Foliar spraying of sulfhydryl iron-functionalized nanosilica enhances coriander growth and reduces cadmium accumulation.

Silica nanoparticles (SiO2 NPs) have emerged as promising nano-agrochemicals for improving crop productivity and reducing Cd uptake. However, the effects of surface functionalization in enhancing their effectiveness remain unclear. Herein, we synthesized sulfhydryl iron-functionalized SiO2 NPs (Si-SF NPs) and investigated the effects of foliar application of SiO2 NPs and Si-SF NPs with different concentrations (25-400 mg/L) on coriander growth and Cd accumulation. Hydroponic experiments demonstrated that Si-SF NPs were more effective than SiO2 NPs in promoting coriander growth and reducing Cd accumulation. Compared to the control, the coriander yield was increased by 92.2 % by Si-SF NPs, and Cd concentrations in root, stem, and leaf were decreased by 28.51 %, 35.71 %, and 48.67 %, respectively. Si-SF NPs enhanced Cd proportions in root, and retained Cd in the cell wall. Furthermore, Si-SF NPs enhanced plant antioxidant enzyme activities, thereby effectively alleviating Cd-induced ultrastructural damage of leaf cells. Transcriptomic analysis revealed that Si-SF NPs upregulated the expression of genes involved in biosynthesis of cell wall component and antioxidant defense systems, mediating Cd detoxification. Additionally, Si-SF NPs enhanced the expression of genes encoding heavy metal-associated isoprenylated plant proteins, inhibiting the upward translocation of Cd. Field experiments confirmed the effectiveness of Si-SF NPs in reducing Cd accumulation and increasing coriander yield. Our findings demonstrated the significant potential of Si-SF NPs as a high-efficiency foliar fertilizer for safe vegetable production.