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PubMed1994

Inhibition of inward K+ channels and stomatal response by abscisic acid: an intracellular locus of phytohormone action.

Abscisic acid (ABA), a plant hormone whose production is stimulated by water stress, reduces the apertures of stomatal pores in the leaf surface, thereby lessening transpirational water loss. It has been thought that inhibition of stomatal opening and promotion of stomatal closure by ABA are initiated by the binding of extracellular ABA to a receptor located in the guard-cell plasma membrane. However, in the present research, we employ three distinct experimental approaches to demonstrate that ABA can act from within guard cells to regulate stomatal apertures. (i) The extent to which ABA inhibits stomatal opening and promotes stomatal closure in Commelina communis L. is proportional to the extent of ABA uptake, as assayed with [3H]ABA. (ii) Direct microinjection of ABA into the cytoplasm of Commelina guard cells precipitates stomatal closure. (iii) Application of ABA to the cytosol of Vicia faba L. guard-cell protoplasts via patch-clamp techniques inhibits inward K+ currents, an effect sufficient to inhibit stomatal opening. These results demonstrate an intracellular locus of phytohormone action and imply that the search for hormone receptor proteins should be extended to include intracellular compartments.

Abscisic Acid↗
PubMed1976

Effects of phytohormones on thermal denaturation profiles of Cymbidium DNA: indication of differential DNA replication.

Protocorm pieces of the orchid Cymbidium were aseptically cultured either without phytohormones, or with one of the growth promoting substances, auxin cytokinin, and gibberellin. The derivative melting profiles of the extracted DNA's differ from each other with respect to the size of various AT- and GC- rich fractions. Evidence has been obtained for the increase of the more AT--rich fractions in auxin-treated cultures, while gibberellin stimulated the expansion of the GC-rich fractions. These results are consistent with earlier cytological and cytochemical findings and indicate the involvement of hormone-controlled differential DNA replication in the development of Cymbidium protocorms in vitro.

Cells, Cultured↗
PubMed2004

Control of nodule number by the phytohormone abscisic Acid in the roots of two leguminous species.

The effects of the phytohormone abscisic acid (ABA) on plant growth and root nodule formation were analyzed in Trifolium repense (white clover) and Lotus japonicus, which form indeterminate and determinate nodules, respectively. In T. repense, although the number of nodules formed after inoculation with Rhizobium leguminosarum bv. trifolii strain 4S (wild type) was slightly affected by exogenous ABA, those formed by strain H1(pC4S8), which forms ineffective nodules, were dramatically reduced 28 days after inoculation (DAI). At 14 and 21 DAI, the number of nodules formed with the wild-type strain was decreased by exogenous ABA. In L. japonicus, the number of nodules was also reduced by ABA treatment. Thus, exogenous ABA inhibits root nodule formation after inoculation with rhizobia. Observation of root hair deformation revealed that ABA blocked the step between root hair swelling and curling. When the ABA concentration in plants was decreased by using abamine, a specific inhibitor of 9-cis-epoxycarotenoid dioxygenase, the number of nodules on lateral roots of abamine-treated L. japonicus increased dramatically, indicating that lower-than-normal concentrations of endogenous ABA enhance nodule formation. We hypothesize that the ABA concentration controls the number of root nodules.

Abscisic Acid↗
PubMed2000

Correlation of structural and physico-chemical parameters with the bioactivity of alkylated derivatives of indole-3-acetic acid, a phytohormone (auxin).

As part of molecular recognition studies on the phytohormone indole-3-acetic acid (IAA) a series of alkylated IAAs has been examined. Phenyl-ring substitution (alkyl = methyl and ethyl) at positions 4-, 6- or 7- as well as pyrrole substitution at the 2-site resulted in the six compounds which are analyzed: 2-Me-IAA, 4-Me-IAA, 6-Me-IAA, 7-Me-IAA, 4-Et-IAA and 6-Et-IAA. The structure-activity relationships investigated include those between the geometrical parameters of the molecular structures determined by X-ray analysis, the growth-promoting activities in the Avena coleoptile straight-growth bioassay and relative lipophilicities calculated from retention times on a reversed-phase HPLC column and from R(F) values in reversed-phase TLC. Lipophilicities are correlated with the moments of inertia, average polarizability, molecular mass, and the van der Waals radii of the ring substituents. The influence of substitution on the electronic properties of the indole ring and its geometry is discussed on the basis of the UV and 1H NMR spectra.

Avena↗
PubMed2006

Multiple phytohormones influence distinct parameters of the plant circadian clock.

