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

Abstract 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 (O2−), and excessive secretion of O2– into the water has been associated with fish mortality. It is known that strong light stimulates the production of O2– in Chattonella spp. but the mechanism of the light-induced production of O2– remains to be clarified. In the present study, we examined the effects of light on extracellular levels of O2– and photosynthesis in C. antiqua. Extracellular levels of O2– rose during growth under high-intensity light, and the level of O2– was correlated with the photosynthetic parameter qP, which reflects the rate of transport of electrons downstream of photosystem II. The production of O2– 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 O2−. By contrast, the production of O2– 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 O2−. Thus, it is likely that the production of O2– is regulated by photosynthesis in C. antiqua.