Microtubule-dependent movement of symbiotic algae and granules in Paramecium bursaria

Paramecia demonstrate rotational cytoplasmic streaming, in which some cytop lasmic granules and organelles, including symbiotic algae, flow in a consta nt direction. To elucidate the mechanism of this streaming, we examined the effects of cytochalasins (cytochalasin B and D: and dihydrocytochalasin B) and nocodazole, which are reagents affecting microfilament and microtubule networks, respectively, in the cell. In previous reports, paramecia have b een compressed with a coverslip to facilitate observation of cytoplasmic st reaming. Here we found that the cytoplasmic streaming of paramecia was supp ressed by such compression and then observed the process without compressio n in this work. In the presence of cytochalasins, cytoplasmic streaming was not affected. Tn contrast, treatment with nocodazole (10 mu g/ml) resulted in discontinuation of cytoplasmic streaming in paramecia. Immunofluorescen t microscopic observations by confocal microscopy revealed that the number of intracellular microtubules in nocodazole-treated cells was markedly decr eased compared to that of controls. Electron microscopic observations confi rmed the decrease. These results suggest that cytoplasmic microtubules play an important role in the cytoplasmic streaming of paramecia. Cell Motil. ( C) 1999 Wiley-Liss, Inc.