Photochemical Formation of Hydroxyl Radicals in Tissue Extracts of the Coral Galaxea fascicularis

Various stresses induce the formation of reactive oxygen species (ROS) in biological cells. In addition to stress-induced ROS, we studied the photochemical formation of hydroxyl radicals (center dot OH), the most potent ROS, in coral tissues using phosphate buffer-extracted solutions and a simulated sunlight irradiation system. center dot OH formation was seen in extracts of both coral host and endosymbiont zooxanthellae. This study is the first to report quantitative measurements of center dot OH photoformation in coral tissue extracts. Our results indicated that whether or not coral bleaching occurred, coral tissues and symbiotic zooxanthellae have the potential to photochemically produce center dot OH under sunlight. However, no significant difference was found in the protein content-normalized formation rates of center dot OH between corals incubated under different temperatures and irradiance conditions. center dot OH formation rates were reduced by 40% by reducing the UV radiation in the illumination. It was indicated that UV radiation strongly affected center dot OH formation in coral tissue and zooxanthellae, in addition to its formation through photoinhibition processes.