Genotype-adaptive regulatory mechanisms of nano-silicon in alleviating cadmium toxicity in pakchoi

Abstract

Nano-silicon (Nano-Si) and ionic silicon (Ion-Si) were compared for their capacity to alleviate cadmium (Cd) toxicity in Cd-tolerant (HG) and Cd-sensitive (HXW) pakchoi (Brassica chinensis L.) cultivars under 10 μM Cd stress. Nano-Si outperformed Ion-Si in enhancing biomass and dry matter accumulation and exhibited genotype-adaptive regulatory effects rather than relying on high Si accumulation for broad-spectrum Cd suppression. In HG, Nano-Si triggered a blockade-sequestration strategy by downregulating the root-to-shoot Cd transporter BcCdR15 and upregulating the vacuolar sequestration transporter BcCAX2, thereby restricting Cd root-to-shoot translocation, protecting leaves, and rapidly restoring photosynthetic efficiency. In HXW, Nano-Si adopted a buffering-dilution strategy by permitting Cd translocation while alleviating toxicity through strengthened leaf antioxidant defenses, optimized subcellular Cd compartmentalization that minimized Cd accumulation in sensitive organelles, and progressive repair of the photosynthetic apparatus. These results demonstrate that Nano-Si acts as a biostimulant that precisely modulates endogenous detoxification pathways in a genotype-dependent manner, conferring superior regulatory efficacy over conventional silicon fertilizers in mitigating Cd stress in leafy vegetables.