Metabolism of abscisic acid and the occurrence of epi-dihydrophaseic acid in Phaseolus vulgaris

When (±)-abscisic acid-2-¹⁴C] or (±)-abscisic acid-4′-¹⁸O] was fed to bean (Phaseolus vulgaris) shoots, phaseic acid (PA) and dihydrophaseic acid (DPA) were the major metabolites, while epi-dihydrophaseic acid (epi-DPA) appeared as a minor metabolite. In the acidic fraction the amount of epi-DPA ranged from 18 to 42% of the DPA content, in the conjugated form from 50 to 200%. The content of endogenous epi-DPA amounted to only 1–2% of that of the DPA. These data indicate that the applied abscisic acid is not metabolised in a manner identical with that of the endogenous material. DPA and epi-DPA were shown to be formed separately from PA and could not be inter-converted either by the extraction conditions employed or when fed to bean shoots during short term experiments.