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Oxalic acid in root exudates confers lead tolerance in Medicago sativa L. via rhizosphere chelation and cellular detoxification
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DOI：10.1007/s10534-026-00877-9.png)
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Abstract
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Root exudates help plants mitigate heavy metal stress. This study investigated organic acid changes in Medicago sativa L root exudates under lead (Pb) stress and the mechanisms by which exogenous oxalic acid alleviates Pb toxicity. Hydroponic experiments were conducted with Pb concentrations of 0, 5, 50, and 150 mg·L−1. Organic acids were analyzed via High-Performance Liquid Chromatography. Seedling growth, physiological indices (chlorophyll, root viability, malondialdehyde, reactive oxygen species, antioxidant enzymes, osmolytes), and subcellular Pb distribution were measured. Pb stress dose-dependently enhanced oxalic acid secretion. Exogenous oxalic acid (especially 5 mM) significantly increased seed germination, root viability. Compared with Pb alone, 5 mM oxalic acid increased vigor index by 316%, reduced hydrogen peroxide and superoxide anion by 55% and 50%, decreased malondialdehyde by 48%, and enhanced superoxide dismutase, peroxidase, and catalase activities. It also increased leaf protein content, improved osmotic adjustment, and protected chlorophyll synthesis (total chlorophyll recovered by 37%). Furthermore, oxalic acid reduced root Pb content by 47.1% and promoted Pb immobilization in root cell walls (Pb decreased by 51.9% in cytoplasm and 65.0% in organelles). These findings provide a multi-level mechanistic framework for understanding how oxalic acid enhances Pb tolerance in alfalfa, offering insights that may inform strategies for using root exudates to improve phytoremediation efficiency.
Keywords:
Pb stress
Medicago sativa L.
Root exudates
Oxalic acid
Subcellular distribution
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