Selenium modulates the antioxidative response in green microalga Monoraphidium cf. contortum

As algae are the main route of selenium (Se) transport from water to other consumers in food webs, the effect of selenite on the total Se content, growth, and antioxidant status of the unicellular green alga Monoraphidium cf. contortum was determined. The basal Se content (<3 mg/kg DW) was lower compared to other green microalgae, but the species showed a high accumulation potential (284.1 mg/kg DW). Despite early Se accumulation and growth inhibition, a significant loss of chlorophylls and carotenoids was observed only after 72 h. The response of antioxidative enzymes corresponded to a lower intensity of lipid peroxidation, despite increased ROS content at lower selenite concentrations. Primarily, selenite increased the activities of ascorbate peroxidase (APX), glutathione reductase, glutathione peroxidase (GPX), and glutathione S-transferase (GST), and inhibited catalase (CAT) in almost all treatments. Higher GST and GPX activities, as well as selenite-induced non-enzymatic glutathione (GSH) oxidation indicated increased GSH depletion.