Evidence supporting nitrite-dependent NO release by the green microalga Scenedesmus obliquus

Studies conducted with respiratory electron transport chain inhibitors and uncouplers such as antimycin A, rotenone, 2,4-dinitrophenol, pentachlorophenol and carbonyl cyanide m-chlorophenylhydrazone resulted in sudden NO bursts in Scenedesmus suspensions incubated under dark-aerobic conditions with supplemented glucose. Anaerobiosis was also found to increase NO production significantly in dark-incubated cells of Scenedesmus. These NO bursts, quite comparable to the usual ‘light-off’ peak (as always appeared after sudden darkening), could be correlated with the increased nitrite concentration under the above-mentioned conditions. Moreover, similar NO bursts concomitant with nitrite accumulation were also observed following supplementation of cycloheximide, MSX, Basta, glutarate and glyphosate. These results therefore support our hypothesis that accumulation of nitrite is the prerequisite for NO production in the case of the chlorophycean microalga Scenedesmus. A hypothetical model for NO formation is proposed.