Restoration of membrane excitability in a behavioral mutant of Paramecium caudatum during conjugation and by microinjection of wild- type cytoplasm

When cells of the behavioral mutant cnrC of Paramecium caudatum were mated with the wild type, phenotype change from CNR (no backward swinning) to wild type in the cnrC mate occurred immediately after the formation of tight pairs. No change of phenotype occurred when cells of cnrA or cnrB were mated with wild type. Phenotypic change from CNR to wild type in cells of cnrC was also induced by microinjection of wild- type cytoplasm. Microinjection of wild-type cytoplasm induced no change in cells of cnrA or cnrB. Phenotypic change in the cnrC mate during conjugation can be explained by cytoplasmic exchange during conjugation, though transfer of membrane sites for excitability through membrane fluidity cannot be ruled out.