Differential Heat Treatment of the Nitella Internodal Cell and Its Relation to Cytoplasmic Streaming

Abstract

Cytoplasmic streaming in internodal cells of Nitella was reversibly or irreversibly stopped by supraoptimal temperatures depending on the temperature and duration of incubation. To analyze the effects of high temperature on the streaming endoplasm and on the stationary cortical layer, the two were temporarily separated by a method of centrifugation developed by the authors (2). Streaming resumed when the cortex alone was heat-treated at 47.5°C for 3 min while the endoplasm was kept intact. In the reciprocal case, no streaming was observed. This demonstrates that one or more factors, that are heat-labile and essential for the streaming to occur, must reside in the endoplasm and not in the cortex. This result supports the idea that myosin, which is far more labile to heat than actin, is located in the endoplasm.