The effect of colchicine on colony formation in the algae Hydrodictyon, Pediastrum and Sorastrum

Uninucleate, biflagellate zoospores of Hydrodictyon, Pediastrum and Sorastrum, derived from multinucleate parental cells, aggregate and adhere to form distinctively patterned colonies; earlier work has shown that microtubules underlie the plasmalemma of these zoospores and are also conspicuous in the developing horns of aggregating cells of Pediastrum and Sorastrum. Colchicine applied to parental cells inhibited cytoplasmic cleavage and production of uninucleate zoospores. When zoospores were treated with colchicine, their peripheral microtubules disappeared; the spores failed to aggregate in ordered arrays and did not develop horns. The microtubules therefore appear to play an important role in determining the arrangement of cells in developing colonies by affecting the shape of the cells at the time of their aggregation.