Bud, root, and growth-regulator activity in Acer saccharum during the dormant season

Abstract

Exposure of dormant sugar maple seedlings to over 2000 h of winter temperatures of 5 °C and below was required for rapid and normal growth when seedlings were transferred to a warm greenhouse and extended photoperiods. Although chilling requirements were not fully satisfied until mid-March, a resurgence of metabolic activity occurred in early February. There was a marked shift in the potential for budbreak from the axillary to the terminal buds, and a surge in root growth occurred after a period of inactivity when the ground was frozen from late December to mid-January. The water content of the buds followed a pattern similar to that of the roots. It fell to a plateau in late fall well before the soil froze but began a steady increase with the resumption of active root growth in February. Inhibitory substances present in the buds did not exhibit significant changes during the overwintering period. However, cytokinin activity was observed beginning in February at the same time that root growth and bud succulence showed upward inflections. By the beginning of April there were two distinct peaks of activity which persisted through budbreak in early May.Seedlings that were brought into the greenhouse in the fall and never exposed to chilling temperatures did not break dormancy or show significant cytokinin activity or exhibit the physiological changes that occur under normal winter conditions.