Phototaxis inEuglena. VI. Correlations between ATP production by light and phototactic rates

Abstract

Using DCMU and CCP to specifically affect the photosynthetic system, the kinetics of inhibition of photophosphorylation and phototaxis inEuglena are shown to be the same. In the case of DCMU, measurements of oxygen evolution demonstrate that the delay observed between exposure to inhibitor and maximum effect is not due to the time required for the DCMU to reach its site of action, thus suggesting the presence of an endogenous pool of electron donors which can bypass photosystem II. Placing a culture in darkness causes a cessation of growth and an increase in ATP content per cell, during the same time period in which phototactic activity remains constant. The results are interpreted in terms of the utilization of photosynthetically generated ATP as an energy source for phototactic orientation and a control system which acts to maintain phototactic energy reserves during an extended period of little or no photosynthetic activity.