The 1′,4′-trans-diol of abscisic acid,a possible precursor of abscisic acid in Botrytis cinerea

The 1′,4′-trans-diol of abscisic acid was isolated from cultures of Botrytis cinerea. The ²H-labelled derivative was converted into abscisic acid by this fungus, but ²H-labelled ABA was not converted into the diol. This suggests that the diol is not a metabolite of ABA but a possible precursor.     

Does abscisic acid influence proline accumulation in stressed leaves?

Root treatments of barley (Hordeum distichum L.) plants with 10^-7 to 10^-4 M abscisic acid (ABA) caused an increase in proline content, especially at higher concentrations, within 2–3 h. Even 3 h after the removal of ABA from the medium the plants continued to accumulate proline. The higher the concentration of the ABA, the higher was the proline level at 6 h. When the highest ABA concentration, 10^-4 M, was tested with polyethylene glycol (PEG) (-5.0 bars) in the medium, the ABA treatment resulted in a higher proline content than in control plants. The treatments PEG alone and PEG + ABA resulted in heavy accumulation of proline, especially, 3 h after releasing the plants from the stress. The proline content in PEG+ABA-treated plants was always higher than plants treated with PGE or ABA alone. In peas (Pisum sativum L. cv Alaska) the same trend occurred although to a lesser degree. These findings indicate an influence of ABA on proline accumulation in water-stressed plants.Abbreviations ABA abscisic acid - PEG polyethylene glycol - RWC relative water content     

Endogenous abscisic acid and 2-trans-abscisic acid in alternate bearing ‘Wilking’ mandarin trees

The relationship of abscisic acid (ABA) and 2-trans-abscisic acid (t-ABA) to alternate bearing has been examined in Wilking mandarin (Citrus reticulata Blanco) trees. Leaves, stems and buds of trees loaded with fruit (on trees) had 4.3, 6.0 and 2.2 fold higher ABA levels than the corresponding organs from off trees. Leaves had higher ABA levels than stems and buds in both on and off trees. t-ABA was non-detectable in Wilking leaf, stem and bud tissue. Amounts of t-ABA not exceeding 40% of the ABA content, were found in Shamouti and Valencia orange buds and in Wilking fruit peel.The elevated levels of ABA in on tree organs may reflect a stress imposed by the fruit overload.     

4′-Alkoxy derivatives of abscisic acid: a promising new probe for mechanisms of abscisic acid perceptions

The preparation of new compounds for exploring the molecular andbiochemical mechanisms of abscisic acid signal perception is described. The4-carbonyl group of abscisic acid was replaced with either benzyloxy orn-octyloxy groups. Both modified products possessedABA-like activity in bioassays using barley aleurone protoplasts. The benzyloxyderivative was active in dehydrin induction tests, but not in inhibition of-amylase induction tests. The difference in the activity of this chemical inthe two assay systems suggests that the perception system for the inhibition ofamylase induction systems differs from that of dehydrin induction.     

Does engineering abscisic acid biosynthesis in Nicotiana plumbaginifolia modify stomatal response to drought?

The consequences of manipulating abscisic acid (ABA) biosynthesis rates on stomatal response to drought were analysed in wild‐type, a full‐deficient mutant and four under‐producing transgenic lines of N. plumbaginifolia. The roles of ABA, xylem sap pH and leaf water potential were investigated under four experimental conditions: feeding detached leaves with varying ABA concentration; injecting exogenous ABA into well‐watered plants; and withholding irrigation on pot‐grown plants, either intact or grafted onto tobacco. Changes in ABA synthesis abilities among lines did not affect stomatal sensitivity to ABA concentration in the leaf xylem sap ([ABA]_xyl), as evidenced with exogenous ABA supplies and natural increases of [ABA]_xyl in grafted plants subjected to drought. The ABA‐deficient mutant, which is uncultivable under normal evaporative demand, was grafted onto tobacco stock and then presented the same stomatal response to [ABA]_xyl as wild‐type and other lines. This reinforces the dominant role of ABA in controlling stomatal response to drought in N. plumbaginifolia whereas roles of leaf water potential and xylem sap pH were excluded under all studied conditions. However, when plants were submitted to soil drying onto their own roots, stomatal response to [ABA]_xyl slightly differed among lines. It is suggested, consistently with all the results, that an additional root signal of soil drying modulates stomatal response to [ABA]_xyl.     

