Metabolism and biological activity of (+)- and (-)-C-1'-O-methyl ABA in maize suspension-cell cultures

(+)-C-1'-O-Methyl abscisic acid is rapidly metabolized by suspension-cultured maize cells (Zea mays L. Black Mexican Sweet) to (+)-C-1'-O-methyl phaseic acid in an analogous process as seen for ABA. The presence of a methyl ether on the 1'-position of ABA does not interfere with enzymic oxidation at the 8'-carbon. The metabolite is demethylated to yield phaseic acid. A small amount of abscisic acid is also produced by direct demethylation. The (+)-C-1'-O-methyl ABA exhibits stronger growth inhibitory activity of the maize cells than (+)-ABA, suggesting that a free C-1'-hydroxyl group is not essential for biological activity of ABA in maize. The (-)-C-1'-O-methyl ABA is metabolized to (-)-ABA and to 7'-hydroxyABA and the corresponding C-1'-0-methyl-7'-hydroxy ABA.