Chemotropic Interactions Between Trichogynes and Conidia of Opposite Mating-Type in Neurospora Crassa

SUMMARY

Interactions between living trichogynes emanating from individual protoperithecia formed on a mature mycelium and transplanted conidia taken from a culture of opposite mating-type have been observed microscopically. An interaction often begins within 3–4 h after transfer if the conidium has settled within several hundred micrometers of a trichogyne. The latter responds to the conidium by approximate adjustments in its direction of growth that, within several hours, will bring the apex of the trichogyne to the conidium. Following plasmogamy between these two cells, the protoperithecium resumes its growth and develops into a perithecium. Since these interactions occur only between trichogynes and conidia of opposite mating-type they must be an expression of a function of the mating-type alleles (A, a) in the sexual phase of the life cycle. This conclusion is corroborated by similar observations of the behavior of a group of strains (designated as a^m mutants) that were known to carry an apparently functionless a allele (i.e., do not form fertile perithecia with wild-type A testers). They all failed to display any of the above interactions with wild-type A testers.