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PubMed1988

Drought- and ABA-Induced Changes in Polypeptide and mRNA Accumulation in Tomato Leaves.

Drought stress triggers abscisic acid (ABA) biosynthesis resulting in ABA accumulation. The ABA-deficient tomato mutant, flacca (Lycopersicon esculentum Mill. cv Ailsa Craig), does not synthesize ABA in response to drought stress. This mutant has been used to distinguish polypeptides and in vitro translation products that are synthesized during drought stress in response to elevated ABA levels from those that are induced directly by altered water relations. A set of polypeptides and in vitro translation products was synthesized during drought stress in the wild type. These polypeptides and in vitro translation products were synthesized to a lesser extent in the drought-stressed ABA-deficient mutant. Treatment of flacca with ABA resulted in the synthesis of the drought-stress-induced polypeptides and in vitro translation products. These results support the hypothesis that many of the polypeptides that are synthesized during drought are regulated by alterations in ABA concentration. Similarly, the mRNA population was altered by ABA during drought stress.

Journal Article↗
PubMed2006

Expression of ABA 8'-hydroxylases in relation to leaf water relations and seed development in bean.

In plants, the level of abscisic acid (ABA) is determined by synthesis and catabolism. Hydroxylation of ABA at the 8' position is the key step in ABA catabolism. This reaction is catalyzed by ABA 8'-hydroxylase, a cytochrome P450 (CYP). The cDNAs of PvCYP707A1 and PvCYP707A2 were isolated from bean (Phaseolus vulgaris L.) axes treated with (+)-ABA and that of PvCYP707A3 from dehydrated bean leaves. The recombinant PvCYP707A proteins expressed in yeast were biochemically characterized. Yeast strains over-expressing any of the three PvCYP707As were able to convert ABA to phaseic acid (PA). The microsomal fractions from these yeast strains also exhibited ABA 8'-hydroxylase activity. Expression of PvCYP707A3 in primary leaves was strongly increased by water stress, whereas PvCYP707A1 and PvCYP707A2 mRNA levels were rapidly increased by rehydration of water-stressed leaves. Northern blot analysis of PvCYP707As in bean showed a high level of expression in the mature fruits, senescent leaves, roots, seed coats and axes. All three PvCYP707As were expressed at varying intensities throughout seed development. Imbibed seeds also had high PvCYP707A mRNA levels. Thus, expression of PvCYP707As is both environmentally and developmentally regulated. Transgenic Nicotiana sylvestris plants over-expressing PvCYP707As displayed a wilty phenotype, and had reduced ABA levels and increased PA levels. These results demonstrate that expression of PvCYP707As is the major mechanism by which ABA catabolism is regulated in bean.

Abscisic Acid↗
PubMed2000

ABA prevents the second cytokinin-mediated event during the induction of shoot buds in the moss Funaria hygrometrica.

The induction of shoot buds in the moss Funaria hygrometrica is a classic and quantitative bioassay for cytokinin. This cytokinin-stimulated response can be inhibited by the plant hormone abscisic acid, ABA; the inhibition is concentration dependent and was proposed for use as a bioassay for ABA. This paper characterizes the ABA inhibition of the cytokinin-stimulated formation of shoot buds. Experiments transferring protonema between cytokinin and cytokinin plus ABA show that ABA does not interfere with the initial perception of cytokinin. Other experiments compare the results of transferring protonema from cytokinin to cytokinin-free medium or to medium with cytokinin plus ABA and reveal that ABA acts by blocking the cytokinin-mediated stable commitment of nascent buds. Extension of the technique of double-reciprocal plots to this whole-organism bioassay finds that ABA is not a competitive inhibitor of cytokinin. Analysis of the ABA inhibition of bud formation identifies a new regulatory step in the developmental process of bud formation in mosses.

Journal Article↗
PubMed2004

[Nitric oxide, a signaling component of ABA-induced stomatal closure].

The present study provided the evidence that exogenous NO and ABA regulated the stomatal movement in poplar leaves. It showed that different levels of SNP and ABA induced the stomatal closure in detached leaves. NO enhanced stomatal closure that induced by ABA. The effect of NO and ABA on stomatal closure was suppressed by c-PTIO, a specific NO scavenger. It was confirmed that NO involved in ABA-mediated stomatal movement. The activities of POD were dramatically inhibited, but those of SOD hardly decreased in different levels of SNP and ABA treatment. However, in vitro experiments indicated that the activities of POD were dramatically inhibited by NO, but not ABA. The results demonstrated that NO mediated ABA-induced stomatal closure of trees, and was a signaling component of ABA-induced stomatal closure.

