Ascospores of Saccharomyces cerevisiae inherited at least one functioning mitochondrion as shown by their ability to germinate on nonfermentable carbon sources. After transfer to germination medium, the optical density of the culture at 600 nm decreased (phase-dark), reaching a minimum within 60 min in the presence of glucose and within 180 min after transfer to acetate medium; thereatter, the optical density increased. Budding cells first appeared 90 min after transfer to glucose and 150 min after transfer to acetate. Augmentation of respiratory components, respiratory activity, and macromolecular synthesis (except for DNA synthesis) started at about the same time on glucose and on acetate, although the highest values for all these processes were reached in the presence of glucose. Mitochondrial inhibitors which affected germination on acetate did not arrest germination on glucose. However, mitochondrial activity was required for germination on galactose in a strain carrying the mutated allele imp] of the nucleomitochondrion-connecting gene IMP].The proteolytic activities that are induced during sporulation of Saccharomyces cerevisiae (3, 10, 23) also effect the content of mitochondrial cytochromes; these are reduced to about 20% of the level present in vegetative derepressed cells, probably as a result of nonselective degradation of inner mitochondrial membrane proteins (4).However, not only degradation but also synthesis and turnover of mitochondrial polypeptides take place during sporulation, since the ratio of mitochondrial protein synthesis to total protein synthesis is not altered during sporulation and the pattern of individual mitochondrial products in vegetative and sporulating cells is similar (4). Moreover, mitochondrial DNA is replicated during sporulation even if not synchronously with nuclear DNA (22).In an attempt to correlate the extrachromosomal inheritance of mitochondrial traits with the physical distribution of the mitochondria and of the mitochondrial material during meiosis, the presence of mitochondrial DNA and of mitochondrial structures in the ascospores has been investigated. Ultrastructural analysis demonstrates the existenice of mitochondrial profiles within ascospores of S. cerevisiae: either three to five according to Sando et al. (18) or one corresponding to the "spore mitochondrion" of Stevens (21) and Brewer and Fangman (5). As to mitochondrial DNA, it appears to be preferentially transmitted to ascospores (5), indicating that its inheritance is not random.Even though the complex array of mRNAs packaged within the spores in a translatable form is known (11) and the role of nuclear information in the germination process has been elucidated (2, 24), it should be considered that the inclusion of at least one mitochondrion within each ascospore may affect its germination ability under certain conditions. In fact there is evidence both for and against the suggestion that germination can occur in the absence of mitochondrial activity (9, 15-17, 19, 20, 22).In this paper, we demonstra...
