Long-day induced bud break in Salix pentandra is associated with transiently elevated levels of GA(1) and gradual increase in indole-3-acetic acid

Initiation of dormancy in woody species is induced by a short photoperiod. In the early stages of dormancy development, growth can be initiated by long days. To study the possible involvement of gibberellins and indole-3-acetic acid in bud break in Salix pentandra, effects on levels of these plant hormones of transfer of seedlings in an early stage of dormancy to a growth-inductive long photoperiod was investigated. The bud break and initiation of growth correlated with a rapid transient increase in GA, in defined zones of shoot tips to levels twice of that in continuously elongating long day-grown control seedlings, followed by a rapid decrease to levels similar to in these control plants. Also, the contents of GA(53), GA(19), GA(201) GA(8) increased upon transfer from short to long days. Levels of indole-3-acetic acid showed a gradual decline under short days, and increased gradually upon transfer to long days up to a level of continuously elongating plants. The present data suggest an interaction between gibberellin and indole-3-acetic acid in the photoperiodic control of dormancy development and bud break in S. pentandra.