[Temperature effects on circadian rhythms of Euglena gracilis under mixotrophic and autotrophic conditions]

1. An automatic test was applied to populations of Euglena gracilis without disturbing the free running rhythm. This test allows to distinguish between the mobility in darkness and the phototactic response in a light trap. The parameters of the rhythm are better represented by the mobility. 2. In mixotrophic cultures the free running frequency decreases with increasing values of constant temperature, while the phase is not affected by sudden temperature changes. A sudden temperature drop temporarily decreases the amplitude; a steplike increase in temperature does not significantly change the amplitude. 3. In autotrophic cultures the spontaneous frequency is independent of different values of constant temperature in the range between 15°C to 35°C. The length of the period is 23,5±0,3 hr. A sudden temperature increase of 5°C and more causes transitory increase of the frequency. The spontaneous frequency is reestablished in the form of an aperiodic logarithmic transient function. The phase shift depends on the phase at which the temperature increase was applied but does not depend on the height of the temperature step. Temperature drops affect the phase only when applied at phases which normally coincide with dawn. In these cases a sudden inversion without transients occurs. A temperature drop following a sudden temperature increase stops the transient function induced by the preceeding rise of the temperature. The amplitude depends on the temperature; the Q10 is about 2,7. 4. The supposed biochemical basis of the different temperature responses under the different conditions of metabolism is discussed.