In this study, protein- and non-protein-thiol-containing compounds (THCC), soluble phenolics (SP), proline (Pro), proteins and malondialdehyde (MDA) contents, and antioxidative enzyme activities were analyzed in floating and submerged leaves of Salvinia minima to establish their role against Cr-induced oxidative stress. We analyzed relationships among biochemical responses to different Cr(VI) concentrations to explore underlying mechanisms of Cr detoxification in plants growing under field conditions during summer and winter seasons. Significant increases in THCC were observed in submerged leaves from both seasons, while in floating leaves THCC increased only in summer being decreased in winter. Contrarily SP increased in floating leaves and decreased in submerged ones. MDA increased significantly in winter-leaves, but in summer-leaves remained unchanged. Antioxidative enzymes, i.e. guaiacol peroxidase (G-POD), superoxide dismutase (SOD) and catalase (CAT) showed different activity patterns. G-POD significantly increased in Cr-treated leaves from both seasons, while SOD increased in submerged leaves only, remaining practically unchanged in floating ones. CAT activity increased in floating leaves from both seasons, whereas in submerged ones was decreased or increased. Proteins increased in both leaf types during summer whereas decreased or remained unchanged in winter. Pro increased in winter-submerged leaves only. Results show that seasonal-induced changes occur in all measured parameters. (C) 2012 Elsevier B.V. All rights reserved.