Trehalose: a potent enhancer of antioxidant responses in <i>Brassica juncea</i> L. under arsenic toxicity

Arsenic contamination poses a major threat to crop productivity by impairing the photosynthetic machinery and inducing oxidative stress. This study explored the protective role of exogenous trehalose (25, 50, and 75 mM) in mitigating arsenic-induced physiological and biochemical disturbances in Brassica juncea at 30, 60, and 90 d after sowing. As stress significantly reduced photosynthetic pigments, including chlorophyll a (up to 72.91%), chlorophyll b (77.71%), total chlorophyll (56.49%), carotenoids (33%–43%), xanthophylls (42%–43%), and anthocyanins (38.82%). Concurrently, oxidative stress markers increased markedly, with malondialdehyde rising by 22%–46% and hydrogen peroxide (H₂O₂) by 12%–59%, indicating severe ROS-induced cellular damage. Foliar application of trehalose effectively alleviated these negative effects in a dose-dependent manner. Trehalose (75 mM) showed the highest efficacy, enhancing chlorophyll a by 49%–88%, chlorophyll b by 56%–78%, total chlorophyll by 52%–66%, carotenoids by 42%–48%, and xanthophylls by 44%–58% compared to As-stressed plants. It also substantially improved the anthocyanin content and decreased MDA levels by 25%–29%, reflecting reduced lipid peroxidation and improved antioxidant defense. While H₂O₂ levels displayed some variability, trehalose consistently moderated its accumulation under As stress. Overall, trehalose significantly restored the pigment profiles, reduced oxidative damage, and enhanced stress tolerance, with 75 mM emerging as the most effective concentration. These results highlight trehalose as a promising and eco-friendly strategy to improve plant resilience and productivity under arsenic-contaminated conditions.