RESPONSE OF THE WILD-TYPE AND HIGH LIGHT-TOLERANT MUTANT OF ANACYSTIS-NIDULANS AGAINST PHOTOOXIDATIVE DAMAGE - DIFFERENTIAL MECHANISM OF HIGH LIGHT TOLERANCE

A high light-tolerant mutant of Anacystis was able to tolerate about t hree-fold higher light energy irradiance (30 W m(-2)) than the wild ty pe (10 W m(-2)). The loss of sulfhydryl content and rate of lipid pero xidation in the wild-type cells is lower than in the mutant cells at h igh light irradiance. This phenomenon in the wild type is probably due to high light-induced severe photoinhibitory conditions resulting in a decreased rate of O-2 evolution. Results on the bleaching of the N,N '-dimethyl-p-nitrosoaniline at high light irradiance show a higher rat e of bleaching in the wild-type than in the mutant cells. Further, res ults on the rate of N,N'-dimethyl-p-nitrosoaniline bleaching in the pr esence of radical scavengers like sodium azide, histidine and sodium f ormate (10 mM, each) suggest that singlet oxygen is the predominant ox ygen species produced in both the wild-type and mutant cells under hig h light. However, a similar quenching effect of formate in the mutant cells is indicative of increased formation of hydroxyl radicals. This observation is further corroborated by higher rate of lipid peroxidati on. In addition to this, the superoxide dismutase activity is higher i n the mutant (1.2 unit) than in the wild type. Taken together, these r esults suggest that the cells of the high light-tolerant mutant have a n efficient intracellular mechanism to transform the free oxygen radic als.