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PubMed2004

Phytohormones and shoot growth in a three-generation hybrid poplar family.

Hybrid vigor for secondary growth in poplar has been linked with increased gibberellin (GA) concentration in cambial tissue, but the relationship between concentrations of GAs and hybrid vigor of primary growth has not been investigated. We explored associations between concentrations of GAs, abscisic acid (ABA) and indoleacetic acid (IAA) and shoot extension in a hybrid family of Populus deltoides Bartr. ex Marsh. (Clone ILL-129) and P. trichocarpa Torr. & Gray (Clone 93-968) and two F1 and 67 F2 genotypes. Rapidly elongating subapical internodes from shoots of 4-year-old clonal saplings were selected for hormone analysis. The F1 hybrids displayed heterosis (hybrid vigor) for primary growth as a result of the complementation of dominance for increased internode length from the P. trichocarpa parent and dominance for increased diameter from the P. deltoides parent. Internodes from the faster-elongating shoots of the P. trichocarpa parent had a fourfold higher concentration of bioactive GA1 and higher concentrations of GA20, GA44, GA29 and GA8 than the P. deltoides parent. However, the two fast-growing F1 hybrids had low concentrations of all five GAs, with concentrations similar to those of the slower-elongating P. deltoides parent. Concentrations of ABA and IAA were correlated with GA concentrations and there was thus no evidence of a consistent promoting or inhibiting effect of ABA or IAA within the F1 family. These results indicate that heterosis for internode growth was not primarily regulated by hormone concentration. The segregating population of F2 hybrids was analyzed to assess the possible utility of hormone screening as a selection tool. The internodes of most of the F2 hybrids were smaller than those of their F1 parents and the larger P. trichocarpa parent. Among the F2 hybrids, mature internode length varied fourfold, and was correlated with lengths of young, subapical internodes from which hormones were analyzed. In these internodes, GA1 concentrations were negatively correlated with length (r = 0.41), diameter (0.33) and mass (0.50). Indoleacetic acid concentration was negatively correlated only with diameter (r = 0.37) and positively correlated with GA1 (r = 0.46), whereas ABA concentration was not correlated with any parameter. Thus, in the F2 population, variation in hormone concentration was not primarily responsible for the variation in shoot growth, indicating that selection for individuals with high GA concentration may not be an effective strategy for identifying vigorous hybrid genotypes.

Abscisic Acid↗
PubMed2004

Induction of phytohormones and differential gene expression in citrus flowers infected by the fungus Colletotrichum acutatum.

Colletotrichum acutatum infects citrus petals and induces premature fruit drop and the formation of persistent calyces. The accumulation of hormones and other growth regulators, and differential gene expression in affected flowers and young fruit, was examined following fungal infection. Ethylene evolution increased threefold and indole-3-acetic acid (IAA) accumulation was as much as 140 times. Abscisic acid (ABA) levels showed no significant response. After infection, both trans- and cis-12-oxo-phytodienoic acid increased 8- to 10-fold. No significant difference of transjasmonic acid (JA) was observed in citrus flower petals or pistils. However, a fivefold increase of cis-JA was detected. The amount of salicylic acid (SA) was elevated twofold in affected petals, but not in pistils. Northern blot analyses revealed that the genes encoding ACC oxidase or ACC synthase, and 12-oxo-phytodienoic acid (12-oxo-PDA) reductase, were highly expressed in affected flowers. The genes encoding auxin-related proteins also were upregulated. Application of 2-(4-chlorophenoxy)-2-methyl-propionic acid (clofibrate; a putative auxin inhibitor), 2,3,5-triiodobenzolic acid (an auxin transport inhibitor), or SA after inoculation significantly decreased the accumulation of the gene transcripts of auxin-responsive, GH3-like protein and 12-oxo-PDA reductase, but resulted in higher percentages of young fruit retention. The results indicate that imbalance of IAA, ethylene, and JA in C. acutatum-infected flowers may be involved in symptom development and young fruit drop.

Citrus↗
PubMed1996

Exogenous phytohormone-independent growth and regeneration of tobacco plants transgenic for the 6b gene of Agrobacterium tumefaciens AKE10.

The 6b gene of Agrobacterium tumefaciens AKE10 (AK-6b) induces crown gall tumors on certain plants but so far there have been no reports of the gene being able to induce tumors on culture medium. We cloned T-DNA segments containing the 6b gene but lacking the auxin and cytokinin biosynthesis genes from A. tumefaciens AKE10. Tobacco (Nicotiana tabacum) leaf discs infected with A. tumefaciens LBA4404 carrying the clones produced shooty calli on hormone-free Murashige-Skoog medium. The relevant T-DNA segment was integrated into plant DNA as determined by Southern hybridization. Some of these immature shoots spontaneously developed into mature shoots, of which several leaves displayed morphological abnormalities. When leaf discs of these mature plants were placed onto the same medium numerous shoots developed from the wounding sites, indicating that the transgenic plants possessed a high regenerative potential. Northern blot and reverse transcriptase-polymerase chain reaction analyses showed a large accumulation of the AK-6b transcripts in the shooty calli, but only a limited degree in mature plants, demonstrating that AK-6b expression is regulated in plants and essential for the early stages of regeneration. Cytokinin levels in the shooty calli were comparable to those in normal shoots, suggesting that shoot regeneration is not mediated by the modulation of cytokinin content.

