Extracellular silicon (Si) nanocoating induced by cationic polymers enhances heavy metal resistance in both Si-accumulating and non-Si-accumulating plants

Heavy metal contamination poses a significant threat to food security, requiring the development of plant protection measures. Silicon (Si) deposition on rice roots can inhibit the uptake and translocation of heavy metal ions. However, the slow process of Si polymerization limits its utilization by many plants. This study explored the use of cation-induced silicic acid polymerization to rapidly form extracellular Si nanocoatings on plant roots using ten cationic polymeric materials. Performance, safety, and cost-effectiveness were comprehensively evaluated in enhancing rice's resistance to heavy metals, particularly trivalent chromium. Guar hydroxypropyl trimonium chloride (GHPT) showed the most promising results among the materials studied. A treatment procedure involving immersion in GHPT and silicic acid was found to be effective when repeated twice for 20 min each time. This method effectively doubled Si concentration in rice roots and reduced shoot chromium concentration by 67%. Furthermore, this approach was successfully applied to pakchoi, enabling Si utilization in this non-Si-accumulating plant. The Si concentration in pakchoi roots increased to levels similar to rice (1577.5 mu g/g), and shoot chromium concentration decreased by 75.0%, accompanied by a 66.2% reduction in chromium translocation factor. These findings provide a safe, economical and practical solution to reduce heavy metal stress.