Silicon mitigates combined cadmium and microplastics toxicity in rice by regulating glyoxalase system, and phytochelatin-mediated cadmium detoxification

Cadmium (Cd) and microplastics (MPs) are common contaminants in paddy fields, posing a serious challenge to rice productivity. Silicon (Si) is widely used globally to counteract abiotic stresses; however, its role in mitigating combined toxicity of Cd and MPs remain unknown. Therefore, this study examined the different mechanisms mediated by silicon to counteract the combined Cd and MPs toxicity in rice. The study performed in CRD design with eight treatments: control (Cd- and MPs free soil), Cd -contaminated soil (20 mg kg−1), MPs contaminated soil (1%), Cd + MPs, control (Cd and MPs free soil) + Si, Cd + Si, MPs + Si, and Cd + MPs + Si. Silicon (SiO2) was sprayed (4.5 mmol L−1) at the tillering and jointing stages. Cadmium and MPs decreased rice yield (~ 40%) by increasing oxidative damage and Cd accumulation, while decreasing chlorophyll production (~ 55%), hormonal synthesis (~ 70%), phytochelatin production, and soil nutrient availability (~ 46%). Silicon mitigated combined Cd and MPs stress by significantly improving chlorophyll content (84.44%) and enhancing antioxidant activities, along with increasing the proline (36.15%) and key phytohormones, including gibberellic acid (97.58%), indole-3-acetic acid (85.93%), jasmonic acid (90.20%), and salicylic acid (69.95%) synthesis. The improved growth was also associated with reduced methylglyoxal (MG) production (23.91%) due to enhanced activity of leaf glyoxalase-I (Gly-I) (31.11%) and glyoxalase-II (Gly-II) (45.45%). Silicon decreased Cd accumulation via increasing soil nutrient availability and phytochelatin (139.20%) production, while decreasing the expression of OsNRAMP1 (21.85%) and OsHMA3 (7.36%) genes involved in Cd uptake. In conclusion, Si alleviates the combined Cd and MPs toxicity by improving redox balance, restricting Cd uptake through phytochelatin induction and gene regulation, and restoring photosynthesis, osmolyte status, and hormone signaling, thereby reducing oxidative stress in rice. These results support Si-based approaches to enhance rice productivity in Cd- and MP-contaminated agroecosystems.