Circadian systems coordinate endogenous events with external signals. In mammals, hormone-clock feedbacks are a well-known integration system. Here, we investigated phytohormone effects on plant-circadian rhythms via the promoter:luciferase system. We report that many hormones control specific features of the plant-circadian system, and do so in distinct ways. In particular, cytokinins delay circadian phase, auxins regulate circadian amplitude and clock precision, and brassinosteroid and abscisic acid modulate circadian periodicity. We confirmed the pharmacology in hormone synthesis and perception mutants, as rhythmic expression is predictably altered in an array of hormone-related mutants. We genetically dissected one mechanism that integrates hormone signals into the clock, and showed that the hormone-activated ARABIDOPSIS RESPONSE REGULATOR 4 and the photoreceptor phytochrome B are elements in the input of the cytokinin signal to circadian phase. Furthermore, molecular-expression targets of this signal were found. Collectively, we found that plants have multiple input/output feedbacks, implying that many hormones can function on the circadian system to adjust the clock to external signals to properly maintain the clock system.

Arabidopsis↗
PubMed2006

Nitrogen-fixing chemo-organotrophic bacteria isolated from cyanobacteria-deprived lichens and their ability to solubilize phosphate and to release amino acids and phytohormones.

AIMS: Cyanobacteria-deprived lichens of the species Canoparmelia caroliniana, Canoparmelia crozalsiana, Canoparmelia texana, Parmotrema sancti-angeli and Parmotrema tinctorum were screened for the presence of chemo-organotrophic nitrogen-fixing bacteria. METHODS AND RESULTS: Fifty-three lichen samples subjected to enrichment selection using a nitrogen-free minimal medium were positive for acetylene reduction. Seventeen isolates, able to fix nitrogen, belonged to Gamma-proteobacteria group and were identified as: Acinetobacter sp., Pantoea sp., Pseudomonas sp., Pseudomonas stutzeri, Serratia marcescens and Stenotrophomonas maltophilia, according to 16S rRNA gene sequences and biochemical tests. The excretion of amino acid and phytohormone and the ability of mineral phosphate solubilization were determined in 14 isolates. All isolates were able to release amino acids and 3-indoleacetic acid. About 64% of the isolates solubilized phosphates and 30% released ethylene. CONCLUSIONS: These data confirm sparse evidence from the literature on the occurrence of chemo-organotrophic nitrogen-fixing bacteria in cyanobacteria-deprived lichens; the isolates presented physiologic features which might benefit the host if they are expressed when the bacteria are harboured by lichens. SIGNIFICANCE AND IMPACT OF THE STUDY: Chemo-organotrophic nitrogen-fixing bacteria were isolated from a high percentage (72.6%) of cyanobacteria-deprived lichens. All isolates presented important physiological characteristics, some of which are being described here for the first time.

Amino Acids↗
PubMed2005

The phytotoxin coronatine and methyl jasmonate impact multiple phytohormone pathways in tomato.

Coronatine (COR) is a phytotoxin produced by several pathovars of Pseudomonas syringae and consists of coronafacic acid (CFA), an analog of methyl jasmonic acid (MeJA), and coronamic acid (CMA), which resembles 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor to ethylene. An understanding of how COR functions, is perceived by different plant tissues, and the extent to which it mimics MeJA remain unclear. In this study, COR and related compounds were examined with respect to structure and function. The results indicate that conjugation of CFA to an amino acid is required for optimal activity in tomato, including chlorosis, changes in chloroplast structure, cell wall thickening, accumulation of proteinase inhibitors, induction of anthocyanins, and root growth inhibition. cDNA microarrays were utilized to understand the molecular processes that are regulated by MeJA, COR, CFA and CMA in tomato leaves. A comparison of COR- and MeJA-regulated transcriptomes revealed that COR regulated 35% of the MeJA-induced genes. There was significant overlap in the number of COR and CFA-regulated genes with CFA impacting the expression of 39.4% of the COR-regulated genes. Taken together, the results of biological assays, ultrastructural studies, and gene expression profiling demonstrate that: (1) the intact COR molecule impacts signaling in tomato via the jasmonic acid, ethylene, and auxin pathways; (2) CMA does not function as a structural analog of ACC; (3) COR has a broader range of functions than either CFA or CMA; and (4) COR and MeJA share similar, but not identical activities and impact multiple phytohormone pathways in tomato.

Acetates↗
PubMed2003

Modulation of vacuolar H+ -pumps and aquaporin by phytohormones in rice seedling leaf sheaths.

