A comparative study of the effects of abscisic acid and new terpenoid abscisic acid analogues on plant physiological processes

The effects of new terpenoid abscisic acid analogues in comparison to abscisic acid (ABA) on some physiological and biochemical processes of various plant species have been investigated. The analogues exhibited ABA-like effects by inhibiting cell elongation and germination, and by promoting abscission, as well as the accumulation of proline and induction of stomatal closure coupled by a reduction in transpiration. In response to low temperature, the analogue-treated plants showed improved resistance to cold accompanied by a decrease in electrolyte leakage.     

Effect of drought stress,abscisic acid,and abscisic acid analogues on the efficacy of diclofop-methyl and tralkoxydim

The effects of drought stress, abscisic acid (ABA), and four ABA analogues on diclofop-methyl and tralkoxydim efficacy were investigated in oat (Avenu sativa). Drought stress conditions (6% soil moisture content) reduced the efficacy of diclofop-methyl at 350 g ha^–1, but not at 700 g ha^–1. Similarly, tralkoxydim efficacy was reduced by drought stress at 62.5 and 125 g ha^–1, but not at 250 g ha^–1. ABA (100 m), applied as a root drench 2 days before the herbicide, protected oat plants against all rates of diclofop-methyl and against low rates of tralkoxydim. Two ABA analogues protected oat plants from diclofop-methyl injury, whereas two others had no effect. Foliage applications of ABA were much less effective than root applications in protecting against herbicide injury. Protection by ABA and the two active analogues was dependent on the relative time of application with respect to the herbicides. Optimal protection by ABA and analogue I was obtained when they were applied between 2 days before and 1 day after diclofop-methyl application. Analogue IV protected plants when applied between 3 days before and 1 day after diclofop-methyl application. Partial protection against tralkoxydim activity by ABA was observed when it was applied between 1 day before and 1 day after herbicide application. Analogue I did not afford any protection against tralkoxydim, and analogue IV afforded partial protection when applied the same day or 1 day after tralkoxydim. The results indicate that protection against these postemergence herbicides, similar to that conferred by water stress, can be induced by ABA and structural analogues that apparently mimic the action of ABA.Abbreviations SMC soil moisture content - ABA abscisic acid     

脱落酸生物合成研究进展

脱落酸作为一种抑制生长的植物激素,是平衡植物内源激素和调节生长代谢的关键因子。脱落酸具有提高作物抗旱耐盐、减少果实褐变的作用,同时可降低疟疾发病率、刺激胰岛素分泌,因此在农业和医药领域有着广阔的应用前景。相较于传统的植物提取法和化学合成法,利用微生物合成脱落酸是一种经济、可持续的来源方式。目前利用天然微生物如灰葡萄孢霉菌、蔷薇色尾孢菌等合成脱落酸的研究已经取得了诸多进展,而脱落酸的异源微生物合成研究相对较少。酿酒酵母、解脂耶氏酵母、大肠杆菌等工程菌株作为天然产物异源合成的常用宿主,具有遗传背景清晰、易于操作、便于工业化生产等优势,因此利用微生物异源合成脱落酸是一种更具潜力的生产方式。本文着重从底盘细胞的选择、关键酶的筛选与表达强化、辅因子的调节、增强前体供应及促进脱落酸外排5个方面对微生物异源合成脱落酸的研究进行综述。最后,对该领域的未来发展方向进行了展望。     

The role of abscisic acid in plant-pathogen interactions

The effect of the abiotic stress hormone abscisic acid on plant disease resistance is a neglected field of research. With few exceptions, abscisic acid has been considered a negative regulator of disease resistance. This negative effect appears to be due to the interference of abscisic acid with biotic stress signaling that is regulated by salicylic acid, jasmonic acid and ethylene, and to an additional effect of ABA on shared components of stress signaling. However, recent research shows that abscisic acid can also be implicated in increasing the resistance of plants towards pathogens via its positive effect on callose deposition.     

