Nitric Oxide Alleviates Zinc Oxide Nanoparticles-Induced Phytotoxicity in Brassica juncea

Nitric oxide (NO) plays a vital role in plant defense against various environmental stresses. However, the study on the defensive effect of NO on the phytotoxicity induced by zinc oxide nanoparticles (ZnO-NPs) remains scarce. In the present study, sodium nitroprusside (SNP, a NO donor) was used to investigate the mechanism of NO in ameliorating the ZnO-NPs toxicity in mustard (Brassica juncea (L.) Czern.) plants. The plants were treated with the different concentrations of SNP (100 µM) and ZnO-NPs (1000 and 2000 µM) either alone or in combination at 25 days after sowing (DAS) for five days consecutively. The results of our study shows that 100 µM of SNP proved highly effective in mitigating the toxicity induced by ZnO-NP. SNP significantly improve chlorophyll content that partially improve photosynthesis in ZnO-NPs stressed plants. Moreover, the defensive role of SNP in relieving the oxidative damage induced by ZnO-NPs is intimately linked to NO-induced antioxidative defense system. The spray of SNP increased the growth biomarkers as well as proline content in control as well as in ZnO-NPs-treated plants. Additionally, microscopic studies further reveal an increase in the size of stomatal aperture on SNP exposure in ZnO-NPs treated plants. Overall, this study provides the first evidence indicating the functions of SNP in alleviating the ZnO-NPs toxicity in mustard plants.