Abstract
1. The isolation of a microconidial strain ofNeurospora crassa which is resistant to ultraviolet irradiation has been described. 2. The resistance character behaves as though it were recessive in heterokaryons with macroconidial strains. 3. Comparison of the survival kinetics of the resistant strain with the parental microconidial strain, a macroconidial strain, and the survival kinetics of heterokaryons, indicate that inactivation of conidia may be attributed to three independent processes. At low doses of irradiation, conidia are inactivated by inactivation of nuclei, or by induction of recessive lethal mutations. At higher doses, cytoplasmic inactivation is added to the process of nuclear inactivation. 4. The development of resistance to ultraviolet irradiation inNeurospora may be attributed to an increase in average number of nuclei per conidium and a concomitant increase in cytoplasmic target number. The latter is directly proportional to the volume of the conidium. 5. The hypothesis of cytoplasmic inactivation has been applied in the analysis of the kinetics of inactivation of other organisms described in the literature.
Published Version
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