The effects of exogenously applied gibberellic acid (GA(3)) or brassinolide (BL) on the H(+)-pumps and aquaporin in the vacuolar membrane of rice seedling leaf sheath were investigated. Antibodies against mung bean H(+)-PPase, the B subunit of V-ATPase, and radish tonoplast intrinsic protein (TIP) cross-reacted with the vacuolar membrane proteins of rice seedling leaf sheath. The results of immunoblot analysis showed that the amounts of H(+)-PPase and V-ATPase were retained at a high level for two days in the presence of GA(3), although the level gradually decreased without phytohormones, indicating that GA(3) has a promotive effect on the activities of vacuolar H(+)-pumps. However, the levels of V-ATPase and H(+)-PPase were increased on day 2 and then decreased when treated with BL. There were no visible differences in the level of TIP upon treatment with GA(3) and BL. In comparison with the water control, the activity of H(+)-PPase treated with BL was also retained at a relatively high level, suggesting that BL has a stimulative effect on the activities of H(+)-PPase. These results indicate that GA(3) and BL might be involved in the regulation of the quantity and activities of plant vacuolar H(+)-pumps.

Aquaporins↗
PubMedDate not supplied

[Phytohormones of rhizomes of the mint of various geographic origin in its annual developmental cycle].

We studied the ratio of cytokinins and abscisic acid in the rhizome tissues of two southern introduced forms of mint (GBS 1-94 and GBS 2-94) in the annual cycle of its development under the climatic conditions of the Middle Zone of Russia. The level of cytokinins exceeded that of free abscisic acid during the entire period of rhizome growth and development. Three peaks of an excess--zeatin riboside over abscisic acid were established: (a) during mass flowering, (b) after dying off terrestrial shoots, and (c) before the appearance of shoots of the next year vegetation. These peaks were most distinct in the GBS 2-94 mint. Zeatin riboside was the major identified cytokinin. The role of balance of phytohormones in rhizome tissues upon adaptation of the introduced mint forms to new climatic conditions is discussed.

Abscisic Acid↗
PubMed2000

[Effects of phytohormones on growth and content of depsides in Salvia miltiorrhiza suspension cells].

This paper deals with the effects of 2,4-D, BA and GA3 on the growth and content of two depsides (rosmarinic acid and lithospermic acid B) in suspension cells of Salvia miltiorrhiza. The results showed cell growth and rosmarinic acid content reached the maximum on the 12th day and lithospermic acid B content on the 16th day after incubating cells in the subculture medium MS + 2, 4-D 1 mg/L + KT 0.1 mg/L. This cell line was a growth-product-associated. With the same concentration (1 mg/L), 2, 4-D stimulated the cell growth but prohibited the formation of lithospermic acid B; GA3 inhabited the cell growth but stimulated the formation of two depsides; The effects of BA is between 2, 4-D and GA3. The concentration optimum of phytohormones tested displayed 3 mg/L for BA and 1 mg/L for GA3. For the optimum time of adding BA and GA3 was in med-term (the 8th day) and early term (at the beginning) of culture period respectively. The synergiatic function of BA and GA3 on the depside formation was also showed that adding GA3 (1 mg/L) was favour for the formation of lithospermic acid B of the suspension cell cultured in the medium containing BA 3 mg/L. The suitable time of adding GA3 was the 6the day after incubating cells in the medium of MS + BA 3 mg/L.

Benzofurans↗
PubMedDate not supplied

[Effect of ambiol and 2-chloroethylphosphonic acid on the content of phytohormones in potato leaves and tubers].

The effects of the antioxidant Ambiol and 2-chlorethylphosphonic acid (2-CEPA) on individual concentrations and concentration ratios of phytohormones, photosynthesis and photophosphorylation rates, sucrose and starch content in tubers, and plant productivity were studied in potato (Solanum tuberosum L). Ambiol increased the ratio of indoleacetic acid (IAA) to abscisic acid (ABA), IAA/ABA, and that of zeatin (Z) and zeatin riboside (ZR) to ABA, (Z + ZR)/ABA. These effects were underlain by an increase in the content of auxins and cytokinins and a decrease in ABA. Unlike Ambiol, 2-CEPA increased the level of ABA, the effect being the most pronounced in the tubers. Ambiol increased the rates of photosynthesis and noncyclic photophosphorylation in chloroplasts isolated from potato leaves. The relation of this phenomenon to auxin and cytokinin accumulation, Ambiol- and 2-CEPA-induced changes in the hormonal balance of potato tubers, carbon metabolism, and plant productivity is discussed.

