Ultrastructural changes accompanying mitosporogenesis in Ectocarpus parvus.

The plurilocular zoosporangium of Ectocarpus parvus Saunders in initiated as a uniseriate branch from a vegetative cell. Subsequent anticlinal and periclinal divisions of the cells leads to enlargement of the sporangium and the formation of multiple locules. Each locule containes a single biflagellate zoospore. Ultrastructural changes accompanying these events include a reduction in the size of chromatophores, a reduction in the number of dictyosomes and the appearance of plasmalemmasomes in later stages. Enlargement of the mitochondria and a decrease in size of the nucleus occur in the final stages of zoospore formation. Comparison with the vegetative and sporogenous cells of other brown algae are made.