Organosilicon-Mediated Cadmium Uptake, Transport, and Detoxification in Rice: Comparison Between Low-Cd and Conventional Rice Varieties

Cadmium (Cd) contamination in rice threatens rice food safety. Organosilicon shows substantial potential to reduce the uptake and accumulation of Cd in crops. However, the current understanding of the mechanisms by which organosilicon reduces Cd toxicity in rice remains fragmented. In a one-season pot experiment using soil with a total Cd concentration of 1.04 mg·kg−1, we examined organosilicon-modulated physiological responses and Cd-transport gene expression in two rice varieties. The three organosilicon compounds tested were KH590 (3-mercaptopropyltrimethoxysilane), DMDCS (dimethyldichlorosilane), and D6 (dodecamethylcyclohexasiloxane). Two-way ANOVA confirmed significant cultivar × treatment interactions for Cd in all organs (p < 0.05). DMDCS treatment reduced grain Cd in Shaoxiang 100 by about 43.4%. Subcellular fractionation revealed that DMDCS enhanced Cd sequestration in root and culm cell walls (60.8% increase in culm), while D6 and KH590 showed greater efficacy in leaves. Gene expression analysis indicated that KH590 most potently suppressed the root uptake gene OsNramp5 (76% reduction), whereas DMDCS and D6 exerted stronger inhibition on the long-distance transport gene OsLCT1 (up to 91.8%). Principal component analysis further confirmed that KH590 primarily inhibited root uptake, DMDCS mainly enhanced root Fe oxide deposition and culm Cd retention, while D6 best maintained biomass and reduced late-stage Cd transport to grains, increasing yield by 28%. These findings provide evidence for differential pathways through which organosilicon compounds mitigate Cd stress in rice under pot conditions, offering a theoretical reference for reducing Cd pollution in farmland.