Assessment the copper-induced changes in antioxidant defense mechanisms and copper phytoremediation potential of common mullein (Verbascum thapsus L.).

In this research, the Cu phytoremediation capacity of common mullein (Verbascum thapsus L.) was evaluated concerning plant growth, antioxidant enzymes, and photosynthetic activities. Plants were subjected to five Cu concentrations (0, 125, 250, 375, and 500 mg/L) under the hydroponic conditions for 2 weeks. The results showed that at 125 mg/L, root and shoot biomass and chlorophylls remained the same as that of the control and then declined with increasing concentrations of Cu, when compared with control. The carotenoid contents remained unchanged up to 250 mg/L compared with control and then dropped with raising Cu dose. The raising of antioxidant enzymes activity reflected the occurrence of stress due to Cu exposure as manifested by increased MDA and ion leakage level. However, increased antioxidant enzymes may be associated with the tolerance capacity of V. thapsus to protect the plant from oxidative damage. Except for the highest concentration (500 mg/L), Cu accumulation in the roots and shoots all increased significantly with increasing Cu concentration, and the Cu accumulation in shoots was greater than roots. The Cu accumulation reached its maximum level at 375 mg/L Cu concentration, with 492.8 and 447.3 mg/kg DW in shoots and roots, respectively, which is highly greater than the threshold value for a Cu (hyper)accumulator plant. The extraction coefficient (EC) close to 1, and translocation factor (TF) > 1 from 125 to 375 mg/L Cu, suggested that V. thapsus could be used as a viable plant species for Cu phytoextraction.