Zinc oxide application alleviates arsenic-mediated oxidative stress via physio-biochemical mechanism in rice

Arsenic (As) pollution in cultivated soils poses a significant risk to the sustainable growth of agriculture and jeopardizes food security. However, the mechanisms underlying how zinc (Zn) regulates the toxic effects induced by As in plants remain poorly understood. Hence, this study aimed to explore the potential of ZnO as an effective and environmentally friendly amendment to alleviate As toxicity in rice, thereby addressing the significant risk posed by As pollution in cultivated soils. Through a hydroponic experiment, the study assessed the mitigating effects of different ZnO dosages (Zn₅, 5 mg L^-1; Zn₁₅, 15 mg L^-1; Zn₃₀, 30 mg L^-1) on rice seedlings exposed to varying levels of As stress (As₀, 0 µM L^-1; As₂₅, 25 µM L^-1). The findings of the study demonstrate significant improvements in plant height and biomass (shoot and root), with a notable increase of 16-40% observed in the Zn₁₅ treatment, and an even more substantial enhancement of 29-53% observed in the Zn₃₀ treatment under As stress, compared to respective control treatment. Furthermore, in the Zn₃₀ treatment, the shoot and root As contents substantially reduced by 47% and 63%, respectively, relative to the control treatment. The elevated Zn contents in shoots and roots enhanced antioxidant enzyme activities (POD, SOD, and CAT), and decreased MDA contents (13-25%) and H₂O₂ contents (11-27%), indicating the mitigation of oxidative stress. Moreover, the expression of antioxidant-related genes, OsSOD-Cu/Zn, OsCATA, OsCATB, and OsAPX1 was reduced when rice seedlings were exposed to As stress and significantly enhanced after Zn addition. Overall, the research suggests that ZnO application could effectively mitigate As uptake and toxicity in rice plants cultivated in As-contaminated soils, offering potential solutions for sustainable agriculture and food security.