<p>Nanopriming is a novel technique to protect plants against various stresses; however the mechanisms by which nanoparticles regulate seed germination and heavy metal tolerance has been not fully understood. Herein, we assessed the role of nitric oxide (NO) in responses induced by seed priming with silicon dioxide nanoparticles (nSiO₂) in <i>Chenopodium quinoa</i>. Results showed that Pb toxicity significantly reduced germination indices and seedling growth of quinoa. Seed priming with nSiO₂ similar to Si improved the germination indices and vigoration and the best effect was obtained with 4 mM of these compounds under 250 µM Pb. Nano priming enhanced α, β amylase activity, reduced starch content, and increased contents of soluble sugars in seeds and consequently improved germination indices and vigor index. Seed priming with nSiO₂ reduced Pb concentration in roots and shoots and improved growth parameters. Interestingly, nanopriming systemically triggered a nitric oxide (NO) burst in both roots and leaves that was closely linked to the mitigation of Pb-incited oxidative damage and the acceleration of the activities of catalase and peroxidase in both organs. The effect of seed priming with nSiO₂ on NO generation and the aforementioned attributes were significantly abolished either through the inhibition of NO biosynthesis by Nx-Nitro- L-arginine methyl ester hydrochloride (L-NAME) and tungstate or via scavenging NO by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxy l-3-oxide (cPTIO). It can be concluded that NO burst generated by nitric oxide synthase and nitrate reductase regulates seed germination and Pb tolerance induced by nSiO₂ in quinoa plants.</p>