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PubMedDate not supplied

Responses of ABA and CTK to soil drought in leafless and leafy apple tree.

The authors tested the contents of ABA (abscisic acid), ZR (zeatin riboside), DHZR (dihydrozeatin riboside) and iPA (isopentenyl adenosine) in leafless and leafy apple trees (Red Fuji/Malus micromalus Makino) during soil drought stress. ABA concentration in drought stressed leafless trees increased significantly compared to the controls. ABA both in roots and xylem rose steadily in the earlier drought stage, reaching a maximum of 1.46 +/- 0.35 nmol g(-1) FW and 117 nmol l(-1) after the 8th day. Similar change patterns of ABA concentration was observed in the leafy trees during soil drought stress; ABA concentrations in roots and xylem sap increased and reached the maximum in the first three days; after 8th day, it decreased slightly, whereas leaf ABA concentration increased steadily in drought stressed plants throughout the duration of the experiment. Between drought stressed and control trees, no significant differences were observed in concentration of ZR and DHZR in both leafless and leafy trees; whereas iPA concentration of the drought stressed leafless and leafy plants decreased markedly in the later stage of drought. These results showed that endogenous ABA originated mainly from the roots in the earlier drought stage, and mainly from the leaves in the later drought stage. Total CTK showed no reduction in the earlier drought stage and decreased in the later drought stage.

Abscisic Acid↗
PubMed2001

The pathway of biosynthesis of abscisic acid in vascular plants: a review of the present state of knowledge of ABA biosynthesis.

The pathway of biosynthesis of abscisic acid (ABA) can be considered to comprise three stages: (i) early reactions in which small phosphorylated intermediates are assembled as precursors of (ii) intermediate reactions which begin with the formation of the uncyclized C40 carotenoid phytoene and end with the cleavage of 9'-cis-neoxanthin (iii) to form xanthoxal, the C15 skeleton of ABA. The final phase comprising C15 intermediates is not yet completely defined, but the evidence suggests that xanthoxal is first oxidized to xanthoxic acid by a molybdenum-containing aldehyde oxidase and this is defective in the aba3 mutant of Arabidopsis and present in a 1-fold acetone precipitate of bean leaf proteins. This oxidation precludes the involvement of AB-aldehyde as an intermediate. The oxidation of the 4'-hydroxyl group to the ketone and the isomerization of the 1',2'-epoxy group to the 1'-hydroxy-2'-ene may be brought about by one enzyme which is defective in the aba2 mutant and is present in the 3-fold acetone fraction of bean leaves. Isopentenyl diphosphate (IPP) is now known to be derived by the pyruvate-triose (Methyl Erythritol Phosphate, MEP) pathway in chloroplasts. (14C)IPP is incorporated into ABA by washed, intact chloroplasts of spinach leaves, but (14C)mevalonate is not, consequently, all three phases of biosynthesis of ABA occur within chloroplasts. The incorporation of labelled mevalonate into ABA by avocado fruit and orange peel is interpreted as uptake of IPP made in the cytoplasm, where it is the normal precursor of sterols, and incorporated into carotenoids after uptake by a carrier in the chloroplast envelope. An alternative bypass pathway becomes more important in aldehyde oxidase mutants, which may explain why so many wilty mutants have been found with this defect. The C-1 alcohol group is oxidized, possibly by a mono-oxygenase, to give the C-1 carboxyl of ABA. The 2-cis double bond of ABA is essential for its biological activity but it is not known how the relevant trans bond in neoxanthin is isomerized.

Abscisic Acid↗
PubMed2006

[The mechanism of ABA-induced apoplastic H2O2 accumulation in maize leaves].

