ROS production is associated with glycolate metabolism in Chlamydomonas reinhardtii (Chlorophyceae) under salt stress

Abstract

:The photorespiration metabolism in unicellular algae is different from that in higher plants because of the absence of peroxisomes, and conversion of glycolate to glyoxylate is catalyzed by glycolate dehydrogenase without the production of reactive oxygen species (ROS). It has been reported that the glycolate–quinone oxidoreductase system (GQOS) also plays a role in the formation of glyoxylate from glycolate that is coupled to photosynthetic electron transport. In this study, we showed that production of ROS was associated with the oxidation of glycolate in chloroplasts of Chlamydomonas reinhardtii cells and that both ROS accumulation and photorespiration were promoted by NaCl stress. Salicylhydroxamic acid (SHAM) and methoxylamine (MOA) are inhibitors that block effectively the GQOS oxidation of glycolate and glycine decarboxylase complex, respectively. Our data showed that in the dark, whether or not the cells were treated with inhibitor, no remarkable difference was found in ROS levels under the same NaCl stress. In the light, however, the ROS level in the cells treated with SHAM or MOA was significantly lower than that in nontreated cells, with SHAM being more effective. The increase in serine:glyoxylate aminotransferase (SGAT) activity and glycine/serine (Gly/Ser) ratio were 8.3% and 30.8% under 50 mM, and reached 34.4% and 1.5-fold under 100 mM NaCl stress.