Metabolism of 5′α,8′-cycloabscisic acid, a highly potent and long-lasting abscisic acid analogue, in radish seedlings Original Research Article

We synthesized 5′α,8′-cycloabscisic acid (CycloABA), a highly potent and long-lasting abscisic acid (ABA) analogue, by a different method from that reported before. CycloABA fed to radish seedlings had more metabolic tolerance than ABA. The major metabolite of CycloABA was the glucose conjugate, which was the minor metabolite of ABA. The 8′-hydroxylated metabolite and its cyclized isomer, which were major metabolites of ABA, were not found as metabolites of CycloABA. The present results suggest that the highly potent and long-lasting activity of CycloABA is caused by resistance to ABA 8′-hydroxylase, and that CycloABA is partially metabolized to the glucose conjugate by ABA glucosyltransferase.