Changes in abscisic acid and its β-D-glucopyranosyl ester levels during tomato (Lycopersicon esculentum Mill.) seed development

Summary The role of abscisic acid (ABA) in tomato (Lycopersicon esculentum Mill.) zygotic embryogenesis was analysed. ABA and ABA ß-D-glucopyranosyl ester (ABA-GE) changes were determined in seeds and fruit tissues — placenta and mesocarp — during seed development, which was defined with eight embryo stages: from globular (stage 1) to mature embryo (stage 8). In whole seeds, ABA changes paralleled fresh and dry weight pattern curves and could be characterized by a high increase during embryo growth followed by a decrease as the seed matured and dehydrated. Moreover this dehydration phase led, at stage 8, to a new ABA distribution within the seed, preferentially into integument and embryo. Fruit tissue analyses provided new information about the ABA origin in seeds. ABA-GE levels were also measured and the results suggested different ABA metabolism in seed and fruit tissues.Abbreviations ABA abscisic acid - ABA-GE abscisic acid ß-D-glucopyranosyl ester - ABTS 2,2 — azino — bis (3 — ethylben-zthiazoline — 6 — sulfonic acid) - BHT butylhydroxytoluene - DW dry weight - ELISA Ezyme linked immunosorbent assay - HPLC high performance liquid chromatography     

Effect of abscisic acid on galactomannan degradation and endo-β-mannanase activity in seeds of Sesbania virgata (Cav.) Pers. (Leguminosae)

Seeds of Sesbania virgata (Cav.) Pers. (Leguminosae) have an endosperm which accumulates galactomannan as a storage polysaccharide in the cell walls. After germination, it is hydrolysed by three enzymes: α-galactosidase (EC 3.2.1.22), endo-β-mannanase (EC 3.2.1.78) and β-mannosidase (EC 3.2.1.25). This work aimed at studying the effect of abscisic acid (ABA) on galactomannan degradation during and after germination. Seeds were imbibed in water or in 10⁻⁴ M ABA, and used to evaluate the effect of exogenous and endogenous ABA. Tissue printing was used to follow biochemical events by detecting and localising endo-β-mannanase in different tissues of the seed. The presence of exogenous ABA provoked a delay in the cellular disassembly of the endosperm and disappearance of endo-β-mannanase in the tissue. This led to a delay in galactomannan degradation. The testa (seed coat) of S. virgata contains endogenous ABA, which decreases ca. fourfold during storage mobilisation after germination, permitting the galactomannan degradation in the endosperm. Furthermore, endo-β-mannanase was immunolocalised in the testa, which has a living cell layer. The ABA appears to modulate storage mobilisation in the legume seed of S. virgata, and a cause–effect relationship between ABA (probably through testa) and activities of hydrolases is proposed.     

What are the evolutionary origins of stomatal responses to abscisic acid in land plants?

The evolution of active stomatal closure in response to leaf water deficit, mediated by the hormone abscisic acid (ABA), has been the subject of recent debate. Two different models for the timing of the evolution of this response recur in the literature. A single‐step model for stomatal control suggests that stomata evolved active, ABA‐mediated control of stomatal aperture, when these structures first appeared, prior to the divergence of bryophyte and vascular plant lineages. In contrast, a gradualistic model for stomatal control proposes that the most basal vascular plant stomata responded passively to changes in leaf water status. This model suggests that active ABA‐driven mechanisms for stomatal responses to water status instead evolved after the divergence of seed plants, culminating in the complex, ABA‐mediated responses observed in modern angiosperms. Here we review the findings that form the basis for these two models, including recent work that provides critical molecular insights into resolving this intriguing debate, and find strong evidence to support a gradualistic model for stomatal evolution.     

Stomatal sensitivity to abscisic acid: can it be defined?

Abstract. Evidence is presented that the sensitivity of stomata to abscisic acid is greatly influenced by two factors which are known to vary in leaves, namely concentrations of potassium and of indol-3-ylacetic acid. It is suggested that the notion of 'quantitative tissue sensitivity', by which Trewavas explains the action of growth substances in developmental phenomena, may be applicable to stomatal responses to abscisic acid.     

2′-(E)-O-p-coumaroylgalactaric acid and 2′-(E)-O-feruloylgalactaric acid in citrus

2′-(E)-O-p-Coumaroyl- and 2′-(E)-O-feruloylgalactaric acids, hitherto unknown in nature, have been isolated and identified from orange peel.     

