Changes in mitochondrial density and succinic dehydrogenase activity in Euglena gracilis as a function of the dependency on light for growth.

Mitochondria from Euglena gracilis strain z grown under strictly heterotrophic conditions have higher equilibrium densities and higher succinate dehydrogenase activities than those grown in the presence of light. There is a consistent trend toward lower mitochondrial density with increasing time of exposure to light. Experiments reported here indicate that the development of dependency upon light for the provision of energy results in the repression of mitochondrial development with respect to both density and enzymatic activity.