The effective sites of some mutations affecting exocytosis in Paramecium tetraurelia

Summary Using a microinjection technique, the functional competence of the trichocysts or of the nontrichocyst cytoplasms of wild-type and mutant stocks of Paramecium tetraurelia was tested. The results indicate that the exocytic (trichocyst discharge) phenotype of P. tetraurelia depends upon the functional competence of the trichocysts themselves and also upon the function of apparently trichocyst-specific cytoplasmic components. Thus, the mutants tam8, ndA and ndB are shown to contain defective trichocysts, but have apparently functional cytoplasms which can properly utilize normal trichocysts if these are supplied. Conversely, the mutant nd9 contains apparently normal trichocysts but is deficient in some cytoplasmic component required for normal trichocyst discharge. Injections of genetically complementary cytoplasm apparently supply nd9 with the missing component and can thus repair the nd9 trichocyst exocytic phenotype.