Circadian Rhythm of Photoaccumulation in Paramecium bursaria

Abstract

Populations of Paramecium bursaria cells display a circadian rhythm of photoac cumulation. Both Chlorella-containing cells and Chlorella-free cells exhibit this rhythm. Sev eral other species of Paramecium do not express rhythmic photoaccumulation when tested under the same conditions. In P. bursaria, photoaccumulation rhythms persist in continuous conditions (constant temperature and either continuous light or continuous darkness). The period of this rhythm is "temperature-compensated," with a Q10of 1.10-1.12. The rhythm can be reset by pulses of light or darkness in a phase-dependent manner. Therefore, an endoge nous circadian oscillator controls photoaccumulation behavior in P. bursaria.