MORPHOLOGICAL CHANGES IN ASCOSPORES OF SACCHAROMYCES CEREVISIAE DURING AEROBIC AND ANAEROBIC GERMINATION

The stainability of ascospores and vegetative cells of Saccharomyces cerevisiae to acid-fast staining, using hot Ziehl's carbolic fuchsin solution, 5% sulfuric acid, and diluted Löffler's methylene blue, was examined. Resting spores and growing haploid cells (a type strain 24428 and α type 3626) retained much fuchsin dye in the cells. Only mature spores of diploid G2-2 resisted methylene blue staining. The stainability of Mycobacterium phlei IFO 3158 also examined. The kinetics of germinationn were examined. The loss of the stainability with acid-fuchsin and of the resistance to methylene blue was used as a criterion of germination. The ascospores germinated anaerobically as well as aerobically. Especially in the early stage of germination, there was found no difference in the germination rates under both conditions. Ultrastructure of germinating ascospores cultured in aerobic and anaerobic conditions was examined by ultrathin sectioning and electron microscopy. At the first stage of germination, the ascospores swelled in aerobic as well as anaerobic cultures. The outer spore coat and the outer zone of inner spore wall disappeared during the germination process, the inner zone of the spore wall then giving rise to a germinated spore cell wall (=extruded germ tube wall). The vacuole became granular. The mitochondria showed no change in shape and number in aerobic cultures, but seemed to swell and disintegrate in the later stages of anaerobic germination.