Exogenous Hydrogen Peroxide Alleviates Chromium Toxicity Through Modulation of Antioxidant Defense, Photosynthetic Machinery, and Cr Uptake in Brassica oleracea L.

Soil pollution with heavy metals, particularly chromium (Cr), poses a major threat to crop productivity and food safety. Brassica oleracea var. capitata L. (cabbage) is highly susceptible to Cr toxicity. This study aimed to evaluate the potential of hydrogen peroxide (H 2 O 2 ) as a signaling molecule to mitigate Cr‐induced stress in cabbage. B. oleracea plants were exposed to 100 and 200 µM Cr stress, with or without foliar application of H 2 O 2 (100 µM). Morphological, physiological, biochemical, and antioxidant responses were assessed to determine the role of H 2 O 2 in alleviating Cr toxicity. Cr stress, especially at 200 µM, markedly reduced growth (shoot length; 38% and root length; 67%), photosynthesis rate (31%), and relative water content (35%). While Cr stress elevated antioxidant activity specifically catalase (55%) and superoxide dismutase (90%), Cr stress also reduced uptake of essential mineral nutrients (calcium; 34% and potassium; 35%) while increasing Cr uptake in root and its translocation toward shoot of plants. Foliar application of H 2 O 2 significantly improved morphological traits and physiological functions under Cr stress. Antioxidant activities were further enhanced by H 2 O 2 application at both stress levels compared to Cr‐only treatments. It also increased photosynthetic pigments, efficiency of photosystem II and net photosynthesis rate compared to stress‐only plants. Total phenolics, proline, and total soluble proteins were also increased with H 2 O 2 application by 42%, 19%, and 23% at 100 µM Cr stress and by 39%, 13%, and 20% at 200 µM Cr stress. These findings highlight the potential use of H 2 O 2 as a management strategy to promote crop tolerance against heavy metal stress.