Abscisic Acid Analogs Research Articles

Achiral cyclohexadienone analogues of abscisic acid: Synthesis and biological activity

Novel achiral cyclohexadienone (divinyl) analogues of abscisic acid (ABA) were synthesized and tested for biological activity. Oxidation of 2,6-dimethylphenol with iodobenzene acetate in ethylene glycol and hexane afforded 2,6-dimethyl-4,4-ethylenedioxycyclohexa-2,5-dienone as the key intermediate which was further transformed to a series of ABA analogues with cyclohexa-2′,5′-dien-4′-one ring and dienoic or enynoic sidechains at different oxidation levels. Their biological activity was compared to racemic ABA in assays for germination of cress seeds and freezing tolerance in bromegrass cell suspension cultures and related to the activity of the corresponding analogues with the ABA ring system. The divinyl dienoic methyl ester was as active as racemic ABA and methyl ABA in inhibiting cress seed germination. The divinyl dienoic methyl ester and divinyl acetylenic methyl ester had comparable activity to methyl ABA in inducing freezing tolerance. The results suggest that the vinyl methyl group is sufficient for recognition by ABA response systems in these assays and the axial methyl is not absolutely required.

8′- and 9′-Methoxyabscisic Acids as Antimetabolic Analogs of Abscisic Acid

8′- and 9′-Methoxyabscisic acids (methoxy-ABAs) were synthesized as antimetabolic analogs of abscisic acid (ABA). The racemic mixtures were resolved by HPLC. (+)-8′-Methoxy-ABA inhibited the elongation of rice seedlings four times more strongly than (+)-ABA did, and (+)-9′-methoxy-ABA inhibited the germination of lettuce seeds and the induction of α-amylase by gibberellin A3 in barley seeds seven and two times more strongly, respectively. These methoxy-ABAs are the first analogs reported to have higher activity than ABA. (+)-8′- and (+)-9′-Methoxy-ABAs were less active in causing stomatal closure than (+)-ABA. These biological activities and 1H-NMR analysis suggest that the activity of methoxy-ABAs involved delayed metabolism, as was expected. The activity of (−)-isomers of ABA and methoxy-ABAs was also tested.

Synthesis and Activity of New Abscisic Acid Analogues Possessing Hetero Five-membered Ring in their Molecules

Synthesis and Activity of New Abscisic Acid Analogues Possessing Hetero Five-membered Ring in their Molecules

Oxidation of the 8′-position of a biologically active abscisic acid analogue

The metabolism of a biologically active abscisic acid (ABA) analogue, (+)-(1′ S,2′ S)-2′,3′-dihydroabscisic acid [(+)-4-(1 E,3 Z)-(

Metabolism of allenic analogues of abscisic acid

We have already reported that some allenic analogues of abscisic acid inhibited growth of duckweed ( Lemna gibba and L. paucicostata) in axenic

Involvement of Abscisic Acid in Ethylene-Induced Cotyledon Abscission in Cotton Seedlings.

Cotton (Gossypium hirsutum L. cv LG102) seedlings raised from seeds exposed to 100 [mu]M norflurazon (NFZ) during imbibition contained reduced levels of free abscisic acid (ABA) and were visibly achlorophyllous. Exposure of untreated cotton seedlings to ethylene concentrations >1 [mu]L/L for 24 h resulted in cotyledon abscission. In contrast, exposure of NFZ-treated seedlings to concentrations of ethylene [less than or equal to]50 [mu]L/L elicited no cotyledon abscission. Application of ABA, an ABA analog, or jasmonic acid to NFZ-treated seedlings restored ethylene-induced abscission. Isolated cotyledonary node explants prepared from NFZ-treated seedlings exhibited an altered dose-response pattern of ethylene-induced petiole abscission. Endogenous levels of free IAA were unaltered in NFZ-treated seedlings. Ethylene treatment (50 [mu]L/L, 24 h) had no effect on free indoleacetic acid (IAA) levels in either control or NFZ-treated seedlings. Levels of conjugated (ester plus amide) IAA were substantially increased in NFZ-treated seedlings regardless of ethylene treatment. These results indicate that endogenous ABA plays an essential, but physiologically undefined, role in ethylene-induced cotyledon abscission in cotton.