The rôle of abscisic acid in root growth and gravireaction: A critical review

A brief account is given of the discovery of abscisic acid (ABA) in roots and root caps of higher plants as well as the techniques by which ABA may be demonstrated in these tissues. The remainder of the review is concerned with examining the rôle of ABA in the regulation of root growth. In this regard, it is well established that when ABA is supplied to roots their elongation is usually inhibited, although at low external concentrations a stimulation of growth may also be found. Fewer observations have been directed at exploring the connection between root growth and the level of naturally occurring, endogenous ABA. Nevertheless, the evidence here also suggests that ABA is an inhibitory regulator of root growth. Moreover, ABA appears to be involved in the differential growth that arises in response to a gravitational stimulus. Recent reports that deny a rôle for ABA in root gravitropism are considered inconclusive. The response of roots to osmotic stress and the changes in ABA levels which ensue, are summarised; so are the interrelations between ABA and other hormones, particularly auxin (e.g. indoleacetic acid); both are considered in the context of the root growth and development. Quantitative changes in auxin and ABA levels may together provide the root with a flexible means of regulating its growth.     

β-carotene from the abscisic acid producing strain of Cercospora rosicola

-carotene was isolated from an extract of Cercospora rosicola mycelia and identified on the basis of chromatographic properties and UV-visible spectroscopic evidence. The accumulation of -carotene was inhibited 71 and 52% by 10 M amounts of decylimidazole and fluridone, resepectively. Abscisic acid accumulation was inhibited 63% by decylimidazole and enhanced about 10% by fluridone. Several other inhibitors of carotenoid synthesis failed to inhibit ABA biosynthesis.     

The effect of abscisic acid on the differential expression of α-amylase isozymes in barley aleurone layers

Summary The treatment of barley aleurone layers with gibberellic acid (GA₃) results in the synthesis of two groups of -amylase isozymes. Addition of abscisic acid (ABA) at the same time as GA₃ inhibited the synthesis of both groups of isozymes. However, midcourse ABA addition (12 h or later after GA₃) had a more inhibitory effect on the high pI -amylase group than on the low pI -amylase group. This midcourse inhibition was detectable within 2 h of ABA addition. Northern analysis results using cDNA probes for the high pI and low pI -amylase groups paralleled the protein synthesis results for both isozyme groups. High pI -amylase mRNA levels began to decrease within 2 h of midcourse ABA treatment and were less than 10% of the original level by 4 h. The levels of low pI -amylase mRNA were decreased less by midcourse ABA addition than were high pI mRNA levels. Cordycepin and cycloheximide blocked the effects of midcourse ABA addition on -amylase mRNA. These observations indicate that ABA inhibits -amylase expression at the pretranslational level and that protein and RNA synthesis are required for midcourse ABA action to occur. Our results also show that -amylase mRNA, which has been thought to be very stable, is degraded after midcourse ABA treatment.     

Interaction between NO 3 − and abscisic acid in the regulation of lateral root elongation in Zea mays L.

Lateral root (LR) elongation rate of 7–8-day maize seedlings depends on the availability of NO ₃ ^? , NO ₂ ^? , and abscisic acid (ABA) in an environment. Four-hour exposure to 0.01–1.5 mM NO ₂ ^? increases the relative LR elongation rate; in the case of NO ₂ ^? , the stimulation occurs only at an NO ₂ ^? concentration equal to 0.01 mM. Exogenous ABA (10^?6 M) inhibits the LR elongation process. In the case of a combined influence of NO ₃ ^? and ABA or NO ₂ ^? and ABA, the character of the response elongation reaction is different. The NO role in the regulation of LR elongation is discussed.     

Occurrence and metabolism of 1′,4′-trans-diol of abscisic acid

The 1′,4′-trans-diol of abscisic acid was first identified in higher plants with GC-ECD and GC-SIM. The ²H-labelled derivative was converted into abscisic acid (ABA) in pea and avocado, but ²H-labelled ABA was not converted into the diol. These results suggest that the diol is one of the precursors of ABA in higher plants.     

Effects of serial subculture in vitro on the endogenous levels of indole-3-acetic acid and abscisic acid and rootability in microcuttings of ‘Jonathan’ apple

Proliferating axillary shoots of the difficult-to-root apple cultivar Jonathan acquired an enhanced ability to form adventitious roots with increasing number of subcultures in vitro. The transition between the difficult-to-root and the easy-to-root condition occurred at the fourth subculture.Endogenous levels of free IAA and ABA in shoot tissues were analysed by gas chromatography/mass spectrometry/single ion monitoring (GC/MS/SIM) using negative ion chemical ionisation. Tissues from the mother plants grown in the glasshouse contained more IAA and ABA than those from tissue-culture material. After establishment in vitro there was no variation in the IAA content throughout the subcultures but a decrease in ABA content was observed after the fourth transfer. The IAA/ABA ratio increased from 0.2 in difficult-to-root shoots from the initial culture up to 0.7 in easy-to-root shoots from the long-term subculture.