Effects of Nanosilica Priming on Rapeseed (<i>Brassica napus</i>) Tolerance to Cadmium and Arsenic Stress by Regulating Cellular Metabolism and Antioxidant Defense

The mechanisms by which seed-primed silicon dioxide nanoparticles (nSi) alleviated arsenic (As) and cadmium (Cd) toxicity in <i>Brassica napus</i> L. remain unclear. A pot study examined the physico-biochemical, cellular, and molecular responses of <i>B. napus</i> exposed to Cd (10 mg/kg soil) and As (50 mg/kg soil) doses with or without nSi priming. The results showed that nSi priming improved photosynthesis, seedling biomass, and metabolite accumulation, and restored the cell structure. Upon Cd and As stress, nSi diminished oxidative stress by downplaying H₂O₂ (24-32%) and O₂^•- (29-36%), MDA, and activating antioxidant defenses. Also, nSi relieved Cd and As accumulation (27-36%) by enhancing root-vacuolar sequestration (upregulating <i>BnHMA3</i>, <i>BnPCs</i>, and <i>BnABCC1</i>), cell wall chelation, and downregulating root transporters (<i>BnNRAMP5</i>, <i>BnIRTI, BnHMA2, BnHMA4, BnPHT1.1</i>, and <i>BnPHT1.4)</i>. Our findings revealed that nSi priming effectively enhanced canola tolerance to Cd and As toxicity by strengthening multiple oxidative defense mechanisms and limiting their accumulation.