In this study of shuttle protoplasmic streaming in plasmodia of the myxomycete Physarum polycephalum, we will show with a laser light scattering technique that streaming velocity decreases or stops during metaphase-anaphse of mitosis. Evidence for ultrastructural changes in the cytoplasma during this time will be sought. We will verify that Physarum myosin light chain becomes phosphorylated, and will establish if calcium is necessary for this reaction. Homogenates of plasmodia from cultures in mitosis will be tested for myosin phosphorylation and compared with interphase cultures.