Asymmetry, Its Importance to the Action and Metabolism of Abscisic Acid

Unlabeled and (14)C-labeled enantiomorphs of abscisic acid (ABA) were obtained through acetylcellulose chromatography and tested as inducers of abscission, as inhibitors of seed germination, and as antagonists of gibberellic acid-induced synthesis and release of alpha-amylase. The activity of the R isomer was either equal to or less than that of the naturally occurring S form. Greatest differences were in the inhibition of root-related growth. In excised beam axes, although uptake of S-(14C)ABA is faster, the internal concentration of R-ABA is higher because of faster conversion of S-ABA to inactive metabolic products. In axes a reversal in chirality is less important to the physiological action of ABA than to its metabolism.