Competitive Inhibition of Abscisic Acid-Regulated Gene Expression by Stereoisomeric Acetylenic Analogs of Abscisic Acid.

The properties of two enantiomeric synthetic acetylenic abscisic acid (ABA) analogs (PBI-51 and PBI-63) in relation to ABA-sensitive gene expression are reported. Using microspore-derived embryos of Brassica napus as the biological material and their responsiveness to ABA in the expression of genes encoding storage proteins as a quantitative bioassay, we measured the biological activity of PBI-51 and PBI-63. Assays to evaluate agonistic activity of either compound applied individually showed a dose-dependent increase in napin gene expression on application of PBI-63. Maximal activity of about 40 [mu]M indicated that PBI-63 was an agonist, although somewhat weaker than ABA. PBI-63 has a similar stereochemistry to natural ABA at the junction of the ring and side chain. In contrast, PBI-51 showed no agonistic effects until applied at 40 to 50 [mu]M. Even then, the response was fairly weak. PBI-51 has the opposite stereochemistry to natural ABA at the junction of the ring and side chain. When applied concurrently with ABA, PBI-63 and PBI-51 had distinctly different properties. PBI-63 (40 [mu]M) and ABA (5 [mu]M) combined gave results similar to the application of either compound separately with high levels of induction of napin expression. PBI-51 displayed a reversible antagonistic effect with ABA, shifting the typical ABA dose-response curve by a factor of 4 to 5. This antagonism was noted for the expression of two ABA-sensitive genes, napin and oleosin. To test whether this antagonism was at the level of ABA recognition or uptake, ABA uptake was monitored in the presence of PBI-51 or PBI-63. Neither compound decreased ABA uptake. Treatments with either PBI-51 or PBI-63 showed an effect on endogenous ABA pools by permitting increases of 5- to 7-fold. It is hypothesized that this increase occurs because of competition for ABA catabolic enzymes by both compounds. The fact that ABA pools did not decrease in the presence of PBI-51 suggests that PBI-51 must exert its antagonistic properties through direct competition with ABA at a hormone-recognition site.

Effect of LAB 173711, an ABA Analogue, on Low Temperature Resistance of Suspension Cultured Sugarcane Cells

Summary The effect of LAB 173711, a synthetic analogue of abscisic acid, on the response of suspension-cultured sugarcane ( Saccharum officinarum L.) cells under low-temperature stress was evaluated. Cells grown at 10°C or 4°C for 5 d showed a remarkably reduced growth rate as evaluated with TTC reduction, but did not exhibit any symptoms of chilling injury. LAB 173711 application did not improve the lowered growth rate observed under such chilling conditions. By stepwise reducing temperature to evaluate freezing tolerance, the LT 50 for sugarcane cells is about -2°C, while 10 -6 M of LAB 173 711 lowered this value significantly to approximately -6°C. LAB 173711 application also affected some physiological processes: Respiration and the activities of a-amylase and peroxidase are increased. Soluble sugars, reducing sugars, soluble proteins, and free amino acid contents were increased, the combination of which would lead to a reduced osmotic potential.

Facile aromatisation of abscisic acid

Treatment of abscisic acid (ABA) or its methyl ester either with acetic anhydride and toluene-p-sulfonic acid or with lithium diisopropylamide and methyl chloroformate led to aromatisation of the cyclohexene ring. A mechanism for the reaction is proposed which involves the initial formation of the 4′,5′-enol followed by a carbocationic rearrangement initiated by loss of the 1′-tertiary alcohol. Analogues of ABA with a saturated side chain do not undergo this aromatisation process.