In maize (Zea mays L.) cells, the sources of apoplast hydrogen peroxide (H(2)O(2)) induced by abscisic acid (ABA) has been proposed. Histochemical and cytochemical localization of ABA-induced H(2)O(2) production in leaves of maize was examined, using 3, 3-diaminobenzidine (DAB) and cerium chloride (CeCl(3)) staining respectively. Pretreatment with two different inhibitors for each enzymes, with diphenylene iodonium (DPI) and imidazole against NADPH oxidase, NaCN and NaN(3) against peroxidases (POD), and quinacrine and guazatine against polyamine oxidases (PAO), reduced H(2)O(2) accumulation induced by ABA. Among them, NADPH oxidase inhibitors arrested the production of apoplastic H(2)O(2) most strongly (Figs.1,2). Further studies showed that exogenous ABA treatment could enhance the activities of plasma membrane (PM) NADPH oxidase, cell wall POD and apoplast PAO significantly. Moreover, the activity of PM NADPH oxidase kept increasing before 1.5 h, while the other two enzymes began to decrease at 0.5 h within 2 h by ABA treatment (Fig.3). The results suggest that exogenous ABA treatment can lead to significant increases in H(2)O(2) accumulation in apoplast through up-regulating the activities of the PM NADPH oxidases, cell wall POD and apoplast PAO, of which the first one plays a central role in ABA-induced apoplastic H(2)O(2) accumulation.

Abscisic Acid↗
PubMed2026

From activation to desensitization: How ABA balances plant growth and abiotic stress response?

Abscisic acid (ABA) signaling is a central regulator of plant adaptation to abiotic stress, dynamically coordinating stress responses with growth and development. Rapid activation of ABA signaling promotes plant survival during the early stages of stress, whereas prolonged stress requires timely attenuation of the pathway to restore growth and prevent excessive stress responses. Recent studies have uncovered diverse mechanisms underlying ABA desensitization, including regulation of SnRK2 kinases, phytohormone crosstalk, nutrient signaling, protein trafficking, post-translational modifications, and feedback regulatory networks. Together, these interconnected mechanisms enable plants to fine-tune ABA signaling in response to developmental and environmental cues. In this review, we summarize recent advances in understanding the molecular mechanisms that attenuate ABA signaling and restore the balance between growth and stress adaptation during prolonged stress. We also highlight outstanding questions and discuss strategies for engineering ABA signaling dynamics to improve crop resilience, productivity, and adaptation to increasingly variable environments.

Abscisic Acid↗
PubMed2006

Improved somatic embryo maturation in loblolly pine by monitoring ABA-responsive gene expression.

During loblolly pine zygotic embryo development, increases in mRNAs for three ABA-responsive LEA-like genes coincided with the two developmental stage-specific peaks of endogenous ABA accumulation (Kapik et al. 1995). These ABA concentration profiles from zygotic embryo development were used to develop several tissue culture approaches that altered the exposure of somatic embryos to exogenous ABA. Elevating exogenous ABA at a time corresponding to mid-maturation improved the germination and resulted in more zygotic-like expression of selected genes in somatic embryos. Extending the time on maturation medium for a fourth month increased embryo yield, dry weight, and germination in high-and low-yield genotypes. Optimizing the amounts of embryogenic suspension, plated and exogenous ABA concentration increased from 22 to 66% in the early-stage bipolar embryos that developed to the cotyledonary stage.

Abscisic Acid↗
PubMed2006

Regulation of carotenoid and ABA accumulation during the development and germination of Nicotiana plumbaginifolia seeds.

Abscisic acid (ABA) is derived from epoxycarotenoid cleavage and regulates seed development and maturation. A detailed carotenoid analysis was undertaken to study the contribution of epoxycarotenoid synthesis to the regulation of ABA accumulation in Nicotiana plumbaginifolia developing seeds. Maximal accumulation of xanthophylls occurred at mid-development in wild type seeds, when total ABA levels also peaked. In contrast, in ABA-deficient mutants xanthophyll synthesis was delayed, in agreement with the retardation in seed maturation. Seed dormancy was restored in mutants impaired in the conversion of zeaxanthin into violaxanthin by zeaxanthin epoxidase (ZEP), by the introduction of the Arabidopsis AtZEP gene under the control of promoters inducing expression during later stages of seed development compared to wild type NpZEP, and in dry and imbibed seeds. Alterations in the timing and level of ZEP expression did not highly affect the temporal regulation of ABA accumulation in transgenic seeds, despite notable perturbations in xanthophyll accumulation. Therefore, major regulatory control of ABA accumulation might occur downstream of epoxycarotenoid synthesis.

