Ultrastructural organization of Rhizophlyctis harderi zoospores and redefinition of the type 1 microbody – lipid globule complex

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Abstract
Because ultrastructural features of zoospores are considered primary characters in Chytridiomycete systematics, computer-aided three-dimensional reconstructions of serial sections were used to analyze zoospore fine structure of Rhizophlyctis harderi, a questionable member of the genus Rhizophlyctis. A secondary centriole was parallel to the kinetosome, but the nucleus was not structurally or spatially associated with the kinetosomes. Mitochondria and cisternae associated with vesicles bounded a ribosomal aggregation in which the nucleus was partially embedded. The peripheral cytoplasm between the plasma membrane and ribosomal aggregation contained α-glycogen particles, vacuoles with osmiophilic globules, vesicles with clear matrices, and vesicles with electron-dense cores. A new, compound form of microbody – lipid globule complex (MLC) was identified. This type of MLC incorporated posteriorly located lipid globules associated with rumposomes and anteriorly located lipid globules associated with simple cisternae, microbodies, and highly branched mitochondria. Based on these and other recent observations, the concept of the type 1 MLC was redefined. Sources for variation in ultrastructural features of zoospores are discussed. Zoospore ultrastructure of R. harderi is different from that described for other chytrid zoospores. Key words: Chytridiomycetes, microbody – lipid globule complex, Rhizophlyctis, taxonomy, ultrastructure, zoospore.

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