Antioxidants↗
PubMed2006

[Sugar beet (Beta vulgaris L.) morphogenesis in vitro: effects of phytohormone type and concentration in the culture medium, type of explants, and plant genotype on shoot regeneration frequency].

In vitro regeneration techniques have been optimized for seven strains and cultivars of sugar beet (Beta vulgaris L.) bred in Russia. The frequency of shoot regeneration from somatic cells and tissues of sugar beet varies from 10 to 97% depending on the explant type, culture-medium composition, and genotype. The in vitro regeneration potential has been estimated in plants with different genotypes. The effect of medium composition (phytohormones and carbohydrates) on the frequency of the formation of a morphogenic callus competent for plant regeneration has been determined. The effect of the types and concentrations of various cytokines (zeatin, kinetin, and 6-benzylaminopurine) on direct shoot regeneration from cotyledon nodes has been estimated. The culture-medium composition has been optimized for direct shoot regeneration from petioles. The effects of different concentrations of abscisic acid on the frequency of shoot regeneration from a morphogenic callus has been studied. Micropropagation has been used to obtain petiole explants and reproduce the shoots obtained by direct regeneration from cotyledon nodes, petioles, and calluses. Improved shoot-regeneration methods can be used for both agrobacterial and bioballistic genetic transformation of the sugar beet genotypes studied.

Beta vulgaris↗
PubMed2006

[Effects of Cd2+ on seedling growth and phytohormone contents of Glycine max].

A laboratory incubation experiment was conducted to study the effects of different Cd2+ concentrations on seedling growth and phytohormone contents of Glycine max through determining some physiological and biochemical indexes. The results showed as follows: (1) Different Cd2+ concentrations inhibited the synthesis of indoleacetic acid (IAA) and gibberellins (GA3) in roots and stimulated the synthesis of zeatin (Z) and abscisic acid (ABA) not only in roots but also in aerial parts of Glycine Max. Cd2+ stimulated the synthesis of IAA and GA3 in aerial parts at lower concentrations, but inhibited the synthesis of IAA and GA3 at higher concentrations. (2) Cd2+ stress for 84h increased the root vitality and the contents of chlorophyll a and b, but no significant difference was found in carotinoid contents compared with the control. (3) Cd2+ stress decreased POD activities and MAD contents atlower concentrations and increased POD activities and MAD contents at higher concentrations. With increasing Cd2+ concentrations, this increase became significant gradually. (4) Cd2+ stress with lower concentrations stimulated the physiological activity of Glycine max seedling in a short time. When Cd2+ concentration was 0.50 mg/L, the root vitality, IAA and GA3 contents of Glycine max were the highest, and POD activity was the lowest.

Abscisic Acid↗
PubMed1990

Phytohormones as specific inhibitors of Legionella pneumophila growth.

Legionellae have been found to be highly susceptible to a variety of biological products, which increases the difficulty of growing these microorganisms. We developed a hypotonic medium in which Legionella pneumophila and other legionellae grow well and multiply rapidly from small inocula. Several amino acids, mainly nonessential ones, inhibited the growth of legionellae at high concentrations (200-1,000 micrograms/ml). We describe a unique biological phenomenon of specific inhibition of growth of L. pneumophila by the plant growth hormone auxin (indole-3-acetic acid) and the closely related indole-3-propionic acid (IPA). The inhibition of growth was probably due to interference with the biosynthesis of L-tryptophan by the phytohormone or IPA. Other bacteria were found to be 50 to 100-fold more resistant to these agents. These findings may explain the peculiar ecology of legionellae. Bacterial susceptibility towards IPA (less than or equal to 5 micrograms/ml) may serve as a specific marker for the presence of legionellae.

Amino Acids↗
PubMed1981

[DNA methylation in wheat seedling and influence of phytohormones].

A labelled DNA is synthesized in the etiolated wheat seedlings 72 hrs after a single addition of [2-14C]orotic acid (1 mCi per 250 seedlings). This DNA does not differ in the methylation degree of cytosine residues and base composition (radioactivity ratios 100.m5C/(C+m5C) and T/(C++m5C) from total seeding DNA. Thus, the radioactivity ratio 100.m5C/(C+m5C) represents in fact the methylation degree of cytosine residues in labelled DNA, and [2-14C]orotic acid can be used for the study of DNA methylation in higher plants. The newly synthesized DNA (21 hr incubation of seedlings with radioactive precursor) is methylated about 2 times less in comparison with fully synthesized radioactive DNA and total seedling DNA. This supports the assumption on a step-wise character of replicative DNA methylation in plants. Phenylacetic acid (30 mg/l) and 6-benzylaminopurine (l mg/l) do not influence the post-replicative DNA methylation, but auxin (FAA) very strongly inhibits the replicative DNA methylation. The phytohormone-induced changes in replicative DNA methylation are considered as a possible mechanism for regulation of DNA replication and, probably, of cell differentiation in higher plants.

