On the chronobiology ofTetrahymena. III. Temperature compensation and temperature dependence in the ultradian oscillation of tyrosine aminotransferase∗∗

In Tetrahymena thermophila, the ultradian rhythm of tyrosine aminotransferase activity was investigated at 3 different constant temperatures (10, 20, 30°C), after the cells had been previously synchronized by temperature cycles of 4 h 20°C/1 h 0°C. In these conditions, the free‐running period of the enzyme rhythm proved to be temperature compensated. By contrast with this steady state behaviour, temperature jumps of 20?10°C or 20?30°C, if applied in an appropriate phase, resulted in marked phase shifts. Hence, the ultradian rhythm investigated shares the temperature behaviour of circadian rhythms, i.e., to be temperature compensated in the steady state, and to be reset by temperature jumps.