Toxicological responses in alfalfa (<i>Medicago sativa</i>) under joint stress of cadmium and napropamide

Abstract

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.