Localization of superoxide anion in the red tide alga Chattonella antiqua

To investigate the localization of superoxide anion generated in the red tide alga Chattonella antiqua, we added to the incubation medium 3,7-dihydro-6-[4-(2-(N'-(5-fluoresceinyl)thioureido) ethoxy)phenyl]-2-methylimidazo(1,2-a)pyrazin-3-one (FCLA), which is a Cypridina luciferin analogue and a specific fluorescent probe for detecting O2- and 1O2. The live phytoplankter was observed with the laser scanning microscope. At high magnification (x 6400) it was found that the plankter has many large and small verruciform protrusions on the cell surface. When the cell was irradiated with an argon laser (488 nm), a very intense fluorescence was noted at each protrusion. This fluorescence was completely inhibited by the addition of superoxide dismutase to the incubation medium, thus suggesting O2- generation at each verruciform protrusion on the cell surface.