a shift of the voltage dependence of the anion channel to hyperpolarized potentials; the shift was attenuated during an increase in the extracellular chloride concentration, indicating that chloride shields the hormone-binding site. The auxin-induced shift was concentration-dependent, characterized by a Michaelis-Menten type of behaviour with a half saturation constant (K
m) of about 10 M naphthalene-1-acetic acid (1-NAA) in the presence of 2 mM Cl– and 12 M in 80 mM Cl–. In the presence of malate, another gating modulator of GCAC1, auxins were less effective, indicating that both ligands compete for common sites. Inactive auxins with respect to stomatal opening or stimulation of the plasma membrane H+-ATPase, such as 2-NAA, modulated the activation threshold and kinetics of GCAC1 similar to the active form 1-NAA. At a concentration of 100 M 2-NAA the peak-current potential shifted by about 30 mV more negative.Abbreviations GCAC1
guard cell anion channel 1
- 1-NAA
naphthalene-1-acetic acid
- 2-NAA
naphthalene-2-acetic acid
- TEA
tetraethylammonium 相似文献
18.
The roles of fungal auxins in the regulation of elongation growth, photo-, and gravitropism are completely unknown. We analyzed the effects of exogenous IAA (indole-3-acetic acid), various synthetic auxins including 1-NAA (1-naphthaleneacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid), and the auxin transport inhibitor NPA (N-1-naphtylphtalamic acid) on the growth rate and bending of the unicellular sporangiophore of the zygomycete fungus, Phycomyces blakesleeanus. Sporangiophores that were submerged in an aqueous buffer responded to IAA with a sustained enhancement of the growth rate, while 1-NAA, 2,4-D, and NPA elicited an inhibition. In contrast, sporangiophores kept in air responded to IAA with a 20 to 40% decrease of the growth rate, while 1-NAA and NPA elicited an enhancement. The unilateral and local application of IAA in the growing zone of the sporangiophore elicited in 30 min a moderate negative tropic bending in wild type C2 and mutant C148madC, which was, however, partially masked by a concomitant avoidance response caused by the aqueous buffer. Auxin transport-related genes ubiquitous in plants were found in a BLAST search of the Phycomyces genome. They included members of the AUX1 (auxin influx carrier protein 1), PILS (PIN-LIKES, auxin transport facilitator protein), and ABCB (plant ATP-binding cassette transporter B) families while members of the PIN family were absent. Our observations imply that IAA represents an intrinsic element of the sensory transduction of Phycomyces and that its mode of action must very likely differ in several respects from that operating in plants. 相似文献
19.
The auxin-resistant diageotropica mutant of tomato responds to gravity via an auxin-mediated pathway
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.
Received: 16 July 1999 / Accepted: 24 September 1999 相似文献
20.
The Arabidopsis concentration-dependent influx/efflux transporter ABCB4 regulates cellular auxin levels in the root epidermis 总被引:1,自引:0,他引:1
Kubeš M Yang H Richter GL Cheng Y Młodzińska E Wang X Blakeslee JJ Carraro N Petrášek J Zažímalová E Hoyerová K Peer WA Murphy AS 《The Plant journal : for cell and molecular biology》2012,69(4):640-654
Arabidopsis ATP-binding cassette B4 (ABCB4) is a root-localised auxin efflux transporter with reported auxin uptake activity in low auxin concentrations. Results reported here demonstrate that ABCB4 is a substrate-activated regulator of cellular auxin levels. The contribution of ABCB4 to shootward auxin movement at the root apex increases with auxin concentration, but in root hair elongation assays ABCB4-mediated uptake is evident at low concentrations as well. Uptake kinetics of ABCB4 heterologously expressed in Schizosaccharomyces pombe differed from the saturation kinetics of AUX1 as uptake converted to efflux at threshold indole-3-acetic acid (IAA) concentrations. The concentration dependence of ABCB4 appears to be a direct effect on transporter activity, as ABCB4 expression and ABCB4 plasma membrane (PM) localisation at the root apex are relatively insensitive to changes in auxin concentration. However, PM localization of ABCB4 decreases with 1-naphthylphthalamic acid (NPA) treatment. Unlike other plant ABCBs studied to date, and consistent with decreased detergent solubility, ABCB4(pro) :ABCB4-GFP is partially internalised in all cell types by 0.05% DMSO, but not 0.1% ethanol. In trichoblasts, ABCB4(pro) :ABCB4-GFP PM signals are reduced by >200 nm IAA and 2,4-dichlorophenoxyacetic acid (2,4-D). In heterologous systems and in planta, ABCB4 transports benzoic acid with weak affinity, but not the oxidative catabolism products 2-oxindole-3-acetic-acid and 2-oxindole-3-acetyl-β-D-glucose. ABCB4 mediates uptake, but not efflux, of the synthetic auxin 2,4-D in cells lacking AUX1 activity. Results presented here suggest that 2,4-D is a non-competitive inhibitor of IAA transport by ABCB4 and indicate that ABCB4 is a target of 2,4-D herbicidal activity. 相似文献