Changes of GA-like activity in 2 types of spring flush including vegetative and leafy-inflorescence shoots of satsuma mandarin trees were investigated seasonaly. Effects of fruit thinning on GA-like activity were also studied. Results are discussed in relation to flower-bud formation.
GA-like activities in leaves and stems of the 2 types of shoots were high in April, followed by a decrease in July, and thereafter showed marked increase until November. In November the activity in leafy-inflorescence shoots was higher than in vegetative shoots.
Fruit thinning had an influence on GA-like activity in stems of the spring flush in autumn; early thinning (in May and June) caused lower levels, similar to vegetative shoots, than did late thinning (in August) and non-thinning.
These results suggested that endogenous GA levels before morphological flower-bud differentiation play a regulatory role in the modulation of flower-bud formation.