Isolation and Quantitation of beta-d-Glucopyranosyl Abscisate from Leaves of Xanthium and Spinach.

From previous work (Zeevaart 1980 Plant Physiol 66: 672-678) Xanthium leaves are known to contain a high level of alkali-hydrolyzable conjugated abscisic acid. This abscisic acid conjugate has been isolated and identified by mass spectrometry, nuclear magnetic resonance, and chemical and enzymic degradation techniques, as the glucosyl ester of abscisic acid, beta-d-glucopyranosyl abscisate. The glucosyl ester of abscisic acid was the only abscisic acid conjugate found in Xanthium leaves. It was also isolated from spinach leaves.An insignificant amount of the glucosyl ester of abscisic acid partitioned into diethyl ether, whereas 12% partitioned into ethyl acetate. Consequently, removal of abscisic acid by partitioning with ethyl acetate will result in considerable losses of the glucosyl ester of abscisic acid from the aqueous phase. Diethyl ether is, therefore, recommended for separation of abscisic acid and the glucosyl ester of abscisic acid by solvent partitioning.A method for quantitation of the glucosyl ester of abscisic acid as the tetraacetate derivative by gas-liquid chromatography with an electron capture detector was developed. The level of beta-d-glycopyranosyl abscisate in Xanthium leaves increased from 3.6 nanomoles per gram fresh weight in turgid leaves to 22.9 nanomoles in leaves from plants subjected to seven wilting-recovery cycles. beta-d-glycopyranosyl abscisate in Xanthium leaves may be a stable end product of abscisic acid metabolism.