Abscission-promoting activities of abscisic acid and five abscisic acid analogs in cotton seedlings and explants

The abscission-promoting activities of abscisic acid (ABA) and 5 ABA analogs were examined in cotton (Gossypium hirsutum L. cv LG102) seedlings and cotyledonary node explants. The analogs tested included a series of acetylenic derivatives that differ in the oxidation state of the C-1 atom, a 2′,3′ dihydro-derivative of ABA and a 2′,3′ dihydro-derivative of an acetylenic analog with a C-1 carboxyl moiety. ABA and all five analogs were active in stimulating petiole abscission in explants. Following treatment with 100,µM ABA or analog, 50% abscission of explants was observed after 29 h and complete abscission occurred within 40 h. With one exception, none of the treatments resulted in an increase in explant ethylene production. Pretreatment of the explants with the ethylene antagonist silver thiosulfate completely abolished the abscission-promoting activities of ABA and all of the analogs. Daily application of ABA or any of the analogs had no effect on cotyledon abscission in intact seedlings. The implications of the results with respect to the development of a commercial ABA-like regulator as well as to ABA structure-activity studies are discussed.

Effect of LAB 173 711, an ABA analogue, on low-temperature resistance of mung bean seedlings

The effect of LAB 173 711, a synthetic analogue of abscisic acid, has been evaluated on chilling-sensitive mung bean (Vigna radiata L. cv. Local V.) seedlings. Electrical conductivity was used for assessing the degree of chilling injury. Exposure of 8-day-old mung bean seedlings to 4°C for 35 h resulted in a 50% electrolyte leakage and induced irreversible chilling injury. The seedlings gained the best protection against chilling injury by pretreatment with LAB 173 711 (5 × 10−4 M) for 3 days. The protection effect could be sustained for 4 days. The LAB 173 711 pretreatment at 28°C did not cause a significant difference in the electrolyte leakage over the ambient temperature (28°C) control. Application of LAB 173 711 at 28°C reduced visible injury and the treated seedlings had higher ethylene production and respiration rate over the untreated control. LAB 173 711 helped maintain the integrity of the cell membrane and thus reduced the leakage of soluble sugar and amino acids. These combined effects led to a higher chilling tolerance in the mung bean seedlings.

Effects of abscisic acid analogues on abscisic acid-induced gene expression in barley aleurone protoplasts: Relationship between structure and function of the abscisic acid molecule

The plant hormone abscisic acid (ABA) mediates gene expression in barley aleurone protoplasts. In order to elucidate the essential functional groups of the ABA molecule, the specificity of a number of ABA analogues for inducing ABA-regulated gene (e.g., RAB, BASI) expression in barley aleurone protoplasts was studied. These analogues have modifications at three different positions of the ABA molecule: (a) the 1′-hydroxyl group (1′-deoxy ABA), (b) the carboxyl group (ABA-methyl ester or ABA-glucose ester), and (c) both the 1′-hydroxyl and 4′-carbonyl groups (α-ionylidene acetic acid). The importance of the different putative functional groups was analyzed. The dose-response analysis of ABA analogues upon the induction gene expression showed the following order: ABA > ABA methyl ester > 1′-deoxy ABA > ABA glucose ester > α-ionylidene acetic acid > α-β-ionone. © 1993 Springer-Verlag New York Inc.

Improvement of chilling resistance in rice by application of an abscisic acid analog in combination with the growth retardant tetcyclacis

The protective effect of a synthetic terpenoid Analog of the plant hormone abscisic acid (ABA) coded LAB 173711 applied alone or in combination with the growth retardant tetcyclacis on chilling injury of rice was studied under growth chamber, greenhouse, and field conditions. The compounds were applied as a foliar spray before and after the onset of chilling treatment, as a substrate via the root system, and as a medium for seed soaking. The ABA analog increased chilling resistance in a manner similar to ABA. Combination of the analog with tetcyclacis revealed additive effects. Increased chilling resistance involved several processes: stomatal closure which reduced water loss during chilling, stabilization of the membranes, stabilization of the chlorophyll level, and stabilization of the root system. Possibilities for practical use of the compounds in rice production are discussed.