Abscisic Acid↗
PubMed2002

Monitoring the expression pattern of around 7,000 Arabidopsis genes under ABA treatments using a full-length cDNA microarray.

Full-length cDNAs are essential for functional analysis of plant genes. Recently, cDNA microarray analysis has been developed for quantitative analysis of global and simultaneous analysis of expression profiles. Microarray technology is a powerful tool for identifying genes induced by environmental stimuli or stress and for analyzing their expression profiles in response to environmental signals. We prepared an Arabidopsis full-length cDNA microarray containing around 7,000 independent full-length cDNA groups and analyzed the expression profiles of genes. The transcripts of 245, 299, 54 and 213 genes increased after abscisic acid (ABA), drought-, cold-, and salt-stress treatments, respectively, with inducibilities more than fivefold compared with those of control genes [corrected]. The cDNA microarray analysis showed that many ABA-inducible genes were induced after drought- and high-salinity-stress treatments, and that there is more crosstalk between drought and ABA responses than between ABA and cold responses. Among the ABA-inducible genes identified, we identified 22 transcription factor genes, suggesting that many transcriptional regulatory mechanisms exist in the ABA signal transduction pathways.

Abscisic Acid↗
PubMed2006

Suppression by ABA of salicylic acid and lignin accumulation and the expression of multiple genes, in Arabidopsis infected with Pseudomonas syringae pv. tomato.

Abscisic acid (ABA) has been implicated in determining the outcome of interactions between many plants and their pathogens. We had previously shown that increased concentrations of ABA within leaves of Arabidopsis induced susceptibility towards an avirulent strain of Pseudomonas syringae pathovar (pv.) tomato. We now show that ABA induces susceptibility via suppression of the accumulation of components crucial for a resistance response. Lignin and salicylic acid concentrations in leaves were increased during a resistant interaction but reduced when plants were treated with ABA. The reduction in lignin and salicylic acid production was independent of the development of the hypersensitive response (HR), indicating that, in this host-pathogen system, HR is not required for resistance. Genome-wide gene expression analysis using microarrays showed that treatment with ABA suppressed the expression of many defence-related genes, including those important for phenylpropanoid biosynthesis and those encoding resistance-related proteins. Together, these results show that resistance induction in Arabidopsis to an avirulent strain of P. syringae pv. tomato is regulated by ABA.

Abscisic Acid↗
PubMed2005

Sorghum bicolor's transcriptome response to dehydration, high salinity and ABA.

Genome wide changes in gene expression were monitored in the drought tolerant C4 cereal Sorghum bicolor, following exposure of seedlings to high salinity (150 mM NaCl), osmotic stress (20% polyethylene glycol) or abscisic acid (125 microM ABA). A sorghum cDNA microarray providing data on 12,982 unique gene clusters was used to examine gene expression in roots and shoots at 3- and 27-h post-treatment. Expression of approximately 2200 genes, including 174 genes with currently unknown functions, of which a subset appear unique to monocots and/or sorghum, was altered in response to dehydration, high salinity or ABA. The modulated sorghum genes had homology to proteins involved in regulation, growth, transport, membrane/protein turnover/repair, metabolism, dehydration protection, reactive oxygen scavenging, and plant defense. Real-time PCR was used to quantify changes in relative mRNA abundance for 333 genes that responded to ABA, NaCl or osmotic stress. Osmotic stress inducible sorghum genes identified for the first time included a beta-expansin expressed in shoots, actin depolymerization factor, inositol-3-phosphate synthase, a non-C4 NADP-malic enzyme, oleosin, and three genes homologous to 9-cis-epoxycarotenoid dioxygenase that may be involved in ABA biosynthesis. Analysis of response profiles demonstrated the existence of a complex gene regulatory network that differentially modulates gene expression in a tissue- and kinetic-specific manner in response to ABA, high salinity and water deficit. Modulation of genes involved in signal transduction, chromatin structure, transcription, translation and RNA metabolism contributes to sorghum's overlapping but nonetheless distinct responses to ABA, high salinity, and osmotic stress. Overall, this study provides a foundation of information on sorghum's osmotic stress responsive gene complement that will accelerate follow up biochemical, QTL and comparative studies.

