Profiles of Abscisic Acid and Its Catabolites in Developing Merlot Grape (Vitis vinifera) Berries

Abstract

The plant hormone abscisic acid (ABA) is a signaling molecule involved in grape berry development and ripening. To obtain a more comprehensive understanding of ABA synthesis and catabolism in developing grape berries, ABA and catabolite profiles of Merlot grapes grown in a commercial vineyard in the southern Okanagan Valley in British Columbia, Canada, were measured using HPLC–MS/MS in multiple-reaction monitoring mode. While pulp and skin of preveraison berries contained low to moderate concentrations of ABA, these tissues had high concentrations of the ABA catabolite dihydrophaseic acid (DPA), indicating that large quantities of ABA had been produced and catabolized early in berry development. In the pulp and skin, two peaks of ABA were found, the first at two weeks preveraison and the second at late veraison, which was followed by a decline in ABA as the berries ripened. Abscisic acid glucose ester (ABA-GE) in the pulp and skin rose just before veraison, and then declined after veraison. In developing seeds similar trends were observed, but with initial high levels of both ABA and DPA and with ABA-GE remaining high into ripeness. ABA applied to berries at veraison had a half life of one week and resulted in a 69% increase in DPA concentration. However, this constituted only a small increase in the total ABA and catabolite pool. The treatment had no effect on berry maturation rate, basic juice composition, or skin and seed tannins, but did increase the anthocyanin content of skins by 7% at berry maturity. These observations indicate that little ABA was taken into the berry and metabolized, while the majority of it remained on the surface.