EVIDENCES OF COMMON‐AB HETEROKARYOSIS IN SCHIZOPHYLLUM COMMUNE

Since preliminary experimental evidence for the existence of common‐ AB heterokaryons in Schizophyllum commune was inconclusive, experiments were performed to test for and to characterize these heterokaryons. Prototrophic mycelia regularly result from the growing together of pairs of mutant strains of identical mating type which carry non‐allelic nutritional deficiencies. Since crossfeeding through a dialyzing Cellophane membrane does not occur, the prototrophic common‐ AB mycelia apparently have both parental nuclear types within a common cytoplasm. Hyphal tips isolated from the peripheries of these prototrophic mycelia usually are not prototrophic. The distributions of the parental nuclear types in the subcultured prototrophic mycelia, as revealed by grid sampling, are irregular in pattern and extent; these patterns probably reflect the nuclear ratios in the transfer inocula, as well as the distributions of nuclear types in various parts of the inocula. Since a common‐ AB prototroph typically consists of regions containing a single nuclear type as well as regions containing both nuclear types, marked fluctuations of the estimated nuclear ratio occur upon subculture, and many small transfer‐inocula are not prototrophic as they contain only a single auxotrophic nuclear type. The patterns of nuclear distributions in prototrophic common‐ AB mycelia are probably maintained by the restriction of nuclear migration.