EFFECTS OF ABSCISIC-ACID ANALOGS 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 (alpha-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 > alpha-ionylidene acetic acid > alpha-beta-ionone.