Agrobacterium tumefaciens↗
PubMed1972

The level of phytohormones in monoecious and gynoecious cucumbers as affected by photoperiod and ethephon.

The endogenous levels of auxin, gibberellin, and inhibitors were followed in monoecious and gynoecious cucumber (Cucumis sativus L.) plants, and in plants treated with the ethylene-releasing compound Ethephon (2-chloroethyl phosphonic acid). Higher auxin inhibitor and lower gibberellin levels were associated with female tendency. The endogenous level of gibberellin and auxin decreased in Ethephon-treated plants. Application of Ethephon induced a rise in abscisic acid. Root application of abscisic acid promoted female tendency of gynoecious cucumbers grown under conditions which increase maleness. High CO(2) levels, which are known to antagonize ethylene, increased maleness of gynoecious cucumbers. The possibility of interrelationship between gibberellin, auxin, ethylene, and abscisic acid on sex expression are discussed.

Journal Article↗
PubMed1983

Phytohormones, Rhizobium Mutants, and Nodulation in Legumes : III. Auxin Metabolism in Effective and Ineffective Pea Root Nodules.

High specific activity [(3)H]indole-3-acetic acid (IAA) was applied to the apical bud of intact pea (Pisum sativum L. cv Greenfeast) plants. Radioactivity was detected in all tissues after 24 hours. More radioactivity accumulated in the nodules than in the parent root on a fresh weight basis and more in effective (nitrogen-fixing) nodules than in ineffective nodules (which do not fix nitrogen).For most samples, thin layer chromatography revealed major peaks of radioactivity at the R(F) values of IAA and indole-3-acetylaspartic acid (IAAsp) and further evidence of the identity of these compounds was obtained by chromatography in other systems. Disintegrations per minute due to IAA per unit fresh weight were significantly greater for root than for nodule tissue, but were not significantly different for effective and ineffective nodules. Radioactivity due to IAAsp, expressed both on a percentage basis and per unit fresh weight, was significantly greater for nodule than for root tissue and significantly greater for the effective nodules than for the ineffective nodules. When [(3)H]IAA was applied to effective nodules, IAAsp was the dominant metabolite in the nodule. The data suggest that metabolism of auxins may be important for the persistence of a functional root nodule.

Journal Article↗
PubMed1984

Phytohormones, Rhizobium mutants, and nodulation in legumes : v. Cytokinin metabolism in effective and ineffective pea root nodules.

[(3)H]Zeatin riboside was supplied to intact pea (Pisum sativum) plants either onto the leaves or onto the root nodules. When applied directly to nodules, approximately 70% of recovered radioactivity remained in the nodules, approximately 15% was detected in the root system, and 15% was in the shoot. However, when supplied to the leaves, little (3)H was transported, with approximately 0.05% of recovered radioactivity being found in the root system and nodules. On a fresh weight basis, nodules accumulated more (3)H than the parent root. In both types of studies, metabolites with an intact zeatin moiety were detected in root nodules.In all experiments, two-dimensional thin layer chromatography revealed that little (3)H remained as zeatin riboside in root or nodule tissue at the end of the labeling period. Nodules metabolized [(3)H]zeatin riboside to the following cytokinins/cytokinin metabolites: zeatin, adenosine, adenine, the O-glucosides of zeatin and zeatin riboside, lupinic acid, nucleotides of adenine and zeatin, and the dihydro derivatives of many of these compounds.Although a few small differences were observed, there were no major differences between root and nodule tissue in their metabolism of [(3)H] zeatin riboside. Furthermore, any differences between effective and ineffective nodules were generally minor.

Journal Article↗
PubMed1989

Roles of carbohydrate supply and phytohormones in maize kernel abortion.

