Extracellular secretion of superoxide is regulated by photosynthetic electron transport in the noxious red-tide-forming raphidophyte Chattonella antiqua

The raphidophyte Chattonella antiqua is a noxious red-tide-forming alga that harms fish culture and the aquatic environment. Chattonella antiqua produces and secretes superoxide anions (O-2(-)), and excessive secretion of O-2(-) into the water has been associated with fish mortality. It is known that strong light stimulates the production of O-2(-) in Chattonella spp. but the mechanism of the light-induced production of O-2(-) remains to be clarified. In the present study, we examined the effects of light on extracellular levels of O-2(-) and photosynthesis in C. antiqua. Extracellular levels of O-2(-) rose during growth under high-intensity light, and the level of O-2(-) was correlated with the photosynthetic parameter qP, which reflects the rate of transport of electrons downstream of photosystem II. The production of O-2(-) was inhibited in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosynthetic electron transport, suggesting that reducing power derived from electron transport might be required for the production of O-2(-). By contrast, the production of O-2(-) was enhanced in the presence of glycolaldehyde, an inhibitor of the Calvin-Benson cycle, suggesting that the accumulation of NADPH might stimulate the production of O-2(-). Thus, it is likely that the production of O-2(-) is regulated by photosynthesis in C. antiqua.