Abscisic Acid Metabolism in Barley Seedlings Subjected to Drought

Abstract

Summary Seedlings of barley (Hordeum vulgare L. cv. Trumpf) were subjected to drought conditions for 24 or 48h. The identity of abscisic acid (ABA) and its acidic metabolites phaseic acid (PA) and dihydrophaseic acid (DPA) was proved by TLC, HPLC, GC, and GC-MS in both stressed and nonstressed plants. Additionally, the endogenous occurrence of another acidic metabolite, 2′-hydroxymethyl-ABA (nigellic acid) was indicated by TLC. Regarding conjugates, the glucosyl ester of ABA was characterized by TLC and HPLC followed by enzymatic hydrolysis, giving ABA and glucose in the ratio 1:1. A neutral conjugate with DPA as aglycone (HPLC, GC) was shown to be present in both water-stressed and non-stressed seedlings, too. There was no evidence for a conjugation of PA. Water deficiency caused a large increase in the content of abscisic acid from 23 ng/g dry wt. in the control leaves to 271 ng and 604ng/g dry wt. after 24 and 48 h drought, respectively. Additionally, the catabolism of ABA to PA and DPA was stimulated. Thus the level of PA was shown to rise from 25ng/g dry wt. in the control to 123 and 256 ng/g dry wt. in the 24 and 48h stressed plants. Similarly, an increase of DPA in the leaves from 46ng/g dry wt. to 237ng/g dry wt. after 48h stress was obtained. However, there were no significant changes in the neutral ABA and DPA conjugate levels during applied stress.