Double staining of mitochondria and mitochondrial nucleoids in the living yeast during the life cycle.

Abstract

Mitochondria and mitochondrial nucleoids (mt-nucleoids) of the yeast, Saccharomyces cerevisiae were vitally double-stained with two fluorochromes, 3, 3′-dihexyloxacarbocyanine iodide [DiOC6(3)] and 4′, 6-diamidino-2-phenylindole (DAPI), respectively in different types of cells during the life cycle. Budded cells at logarithmic phase had a single, branched, giant mitochondrion, a part of which migrated into the daughter cell prior to nuclear division. Mt-nucleoids appeared as a string-of-beads within a giant mitochondrion. Single cells at stationary phase had numerous fragmented mitochondria with dot-like mt-nucleoids. When stationary-phase cells were transferred to the sporulation medium, fragmented mitochondria fused with each other and a network of mitochondrion changed its configuration as the meiotic division proceeded. Finally, mitochondria formed four rings which enclosed each daughter nucleus in premature spores. Mitochondria were hardly stained with DiOC6(3) in mature spores. Fused mitochondria were clearly observed again in cells at germination and outgrowth. When cells of opposite mating type were mixed in mating medium, zygote formation and first bud emergence occurred in 4h. Just after mating, string-like and fragmented mitochondria transmitted from each parent cell were separately visible on both sides of a dumbbell-shaped zygote. In contrast, extensive fusion of mitochondria occurred in zygotes with a first bud.