Stress-induced abscisic acid transients and stimulus-response-coupling

Loss of cell turgor and distortion of the plasma membrane occur as a result of dehydration and precede the stress-induced bulk increase in concentration of tissue abscisic acid. The latter has been correlated with induction of stress-related gene expression. However, several different stresses may trigger the same coupling mechanism. Thus, at least three signalling pathways have been proposed: abscisic acid-requiring, abscisic acid-responsive, and mechanosensory. In this paper, the role and contribution of stress-induced abscisic acid transients is examined in an attempt to explain apparent abscisic acid-dependent and -independent stimulus-response-coupling. Early, intermediate, and late response stages are defined within the stress-induced abscisic acid transient and at least four signalling mechanisms are identified. These include, early and late intracellular modulation of gene expression through depression and/or negative regulation, rapid membrane-initiated calcium release and ion channel activation, and late (slow) hormone-receptor induction of gene expression. An assessment of these proposed ABA signalling mechanisms in terms of AABA-dependent and -independent stimulus-response-coupling strongly suggests that rapid responses may not be a prerequisite for slow responses and that the receptor proteins involved have different steric requirements, i.e., they are tissue- and/or cell-specific.     

New developments in abscisic acid perception and metabolism

Abscisic acid is a powerful signaling molecule that accumulates in response to abiotic stress. However, no potential receptors that could perceive this increase in abscisic acid had been identified until recent reports of three abscisic acid binding proteins: the nuclear protein Flowering Time Control Locus A, the chloroplast protein Magnesium Protoporphyrin-IX Chelatase H subunit, and the membrane-associated protein G Protein Coupled Receptor 2. Abscisic acid metabolism also has a new and prominent component with the identification of a beta-glucosidase capable of releasing biologically active abscisic acid from inactive abscisic acid-glucose ester in a stress-inducible manner. These observations refocus our attention on the metabolism underlying abscisic acid accumulation, sites of abscisic acid perception, and delivery of abscisic acid to those sites.     

A new lead compound for abscisic acid biosynthesis inhibitors targeting 9-cis-epoxycarotenoid dioxygenase

9-cis-Epoxycarotenoid dioxygenase (NCED), a key enzyme in abscisic acid (ABA) biosynthesis, cleaves the olefinic double bond of 9-cis-epoxycarotenoid. Several analogues of nordihydroguaiaretic acid (NDGA) were designed and synthesized, and their efficacy as inhibitors of NCED was examined. One of the synthesized compounds (20) was found to be an inhibitor of this enzyme, and inhibited ABA accumulation and stomatal closing, suggesting that 20 should be ABA biosynthesis inhibitor.     

A radioimmunoassay for abscisic acid

We have developed a radioimmunoassay (RIA) for abscisic acid (ABA) in the 0.1 ng to 2.5 ng range. Antibodies were obtained from rabbits immunized with ABA bound via its carboxyl group to bovine serum albumin. Cross-reactivity studies indicate that ABA esters are completely cross-reactive with ABA, while trans, trans abscisic acid (t-ABA) phaseic acid (PA) and dihydrophaseic acid (DPA) have much lower but significant cross-reactivities. Purification methods which reduce the levels of cross-reacting substances are described.Abbreviations RIA radioimmunoassay - DPA 4-dihydrophaseic acid - PA phaseic acid - GC gas chromatography - HPLC high performance liquid chromatography - TLC thin-layer chromatography - BSA bovine serum albumin - ABA abscisic acid - t-ABA trans, trans abscisic acid - IAA indoleacetic acid     

3'-Azidoabscisic acid as a photoaffinity reagent for abscisic acid binding proteins

3'-Azidoabscisic acid was synthesized as a potential photoaffinity reagent for abscisic acid binding proteins. This compound was stable in organic and aqueous solutions in the dark, but was decomposed by UV irradiation. Its biological activity was equivalent to that of abscisic acid, suggesting that it may be an effective photoaffinity reagent.     

