Estimation of hyperauxinity during tumour formation in castor bean hypocotyls

The hyperauxinity of tumourous tissues of castor bean plants(Ricinus communis L. variety Pacific 6), infected by Agrobacteriumtumefaciens (Smith and Town) Conn, strain B6, was quantitativelyestimated. The auxin extracted was found to be indole-aceticacid (IAA), which gave a typical Ehrlich's reaction, an equalR.f. value and a characteristic indole UV spectrum which weresimilar to those of authentic IAA. The Avena coleoptile straightgrowth test revealed a higher auxin concentration in the typicalR.f. region (0.2–0.4) in the tumourous tissues than inthe control. Colorimetric estimation of the auxin concentrationin developing tumourous tissues revealed fluctuating hyperauxinitiesthroughout the test period. The possible nature of this fluctuationis discussed but it is still unexplained. (Received January 28, 1975; )     

Differentiation between indoleacetic Acid and the citrus auxin by column chromatography

A gradient elution column chromatography technique and a step-wise technique succeeded in differentiating between IAA and the citrus auxin. IAA was eluted ahead of the citrus auxin in both systems. The highest Avena curvature ever obtained from the citrus auxin occurred after the auxin had passed through the 2 purification techniques and a paper chromatography step. This is probably due to the elimination of inhibitors. Fluorometric assay, Ehrlich's reaction, thin-layer chromatography, and biological assay were used for the detection of IAA or citrus auxin in the column eluates.     

Habituation in sugarbeet callus: auxin content, auxin protectors, peroxidase pattern and inhibitors

A GC-ECD titration of IAA in normal auxin (2,4-D)-requiring and auxin-independent (habituated) sugarbeet callus revealed an equal amount in both tissues. A comparison of the content and pattern (through starch gel electrophoresis) of soluble, membrane and wall peroxidases indicated that normal tissues contained a higher level of isoperoxidases. Normal tissues also were found to contain higher levels of peroxidase inhibitors and auxin protectors. The hypothesized peroxidase-mediated higher rate of auxin destruction in normal sugarbeet callus is supposed to be counterbalanced by the 2,4-D-controlled auxin protectors.     

Functional characterization of PaLAX1, a putative auxin permease, in heterologous plant systems

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.     

The Effect of Kinetin on the Occurrence of Acid Auxin in Coleus blumei

Excised shoots and potted plants of Coleus blumei Benth, were subjected to different treatments with kinetin solutions. Control treatments were made with water. Free and bound auxin were extracted with ether. The acid fractions were purified by electrophoresis to remove all traces of kinetin, and were then analyzed with the Avena straight-growth test. As compared with the controls, kinetin treatment increases the bound auxin, whereas the corresponding free auxin is unchanged. Also methanol extracts of treated stems contain more acid auxin than corresponding extracts of water-treated stems. This indicates that on methanol extraction not only free auxin but also some bound auxin is obtained. The extracted auxin behaves like indoleacetic acid in paper chromatography with four different solvent systems, as well as in gel filtration through Sephadex. New formation or decreased breakdown of auxin seem the most likely explanations for the observed effects of kinetin.     

Abscission responses to moisture stress, auxin transport inhibitors, and ethephon

The three abscission-inducing agents - water stress, Ethephon, and auxin transport inhibitors-acted synergistically to promote leaf fall in cotton (Gossypium hirsutum L.). However, the synergism was primarily between stress and Ethephon. Auxin transport inhibitors did not promote the effect of stress alone, only promoted the effect of Ethephon in well watered plants and gave a very small promotion with stress and Ethephon together. Abscission was rapid in stressed plants treated with Ethephon and an auxin transport inhibitor, while leaves fell more slowly from well watered plants treated with Ethephon alone. This suggests that water stress or auxin transport inhibitors influence initial events in abscission; since an auxin transport inhibitor will replace the effect of stress but not Ethephon, an initial event in stress-induced abscission appears to be inhibition of auxin transport. Ethephon promoted lateral bud release, and auxin transport inhibitors did not duplicate that effect alone or promote it in combination with Ethephon.     

