Water stress and the catabolism of (�)-abscisic acid by excised leaves of Hordeum vulgare L. cv. Dyan

Abstract

When excised, light-grown leaves of Hordeum vulgare were fed with (±)-[2-14C]-abscisic acid and stressed until they had lost 12% of their original fresh weight, marked changes in the distribution of radioactivity between abscisic acid and its catabolites were observed. Wilted leaves were less able than their turgid counterparts to transform (±)-[2-14C]-abscisic acid into 2′-hydroxymethyl abscisic acid, dihydrophaseic acid and water-soluble conjugates of abscisic acid. Water stress had little effect on the production of phaseic acid although refeeding studies with [14C]-phaseic acid showed that the step from phaseic acid to dihydrophaseic acid was inhibited in wilted leaves. Evidence was obtained which suggested that these changes did not result from dilution of applied, radiolabelled substrate by endogenous abscisic acid. The catabolites of (±)-abscisic acid were identified by capillary gas chromatography-mass spectrometry.