Selenium Nanobiostimulants Attenuate Copper-Induced Oxidative Damage in Brassica napus Through Genotype-Specific Antioxidant and Metabolic Adaptation

Copper (Cu) contamination poses severe threats to agricultural productivity and food safety, particularly affecting economically important crops such as rapeseed (Brassica napus L.). This study investigated the protective effects of selenium nanoparticles (SeNPs) against Cu toxicity in four B. napus cultivars. Exposure to Cu (200 μM) caused severe reductions in growth and photosynthetic efficiency while significantly elevating oxidative stress markers across all cultivars. Application of SeNPs (25 μM) effectively mitigated these adverse effects, improving biomass, restoring chlorophyll content, and enhancing photosynthetic performance compared to Cu-stressed plants. SeNP treatment significantly enhanced antioxidant enzyme activities, with corresponding upregulation of antioxidant gene expression. Secondary metabolite profiling revealed cultivar-specific responses, with sensitive cultivar Zheda 622 exhibiting metabolic adaptation and higher volatile organic compound (VOC) accumulation, while tolerant cultivar Zheda 635 maintained metabolic stability. PCA analysis demonstrated distinct metabolic clustering patterns, reflecting differential stress-responsive strategies. The study demonstrates that SeNPs attenuate Cu-induced toxicity through integrated mechanisms encompassing diminished Cu acquisition, augmented antioxidant defense systems, and comprehensive metabolic reprogramming. Cultivar-specific responses highlighted substantial genetic variation in tolerance mechanisms across B. napus genotypes. These findings substantiate SeNPs as a viable and efficacious nanomaterial for sustainable agronomic management in Cu-contaminated edaphic environments. The approach offers dual benefits of improved crop productivity and reduced Cu accumulation, ensuring enhanced food safety.