Changes in the levels of abscisic acid and its metabolites resulting from chilling of tomato fruits

The 6,6,6-[2H]-analogues of abscisic acid (ABA), phaseic (PA) and dihydrophaseic (DPA) acids were used in GC-MS-SIM determination of free and total alkali hydrolyzable ABA, PA and DPA in the pericarp of tomato (Lycopersicon esculentum L. cv. Pik Red) fruit. Determinations were made on breaker-stage fruit stored 1, 2, 3 or 4 weeks at 2.5°C or at 10°C, and after subsequent ripening for 1 week in darkness at 20°C. Two-fold increases in levels of ABA occurred after storage at low temperatures with a slightly but significantly greater increase in ABA level occurring with 2.5°C storage. These increases in ABA levels were not associated with the appearance of damage symptoms that occurred with storage at the chilling temperature (2.5°C). Differences in ABA metabolism were found resulting from storage at the two temperatures, 2.5 or 10°C. Significantly greater DPA levels were found after 10°C storage than after 2.5°C storage (2 weeks). Levels of ABA ester-conjugates increased with 20°C ripening only after 10°C storage while free ABA levels decreased after both storage temperature conditions. Levels of DPA conjugates also increased only after 20°C ripening following 10°C storage. A longer period of storage resulted in decreases of free DPA levels after 10°C storage but increased DPA levels were found after 2.5°C storage.

The effect of abscisic acid and abscisic acid metabolites on the germination of cress seed

Optical isomers of abscisic acid (ABA) and racemic mixtures of both abscisic acid and abscisic acid metabolites were studied to determine their effects on the emergence of root primordia and cotyledons from cress seed. The relative emergence sensitivity of cress seed to the racemic compounds was (±)-ABA aldehyde ≥ (±)-ABA alcohol > (±)-ABA > (±)7′-hydroxy ABA > (±)-phaseic acid. Thus ABA and ABA precursors were effective inhibitors whereas the ABA catabolites, phaseic acid, and 7′-hydroxy ABA had little or no effect on germination. The naturally occurring optically pure enantiomer (+)ABA was a more potent germination inhibitor than synthetic (−)-ABA. An ABA analog, 2′,3′-cis dihydro ABA (DHABA), that is not metabolized to phaseic acid was also studied for inhibitory activity. Although optically pure DHABA has the same configuration at C-1 as (+)-ABA, it was less inhibitory than (+)-ABA and its (−) enantiomer was inactive. The pattern of activity observed in treatments with the enantiomers of DHABA indicates that the configuration at C-1′ is important for maximum inhibition of cress seed germination. It also suggests that in contrast to monocot seeds, the formation of phaseic acid is not required for the inhibition of cress seed germination. Key words: abscisic acid, phaseic acid, ABA alcohol, ABA aldehyde, 7′OHABA, germination, ABA analogs.

Characterization of a gene family encoding abscisic acid- and environmental stress-inducible proteins of alfalfa.

