Biochar application alleviates drought-induced oxidative stress by activating the salicylic acid-mediated glutathione synthesis pathway in Brassica napus.

Drought stress induces oxidative damage that disrupts cellular redox homeostasis. Biochar has recently attracted attention for its potential to enhance antioxidant defense systems and reduce reactive oxygen species (ROS) accumulation under drought conditions. This study aimed to investigate the mechanisms by which biochar alleviates drought-induced oxidative stress in Brassica napus, focusing on hormonal regulatory pathway in glutathione (GSH)-based redox control. The plants were grown under well-watered (Control), drought stress (Drought), or drought stress with biochar application (Drought + Biochar) conditions for 43 days. Drought increased ROS (O₂⁻and H₂O₂) and malondialdehyde levels, while reducing soil water content, shoot biomass, relative water content, and chlorophyll concentration. These changes were accompanied by increased abscisic acid (ABA) levels and the upregulation of ABA biosynthesis and signaling genes (NCED3 and ABI5). Drought also decreased GSH content, GSH/GSSG ratio, GSH1 expression, and GR activity, indicating severe oxidative stress and impaired redox homeostasis. Biochar application significantly alleviated drought-induced ROS accumulation and lipid peroxidation. Compared with drought alone, biochar promoted SA accumulation by 1.5-fold, upregulated the expression of SA biosynthesis (ICS1) and signaling (NPR1) by 5.6- and 3.3-fold, respectively, and reduced ABA content by 28%. Biochar also enhanced GSH levels (2.9-fold) and GSH/GSSG ratio (4.5-fold), accompanied by the upregulation of GSH1 (4.2-fold) and suppression of GPX7 (60.7%), relative to drought alone. Correlation analysis revealed a strong association between SA, GSH, and ROS. These findings indicate that biochar alleviates drought-induced oxidative stress by activating the SA-mediated GSH biosynthesis pathway and antagonizing ABA signaling, thereby enhancing antioxidant defense mechanisms and improving drought stress resilience in Brassica napus.