Electron cytochemical determinations of periodic acid-reactive sites in Histoplasma capsulatum

Electron cytochemical determinations of periodic acid-thiocarbohydrazide-silver proteinate (PATAg)-reactive sites in the vegetative and reproductive cells of the pathogenic dimorphic fungus Histoplasma capsulatum, are described an illustrated by electron micrographs. Ultrastructural sites of PATAg-reactive substances were detected at the plasma membrane, along various cytomembranes of the cytoplasm, and in aggregates of storage material believed to be partly composed of glycogen or a glycogen-like polymer. Cell walls were either minimally or negatively stained. The positive staining of PATAg-reactive sites was eliminated by use of the aldehyde-blocking agent sodium borohydride. The limiting membrane and matrix of Woronin bodies seen at the hyphal cell septum were devoid of PATAg reactivity.