The mitochondrion in mitotic and starved cells of Bullera alba

Three-dimensional reconstruction of a pathogenic yeast Exophiala dermatitidis cell by freeze-substitution and serial sectioning electron microscopy

The structure of a budding cell of the pathogenic yeast Exophiala dermatitidis was observed in three dimensions after freeze-substitution, serial ultrathin sectioning and computer reconstruction. The nucleus occupied about 10% of the cell volume. The spindle pole body was composed of two disk elements connected by an intervening midpiece, and occupied about 0.01% of the cell volume. The cell wall consisted of an inner transparent layer, a middle electron-opaque layer, and an outer fibrous layer. The mitochondria occupied about 10% of the cell volume. There were numerous mitochondria in the mother cell and the bud, but no 'giant mitochondrion' was seen. The ratio of mitochondrial volume within the bud to the mitochondrial volume of the cell was close to the ratio of bud:cell cytoplasmic volume. The results emphasize the importance of good cryofixation for 'perfect' preservation of yeast cell structure.

Mitochondrial kinetics during mitosis in Cryptococcus neoformans--an ultrastructural study

Mitochondrial kinetics during mitosis in Cryptococcus neoformans was examined with ultrathin serial sections using a computer-aided three-dimensional reconstruction technique. The number of mitochondria varied during mitosis: there was an increase in prophase to telophase cells and a decrease in interphase cells. No appreciable differences in the form and number of mitochondria were found between the cells in the logarithmic growth phase and stationary phase. Fluctuations in the ratio of mitochondrial volume/total cytoplasmic volume were minimum during mitosis. However, the ratio was affected by the growth condition of the cells; that is, the ratio in the logarithmic growth cells was significantly higher than that in stationary cells. A giant mitochondrion, which is composed of a coalescence of all the mitochondria in a cell, was not found in this study.

Fluorescence microscopic studies on mitochondria and mitochondrial nucleoids in a wild-type strain and respiratory mutants of Candida albicans

A wild-type strain and two respiratory mutants of Candida albicans were examined for mitochondria and mitochondrial nucleoids (mt-nucleoids) using the fluorescent dyes, 2-(4-dimethylaminostyryl)-1-methylpyridinium iodide (DASPMI) and 4', 6-diamidino-2-phenylindole (DAPI). Rapidly growing cells of the wild type possessed one or a few giant branched mitochondria that were intensely stained with DASPMI. When a bud emerged, an end of the giant mitochondrion extended into the bud and the mitochondrion was divided and partitioned into mother and daughter cells by cytokinesis. Cell cycle-associated fragmentation or fusion of mitochondria were not demonstrated. The mutant KRD-8, that possesses cristate mitochondria but respires at a lower level, was shown to contain one or a few, less stainable giant mitochondria per cell. DASPMI failed to stain cells of the mutant KRD-19 which lacks cytochrome aa3 and cristate mitochondria. About eight and 10 mt-nucleoids were detected as discrete fluorescent spots in DAPI-stained cells of the wild type and KRD-8, respectively. KRD-19 cells also possessed mt-nucleoids, although the number of mt-nucleoids per cell seemed to be smaller than that of the wild type. In all the strains, mt-nucleoids existed discretely throughout the budding cycle, and the increase of their number per cell appeared to correlate with the cellular volume but not with nuclear division.