Zoospore ultrastructure of Nowakowskiella elegans and Cladochytrium replicatum (Chytridiales)

Abstract

The ultrastructural cytology of the zoospores of the polycentric chytrids, Nowakowskiella elegans (Nowak.) Schroeter and Cladochytrium replicatum Karling is very similar. In both there is a single lipid globule. A microbody lies between the lipid globule and a central, disc-shaped nucleus. On the other side of the nucleus there is a cluster of ribosomes. The ribosome cluster and nucleus are enveloped by a common double membrane. A number of mitochondria are appressed to the outside of the double membrane. A nonkinetosomal centriole is adjacent and parallel to the kinetosome, and there is an electron-opaque area at the base of the flagellum. Linked microtubules, numbering approximately 25 in N. elegans and 19 in C. replicatum, emerge from an area lateral to the kinetosome and run to the rumposome which lies on the surface of the lipid globule and faces the exterior of the zoospore. A number of the kinetosome-associated microtubules lie over the surface of the rumposome and appear connected to it. The significance of these results on taxonomic and phylogenetic concepts of the Chytridiales is discussed.