The control by gibberellic acid of stem elongation and flowering in biennial plants of Centaurium minus Moench

Application of a small amount of gibberellic acid (GA3) to unvernalized rosettes of a biennial strain of Centaurium minus Moench brings about immediate stem elongation under both long days (LD) and short days (SD), but the rate of stem elongation falls after the cessation of treatment. Under LD, but not SD, a second period of rapid and prolonged stem elongation may subsequently take place, associated with flowering. Extended GA3 treatment under SD leads to the formation of a long stem but not to flowering; after the treatment the plants revert to vegetative “aerial rosettes” unless transferred to LD prior to the cessation of stem elongation; after such a transfer, rapid stem elongation and flowering may be initiated. If flower primordia are initiated under LD, stem elongation and formation of flower primordia continue after transfer to SD, though flowers do not develop fully. It is suggested that under LD but not SD applied GA3 may bring about the production of endogenous gibberellin, and that this synthesis of endogenous gibberellin occurs in the flower primordia