Silica nanoparticles outperform sodium silicate in enhancing trivalent chromium resistance in rice through their...

Excessive accumulation of heavy metals such as trivalent chromium [Cr(Ⅲ)] threatens environmental sustainability and crop health. While silicon fertilizers are known to mitigate Cr(III) toxicity in plants, and silica nanoparticles (SiO₂ NPs) show promise for heavy metal stress alleviation, their comparative efficacy and underlying mechanisms remain unexplored. In this study, we compared the effects of SiO₂ NPs and sodium silicate (Na₂SiO₃) in alleviating Cr(Ⅲ) stress in rice and elucidated the mechanisms behind. Results showed that SiO₂ NPs reduced Cr(Ⅲ) accumulation more effectively than Na₂SiO₃ in rice shoots, roots and xylem sap. Trisodium-8-hydroxy-1,3,6- pyrenetrisulfonic (PTS) tracer analysis confirmed that SiO₂ NPs more significantly inhibited Cr(Ⅲ) apoplastic transport. Consequently, SiO₂ NPs better alleviated Cr(Ⅲ)-induced growth inhibition and malondialdehyde (MDA) accumulation. Both SiO₂ NPs and Na₂SiO₃ exhibited tissue-specific regulation of hydrogen peroxide (H₂O₂) detoxification: SiO₂ NPs more effectively reduced H₂O₂ accumulation in roots and increased catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) activities in shoots, while Na₂SiO₃ showed the opposite pattern. The mechanistic studies demonstrated that the root-specific distribution of SiO₂ NPs facilitated their stronger physical barrier formation in roots. Furthermore, SiO₂ NPs outperformed Na₂SiO₃ in reinforcing endodermal apoplastic barriers by promoting lignin accumulation and upregulating lignin biosynthesis-related genes (OsCCR, OsC4H, Os4CL, OsCAD, OsPAL), while also promoting earlier initiation of endodermal suberin deposition near root tips. Overall, our study indicates that SiO₂ NPs more effectively reinforced apoplastic barriers, restricted the apoplastic transport of Cr(Ⅲ) and consequently alleviated Cr(Ⅲ)-induced stress in rice.