Starch Synthetase, Phosphorylase, ADPglucose Pyrophosphorylase, and UDPglucose Pyrophosphorylase in Developing Maize Kernels

Three types of whole plant experiments are presented to substantiate the concept that an important function of ethylene in abscission is to reduce the transport of auxin from the leaf to the abscission zone. (a) The inhibitory effect of ethylene on auxin transport, like ethylene-stimulated abscission, persists only as long as the gas is continuously present. Cotton (Gossypium hirsutum L. cv. Stoneville 213) and bean (Phaseolus vulgaris L. cv. Resistant Black Valentine) plants placed in 14 μl/l of ethylene for 24 or 48 hours showed an increase in leaf abscission and a reduced capacity to transport auxin; but when returned to air, auxin transport gradually increased and abscission ceased. (b) Ethylene-induced abscission and auxin transport inhibition show similar sensitivities to temperature. A 24-hour exposure of cotton plants to 14 μl/l of ethylene at 8 C resulted in no abscission and no significant inhibition of auxin transport. Increasing the temperature during ethylene treatment resulted in a progressively greater reduction in auxin transport with abscission occurring at [unk]27 C where auxin transport was inhibited over 70%. (c) Auxin pretreatment reduced both ethylene-induced abscission and auxin transport inhibition. No abscission occurred, and auxin transport was inhibited only 18% in cotton plants which were pretreated with 250 mg/l of naphthalene acetic acid and then placed in 14 μl/l of ethylene for 24 hours. In contrast, over 30% abscission occurred, and auxin transport was inhibited 58% in the corresponding control plants.     

The Interactions among DWARF10, Auxin and Cytokinin Underlie Lateral Bud Outgrowth in Rice

Previous studies have shown that DWARF10 (D10) is a rice ortholog of MAX4/RMS1/DAD1, encoding a carotenoid cleavage dioxygenase and functioning in strigolactones/strigolactone-derivatives (SL)biosynthesis. Here we use D10- RNA interference (RNAi) transgenic plants similar to d10 mutant in phenotypes to investigate the interactions among D10, auxin and cytokinin in regulating rice shoot branching. Auxin levels in node 1 of both decapitated D10-RNAi and wild type plants decreased significantly, showing that decapitation does reduce endogenous auxin concentration, but decapitation has no clear effects on auxin levels in node 2 of the same plants. This implies that node 1 may be the location where a possible interaction between auxin and D10 gene would be detected. D10 expression in node 1 is inhibited by decapitation, and this inhibition can be restored by exogenous auxin application,indicating that D10 may play an important role in auxin regulation of SL. The decreased expression of most OsPINs in shoot nodes of D10- RNAi plants may cause a reduced auxin transport capacity.Furthermore, effects of auxin treatment of decapitated plants on the expression of cytokinin biosynthetic genes suggest that D10 promotes cytokinin biosynthesis by reducing auxin levels. Besides, in D10- RNAi plants, decreased storage cytokinin levels in the shoot node may partly account for the increased active cytokinin contents, resulting in more tillering phenotypes.     

Over-expression of OsAGAP, an ARF-GAP, interferes with auxin influx, vesicle trafficking and root development

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.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

The auxin content (extractable and ‘diffusible’ auxin) of non-sterile corn plants is much more increased by a tryptophan application than the auxin content of sterile plants. This effect is independent of the mode of tryptophan application (spray or supply with the transpiration stream). The epiphytic bacteria settling the shoot surface are responsible for this effect, since in special experiments the rhizosphere was separated from the tryptophan treatment. Sterilized plants which were artificially reinfected with epiphytic IAA-producing bacteria strains behave like non-sterile plants. Non-sterile plants which were superinfected with these bacteria strains have a still higher capacity to convert tryptophan to auxin.     

Effect of simulated microgravity on auxin polar transport in inflorescence axis of Arabidopsis thaliana.

The morphology, growth and development of higher plants are strongly influenced by environmental stimuli on the earth, which affect the changes in the dynamics of plant hormones in plants. Qualitative and quantitative changes in plant hormones are the most important internal factor to regulate plant growth and development. Among them, auxin (IAA) is of most significant. There are numerous reports concerning the physiological roles of auxin in plant growth and development (Matthysse and Scott 1984). One of the characteristics of auxin is to have the ability of polar transport along the vector of gravity on the earth (Schneider and Wightman 1978), suggesting that the activity of auxin polar transport is also important for the growth and development of plants. It has recently been reported that the normal activity of auxin polar transport in inflorescence axis of Arabidopsis thaliana was required for flower formation (Okada et al. 1991, Ueda et al. 1992). Considering the above evidence together with the fact that gravity affects the morphology, growth and development of higher plants, gravity might affect the qualitative and quantitative changes in plant hormones including the activity of auxin polar transport. In this paper, we report the effect of microgravity condition simulated by a three-dimensional (3-D) or a horizontal clinostat on the activity of auxin polar transport in inflorescence axis of Arabidopsis thaliana.     