Abscisic Acid↗
PubMed2006

Modification of plasma membrane and vacuolar H+ -ATPases in response to NaCL and ABA.

The role of ABA in the modification of membrane proton pump activity in cucumber roots which had been stressed for 24h with 200 mmol/dm(3) NaCl was investigated. It was shown that treatment of plants with salt distinctly increased the activity of the plasma membrane H(+)-ATPase (EC 3.6.3.6) as well as of the vacuolar H(+)-ATPase (EC 3.6.3.14). In roots treated with NaCl, an increase of ABA level was observed. Moreover, 24-h treatment of seedlings with 50 micro mol/dm(3) ABA increased the activity of proton pumps in both membranes. However, when ABA was added to the reaction medium, no changes in ATPase activities were observed. The increased H(+)-ATPase activity in plasma membranes isolated from the ABA-treated roots was positively correlated with a higher level of PM-H(+)-ATPase transcript. These data have provided evidence that under salt stress conditions, the role of ABA action due to salinity on the induction of the PM-H(+)-ATPase could be at the level of gene expression.

Abscisic Acid↗
PubMed1997

Induction of ABA 8'-hydroxylase by (+)-S-, (-)-R- and 8'-8'-8'-trifluoro-S-abscisic acid in suspension cultures of potato and Arabidopsis.

Suspension cultures of potato and Arabidopsis were incubated with 50 microM of (+)-ABA and (-)-ABA for 3 hr. These pretreatments were found to increase the rate, by two- to seven-fold, of formation of [2H6] phaseic acid (PA) from [2H6] ABA, applied in a subsequent incubation. Pretreatment with trifluoro-ABA had a higher efficacy, increasing the rate of conversion 15-fold. Suspension cell cultures that had been dehydrated and then rehydrated in the presence of [2H6] ABA displayed a much lower enhancement of PA formation. We conclude that ABA induces its own oxidative catabolism in suspension cultures.

Abscisic Acid↗
PubMed1998

Biocompatibility testing of ABA triblock copolymers consisting of poly(L-lactic-co-glycolic acid) A blocks attached to a central poly(ethylene oxide) B block under in vitro conditions using different L929 mouse fibroblasts cell culture models.

The biocompatibility of ABA triblock copolymers consisting of poly(L-lactide-co-glycolide) A blocks attached to a central poly(ethylene oxide), (PEO), B block was investigated under in vitro conditions. The ABA triblock copolymer was compared to commercially available Poly(D,L-lactide-co-glycolide) (PLGA) and reference materials in different L929 cell culture models according to the procedure recommended by the International Standard Organization (ISO). Different preparation methods: namely extraction, indirect contact and direct contact with polymer samples were compared. The extraction method seems to be the most sensitive assay, allowing estimates of IC50 values. ABA and PLGA polymers showed excellent compatibility with L929 fibroblasts with all preparation techniques used. The influence of polymer composition and molecular weight on degradation rate as well as in vitro biocompatibility was then investigated. Changes in pH and osmolarity as well as lactic acid content of the extracts were determined and compared to in vitro degradation data of polymer films in phosphate buffered saline at 37 degreesC evaluating molecular weight (GPC) and massloss (gravimetry). An acceleration of the degradation rate of the ABA triblock copolymers with increasing PEO content was observed. The in vitro cytotoxicity studies demonstrated that the three ABA polymers were well tolerated by fibroblasts in cell culture. One ABA polymer batch ABA2 showed unusual in vitro cytotoxicity in L929 fibroblasts, possibly related to the molecular weight of the PEO used for this particular batch or residual glycolic acid. Cell culture models for biocompatibility testing of polymers according to ISO are useful as screening models in characterizing biodegradable polymers, but they cannot replace animal testing. The extraction method in combination with the MTT assay allows quantitative ranking of cytotoxic properties with high sensitivity.

Animals↗
PubMed1995

The ABA-1 allergen of the parasitic nematode Ascaris suum: fatty acid and retinoid binding function and structural characterization.

