Activity of the asymmetric isomers of abscisic acid in a rapid bioassay.

Highly purified preparations of (+)- and (-)-abscisic acid (ABA) were compared for biological activity in a rapid bioassay based on closure of stomates on excised leaves of Hordeum vulgare. The naturally-occurring (+)-enantiomer was markedly more active. It causes speedier closure of the stomates, as measured by changes in leaf temperature. The differences in the activities of the ABA enantiomers are greater than have yet been reported for any other system.