Metal accumulation and physiological responses induced by copper and cadmium in Lemna gibba, L. minor and Spirodela polyrhiza

The effects of cadmium (Cd) and copper (Cu) stress on antioxidant enzyme activities, pigment (total chlorophyll and carotenoid), malondialdehyde (MDA) and total soluble protein contents were determined in Lemna gibba L., Lemna minor L. and Spirodela polyrhiza (L.) Schleid under laboratory conditions. Cd and Cu were separately applied at concentrations of 0.01, 0.05, 0.1, 0.5 and 1.5 mg L-1 for 96 hours. The results of this study showed that Cd and Cu affected the physiological status of L. gibba, L. minor and S. polyrhiza. Decreased total chlorophyll and increased total soluble protein contents were evident in S. polyrhiza under Cu and Cd exposure. Cd treatment caused increased MDA contents in L. minor (0.5 and 1.5 mg L-1) and S. polyrhiza (0.5 mg L-1), while exposure to Cu caused an increase only in S. polyrhiza (0.05 and 0.1 mg L-1). Catalase (CAT) activity showed increases only in L. minor under Cd and Cu treatment. For ascorbate peroxidase (APX) activity, significant effects of Cu and Cd were determined in L. gibba. However, no significant changes were observed in L. minor treated with Cu and Cd (except for at 1.5 mg L-1). APX activity started to increase at 0.5 mg L-1 Cd in S. polyrhiza. Guaiacol peroxidase (POD) activity significantly increased in all plants (with a few exceptions in S. polyrhiza) under Cd and Cu exposure. According to principal component analysis, the three plant species were separated from each other on the basis of activities of antioxidant enzymes (L. gibba), pigment contents (L. minor), MDA and soluble protein contents (S. polyrhiza).