Abscisic acid relationships in dormancy of apple buds

Abstract

When potted, dormant, leafless seedling of ‘Antonovka’ apple were held for 15 weeks at 4 or 24°C, the patterns of change for abscisic acid (ABA) in buds were similar. At both temperatures, ABA concentration had decreased to a low level by 6 weeks and remained at a fairly low level until Week 12. The ABA concentration showed a tendency to rise in both treatments by Week 15. When excised axillary buds of ‘Northern Spy’ seedings were placed on 10 −4 M ABA medium immediately after excision, their growth was inhibited substantially depending on the length of exposure to ABA. When similar axillary buds were first allowed to begin growth on ABA-free medium, and then subsequently transferred to 10 −4 M ABA medium, no inhibition of growth occurred, even though these buds contained about twice as much ABA as did the buds placed directly on ABA medium prior to the beginning of growth. Thus, growing buds responded much less to exogenous applications of ABA than did non-growing buds. Diminishing of bud reaction to ABA responded to emergence from dormancy after 18 weeks of chilling.