Metabolism of (+)- and (−)-abscisic acid by somatic embryo suspension cultures of white spruce

Abstract

Somatic embryo suspension cultures of white spruce in medium containing (+)-abscisic acid [(+)-ABA], at an initial concentration of 15 μM, metabolized the ABA essentially completely within seven days. The metabolites accumulated in the liquid medium. The (+)-ABA was converted almost quantitively to phaseic acid, with little further transformation into dihydrophaseic acid. The sum of the concentrations of the two metabolites in the medium closely approximated the concentration of (+)-ABA initially supplied. (−)-ABA remained essentially unchanged under the same culture conditions, and when the cells were supplied with racemic (±)-ABA, only the (+) enantiomer was metabolized. When (+)- or (±)-ABA was present in the medium, the size of the embryos and their suspensors increased during the culture period, a development consistent with somatic embryo maturation. Embryos in control cultures lacking exogenously supplied ABA, and embryos in cultures provided with only (−)-ABA, did not increase in size. The early disappearance of the (+)-ABA from the suspension medium, and the completeness of its conversion to phaseic acid, raises the question of the relative roles of ABA and phaseic acid in the maturation of conifer somatic embryos.