Abscisic Acid↗
PubMed2006

[Involvement of nitric oxide in regulation of salt stress-induced ABA accumulation in maize seedling].

Possible regulation of salt stress-induced ABA accumulation by nitric oxide (NO) in maize seedling was investigated. Both NO and ABA contents of maize leaves and root tips were increased in response to salt stress (Fig.1,2). Similar to the effects of salt stress, ABA contents of maize leaves and root tips were increased after the treatment of maize leaves with sodium nitroprusside (SNP, a nitric oxide donor) alone (Fig.3). Compared to the salt stress-induced ABA accumulation, this SNP-induced ABA increase was much faster, suggesting that NO may be an intermediate signal from salt stress to ABA accumulation. When NO production inhibitors L-NAME and NaN(3) treatments were applied, salt stress-induced ABA accumulation was lowered (Fig.4). Treatment with NO scavenger cPTIO also inhibited the salt stress-induced ABA increase (Fig.5). From these results it is deduced that NO is involved in regulation of ABA accumulation under salt stress.

Abscisic Acid↗
PubMed1986

ABA-specific responses are I region restricted by the carriers used for immunization.

Immunization of mice with ABA coupled to carriers to which they are nonresponders gives rise to ABA-specific proliferative responses in lymph node cells. When C3H/HeN and CBA/J nonresponder mice are immunized with ABA on (T,G)-A-L (an I-A-restricted carrier in responder mice), the responses to ABA-tyr and ABA coupled to a variety of unrelated carriers are solely I-A restricted as determined by inhibition with anti-IA and anti-I-E sera. When ABA on GLT (an I-E-restricted carrier in responder mice) is used for immunization, the responses are both I-A and I-E restricted. Thus, ABA-specific responses in nonresponder mice appear in part to be restricted by the carrier used for immunization. B10.S mice, lacking functional I-E molecules, channel their ABA-specific responses entirely through I-A when immunized with ABA-GLT. These results support the hypothesis that the failure in nonresponders lies in a functional deficit in the T cell repertoire rather than an inability of accessory cells to present antigen.

Animals↗
PubMed1989

Differential regulation of ABA-induced 23-25 kDa proteins in embryo and vegetative tissues of the viviparous mutants of maize.

Previous studies have identified a set of highly phosphorylated proteins of 23-25 kDa accumulated during normal embryogenesis of Zea mays L. and which disappear in early germination. They can be induced precociously in embryos by abscisic acid (ABA) treatment. Here the synthesis and accumulation of this group of proteins and their corresponding mRNAs were examined in ABA-deficient viviparous embryos at different developmental stages whether treated or not with ABA, and in water-stressed leaves of both wild-type and viviparous mutants. During embryogenesis and precocious germination of viviparous embryos the pattern of expression of the 23-25 kDa proteins and mRNAs closely resembles that found in non-mutant embryo development. They are also induced in young viviparous embryos by ABA treatment. In contrast, leaves of ABA-deficient mutants fail to accumulate mRNA in water stress, yet do respond to applied ABA. In water-stressed leaves of wild type plants the mRNAs are induced and translated into 4 proteins with a molecular weight and isoelectric point identical to those found in embryos. These results indicate that the 23-25 kDa protein set is a new member of the recently described class of proteins involved in generalized plant ABA responses. The different pattern of expression for the ABA-regulated 23-25 kDa proteins and mRNAs found in embryo and in vegetative tissues of viviparous mutants is discussed.

Abscisic Acid↗
PubMed1996

Effects of internal K+ and ABA on the voltage- and time-dependence of the outward K(+)-rectifier in Vicia guard cells.

One of the main effects of abscisic acid (ABA) is to induce net loss of potassium salts from guard cells enabling the stomata to close. K+ is released from the vacuole into the cytosol and then to the extracellular space. The effects of increasing cytosolic K+ on the voltage- and time-dependence of the outwardly rectifying K(+)-current (IK,out) in guard cell protoplasts (GCP) was examined in the whole-cell configuration of the patch-clamp technique. The same quantitative analysis was performed in the presence of ABA at different internal K+ concentrations ([K+]i). Varying [K+]i in the patch pipette from 100 to 270 mM increased the magnitude of IK,out in a nonlinear manner and caused a negative shift in the midpoint (V0.5) of its steady-state activation curve. External addition of ABA (10-20 microM) also increased the magnitude of IK,out at all [K+]i, but caused a shift in V0.5 of the steady-state activation curve only in those GCP loaded with 150 mM internal K+ or less. Indeed, V0.5 did not shift upon addition of ABA when the [K+]i was above 150 mM and up to 270 mM, i.e., the shift in V0.5 caused by ABA depended on the [K+]i. Both increase in [K+]i and external addition of ABA, decreased (by approximately 20%) the activation time constant (tau n) of IK,out. The small decrease in tau n, in both cases, was found to be independent of the membrane voltage. The results indicate that ABA mimics the effect of increasing cytoplasmic K+, and suggest that ABA may increase IK,out and alter V0.5 of its steady-state activation curve via an enhancement in cytosolic K+. This report describes for the first time the effects of [K+]i on the voltage- and time-dependence of IK,out in guard cells. It also provides an explanation for the quantitative (total membrane current) and qualitative (current kinetics) differences found between intact guard cells and their protoplasts.

