Silicon alleviates aluminum-induced programmed cell death through regulating the antioxidant defenses in soybean roots

Silicon (Si) is involved in the mitigation effect of plants to various environmental stresses. However, the mechanisms of aluminum (Al) detoxification by Si needs to be further clarified, especially in soybean. Here, the role of Si in the amelioration of programmed cell death (PCD) caused by Al exposure was explored in soybean roots. Results showed that supplying Si reduced the cell death, Hsr203J (a PCD marker gene) expression, mitochondrial cytochrome c release and caspase-3-like protease activity under Al stress, indicating that Si alleviated Al-induced PCD dependent on mitochondrial pathway. Exogenous H₂O₂ treatment could induce PCD of root tips exposed to Al, and applying Si reduced the production of H₂O₂ and O₂⁻• in Al-treated roots, indicating that Si alleviated the occurrence of PCD by removing the accumulation of reactive oxygen species (ROS) under Al exposure. Furthermore, the activities of antioxidant enzymes and the contents of small molecule antioxidants were increased by applying Si under Al exposure. Overall, these results indicate that Si can eliminate Al-induced ROS accumulation and thus alleviate PCD by increasing the activity of antioxidant systems, which provides a theoretical basis for the improvement of crop growth in acid soils.