ABSCISIC-ACID STRUCTURE-ACTIVITY-RELATIONSHIPS IN BARLEY ALEURONE LAYERS AND PROTOPLASTS - BIOLOGICAL-ACTIVITY OF OPTICALLY-ACTIVE, OXYGENATED ABSCISIC-ACID ANALOGS

Optically active Corms of abscisic acid (ABA) and their oxygenated met abolites were tested for their biological activity by examining the ef fects of the compounds on the reversal of gibberellic acid-induced Lu- amylase activity in barley (Hordeum vulgare cv Himalaya) aleurone laye rs and the induction of gene expression in barley aleurone protoplasts transformed with a chimeric construct containing the promoter region of an albumin storage protein gene. Promotion of the albumin storage p rotein gene response had a more strict stereochemical requirement for elicitation of an ABA response than inhibition of cu-amylase gene expr ession. The naturally occurring stereoisomer of ABA and its metabolite s were more effective at eliciting an ABA-like response. ABA showed th e highest activity, followed by 7'-hydroxyABA, with phaseic acid being the least active. Racemic 8'-hydroxy-2',3'-dihydroABA, an analog of 8 '-hydroxyABA, was inactive, whereas racemic 2',3'-dihydroABA was as ef fective as ABA. The differences in response of the same tissue to the ABA enantiomers lead us to conclude that there exists more than one ty pe of ABA receptor and/or multiple signal transduction pathways in bar ley aleurone tissue.