Abscisic Acid↗
PubMed2005

Crosstalk between ABA and auxin signaling pathways in roots of Arabidopsis thaliana (L.) Heynh.

Studies of abscisic acid (ABA) and auxin have revealed that these pathways impinge on each other. The Daucus carota (L.) Dc3 promoter: uidA (beta-glucuronidase: GUS) chimaeric reporter (ProDc3:GUS) is induced by ABA, osmoticum, and the auxin indole-3-acetic acid (IAA) in vegetative tissues of transgenic Arabidopsis thaliana (L.) Heynh. Here, we describe the root tissue-specific expression of ProDc3:GUS in the ABA-insensitive-2 (abi2-1), auxin-insensitive-1 (aux1), auxin-resistant-4 (axr4), and rooty (rty1) mutants of Arabidopsis in response to ABA, IAA and synthetic auxins naphthalene acetic acid (NAA), and 2, 4-(dichlorophenoxy) acetic acid. Quantitative analysis of ProDc3:GUS expression showed that the abi2-1 mutant had reduced GUS activity in response to ABA, IAA, or 2, 4-D: , but not to NAA. Similarly, chromogenic staining of ProDc3:GUS activity showed that the aux1 and axr4 mutants gave predictable hypomorphic ProDc3:GUS expression phenotypes in roots treated with IAA or 2, 4-D: , but not the diffusible auxin NAA. Likewise the rty mutant, which accumulates auxin, showed elevated ProDc3:GUS expression in the absence or presence of hormones relative to wild type. Interestingly, the aux1 and axr4 mutants showed a hypomorphic effect on ABA-inducible ProDc3:GUS expression, demonstrating that ABA and IAA signaling pathways interact in roots. Possible mechanisms of crosstalk between ABA and auxin signaling are discussed.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2005

O-acetylserine (thiol) lyase activity in Phragmites and Typha plants under cadmium and NaCl stress conditions and the involvement of ABA in the stress response.

The roles of O-acetylserine (thiol) lyase (OASTL, EC 4.2.99.8) and abscisic (ABA) acid in stress responses to NaCl and cadmium treatments were investigated in Typha latifolia L. and Phragmites australis (Cav.) Trin. ex Steudel plants. OASTL activity increased under stress (25-300 microM Cd, 100mM NaCl, 1 microM ABA) in both Typha and Phragmites mainly in roots, contributing substantially to satisfy the higher demand of cysteine for adaptation and protection. The earliest significant responses in intact roots were recorded after 12-24 h of Cd treatments, but different levels of stimulation were also observed after 3 and 7 days of exposure. The OASTL activity responses of Phragmites to salinity (100mM NaCl) were higher than those of Typha. Cysteine synthesis in Typha is much higher than in Phragmites, which supports the efficiency of the thiol-metabolism-based protection shown in Typha. Exogenous ABA increased OASTL activity in both species. Cd treatments led to increased ABA levels in roots. Phragmites showed higher ABA levels compared to Typha. The increase of ABA content indicates the involvement of this phytohormone in early stress responses, while the stimulation of OASTL following the ABA application suggests that ABA has a role in an OASTL activation pathway.

Abscisic Acid↗
PubMed2006

The T-box factor TBX-2 and the SUMO conjugating enzyme UBC-9 are required for ABa-derived pharyngeal muscle in C. elegans.

