Micronutrient nanoprotectants curtail arsenic-induced physio-oxidative damage by differentially regulating antioxidant and metabolic mechanisms across Brassica napus genotypes

Abstract

Oilseed rape (Brassica napus L.) cultivation increasingly faces challenges from arsenic (As) contamination, which disrupts plant metabolism through oxidative stress and antioxidant enzyme inhibition. This study investigated the potential of manganese nanoparticles (MnNPs) to alleviate As toxicity across five genetically distinct B. napus cultivars under hydroponic conditions. Plants were exposed to varying concentrations of As (0, 100, and 200 μM) and MnNPs (0, 50, and 100 μM) to evaluate treatment efficacy. Results demonstrated that As stress (200 μM) severely reduced leaf fresh weight (43.88–77.57%), root fresh weight (69.35–91.2%), and photosynthetic efficiency while significantly increasing reactive oxygen species (ROS) accumulation across all cultivars. Conversely, the application of 100 μM MnNPs substantially ameliorated these effects, increasing leaf fresh weight by 25.26–70.65%, improving photosynthetic rate by 61.94–77.27%, and restoring stomatal conductance by 43.48–58.83% compared to As-only treatment. Additionally, MnNPs significantly reduced oxidative stress markers in both leaf and root tissues while upregulating antioxidant enzyme activities beyond levels induced by As stress alone. Metabolic analysis complemented these physiological findings, revealing variety-specific profiles with ZD 622 exhibiting high hexenol acetates, while the combined MnNPs + As treatment induced the strongest metabolic response, suggesting synergistic stress defense effects. Notably, cultivars exhibited distinct genotype variations, with ZD 635 and ZY 758 demonstrating superior As tolerance following MnNP treatment, whereas ZD 622 showed the least tolerance. These findings collectively highlight MnNPs' effectiveness in enhancing B. napus productivity in As-contaminated environments by improving stress tolerance mechanisms, underscoring their potential as a valuable nano-agronomic intervention.