Seasonal Levels of Abscisic Acid in Buds and Stems of Acer saccharum

Changes in abscisic acid (ABA) were followed in the buds and youngest stems of 6-year-old sugar maple (Acer saccharum Marsh.) saplings at approximately monthly intervals during the year. High levels present in the buds in July and August showed a moderate decline through early October, but subsequently increased following leaf fall and reached the maximum values detected during the study in November and December. Thereafter ABA fell sharply, reaching its lowest point immediately prior to budbreak in early May. While ABA in the stems followed a somewhat similar pattern, only minor changes were observed in the relatively low values detected between June and November. Except for the spring months, when concentrations of ABA in the stems and buds were at minimum levels, the buds always contained several times more inhibitor per unit dry weight of tissue. Analysis of selected samples from both tissues showed that bound (alkaline-hydrolyzable) ABA increased during the overwintering season, with the highest values noted in the spring. Although the patterns of change observed in this study are indicative of a role for ABA in the overwintering process, ABA does not appear to be the primary endogenous factor responsible for initiation of the dormant state.