The C. elegans pharynx is produced from the embryonic blastomeres ABa and MS. Pharyngeal fate in the ABa lineage is specified by the combined activities of GLP-1/Notch-mediated signals and the TBX-37 and TBX-38 T-box transcription factors. Here, we show another T-box factor TBX-2 also functions in ABa-derived pharyngeal development. tbx-2 mutants arrest as L1 larvae lacking most or all ABa-derived pharyngeal muscles. In comparison, tbx-2 mutants retain ABa-derived marginal cells and pharyngeal muscles derived from MS. A tbx-2Colon, two colonsgfp translational fusion is expressed in a dynamic pattern in C. elegans embryos beginning near the 100-cell stage. Early expression is limited to a small number of cells, which likely include the ABa-derived pharyngeal precursors, while later expression is observed in body wall muscles and a subset of pharyngeal neurons. TBX-2 contains 2 consensus sumoylation sites, and it interacts in a yeast two-hybrid assay with the UBC-9 and GEI-17 components of the C. elegans SUMO-conjugating pathway. ubc-9(RNAi) has been previously shown to cause variable embryonic and larval arrest, and we find that, like tbx-2 mutants, ubc-9(RNAi) animals lack ABa-derived pharyngeal muscles. ubc-9(RNAi) also alters the subnuclear distribution of TBX-2::GFP fusion protein, suggesting that UBC-9 and TBX-2 interact in C. elegans. Together, these results indicate that TBX-2 and SUMO-conjugating enzymes are necessary for ABa-derived pharyngeal muscle, and we hypothesize that TBX-2 function requires sumoylation. Sumoylation is increasingly recognized as an important mechanism controlling activity of many nuclear factors, and these results provide the first evidence that T-box factor activity may require sumoylation.

Animals↗
PubMed2003

Regulation of the ABA-sensitive Arabidopsis potassium channel gene GORK in response to water stress.

The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time- and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abi1-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 12-24 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, GORK expression as well as K+(out) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately.

Abscisic Acid↗
PubMed2002

Complex regulation of ABA biosynthesis in plants.

Abscisic acid (ABA) is a plant hormone that plays important roles during many phases of the plant life cycle, including seed development and dormancy, and in plant responses to various environmental stresses. Because many of these physiological processes are correlated with endogenous ABA levels, the regulation of ABA biosynthesis is a key element facilitating the elucidation of these physiological characteristics. Recent studies on the identification of genes encoding enzymes involved in ABA biosynthesis have revealed details of the main ABA biosynthetic pathway. At the same time, the presence of gene families and their respective organ-specific expression are indicative of the complex mechanisms governing the regulation of ABA biosynthesis in response to plant organ and/or environmental conditions. There have been recent advances in the study of ABA biosynthesis and new insights into the regulation of ABA biosynthesis in relation to physiological phenomena.

Abscisic Acid↗
PubMed1999

Formation and breakdown of ABA.

The phytohormone, abscisic acid (ABA) is found in all photosynthetic organisms. The amount of ABA present is determined by the dynamic balance between biosynthesis and degradation: these two processes are influenced by development, environmental factors such as light and water stress, and other growth regulators. ABA is synthesized from a C40 carotenoid precursor and the first enzyme committed specifically to ABA synthesis is a plastid- localized 9-cis-epoxycarotenoid dioxygenase, which cleaves an epoxycarotenoid precursor to form xanthoxin. Subsequently, xanthoxin is converted to ABA by two cytosolic enzymes via abscisic aldehyde, but there appears to be at least one minor alternative pathway. The major catabolic route leads to 8'-hydroxy ABA and phaseic acid formation, catalyzed by the cytochrome P450 enzyme ABA 8'-hydroxylase. In addition, there are alternate catabolic pathways via conjugation, 4'-reduction and 7'-hydroxylation. As a consequence of recent developments, the mechanism by which the concentration of hormonally active ABA is controlled at the cellular, tissue and whole plant level can now be analyzed in detail.

Journal Article↗
PubMed2004

A novel zinc-finger protein with a proline-rich domain mediates ABA-regulated seed dormancy in Arabidopsis.

Seed dormancy is an important developmental process that prevents pre-harvest sprouting in many grains and other seeds. Abscisic acid (ABA), a plant hormone, plays a crucial role in regulating dormancy but the underlying molecular regulatory mechanisms are not fully understood. An Arabidopsis zinc-finger gene, MEDIATOR OF ABA-REGULATED DORMANCY 1 ( MARD1 ) was identified and functionally analyzed. MARD1 expression is up-regulated by ABA. A T-DNA insertion in the promoter region downstream of two ABA-responsive elements (ABREs) renders MARD1 unable to respond to ABA. The mard1 seeds are less dormant and germinate in total darkness; their germination is resistant to external ABA at the stage of radicle protrusion. These results suggest that this novel zinc-finger protein with a proline-rich N-terminus is an important downstream component of the ABA signaling pathway that mediates ABA-regulated seed dormancy in Arabidopsis.

Abscisic Acid↗
PubMed2002

ABA and polyamines act independently in primary leaves of cold-stressed tomato (Lycopersicon esculentum).

