Nickel (Ni) is a trace element that is toxic to plants and consequently results in toxicity symptoms and hazardous fitness problems in human beings through food chains. Nanoparticles (NPs) are being used in new ways to directly help plants handle Ni stress and act as nano-fertilizers. The purpose of the current study was to establish the use of biogenically produced zinc oxide nanoparticles (ZnONPs) to reduce Ni-induced toxic effect on the growth and development of watermelon (Citrullus lanatus). Watermelon seeds were sown in pot filled with five kg of soil and placed in a greenhouse. The watermelon plants were treated with Ni stress (70 mg/kg soil) at 20 DAS (days after sowing), and the treatment was applied directly into the soil. The supply of ZnONPs (100 mg/L) as foliar spray was given at 30 DAS and 38 DAS, and the sampling was performed at 55-60 DAS for biochemical and physiological analysis. The results showed that watermelon plants that were exposed to Ni had oxidative damage, which was shown by more electrolyte leakage, hydrogen peroxide, lipid peroxidation, pigment and osmolyte loss, and a loss of ultrastructural integrity in the chloroplasts. However, watermelon plants supplemented with ZnONPs under the Ni toxicity revealed significantly increased plant fresh weight (53.18%), plant dry weight (51.25%), and root length (32.14%). Moreover, the ZnONPs supplement has beneficial impacts on photosynthesis attributes, SPAD value (21.93%), and chloroplast structure observed by transmission electron microscopy (TEM) under Ni stress. Application of ZnONPs also substantially reduced the oxidative stress by lowering the levels of superoxide radical (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:{\text{O}}_{2}<^>{-\cdot\:}$$\end{document}; 22.68%), hydrogen peroxide (H2O2; 21.18%), malondialdehyde (MDA; 21.34%), and electrolyte leakage (EL; 34.613%). The results showed that ZnONPs enhanced enzymatic activities of superoxide dismutase (SOD; 39.95%), peroxidase (POD; 19.95%), catalase (CAT; 32.85%), ascorbate peroxidase (APX; 25%) that metabolize reactive oxygen species (ROS); these increases correlated with the changes observed in the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:{\text{O}}_{2}<^>{-\cdot\:}$$\end{document}, H2O2 and MDA after ZnONPs application. Application of ZnONPs increased the transcriptional levels of antioxidant defense genes as compared to the Ni plants alone. In conclusion, spraying ZnONPs on foliage has high effectiveness in increasing biomass, photosynthesis, protein and antioxidant enzymes, mineral nutrient concentrations, and lowering Ni concentrations in watermelon. The results indicate biogenically produced ZnONPs can be a promising technique for the remediation of Ni-contaminated soils.

来源平台：JOURNAL OF SOIL SCIENCE AND PLANT NUTRITION