ARE ACTIVE OXYGEN SPECIES INVOLVED IN INDUCTION OF BETA-CAROTENE IN DUNALIELLA-BARDAWIL

The purpose of this work was to test whether induction of massive beta -carotene synthesis in the alga Dunaliella bardawil is triggered by ox ygen radicals. The following results were obtained: (i) The induction of beta-carotene synthesis is preceded by a lag period of about 4 h du ring which the cells swell and photosynthesis is partially inhibited. (ii) Addition of promoters of oxygen radicals or of azide (an inhibito r of catalase and superoxide dismutase) during the induction period, u nder conditions which are suboptimal for massive beta-carotene accumul ation, greatly enhances beta-carotene synthesis, photodegradation of c hlorophyll and inhibition of photosynthesis. (iii) High irradiance, wh ich induces massive beta-carotene accumulation, also induces a high ca talase activity. It is suggested that photosynthetically produced oxyg en radicals are involved in triggering massive beta-carotene accumulat ion in D. bardawil.