The circadian rhythm of carbon-dioxide metabolism in Bryophyllum: the mechanism of phase-shift induction by thermal stimuli.

The detailed characteristics have been established for the phase shifts induced by high-temperature (35° C) stimuli in the circadian rhythm of phosphoenolpyruvate-carboxylase activity in leaves of Bryophyllum fedtschenkoi otherwise kept under constant environmental conditions. The magnitude and direction of the shifts depend upon the duration of the stimulus and its position in the cycle, and are closely similar to those induced by light. An hypothesis is advanced which accounts for all the characteristics of the phase shifts induced by both high-temperature and light stimuli in terms of the leakage of malate from the vacuole to the cytoplasm though "gates" in the tonoplast which are open only during exposure to these stimuli.