Zoospore development and fine structures in Phlyctochytrium arcticum (Chytridiales)

Abstract

The fine structures of Phlyctochytrium arcticum zoospores, from early differentiation in the sporangium until they encyst and germinate, are described. Cytoplasm cleavage and flagellum formation have been studied. A complex rhizoplast–kinetosome structure is present. The Stüben body associating with a nucleus in a differentiating zoospore apparently divides into a number of similar bodies which are observed in the subsequent stages. Mitochondria, which are scattered about in the cytoplasm of maturing zoospores, are clustered at the posterior end of the motile zoospore, surrounding the kinetosome and the rhizoplast. On encystment, the flagellum is retracted, the rhizoplast disappears, the mitochondria again become scattered in the cytoplasm, and a wall is rapidly laid down. The morphology of the P. arcticum zoospore is compared with other chytridiaceous zoospore types.