Conditionality of circadian rhythmicity: Synergistic action of light and temperature

Summary With cells which have been grown at 20°C, the circadian rhythm of bioluminescence inGonyaulax polyedra disappears at a critical temperature, which is about 12°C. The transition from the rhythmic to the arrhythmic state is very sharp with temperature: the two states are separated by only 1–2°C. Following a return to a higher temperature (20°C) under otherwise constant conditions, the rhythm resumes with its new phase defined by the time of the cool to warm transition. Loss of rhythmicity also occurs in constant bright light, with a similar resumption and phase determination upon transfer to darkness. The experiments described here show that the effects of light and low temperature are additive: rhythmicity is lost under combined low temperature and light intensity treatments which are ineffective individually.Abbreviations CT circadian time - ft-c footcandle - LD 12:12 12 h light/12 h dark cycle NIH Predoctoral Trainee in Biophysics, 2 T01 GM00782-16.