Effect of heavy metal stress on antioxidant enzymes and DNA damage in Nasturtium officinale R.Br. (watercress)

Cerium improves the physiology and medicinal components of Dendrobium nobile Lindl. under copper stress

Heavy metal stress affects the quality of medicinal plants, and rare earth elements can effectively alleviate heavy metal stress. In this paper, we investigated the effects of rare earth element cerium (0, 5, 10, 20, 40, 80, and 160 mg/L) on the physiological and medicinal components of Dendrobium nobile Lindl. under copper (200 mg/L) stress. The results revealed that cerium (Ce) had a good alleviating effect on copper (Cu) stress, low concentrations of Ce (10-20 mg/L) significantly improved the resistance and medicinal qualities of the plant such as polysaccharide, polyphenol and flavonoid, it also increased the content of photosynthetic pigment, proline, soluble sugar and soluble protein of D. nobile Lindl., effectively balance the osmotic pressure and the generation and removal of reactive oxygen species in the plant, thereby the toxic effect of copper on D. nobile Lindl. is alleviated. From the point of view of the treatment time when the optimal relieving concentration appeared, the optimal concentration for relieving antioxidant enzyme activity all appeared at the treatment time of 10 d, the optimum concentrations of other indicators all appeared at the treatment time of 15 d. Overall, this study suggests that the optimum level of Ce (10-20 mg/L) might be promising for alleviating the adverse impacts of copper stress and promoting the accumulation of medicinal components in D. nobile Lindl.

Effects of Heavy Metal Stress on Physiology, Hydraulics, and Anatomy of Three Desert Plants in the Jinchang Mining Area, China

The physiological mechanisms and phytoremediation effects of three kinds of native quinoa in a desert mining area were studied. We used two different types of local soils (native soil and tailing soil) to analyze the changes in the heavy metal content, leaf physiology, photosynthetic parameters, stem hydraulics, and anatomical characteristics of potted quinoa. The results show that the chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate of Kochia scoparia were decreased, but intercellular CO₂ concentration (Ci) was increased under heavy metal stress, and the net photosynthetic rate (Pn) was decreased due to non-stomatal limitation. The gas exchange of Chenopodium glaucum and Atriplex centralasiatica showed a decrease in Pn, stomatal conductance (Gs), and transpiration rate (E) due to stomatal limitation. The three species showed a similar change in heavy metal content; they all showed elevated hydraulic parameters, decreased vessel density, and significantly thickened vessel walls under heavy metal stress. Physiological indicators such as proline content and activity of superoxide dismutase (SOD) and peroxidase (POD) increased, but the content of malondialdehyde (MDA) and glutathione (GSH), as well as catalase (CAT) activity, decreased in these three plants. Therefore, it can be concluded that these three species of quinoa, possibly the most dominant 30 desert plants in the region, showed a good adaptability and accumulation capacity under the pressure of heavy metal stress, and these plants can be good candidates for tailings remediation in the Jinchang desert mining area.

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.