The structure of microbodies and their associations with other organelles in zoosporangia ofEntophlyctis variabilis

Summary The ultrastructure of microbodies in developing zoosporangia ofEntophlyctis variabilis was studied by three dimensional reconstructions from serial sections and by cytochemical localization of catalase activity. The morphology of microbodies and the spatial association of microbodies with other organelles varied during fungal development. In incipient zoo-sporangia, granular dilations resembling microbodies arose from rough ER. Young, enlarging zoosporangia contained elongate, contorted microbodies continuous with ER and aligned along bundles of microtubules. Oval, paired microbodies, lying on each side of an ER cisternae, were found in all zoosporangia, but in older zoosporangia this configuration of microbodies predominated. Analysis of serial sections revealed that these oval, paired microbodies were sometimes continuous with each other, with ER, and also apparently with the ER cisterna interposed between them. Other paired, oval microbodies were clearly discrete. Constrictions were found along the length of elongate microbodies and at junctions between oval microbodies. These constrictions may represent stages in fragmentation of microbodies from pre-existing microbodies. These observations suggest that microbodies originated in three ways: 1. as local dilations in tubular ER, 2. as lateral buds from opposite sides of ER cisternae, and 3. as fragments from elongate microbodies.Microbodies were consistently spatially associated with ER, nuclear envelopes, and mitochondria. The cisterna of ER passing between paired microbodies sometimes extended into a branching, tubular system of ER which curved around the side of one microbody and lay between this microbody and the forming face of a dictyosome. The cytochemical localization of thiamine pyrophosphatase activity in this cisterna when it is not associated with dictyosomes suggests a role in metabolic control. These spatial associations indicate that the microbody assemblage with other organelles represents functional units where propinquity to other organelles and intraluminal continuities insure a system for transport of substrates and products.