What Are the Chromidia of Polyphagus Euglenae?

Abstract

Zoospores, prosporangia, and asexual sporangia were studied with electron microscopy to determine the ultrastructural identification of “chromidia,” granular masses surrounding nuclei that classical mycologists believed to be extruded chromatin used for lipid synthesis. In the zoospore the nucleus was enclosed by an aggregation of ribosomes. In other developmental stages the behavior of microbodies was identical to that described for “chromidia.” A microbody network with interspersed ER surrounded nuclei in young prosporangia. As the prosporangium matured, lipid globules became associated with the microbodies. When the single, large nucleus migrated into the elongate asexual sporangium, microbodies still surrounded the nucleus; but after the nucleus divided and a multinucleate sporangium formed, microbodies were scattered throughout the cytoplasm. When incubated in the diaminobenzidine medium for the cytochemical detection of catalase, reaction product was found in these microbodylike structures, confirming that “chromidia” described in prosporangia and asexual sporangia by classical mycologists are really microbodies. Rather than giving rise to lipid, these microbodies are probably involved in the metabolism of the lipid globules with which they are associated. The “chromidia” in zoospores are not extruded chromatin as suggested earlier, but correspond in their location around the nucleus to an aggregation of ribosomes.