Elevating Ascorbate in Arabidopsis Stimulates the Production of Abscisic Acid, Phaseic Acid and to a Lesser Extent Auxin (IAA) and Jasmonates, Resulting in Increased Expression of DHAR1 and Multiple Transcription Factors Associated with Abiotic Stress Tolerance

Gene expression and phytohormone contents were measured in response to elevating ascorbate in the absence of other confounding stimuli such as high light and abiotic stresses. Young Arabidopsis plants were treated with 25 mM solutions of l-galactose pathway intermediates l-galactose (l-gal) or l-galactono-1,4-lactone (l-galL), as well as L-ascorbic acid (AsA), with 25 mM glucose used as control. Feeding increased rosette AsA 2- to 4-fold but there was little change in AsA biosynthetic gene transcripts. Of the ascorbate recycling genes, only Dehydroascorbate reductase 1 expression was increased. Some known regulatory genes displayed increased expression and included ANAC019, ANAC072, ATHB12, ZAT10 and ZAT12. Investigation of the ANAC019/ANAC072/ATHB12 gene regulatory network revealed a high proportion of ABA regulated genes. Measurement of a subset of jasmonate, ABA, auxin (IAA) and salicylic acid compounds revealed consistent increases in ABA (up to 4.2-fold) and phaseic acid (PA; up to 5-fold), and less consistently certain jasmonates, IAA, but no change in salicylic acid levels. Increased ABA is likely due to increased transcripts for the ABA biosynthetic gene NCED3. There were also smaller increases in transcripts for transcription factors ATHB7, ERD1, and ABF3. These results provide insights into how increasing AsA content can mediate increased abiotic stress tolerance.

Contrasting dynamics in abscisic acid metabolism in different Fragaria spp. during fruit ripening and identification of involved enzymes

Abscisic acid (ABA) is a key hormone in non-climacteric Fragaria spp, regulating multiple physiological processes throughout fruit ripening. Its level increases during ripening, and it promotes fruit (receptacle) development. However, its metabolism in the fruit is largely unknown. We analyzed the levels of ABA and its catabolites at different developmental stages of strawberry ripening in diploid and octoploid genotypes and identified two functional ABA-glucosyltransferases (FvUGT71A49 and FvUGT73AC3) and two regiospecific ABA-8’-hydroxylases (FaCYP707A4a and FaCYP707A1/3). ABA-glucose-ester content increased during ripening in diploid F. vesca varieties but decreased in octoploid F. xananassa. Dihydrophaseic acid content increased throughout ripening in all analyzed receptacles, while 7’-hydroxy-ABA and neo-phaseic acid did not show significant changes during ripening. In the studied F. vesca varieties, the receptacle seems to be the main tissue for ABA metabolism, as the content of ABA and its metabolites in the receptacle was generally 100 times higher than in achenes, respectively. The accumulation patterns of ABA catabolites and transcriptomic data from the literature show that all strawberry fruits produce and metabolize considerable amounts of the plant hormone ABA during ripening, which is therefore a conserved process, but also illustrate the diversity of this metabolic pathway which is species, variety and tissue dependent.

Enantioselective synthesis of (−)-phaseic acid

A short, enantioselective synthesis of a newly identified ABA receptor agonist (−)-phaseic acid is described.

Involvement of abscisic acid metabolites and the oxidative status of barley genotypes in response to drought

Thameur, A., Ferchichi, A. and López-Carbonell, M. 2014. Involvement of abscisic acid metabolites and the oxidative status of barley genotypes in response to drought. Can. J. Plant Sci. 94: 1481–1490. Endogenous concentrations of free abscisic acid (ABA), abscisic acid glucosyl ester (ABAGE), phaseic acid (PA), dihydrophaseic acid (DPA) and 7′-hydroxy ABA (7′-OH ABA) were analysed by means of a LC–MS/MS system in five genotypes of barley (Hordeum vulgare L.) grown under well-watered and drought stress conditions. For this purpose a drought treatment was conducted using genotypes: ‘Ardahoui’, ‘Manel’, ‘Pakistan’, ‘Rihane’ and ‘Roho’. Our results show that free and conjugated ABA levels increased in all genotypes grown under water stress, except in Manel genotype, in which ABAGE levels were the lowest. In contrast, genotypes Ardhaoui and Roho showed the highest ABA and ABAGE levels. Nevertheless, drought Rihane plants showed the maximum ability to increase the endogenous ABA concentrations. PA, DPA and 7′-OH ABA increased also in all drought genotypes, especially in the leaves of Manel and Roho genotypes, while the highest ability to increase the endogenous PA content corresponded to genotypes Ardahoui and Pakistan. To evaluate the plant oxidative status, some antioxidant compounds were analysed. Under drought conditions, small changes in some of them were seen. Among the genotypes studied, Manel was the only one which did not show increases in malondialdehyde (MDA) and, in parallel, showed a decrease in ABAGE content. These results provide us valuable information and contribute to the knowledge of the different responses of these genotypes to drought stress.

Abscisic Acid Metabolism during Fruit Development and Maturation of Mangosteens

Endogenous abscisic acid (ABA), its 2-trans isomer (trans-ABA), phaseic acid (PA), and dihydrophaseic acid (DPA) concentrations were quantified in the peel, aril, and seed of mangosteen (Garcinia mangostana L.). Changes in carbon dioxide (CO2) and ethylene (C2H4) production and 1-aminocyclopropane-1-carboxylic acid (ACC) concentration in the peel and aril were also examined. ACC concentration and CO2 and C2H4 production were high at the beginning of fruit development and gradually decreased toward harvest, which confirms that mangosteen is a nonclimacteric fruit. In the peel and aril, the increase in ABA concentration preceded the decrease in peel firmness and coloring of the peel. This suggests that ABA may induce the maturation of mangosteens. The state of ABA metabolism varied with the part of fruit. In the peel, PA and DPA were not considered to be predominant metabolites of ABA because their concentrations were low compared to ABA throughout fruit development. In contrast, in the aril and seed, it is possible that the PA-DPA pathway may be a main pathway of ABA metabolism because the concentrations of DPA in the aril and of PA in the seed directly coincided with the concentrations of ABA. The differences in the ABA metabolites between aril and seed may be caused by the rate of ABA metabolism. The concentrations of ABA and its metabolite in the seed decreased toward harvest.