We report here on the structure and function of the ABA-1 allergen protein of the parasitic nematode Ascaris, the first nematode allergen to be characterized in detail. Using the fluorescent fatty acid analog 11-(((5-(dimethylamino)-1-naphthalenyl)sulfonyl)amino)undecanoic acid (DAUDA), it was demonstrated that ABA-1 is a fatty acid binding protein (FABP) with a high affinity for the fluorescent analog (8.8 x 10(-8) M) and for oleic acid in competition experiments (1.3 x 10(-8) M), with a single binding site for ligand per monomer unit. Blue-shifting of fluorescence emission of DAUDA upon binding was unprecedented in degree among FABPs, being equivalent to that occurring in cyclohexane. A similarly blue-shifted spectrum was obtained with a probe in which the fluorophore was bound to the alpha carbon of a fatty acid, indicating that the carboxylate group of bound fatty acids is probably not exposed to solvent. In competition experiments and by observation of changes in their intrinsic fluorescence, retinol and retinoic acid were also found to bind in the fatty acid binding site. Circular dichroism (CD) of the ABA-1 protein revealed a high alpha-helix content (59%) which was consistent with the four-helix structure for the protein predicted from sequence algorithms. Fluorescence measurements showed that the single, highly conserved tryptophan residue is deeply buried in an unusually apolar environment and that this was unaffected by ligand binding. DSC studies of thermal stability indicate that unfolding of the ABA-1 dimer is cooperative and biphasic (Tm approximately 71 and 89 degrees C), suggesting a two-domain thermal unfolding process, again consistent with the predicted structure. Only the folding of the high-temperature domain is reversible on cooling. DSC confirmed the gel filtration analysis, which indicated that ABA-1 forms a dimer. Aside from being the first nematode allergen for which structure or function has been elucidated, ABA-1 provides a highly manipulable model for investigation of the interaction between hydrophobic ligands and alpha-helical proteins.

Allergens↗
PubMed2002

Molecular cloning of a functional protein phosphatase 2C (FsPP2C2) with unusual features and synergistically up-regulated by ABA and calcium in dormant seeds of Fagus sylvatica.

Phosphorylation/dephosphorylation of proteins is a general mechanism of hormonal signal transduction, including ABA, and serine/threonine protein phosphatases 2C (PP2C, EC 3.1.3.16) have been suggested to play an important role in this process. By means of differential reverse transcriptase-polymerase chain reaction (RT-PCR) and further screening of a cDNA library made from mRNA of ABA-treated Fagus sylvatica L. seeds, a full-length cDNA clone (FsPP2C2) encoding a putative PP2C was obtained. Comparison to the databases revealed high homology to plant PP2C and most features of these enzymes, but unusual characteristics were found within the catalytic domain and the N-terminal region of the amino acid sequence. The coding region of FsPP2C2 was expressed in Escherichia coli as histidine tag fusion protein and shows Mg2+-dependent in vitro phosphatase activity. Transcription of the FsPP2C2 gene is low during seeds stratification at 4 degrees C or under gibberellic acid (GA3) treatment and clearly increases when seeds are treated with ABA and calcium (Ca2+) together, while the addition of calcium chelators (EGTA or TMB-8) decreases its expression. Furthermore, FsPP2C2 is only expressed in ABA-treated tissues, preferentially in seeds, which suggests that this PP2C is specifically induced by ABA in dormant seeds, in a Ca2+-dependent manner, and also in other ABA-treated tissues.

Journal Article↗
PubMed2003

Identification of ABA-responsive genes in rice shoots via cDNA macroar-.

Phytohormone abscisic acid (ABA) was critical for many plant growth and developmental processes including seed maturation, germination and response to environmental factors. With the purpose to detect the possible ABA related signal transduction pathways, we tried to isolate ABA-regulated genes through cDNA macroarray technology using ABA-treated rice seedling as materials (under treatment for 2, 4, 8 and 12 h). Of 6144 cDNA clones tested, 37 differential clones showing induction or suppression for at least one time, were isolated. Of them 30 and 7 were up- or down-regulated respectively. Sequence analyses revealed that the putative encoded proteins were involved in different possible processes, including transcription, metabolism and resistance, photosynthesis, signal transduction, and seed maturation. 6 cDNA clones were found to encode proteins with unknown functions. Regulation by ABA of 7 selected clones relating to signal transduction or metabolism was confirmed by reverse transcription PCR. In addition, some clones were further shown to be regulated by other plant growth regulators including auxin and brassinosteroid, which, however, indicated the complicated interactions of plant hormones. Possible signal transduction pathways involved in ABA were discussed.

