Toxicological responses in alfalfa (Medicago sativa) under joint stress of cadmium and napropamide
Joint effects of Cd2+ and napropamide in seeds, roots or leaves of alfalfa were investigated under different treatments. It was shown that single stress of Cd2+ or napropamide decreased chlorophyll content after 30 days of treatment in different concentrations. The decrease in chlorophyll content became insignificant under joint stress of Cd2+ and napropamide. It can be concluded that the interaction of Cd2+ and napropamide would aggravate the toxic effects on chlorophyll synthesis in leaves of alfalfa. The joint effect of Cd2+ and napropamide was markedly significant (p < 0.05) on the change of SP content in leaves in all treatment. Moreover, Cd2+ and napropamide mixture exposure can increase lignin content and present synergistic effect. In a mixture treated with Cd2+ and napropamide, 52% decrease in β-carotene content contrasted with the control in young leaves. The contents of protein thiols and non-protein thiols in the roots of alfalfa were significantly increased by Cd2+ treatment in all treatment levels. In contrast, increasing napropamide supply did not have any significant effect on the protein thiols and non-protein thiols content. The Cd2+ induced accumulation of O2•- in seeds could be increased by treatment with different Cd2+ concentration. Production of H2O2 and O2•- was also higher in the napropamide treatments than in the control. The addition of napropamide significantly increased the H2O2 and O2•- level in the seeds of alfalfa.
Key words: Alfalfa, joint stress, cadmium, napropamide.