Germination of Yeast Spores Lacking Mitochondrial Deoxyribonucleic Acid

A population of petite ascospores (mitochondrial deoxyribonucleic acid mtDNA]-less), produced by brief ethidium bromide (EthBr) mutagenesis prior to transfer to sporulation medium, was used to examine the role of the mitochondrial genetic system on germination and outgrowth in Saccharomyces cerevisiae. Petite ascospores, which are morphologically indistinguishable by phase-contrast microscopy from wild-type spores, germinate and proceed through outgrowth at a rate and extent only slightly less than that of wild-type spores. Both developmental processes occurred in the absence of mtDNA synthesis and measurable cytochrome oxidase activity. These results indicate that neither respiration nor a functional mitochondrial genome are required for germination and outgrowth. The properties of the petite clones were typical of petites formed during vegetative growth. Individual sporal clones differed markedly from each other in suppressiveness. Petite sporal clones which exhibited a high degree of supressiveness also contained a reduced but detectable amount of mtDNA of altered buoyant density. One clone contained a unique mtDNA with a buoyant density higher than that of wild-type mtDNA.