Abscisic Acid↗
PubMed2001

ABA plays a central role in mediating the regulatory effects of nitrate on root branching in Arabidopsis.

The formation of lateral roots (LR) is a major post-embryonic developmental event in plants. In Arabidopsis thaliana, LR development is inhibited by high concentrations of NO3(-). Here we present strong evidence that ABA plays an important role in mediating the effects of NO3(-) on LR formation. Firstly, the inhibitory effect of NO3(-) is significantly reduced in three ABA insensitive mutants, abi4-1, abi4-2 and abi5-1, but not in abi1-1, abi2-1 and abi3-1. Secondly, inhibition by NO3(-) is significantly reduced, but not completely abolished, in four ABA synthesis mutants, aba1-1, aba2-3, aba2-4 and aba3-2. These results indicate that there are two regulatory pathways mediating the inhibitory effects of NO3(-) in A. thaliana roots. One pathway is ABA-dependent and involves ABI4 and ABI5, whereas the second pathway is ABA-independent. In addition, ABA also plays a role in mediating the stimulation of LR elongation by local NO3(-) applications.

Abscisic Acid↗
PubMed1995

Structural characteristics of the Ascaris allergen, ABA-1.

The structure of the Ascaris allergen, ABA-1 was characterized at several levels. Purified allergen monomers eluted from reducing PAGE were found to reassociate into dimers in phosphate buffered saline containing 0.9 mM Ca2+. This association may involve the formation of disulfide bonds between monomers. The primary amino acid sequence was used to predict secondary structure and compare the allergen to other known proteins sequences. ABA-1 appears to be highly helical protein of two domains. Sequence analysis reveals short regions (25 amino acids) of high homology (76%) between ABA-1 and the major body wall myosin of Onchocerca volvulus. In addition, ABA-1 has sequence similarity to a family of EF-hand containing calcium binding proteins called S100 proteins. The dimerization and two-domain structure of ABA-1 is consistent with the possibility that ABA-1 is a member of the S100 family of calcium binding proteins.

Allergens↗
PubMed2007

Regulation of summer dormancy by water deficit and ABA in Poa bulbosa ecotypes.

BACKGROUND AND AIMS: Survival of many herbaceous species in Mediterranean habitats during the dry, hot summer depends on the induction of summer dormancy by changes in environmental conditions during the transition between the winter (growth) season to the summer (resting) season, i.e. longer days, increasing temperature and drought. In Poa bulbosa, a perennial geophytic grass, summer dormancy is induced by long days, and the induction is enhanced by high temperature. Here the induction of summer dormancy in a Mediterranean perennial grass by water deficit under non-inductive photoperiodic conditions is reported for the first time. METHODS: Plants grown under 22/16 degrees C and non-inductive short-day (9 h, SD) were subjected to water deficit (WD), applied as cycles of reduced irrigation, or sprayed with ABA solutions. They were compared with plants in which dormancy was induced by transfer from SD to inductive long-day (16 h, LD). Responses of two contrasting ecotypes, from arid and mesic habitats were compared. Dormancy relaxation in bulbs from these ecotypes and treatments was studied by comparing sprouting capacity in a wet substrate at 10 degrees C of freshly harvested bulbs to that of dry-stored bulbs at 40 degrees C. Endogenous ABA in the bulbs was determined by monoclonal immunoassay analysis. KEY RESULTS: Dormancy was induced by WD and by ABA application in plants growing under non-inductive SD. Dormancy induction by WD was associated with increased levels of ABA. Bulbs were initially deeply dormant and their sprouting capacity was very low, as in plants in which dormancy was induced by LD. Dormancy was released after 2 months dry storage at 40 degrees C in all treatments. ABA levels were not affected by dormancy relaxation. CONCLUSIONS: Summer dormancy in P. bulbosa can be induced by two alternative and probably additive pathways: (1) photoperiodic induction by long-days, and (2) water deficit. Increased levels of endogenous ABA are involved in both pathways.

Abscisic Acid↗