The effects of ABA and putrescine, a polyamine, on cold-induced membrane leakage were investigated using primary leaves of wild-type and an ABA-deficient mutant, flacca, of tomato (Lycopersicon esculentum Mill.). The amount of chilling-induced electrolyte leakage from flacca leaves was much higher than that from the wild-type leaves. When applied exogenously ABA reduced cold-induced electrolyte leakage from leaves of both wild-type and the flacca mutant. However, the cold-induced electrolyte leakage from flacca leaves was not as pronounced as in the wild-type indicating that ABA is an important mediator in response to cold stress in the leaves. Putrescine reduced cold-induced electrolyte leakage from both wild-type and flacca leaves. Synthesis of putrescine in the leaves was increased by cold treatment. DFMO, a biosynthetic inhibitor of the polyamine, increased electrolyte leakage from cold-treated leaves, and exogenously applied putrescine decreased the enhanced leakage to the control level. Therefore, this polyamine is thought also to be involved in the response to cold stress of tomato leaves. Both ABA and putrescine were protective against cold stress, but exogenously applied ABA decreased the endogenous level of putrescine in the leaves. Furthermore, the DMFO-increased electrolyte leakage in cold-stressed leaves was completely abolished by the application of ABA. These results suggest that ABA is a major regulator in the response to cold stress in tomato leaves and that it does not exert its role via putrescine in the response to cold stress.

Journal Article↗
PubMed2003

Maintenance of shoot growth by endogenous ABA: genetic assessment of the involvement of ethylene suppression.

Previous work demonstrated that normal levels of endogenous abscisic acid (ABA) are required to maintain shoot growth in well-watered tomato plants independently of effects of hormone status on plant water balance. The results suggested that the impairment of shoot growth in ABA-deficient mutants is at least partly attributable to increased ethylene production. To assess the extent to which ABA maintains shoot growth by ethylene suppression, the growth of ABA-deficient (aba2-1) and ethylene-insensitive (etr1-1) single- and double-mutants of Arabidopsis was examined. To ensure that the results were independent of effects of hormone status on plant water balance, differential relative humidity regimes were used to achieve similar leaf water potentials in all genotypes and treatments. In aba2-1, shoot growth was substantially inhibited and ethylene evolution was doubled compared with the wild type, consistent with the results for tomato. In the aba2-1 etr1-1 double mutant, in which ABA was equally as deficient as in aba2-1 and shoot growth was shown to be insensitive to ethylene, shoot growth was substantially, although incompletely, restored relative to etr1-1. Treatment with ABA resulted in the complete recovery of shoot growth in aba2-1 relative to the wild type, and also significantly increased the growth of aba2-1 etr1-1 such that total leaf area and shoot fresh weight were not significantly lower than in etr1-1. In addition, ABA treatment of aba2-1 etr1-1 restored the wider leaf morphology phenotype exhibited by etr1-1. The results demonstrate that normal levels of endogenous ABA maintain shoot development, particularly leaf expansion, in well-watered Arabidopsis plants, partly by suppressing ethylene synthesis and partly by another mechanism that is independent of ethylene.

Abscisic Acid↗
PubMed2004

Rapid and tissue-specific changes in ABA and in growth rate in response to salinity in barley leaves.

The addition of 100 mM NaCl to the root medium of barley plants caused the rapid cessation of elongation of the growing leaf three, followed by a sudden resumption of growth during the following hour. The idea that resumption of growth is preceded and mediated by rapid and tissue-specific changes in ABA concentration and by changes in transpiration was tested. Leaf elongation velocity was recorded continuously using linear variable displacement transducers (LVDT), ABA was determined by immunoassay, and transpiration and stomatal conductivity were measured gravimetrically and by porometry, respectively. Within 10 min following addition of salt, ABA increased 6-fold in the distal portion of the leaf elongation zone; in the proximal portion, ABA accumulated with a delay. In the portion of the growing blade that had emerged ABA increased 3-fold and remained elevated during the following 20 min. This preceded a decrease in transpiration and stomatal conductivity, which, in turn, coincided with growth resumption. Twenty hours following the addition of salt, the ABA concentrations had returned to the level before stress. Leaf elongation velocity was still reduced. It is concluded that NaCl causes a rapid increase in ABA in the transpiring portion of the growing leaf. This leads to a decrease in transpiration. As a result, xylem water potential is expected to rise. The moment that the water potential gradient between the xylem and the peripheral cells in the growth zone favours water uptake again into the latter, leaf elongation resumes. The results suggest that ABA causes different responses in different leaf regions, all aimed at promoting the resumption of leaf growth.

Abscisic Acid↗