Regulation of the Photosynthesis Rhythm in Euglena gracilis

Abstract
Rhythmic changes in the light reactions of Euglena gracilis have been found which help to explain the basic reactions effected in the circadian rhythm of O2 evolution. Diurnal changes in the slope of light intensity plots indicated that the maximal rate of photosynthesis changed throughout the circadian cycle. No evidence was obtained consistent with the premise that changes in chlorophyll content, as measured by total chlorophyll or chlorophyll a/b ratio, or photosynthetic unit size are responsible for this rhythim.