The respiratory chain of colorless algae: III. Electron microscopy

Abstract

Electron micrographs of KMnO4-fixed Prototheca zopfii, Polytoma uvella, and Polytomella agilis show the presence of mitochondria with typical discoidal cristae of random orientation, a result expected from their cytochrome content. The mitochondria are usually localized near the outer margin of the cell. All three organisms contain starch granules and proplastid-like structures, both bounded by two membranes. Although Prototheca has been called “a colorless Chlorella,” the existence of significant differences in their ultrastructure makes this classification unlikely. Astasia longa does not contain cytochrome oxidase, but its mitochondria show the same type of ultrastructure as the Chlorophyta, and it too has a eucaryotic cellular structure. The Cyanophyta, Leucothrix mucor, and Vitreoscilla sp. have a typical procaryotic cellular structure, a result consistent with the fact that their respiratory characteristics are like those of the Eubacteria. The cell walls of Leucothrix and Vitreoscilla resemble the cell walls of their procaryotic relatives, the photosynthetic blue-green algae.