Silicon dioxide nanoparticles alleviated Cd toxicity and promoted Cd accumulation of Sedum alfredii: presenting evidence from physiology and transcriptomics

Silicon dioxide nanoparticles (SiO 2 NPs) have been shown to alleviate cadmium (Cd) toxicity in plants, but the mechanisms regarding SiO 2 NPs-mediated Cd uptake and detoxification on hyperaccumulators are unknown. In this study, physiological and transcriptomic analyses were performed to investigate the impact of SiO 2 NPs on the growth and Cd accumulation of the Cd- hyperaccumulator Sedum alfredii. The results showed that SiO 2 NPs significantly increased root fresh weight (32.71% to 121.50%) and shoot fresh weight (22.72% to 86.36%). Simultaneously, SiO 2 NPs enhanced the Cd uptake and accumulation by S. alfredii (with maximum increases of 232.14%). In the leaves, the Cd content in the phloem of the Si treatment group increased by 1.24 to 1.79-fold, indicating that SiO 2 NPs enhanced the transport of Cd to the shoots. Furthermore, SiO 2 NPs improved the photosynthetic parameters, with the net photosynthetic rate, transpiration rate and stomatal conductance increasing by 2.86-fold, 1.14-fold, and 1.84-fold of the control, respectively. Furthermore, SiO 2 NPs significantly strengthened the antioxidative enzymes activities (SOD, CAT, POD). Transcriptomic analysis revealed that SiO 2 NPs enhanced the Cd tolerance and accumulation capacity of S. alfredii by upregulating the expression of genes encoding photosynthesis-related functions (PSI, PSII), antioxidant enzymes, cell wall synthesis functions, heavy metal-responsive transcription factors ( WRKY , NAC , bZIP , MYB ), and Cd chelation and transport protein functions. Combining physiological and transcriptomic analyses, our findings provide the mechanisms of SiO 2 NPs in promoting Cd accumulation and enhancing Cd tolerance in S. alfredii , highlighted the potential of SiO 2 NPs to enhance phytoremediation efficiency. • SiO 2 NPs increased uptake and accumulation of Cd by S. alfredii. • SiO 2 NPs enhanced the growth and Cd tolerance of S. alfredii by regulating physiological indicators. • SiO 2 NPs upregulated genes involved in photosynthesis, antioxidant defense, and Cd chelation/transport. • SiO 2 NPs has potential in facilitating Cd phytoremediation by S. alfredii.