Exogenous ascorbic acid alleviates sodium fluoride toxicity by enhancing growth and mitigating oxidative stress in green amaranth (Amaranthus viridis L.)

Abstract

Fluoride (F) contamination is an emerging threat to agricultural soils, plants and environments. How F contamination impairs the growth and development of green herbs is still elusive. Therefore, the aim of the study was to evaluate how exogenous ascorbic acid (AsA) alleviates sodium fluoride (NaF)-induced stress in green amaranth (Amaranthus viridis L.). In this study, NaF stress reduced fresh and dry weight, leaf greenness, root length, and shoot length, while the AsA supplementation significantly recovered these parameters. The 1.0 mM AsA treatment showed the best efficiency, followed by the 0.5 mM AsA treatment against 50 mM NaF stress. NaF-induced oxidative stress in amaranth plants was indicated by the production of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂). However, the AsA treatment significantly declined that oxidative stress markers in response to AsA-treated plants. AsA application also modulated proline accumulation and catalase activity, indicating involvement of both osmotic adjustment and antioxidant defense in stress mitigation. Overall, the results indicate that exogenous AsA alleviates NaF stress-induced growth inhibition and oxidative damage in green amaranth, although its protective capacity of the plant varies with NaF stress level and AsA mitigating doses. These findings suggest that AsA-mediated mitigation of F-contamination could be a cost-effective and eco-friendly strategy for amaranth and green plant resilience to F-contaminated soils.