Resistance to ionizing radiation and antioxidative defence in yeasts. Are antioxidant-deficient cells permanently stressed?

Radiation sensitivity of the yeast (Saccharomyces cerevisiae) strains defective in catalase and superoxide dismutase, and of decreased level of glutathione was compared. Small differences in the radiation sensitivity pointed to the highest sensitivity of the wild-type strain as compared with the antioxidant-defective mutants. Heat shock increases the radiation resistance to a different extent, the response being highest in the wild-type strain and lowest in the glutathione-deficient strain. Catalase induction by heat shock follows the same pattern, significant activity of this enzyme being detectable in the glutathione-deficient mutant under normal growth conditions. These results suggest that compensatory induction of elements of the antioxidant defence system may occur in yeast mutants deficient in antioxidants under normal growth conditions.