Printed in Great Britain A LIGHT-MICROSCOPE STUDY OF THE ACTION OF CYTOCHALASIN B ON THE CELLS AND ISOLATED CYTOPLASM OF THE

The reversible inhibition of cytoplasmic streaming in cells of Nitella translucent by cyto-chalasin B was found to be accompanied by an increase in the number of mini-vacuoles in the endoplasm. Fibrils thought to drive the streaming were still present in inhibited cells. In droplets of cytoplasm obtained from cut cells of Chara corralina, the final number of fibrils formed was not sensitive to cytochalasin B, although the motility of these fibrils was highly so. The movement of organelles in the absence of visible fibrils and the rotation of chloroplasts were also inhibited. The evidence for the involvement of the microfilament system in cyto-plasmic streaming is discussed. The way in which such microfilaments seem to be operating in characean cells differs from the most likely mechanism for their operation in other cytochalasin-sensitive processes