Colony formation and inversion in the green algaEudorina elegans

Summary During development of daughter coenobia in the volvocalean algaEudorina a rapid synchronized series of mitotic divisions and cytokineses gives rise to a slightly cup-shaped, patterned array of 16 or 32 cells, the plakea; the nuclei and centrioles of each cell lying at the concave face and the plastids at the convex face. Each cell is connected to its neighbours by cytoplasmic bridges. All cells within a plakea simultaneously elongate and enlarge their nuclear poles; while remaining interconnected by the cytoplasmic bridges at their plastid poles. The result is inversion of the developing coenobia so that the nuclei and centrioles come to lie on the convex, outer surface. Inversion is inhibited by colchicine and cytochalasin B. Both lengthening of the cells and expansion of their nuclear end is apparently mediated by microtubules. Striations on the plasmalemma encircling the bridges are thought to stablize the membrane at these sites during inversion.