Detection of Hydroxyl Radical in Intact Cells of Chlorella Vulgaris

Using ESR with 5,5-dimethyl-l-pyrroline N-oxide (DMPO) as a spin-trapping reagent, we measured the levels of free radical species generated from living cells of Chlorella vulgaris var. vulgails (IAM C-534). To investigate the production of free radicals in the living Chlorella vulgaris cells, the influence of DMPO toward the intact cells of the Chlorella vulgaris using the O₂ evolution rate was first studied as a guide. Since the 0₂ evolution rate was not changed by DMPO, it was judged that DMPO has no toxicity toward the intact cells of Chlorella vulgaris.

Only hydroxyl radicals (-OH) were detected as the DMPO-OH adduct in the suspension of intact cells of Chlorella vulgaris irradiated with visible light. Moreover, since production of -OH was inhibited by some hydroxyl radical scavengers such as KI and ethanol, production of -OH was proved to be due to hydroxyl radicals. It was also clear that the intensity of OH increased with increasing irradiation intensity of visible light. Therefore, it was suggested that -OH might be one of the photoinhibition factors of the intact Chlorella vulgaris cells in severe light conditions.