Adenine↗
PubMed2000

Rice (Oryza sativa L.) OsPR1b gene is phytohormonally regulated in close interaction with light signals.

Strategies evolved by plants to counteract a variety of biotic/abiotic stresses include induction of genes encoding pathogenesis-related (PR) protein, in particular the PR class 1 (PR1) gene family, widely used in stress response studies. In spite of its immense importance as a PR family member, and an accepted gene marker in plant disease/defense in dicots, little is known about rice PR1 genes. Recently, we cloned and characterized the first OsPR1a (rice acidic PR1) gene (Agrawal et al. (2000) Biochem. Biophys. Res. Commun. 274, 157-165). Here, we report characterization of a rice basic PR1 (OsPR1b) gene, identified from screening a cDNA library prepared from jasmonic acid (JA)-treated rice seedling leaf, providing detailed and valuable insights into rice PR1 gene expression. The deduced amino acid sequence of OsPR1b reveals only 63.1% homology with the OsPR1a protein, whereas Southern blot analyses indicate that OsPR1b is a multigene family. The JA-inducible OsPR1b gene was also up-regulated by salicylic acid (SA), abscisic acid (ABA), and kinetin (KN). Furthermore, protein phosphatase inhibitors, cantharidin (CN) and endothall (EN) strongly induced the OsPR1b transcript. However, OsPR1b was not cut-responsive, diagrammatically opposite to cut inducibility of OsPR1a. This induction was light-, time-, and dose-dependent, as demonstrated by using, JA, CN, and EN, and completely inhibited by cycloheximide, but not by tetracycline. The simultaneous application of SA, and ABA, with JA, respectively, showed almost complete inhibition of the JA-induced OsPR1b transcript by 200 microM SA or ABA, but not by 100 microM concentrated solutions, suggesting a potential interaction among JA, SA, and ABA, whereas KN dramatically enhanced JA-induced OsPR1b transcript upon simultaneous application. Moreover, a simultaneous application of staurosporine enhances JA-, CN-, and EN-induced OsPR1b transcript, in particular with CN. Finally, a comparative analysis with the OsPR1a gene gives us insight into the differential regulation of the PR1 gene family, while proposing OsPR1 genes as important gene markers in rice, with potential use(s) in analyzing plant defense responses.

Amino Acid Sequence↗
PubMed1996

Phytohormone control of the tobacco anionic peroxidase promoter.

The tobacco anionic peroxidase gene encodes the predominant peroxidase isoenzyme in the aerial portions of tobacco. Three kb of the peroxidase promoter was joined to the coding region of the Escherichia coli beta-glucuronidase gene (GUS), and transiently expressed in tobacco mesophyll protoplasts in the presence or absence of plant growth regulators. Benzyladenine, ethylene, and gibberellic acid did not affect peroxidase gene expression. Abscisic acid slightly inhibited expression at high concentrations. The auxins indole-3-acetic acid (IAA) and naphthaleneacetic acid strongly suppressed peroxidase expression. We observed half maximal suppression at 30 microM IAA. An anti-auxin, p-chlorophenoxyisobutyric acid (PCIB), enhanced expression from the peroxidase promoter above that of untreated controls or restored activity when used in combination with IAA. Sequencing 3 kb of the peroxidase promoter revealed many potential regulatory elements based on sequence homology to previously characterized genes. This includes several consensus transcription factor binding sites found in auxin-regulated promoters. 5' deletions of the peroxidase promoter/GUS fusion revealed several positive and negative regulatory elements. An upstream enhancer element was found between -3146 and -638 from the start of transcription. A strong silencer element was observed between -638 and -220. Removal of this silencer resulted in a truncated promoter (-220) with 100% activity of the full-length promoter (-3146). Inhibition by auxin was observed with all 5' deletions.

Base Sequence↗
PubMed2000

Inoculation and nitrate alter phytohormone levels in soybean roots: differences between a supernodulating mutant and the wild type.

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 micromol (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-.

Abscisic Acid↗