CYTOCHALASIN-B INFLUENCES DICTYOSOMAL VESICLE PRODUCTION AND MORPHOGENESIS IN THE DESMID EUASTRUM

Cytochalasin B (CB) applied to young developing cells of the desmid Eu astrum oblongum Ralfs ex Ralfs, at concentrations that do not entirely inhibit cytoplasmic streaming, retarded cell growth and caused malfor mations of cell shape. While the basic symmetry of the cell was mainta ined, only the first indentations were formed and the cell body appear ed to be swollen. Electron microscopic investigations revealed that ve sicle production at the dictyosomes was disturbed by cytochalasin. In contrast to untreated control cells, where vesicles with electron-dens e contents (''dark vesicles'') were formed during primary wall formati on, vesicles pinched off by the dictyosomes during CB treatment exhibi ted an ''empty'' appearance. These vesicles, which correspond to the ' 'dark vesicles'' in size, were accumulated around the dictyosomes with out being transported to the plasma membrane and were frequently conne cted to the trans-cisternae of the Golgi bodies. We speculate that CB may influence the transfer of products from the endoplasmic reticulum (ER) to the dictyosomes via transition vesicles, which results in a di sturbed vesicle production at the Golgi bodies. CB also causes a shift in ER and dictyosome distribution. Moreover, a cortical actin system appears to be involved in the cell shaping of Euastrum. The arrangemen t of microtubules around the nucleus is not affected by the drug.