Arsenic (As) contamination poses a critical threat to agricultural productivity, affecting rapeseed (Brassica napus L.), an agronomically important crop. A comparative assessment was performed to evaluate the efficacy of chemogenic and biogenic manganese nanoparticles (C-MnNPs and B-MnNPs) for mitigating As toxicity. B-MnNPs were biosynthesized using cell-free filtrate of Bacillus pumilus MAY4, while C-MnNPs were obtained from Cwnano Co., Ltd. (Shanghai, China). Greenhouse assays demonstrated that both C-MnNPs and B-MnNPs alleviated detrimental effects of As; however, B-MnNPs exhibited superior performance compared to their chemical counterparts. Compared to As-stressed plants, B-MnNPs enhanced leaf and root biomass (26.4% and 56.15%, respectively), net photosynthetic rate (64.8%), and stomatal conductance (50%). B-MnNPs more effectively reduced oxidative stress markers by activating antioxidant defense systems in both leaf and root tissues. Furthermore, B-MnNPs reduced in planta As accumulation while significantly improving uptake of essential nutrients, including potassium, phosphorous, magnesium, and manganese, etc., in rapeseed plants. Expression studies revealed that B-MnNPs upregulated antioxidant defense and redox homeostasis related stress-responsive genes under induced As stress. Biochemical assays further confirmed the enrichment of stress-responsive phytohormones, including salicylic acid, jasmonic acid, and abscisic acid, in B-MnNP-treated As-stressed rapeseed plants, indicating activation of multi-tier defense response by B-MnNPs to cope with As stress. These findings establish B-MnNPs as a highly effective nano-enabled strategy for managing As toxicity in the rapeseed cultivation system. This research provides critical insights into the molecular and physiological mechanisms underlying MnNP-mediated stress tolerance and offers a promising green nanotechnology approach for heavy metal-resilient crops.

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.