The phytohormone abscisic acid (ABA) has been proposed as a common mediator controlling adaptive plant responses to a variety of environmental stresses, including water deficit, salinity, wounding, and low temperature. We have recently isolated three cDNAs, pUM90-1, pUM90-2, and pUM91-4, from a cDNA library of ABA-induced mRNAs of alfalfa. These cDNA clones exhibit a very high degree of sequence homology with one another and sequence similarities with certain regions of several stress- and ABA-inducible genes. The polypeptides encoded by these cDNAs are very rich in glycine (35-40%), histidine (7-15%), asparagine (8-14%), and tyrosine (5-10%) and have no tryptophan and proline. All of the encoded polypeptides contain characteristic tandem repeats comprising glycine residues intercepted with histidine and/or tyrosine. The RNAs corresponding to a representative cDNA, pUM90-1, were induced after treatment of seedlings with low temperature, drought, salt, and wounding stress, but not by heat; the induction was maximal under low temperature treatment. ABA and ABA analog rapidly induced the expression of these genes, whereas gibberellic acid treatment exhibited no induction whatsoever. These genes appear to be specifically induced in the shoot tissues. Analysis of ABA induction of genes corresponding to pUM90-1 in alfalfa seedlings of different age groups demonstrated that these genes were inducible in seedlings/plants of all age groups examined. Taken together these results suggest that these cDNA clones encode a group of proteins that are inducible by ABA and multiple environmental stresses and correspond to a new family of genes of plants, designated as ABA- and environmental stress-inducible genes.

Optically Pure Abscisic Acid Analogs—Tools for Relating Germination Inhibition and Gene Expression in Wheat Embryos

We report an examination of the structural requirements of the abscisic acid (ABA) recognition response in wheat dormant seed embryos using optically pure isomers of ABA analogs. These compounds include permutations to the ABA structure with either an acetylene or a trans bond at C-4 C-5, and either a single or double bond at the C-2' C-3' double bond. (R)-ABA and the three isomers with the same configuration at C-1' as natural ABA were found to be effective germination inhibitors. The biologically active ABA analogs exhibited differential effects on ABA-responsive gene expression. All the ABA analogs that inhibited germination induced two ABA-responsive genes, wheat group 3 lea and dhn (rab). However, (R)-ABA and (S)-dihydroABA were less effective in inducing the ABA-responsive gene Em within the time that embryonic germination was inhibited.

Role of Abscisic Acid in the Induction of Desiccation Tolerance in Developing Seeds of Arabidopsis thaliana

In contrast to wild-type seeds of Arabidopsis thaliana and to seeds deficient in (aba) or insensitive to (abi3) abscisic acid (ABA), maturing seeds of recombinant (aba,abi3) plants fail to desiccate, remain green, and lose viability upon drying. These double-mutant seeds acquire only low levels of the major storage proteins and are deficient in several low mol wt polypeptides, both soluble and bound, and some of which are heat stable. A major heat-stable glycoprotein of more than 100 kilodaltons behaves similarly; during seed development, it shows a decrease in size associated with the abi3 mutation. In seeds of the double mutant from 14 to 20 days after pollination, the low amounts of various maturation-specific proteins disappear and many higher mol wt proteins similar to those occurring during germination are induced, but no visible germination is apparent. It appears that in the aba,abi3 double mutant seed development is not completed and the program for seed germination is initiated prematurely in the absence of substances protective against dehydration. Seeds may be made desiccation tolerant by watering the plants with the ABA analog LAB 173711 or by imbibition of isolated immature seeds, 11 to 15 days after pollination, with ABA and sucrose. Whereas sucrose stimulates germination and may protect dehydration-sensitive structures from desiccation damage, ABA inhibits precocious germination and is required to complete the program for seed maturation and the associated development of desiccation tolerance.

Synthesis of chiral acetylenic analogs of the plant hormone abscisic acid

Syntheses of optically active acetylenic analogs of abscisic acid are described. The key step involves the diastereoselective alkylation of the (2S,3S)-butanediol ketal of oxoisophorone, which produces a 3:1 mixture of separable diastereoisomers. The absolute stereochemistry of the analogs was established by conversion to a known derivative and by correlation of ORD data.

Inhibition ofα-Amylase Induction in Barley Seed and the Induction of Stomatal Pore Closure by Artificial Abscisic Acid Analogs (RCA Series)

Inhibition of<i>α</i>-Amylase Induction in Barley Seed and the Induction of Stomatal Pore Closure by Artificial Abscisic Acid Analogs (RCA Series)