高等植物局部生长素合成的生物学功能及其调控机制

局部生长素合成是目前植物生长素研究领域中的重要热点之一, 受内源发育信号和外界环境因子的时空调控。局部生长素合成在植物配子体发生、胚胎与果实发育、器官发生、向性生长和逆境响应中具有重要的生物学功能。该文在扼要介绍生长素局部合成与顶端合成、极性运输及其稳态之间互作的基础上, 重点介绍了近年来有关局部生长素合成的生物学功能及其调控机制的最新进展。     

Arabidopsis monothiol glutaredoxin, AtGRXS17, is critical for temperature-dependent postembryonic growth and development via modulating auxin response

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.     

WEG1, which encodes a cell wall hydroxyproline-rich glycoprotein,is essential for parental root elongation controlling lateral root formation in rice

Lateral roots (LRs) determine the overall root system architecture, thus enabling plants to efficiently explore their underground environment for water and nutrients. However, the mechanisms regulating LR development are poorly understood in monocotyledonous plants. We characterized a rice mutant, wavy root elongation growth 1 (weg1), that produced higher number of long and thick LRs (L-type LRs) formed from the curvatures of its wavy parental roots caused by asymmetric cell growth in the elongation zone. Consistent with this phenotype, was the expression of the WEG1 gene, which encodes a putative member of the hydroxyproline-rich glycoprotein family that regulates cell wall extensibility, in the root elongation zone. The asymmetric elongation growth in roots is well known to be regulated by auxin, but we found that the distribution of auxin at the apical region of the mutant and the wild-type roots was symmetric suggesting that the wavy root phenotype in rice is independent of auxin. However, the accumulation of auxin at the convex side of the curvatures, the site of L-type LR formation, suggested that auxin likely induced the formation of L-type LRs. This was supported by the need of a high amount of exogenous auxin to induce the formation of L-type LRs. These results suggest that the MNU-induced weg1 mutated gene regulates the auxin-independent parental root elongation that controls the number of likely auxin-induced L-type LRs, thus reflecting its importance in improving rice root architecture.     

The role of auxin transport during inflorescence development in maize (Zea mays, Poaceae)

Axillary meristems play a fundamental role in inflorescence architecture. Maize (Zea mays) inflorescences are highly branched panicles because of the production of multiple types of axillary meristems. We used auxin transport inhibitors to show that auxin transport is required for axillary meristem initiation in the maize inflorescence. The phenotype of plants treated with auxin transport inhibitors is very similar to that of barren inflorescence2 (bif2) and barren stalk1 (ba1) mutants, suggesting that these genes function in the same auxin transport pathway. To dissect this pathway, we performed RNA in situ hybridization on plants treated with auxin transport inhibitors. We determined that bif2 is expressed upstream and that ba1 is expressed downstream of auxin transport, enabling us to integrate the genetic and hormonal control of axillary meristem initiation. In addition, treatment of maize inflorescences with auxin transport inhibitors later in development results in the production of single instead of paired spikelets. Paired spikelets are a key feature of the Andropogoneae, a group of over 1000 grasses that includes maize, sorghum, and sugarcane. Because all other grasses bear spikelets singly, these results implicate auxin transport in the evolution of inflorescence architecture. Furthermore, our results provide insight into mechanisms of inflorescence branching that are relevant to all plants.     

Auxin, self-organisation, and the colonial nature of plants

Evolution has provided at least two particularly successful independent solutions to the problems of multicellularity - animals and higher plants. An obvious requirement for successful multicellularity is communication between different parts of the organism, both locally, for example between neighbouring cells, and over very long distances. Recent advances in understanding hormone signalling networks in plants are beginning to reveal how co-ordination of activity across the whole plant body can be achieved despite the lack of a control centre, typical of animal systems. Of particular importance in this distributed regulatory approach are the self-organising properties of the transport system for the plant hormone auxin. This review examines the integrative role of the auxin transport network in co-ordinating plant growth and development.