Influence of valinomycin on circadian leaf movements of Phaseolus

Phaseolus coccineus was exposed to valinomycin via the transpiration stream for 5-hr periods. The treatment started at various phases of the free-running circadian rhythm in continuous light; it resulted in phase shifts that varied in a manner dependent on the affected phases. The response curves are similar to those for transient withdrawal of water and for light pulses. The results support the hypothesis that membrane processes are important pacemakers in circadian rhythms.