Nitric oxide donor modulates cadmium-induced physiological and metabolic changes in the green alga Coccomyxa subellipsoidea

The impact of two concentrations (10 and 100 μM) of cadmium (Cd) and nitric oxide (NO) donor (sodium nitroprusside, SNP) alone or together on green alga Coccomyxa subellipsoidea was studied. Stimulatory impact of Cd and SNP on NO formation was synergistic in combined treatments and correlated with the increase of ascorbic acid. Exogenously applied Cd concentration (and not SNP co-application) was the main determinant of Cd uptake, phytochelatin 2, and reduced (GSH) and oxidized (GSSG) glutathione amounts. Glutathione reductase activity was depleted while ascorbate peroxidase activity enhanced by high SNP under both Cd concentrations. This may be related to the appearance of oxidative stress detected by fluorescence microscopy of oxygen radicals and lipid peroxidation in high SNP and/or Cd treatments. Among organic acids, the increase in pyruvate indicates enhancement of glycolysis under Cd excess, while quantitative changes of malic acid evoked by SNP co-application rather correlated with Cd accumulation. Relatively negligible alterations of phenolic metabolites (benzoic acids and total soluble phenols) and free amino acids were also observed. Overall, the generation of NO was not sufficient to counteract the oxidative stress in high Cd or SNP doses but our data clearly show that NO regulates accumulation of ascorbic acid while Cd uptake correlates with the amount of thiols.