Plant growth substances and effects of photoperiod on flower bud development in Phaseolus vulgaris

Abstract

THE flower buds of certain varieties of Phaseolus vulgaris absciss in British summers, a phenomenon which is induced when the plants are grown in day lengths longer than 13–14 h¹. The number of buds which absciss increases as the day length is extended^1–3. This post-initiation effect is truly photoperiodic, the photoperiodic stimulus being received in the leaves and the inhibitory effects expressed in the buds, the growth of which is inhibited before they finally drop^2–5. Experiments in which a single trifoliate leaf was exposed to a photoperiod different from the rest of the plant provided indirect evidence that the effects of photoperiod on flower bud development were mediated through the production of substances in the leaves, with a predominance of inhibitor(s) being formed in long days and of promoter(s) in short days^3,4. We describe here the determination in a single sensitive variety, classified as P47, of the chemical basis for the inhibitory and promotory effects of long and short days respectively.