The effects of abscisic acid,kinetin and 5-fluorouracil on ribonucleic acid and protein synthesis in senescing radish leaf disks

Summary The effects of abscisic acid and kinetin on RNA synthesis in senescing radish leaf disks were investigated using the improved resolution afforded by polyacrylamide gel electrophoresis. Kinetin stimulated and abscisic acid inhibited incorporation of radioactivity into cytoplasmic ribosomal RNA and soluble RNA. Chloroplast ribosomal RNA synthesis appeared to be confined to the period of leaf expansion and was not detected in fully mature leaves. The effects of kinetin in retarding and of abscisic acid in accelerating leaf senescence were not altered by the inhibition of cytoplasmic ribosomal RNA synthesis with 5-fluorouracil. Following inhibition of cytoplasmic ribosomal RNA synthesis with 5-fluorouracil, kinetin stimulated and abscisic acid inhibited incorporation of radioactivity into polydisperse RNA. These results are discussed in relation to the possible mode of action of kinetin and abscisic acid in senescing leaf tissue.     

Carotenogenic and abscisic acid biosynthesizing activity in a cell-free system

Abscisic acid is considered an apocarotenoid formed by cleavage of a C-40 precursor and subsequent oxidation of xanthoxin and abscisic aldehyde. Confirmation of this reaction sequence is still awaited, and might best be achieved using a cell-free system capable of both carotenoid and abscisic acid biosynthesis. An abscisic acid biosynthesizing cell-free system, prepared from flavedo of mature orange fruits, was used to demonstrate conversion of farnesyl pyrophosphate, geranylgeranyl pyrophosphate and all-trans-β-carotene into a range of β,β-xanthophylls, xanthoxin, xanthoxin acid, 1′,4′-trans-abscisic acid diol and abscisic acid. Identification of product carotenoids was achieved by high-performance liquid chromatography and on-line spectral analysis of individual components together with co-chromatography. Putative C-15 intermediates and product abscisic acid were identified by combined capillary gas chroma-tography-mass spectrometry. Kinetic studies revealed that β-carotene, formed from either famesyl pyrophosphate or geranylgeranyl pyrophosphate, reached a maximum within 30 min of initiation of the reaction. Thereafter, β-carotene levels declined exponentially. Catabolism of substrate β-carotene into xanthophylls, putative abscisic acid precursors and product abscisic acid was restricted to the all-trans-isomer. However, when a combination of all-trans- and 9-cis-β-carotene in the ratio 1:1 was used as substrate, formation of abscisic acid and related metabolites was enhanced. Biosyn-thetically prepared [¹⁴C]-all-trans-violaxanthin, [¹⁴C]-all-trans-neoxanthin and [¹⁴C]-9′-cis-neoxanthin were used as substrates to confirm the metabolic interrelationship between carotenoids and abscisic acid. The results are consistent with 9′-cis-neoxan-thin being the immediate carotenoid precursor to ABA, which is oxidatively cleaved to produce xanthoxin. Formation of abscisic aldehyde was not observed. Rather, xanthoxin appeared to be converted to abscisic acid via xanthoxin acid and 1′,4′-trans-abscisic acid diol. An alternative pathway for abscisic acid biosynthesis is therefore proposed.     

The role of abscisic acid in the ripening of grapes

Ripening in grapes ( Vitis vinifera L. cv. Thompson seedless) was accompanied by an increase in the levels of sucrose, glucose and fructose and a decrease in the levels of acids. The activity of glucose-6-phosphatase and fructose-l–6-bisphospbatase was lower in sweet grapes as compared to sour ones. Abscisic acid (10⁻⁶ M) stimulated the gluconeogenic process in sour grapes. The levels of some gluconeogenic enzymes were also elevated in its presence. Cyclohexitnide (0.036–1.8 mM) nullified the abscisic acid effect, suggesting that this effect involves de novo protein synthesis. The incorporation of [¹⁴C]-leucine into proteins was enhanced about 80% by abscisic acid, confirming that abscisic acid promoted protein synthesis. Again, cycloheximide blocked the hormone mediated increase in the incorporation of radioactivity into proteins. The results indicate that one of the factors for sourness in certain mature ripe grapes may be that abscisic acid is not available.     

