Effect of ABA-β-d-glucopyranosyl ester and activity of ABA-β-d-glucosidase in Arabidopsis thaliana

Exogenously applied ABA-β-d-glucopyranosyl ester (ABA-GE) inhibited hypocotyl growth of Arabidopsis seedlings at concentrations greater than 0.3 μmol/L, and the concentration for 50% inhibition of hypocotyl growth was 1.8 μmol/L. ABA-β-d-glucosidase activity in Arabidopsis seedlings was 17 nmol/mg protein/mim and increased by exogenously applied ABA-GE. The pH optimum of this enzyme in crude extract of Arabidopsis seedlings was 6.0 for the assay in the ABA-GE to ABA direction and its Km value for ABA-GE (pH 6.0) was 0.41 mmol/L. These results suggests that exogenously applied ABA-GE may be absorbed by roots and hydrolyzed by ABA-β-d-glucosidase and librated free ABA may induce growth inhibition in Arabidopsis hypocotyls.