Motive force of cytoplasmic streaming during plasmodial mitosis of physarum polycephalum

Abstract The relationship between mitosis and cytoplasmic streaming in the plasmodium of Physarum polycephalum was investigated by simultaneously conducting the following three experiments: (1) identification of the mitotic stages under phase contrast optics, (2) measurement of the rate of oriented migration of the plasmodium on an agar ribbon, and (3) measurement of the motive force of cytoplasmic streaming by the double‐chamber method of Kamiya. The migration of the plasmodium almost stopped during synchronous mitosis and the motive force of the flow decreased to 1/4 of the normal level in this period. Gelation of the endoplasm did not occur during the mitotic period, and thus the cessation of the plasmodial migration must have been caused by the diminution of the motive force responsible for cytoplasmic streaming.