Oxygen Uptake and Mitochondrial Enzyme Activities in the Mitotic Cycle of Physarum polycephalum

Abstract

135The rate of oxygen uptake by single macroplasmodia of Physarum polycephalum increased in two steps during each synchronous mitotic cycle. Plateaux in the respiratory pattern, of 0.22 cycles duration, occurred in mid-interphase and in the period up to and including mitosis. A fall in the rate of respiration was frequently associated with mitosis itself. This pattern of respiration continued for more than 10 mitotic cycles after inoculation and was unaffected by omission of an initial routine period of starvation. A similar stepped pattern of respiration was observed in synchronously germinating spherules during the period between outgrowth and the first mitosis. The specific activities of succinate dehydrogenase, fumarase and malate dehydrogenase remained relatively constant during the mi totic cycle, while fluctuations in cy tochrome oxidase activity paralleled those in specific respiratory activity. Possible mechanisms for controlling the pattern of respiration are discussed with reference to published data on protoplasmic streaming and ATP concentrations during the mitotic cycle.