Kernels at the ear tip of field grown maize (Zea mays L.) often abort during flowering, resulting in significant yield loss. The objective of this study was to determine if abortion is initiated by an inadequate supply of carbohydrates for growth of ear tip kernels, and/or by a hormonal signal. Field grown maize plants were either unshaded or shaded during flowering to increase kernel abortion. Nonstructural carbohydrates, indoleacetic acid (IAA), abscisic acid (ABA), and cytokinins were measured in aborting and nonaborting kernels, before and after abortion occurred. Kernel abortion was initiated 8 days after anthesis (DAA) and was complete by 12 DAA, when kernels ceased dry weight accumulation. Concentrations of reducing sugars, sucrose, and starch in aborting kernels were not significantly different from those in nonaborting kernels up to 12 DAA. Also, total carbohydrate concentrations were higher in the cob of aborting than of nonaborting kernels from 8 to 26 DAA. These data suggest that kernel abortion is not initiated by an inadequate supply of carbohydrates. However, accumulation of reducing sugars in the cob of aborting kernels suggests that transfer of sugars from cob to kernels is impaired early in the abortion process. Differences in IAA, ABA, and cytokinin concentrations between aborting and nonaborting kernels were only observed after abortion was complete. Kernel abortion is apparently not initiated by a signal of these hormones. After completion of abortion, aborted kernels contained higher concentrations of ABA and lower concentrations of IAA than nonaborted kernels. There was also a trend toward higher concentrations of zeatin riboside in nonaborted kernels. Abscisic acid may promote kernel abortion after the process has been initiated. A mechanism for kernel abortion is discussed.

Journal Article↗
PubMed2006

Integration of plant responses to environmentally activated phytohormonal signals.

Plants live in fixed locations and survive adversity by integrating growth responses to diverse environmental signals. Here, we show that the nuclear-localized growth-repressing DELLA proteins of Arabidopsis integrate responses to independent hormonal and environmental signals of adverse conditions. The growth restraint conferred by DELLA proteins is beneficial and promotes survival. We propose that DELLAs permit flexible and appropriate modulation of plant growth in response to changes in natural environments.

Abscisic Acid↗
PubMed1996

Modification of phytohormone response by a peptide encoded by ENOD40 of legumes and a nonlegume.

The gene ENOD40 is expressed during early stages of legume nodule development. A homolog was isolated from tobacco, which, as does ENOD40 from legumes, encodes an oligopeptide of about 10 amino acids. In tobacco protoplasts, these peptides change the response to auxin at concentrations as low as 10(-12) to 10(-16)M. The peptides encoded by ENOD40 appear to act as plant growth regulators.

Amino Acid Sequence↗
PubMed2004

Plant G proteins, phytohormones, and plasticity: three questions and a speculation.

Heterotrimeric guanine nucleotide-binding proteins (G proteins) composed of Galpha, Gbeta, and Ggamma subunits are important transducers of hormonal signals in organisms as evolutionarily distant as plants and humans. The genomes of diploid angiosperms, such as that of the model species Arabidopsis thaliana, encode only single canonical Galpha and Gbeta subunits, only two identified Ggamma subunits, and just one regulator of G protein signaling (RGS) protein. However, a wide range of processes-including seed germination, shoot and root growth, and stomatal regulation-are altered in Arabidopsis and rice plants with mutations in G protein components. Such mutants exhibit altered responsiveness to a number of plant hormones, including gibberellins, brassinosteroids, abscisic acid, and auxin. This review describes possible mechanisms by which such pleiotropic effects are generated and considers possible explanations for why G protein component mutations in plants fail to be lethal. A possible role of G protein signaling in the control of phenotypic plasticity, a hallmark of plant growth, is also discussed.

Animals↗
PubMed1990

p34cdc2 homologue level, cell division, phytohormone responsiveness and cell differentiation in wheat leaves.

Formation of a plant involves generation of new cells by the division cycle and development in these of specialised structure and metabolism. Specialisation is accompanied by a decreasing capacity for division, which declines with particular rapidity in cells of monocotyledonous plants such as the cereals. Here we report that in wheat leaves a homologue of the cell cycle control protein p34(cdc2) participates in the control of these developmental programmes. Accumulation of p34(cdc2) to a maximum level in dividing cells and the cessation of its accumulation during subsequent cell growth and expansion indicate that it contributes specifically to division. There is a decline in p34(cdc2) level as cell differentiation proceeds, in close parallel with the previously established decline of cell division in response to auxin hormones. A basal level of p34(cdc2) in fully differentiated cells that is one-sixteenth of that in dividing cells correlates with their loss of capacity to divide. We conclude that p34(cdc2) level is controlled in diverse multicellular eukaryotes and suggest that it is an important element in the switch from cell division to differentiation.

Amino Acid Sequence↗
PubMed2002

A novel piezoelectric biosensor for the detection of phytohormone beta-indole acetic acid.

A novel piezoelectric immunosensor has been developed for the determination of beta-indole acetic acid (IAA) in dilute solutions. The detection is based on competitive immunoreaction between a hapten (IAA) and an antigen (IAA-BSA, hapten-protein conjugation) bound to an anti-IAA antibody, immobilized on a quartz crystal microbalance (QCM). The frequency change (y) of the sensor caused by antigen is linearly related to the logarithm of the concentration of IAA (x) in the range of 0.5 ng/ml - 5 microg/ml with a regression equation of the form y = -23x + 151 (r = 0.9937).

Animals↗