Interactive effects of cadmium and copper on metal accumulation, oxidative stress, and mineral composition in Brassica napus

Heavy metals' frequent occurrence and toxicity caused considerable concerns in assessing the interactive effects of metals on exposed plants. Therefore, a hydroponic study was conducted to assess the growth response and physio-chemical changes in Brassica napus plants under single and combined stress of two environmentally alarming metals (Cd and Cu). Results showed that 15-day metal exposure to different metal concentrations (0, 50, 200 A mu M) significantly enhanced Cd accumulation, while lesser extent of Cu was observed in plant tissues. Nonetheless, Cu caused more pronounced oxidative damages and plant growth retardation. Both metals showed similar trend of changes in mineral composition, although Cu proved more damaging effect on K and Mn contents, and Cd on Zn contents. In combined treatments, Cd stimulated Cu uptake, notably at low concentration, while its own uptake was restricted by the presence of Cu. At either level of concentration, combined stress of these metals exacerbated plant growth inhibition and caused further oxidative damages compared to their individual stress. However, metals synergistic effects occurred only in conditions where Cu uptake was enhanced by Cd. A greater synergistic effect was observed in sensitive cultivar Zheda 622 as compared to the tolerant cultivar ZS 758. As to mineral composition, no metals synergistic effects were noted. This study highlighted the ecotoxicological significance of Cd-led Cu uptake in B. napus, which was assumed to drive metals' synergistic toxicity, and showed that the relationship between Cd-led Cu uptake and plant growth responses could vary with respect to cultivar.