Long-Day Induced Bud Break in Salix pentandra Is Associated with Transiently Elevated Levels of GA1 and Gradual Increase in Indole-3-Acetic Acid

Initiation of dormancy in woody species is induced by a shortphotoperiod. In the early stages of dormancy development, growthcan be initiated by long days. To study the possible involvementof gibberellins and indole-3-acetic acid in bud break in Salixpentandra, effects on levels of these plant hormones of transferof seedlings in an early stage of dormancy to a growth-inductivelong photoperiod was investigated. The bud break and initiationof growth correlated with a rapid transient increase in GA₁in defined zones of shoot tips to levels twice of that in continuouslyelongating long day-grown control seedlings, followed by a rapiddecrease to levels similar to in these control plants. Also,the contents of GA₅₃, GA₁₉, GA₂₀, GA₈ increased upon transferfrom short to long days. Levels of indole-3-acetic acid showeda gradual decline under short days, and increased graduallyupon transfer to long days up to a level of continuously elongatingplants. The present data suggest an interaction between gibberellinand indole-3-acetic acid in the photoperiodic control of dormancydevelopment and bud break in S. pentandra. (Received October 14, 1996; Accepted February 18, 1997)