Effects of abscisic acid on in vitro growth of cotton fiber

Summary Abscisic acid (ABA) inhibits in vitro growth of cotton (Gossypium hirsutum L.) fiber and is effective only when applied during the first four days of culture started on the day of anthesis. Abscisic acid causes a small increase in potassium uptake by the ovules and also enhances leakage of potassium from them. During their period of rapid growth, fibers produced by ABA-treated ovules have a higher potassium content and a lower malate content as compared to fibers on untreated control ovules. Results are discussed in the light of earlier reports on the in vitro growth of cotton fiber and effects of abscisic acid on other plant tissues. It is suggested that ABA inhibits fiber growth, in part, by interfering with malate metabolism.Abbreviations ABA abscisic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - TFU total fiber units     

A comparative study of the effects of methyl jasmonate and abscisic acid on some rice physiological processes

The effects of methyl jasmonate (MJ) and abscisic acid (ABA) on some physiological processes of rice were compared. MJ exhibited ABA-like effects by promoting senescence of detached leaves, by inducing acid phosphatase activity of detached leaves, by inhibiting ethylene production and shoot growth of seedlings, as well as inhibiting callus formation from anthers. However, MJ and ABA had opposite effects on 1-aminocyclopropane-1-carboxylic acid-dependent ethylene production in detached leaves. The regeneration ability of anther-derived callus was inhibited by MJ but not by ABA. MJ but not ABA markedly induced peroxidase activity in senescing detached leaves. It is concluded that not all physiological processes of rice affected by MJ are similar to those by ABA.Abbreviations ABA abscisic acid - MJ methyl jasmonate - ACC 1-aminocyclopropane-l-carboxylic acid - Apase acid phosphatase     

Studies on the role of abscisic acid in the initiation of bud dormancy in Alnus glutinosa and Betula pubescens

Summary The effects of leaf-applied (+-)-abscisic acid on the growth and dormancy of Betula pubescens Ehrh. and Alnus glutinosa Gaertn. growing under long days provide no evidence that leaf-applied abscisic acid induces or promotes the formation of resting buds in these species. Radiotracer studies show that a small percentage of the radioactivity applied as [2-¹⁴C]abscisic acid to the leaves accumulates in the apical region of the shoot. Of the radioactivity that was recovered from this region after 8 days, less than 10% was chromatographically similar to [2-¹⁴C]abscisic acid. The significance of these results with respect to the role of abscisic acid in regulating the induction of bud dormancy is discussed.Abbreviation ABA abscisic acid     

Stomatal responses to jasmonic acid, linolenic acid and abscisic acid in wild-type and ABA-deficient tomato plants

Wild-type and abscisic acid (ABA) -deficient (sitiens) tomato plants were used to analyse the effects of abscisic acid (ABA), butyric acid (BA), jasmonic acid (JA) and linolenic acid (LA) on assimilation and transpiration rates in detached leaves taking up those substances into the transpiration stream. BA did not affect assimilation and transpiration rates. ABA decreased assimilation and transpiration in both wild-type and ABA-deficient mutants. JA reduced the assimilation rate in both lines but induced a significant reduction of transpiration in the wild type only. The response to LA in both lines was slower than that to JA.     

A simple bioassay for abscisic acid using cucumber hypocotyls

A simple bioassay based on the inhibition by abscisic acid (ABA) of cucumber (Cucumis sativus L., cv. National Pickling) hypocotyl elongation was developed. Sections of 3-day-old dark-grown cucumber hypocotyl taken from 0–5 mm immediately below the cotyledon were used for the assay. A dark incubation period of 20 h was followed by an exposure to light for 24 h. Under these conditions, the inhibition of hypocotyl elongation is proportional to the abscisic acid applied. The minimum detectable level of abscisic acid was 10^–9 M, and the range of linear response to abscisic acid was between 10^–7 and 10^–3 M. This assay is 10 times more sensitive than the cucumber cotyledon greening bioassay for abscisic acid.