Nitrate reduces copper toxicity by preventing oxidative stress and inhibiting copper translocation from roots to shoots in Liriodendron Chinense

Abstract

Nitrogen forms can affect metal accumulation in plants and tolerance to metals, but a few published studies on the effects on Cu toxicity and Cu accumulation in plants are scarce. Thus, the objective of this study was to evaluate the responses of Liriodendron chinense to different nitrogen forms, by the oxidative stress, antioxidant enzymes system, GSH-AsA cycle, Cu uptake, translocation, and accumulation under Cu stress. We found that Cu-induced growth inhibiting was alleviated by added exclusive NO₃^--N. Adding N as NH₄⁺-N with or without NO₃^--N was aggravated as evidenced by significantly elevated malonaldehyde (MDA) and hydrogen peroxide (H₂O₂) compared to N-Null. Cu exposure and adding NH₄⁺-N inhibited superoxide dismutase activity, but remarkably stimulated the activities of catalase and peroxidase, the efficiency of glutathione-ascorbate (GSH-AsA) cycle, and the activity of glutathione reductase and nitrate reductase, with respect to the control. However, adding exclusive NO₃^--N progressively restored the alteration of antioxidant to prevent Cu-induced oxidative stress. Additionally, adding exclusive NO₃^--N significantly promoted the Cu uptake and accumulation in roots, but reduced Cu concentration in leaves, accompanied by the inhibited Cu translocation factor from roots to shoots by 36.7%, when compared with N-Null. Overall, adding NO₃^--N alleviated its Cu toxicity by preventing Cu-induced oxidative stress and inhibiting Cu translocation from roots to shoots, which provides an effective strategy for phytostabilization in Cu-contaminated lands.

Keywords: Copper toxicity; Enzyme activity; Metal translocation; Nitrogen form.