Unlocking key factors and mechanistic insight of cadmium toxicity mitigation using green-synthesized ZnO nanoparticles in soybean through advanced metabolomics

초록

Cadmium (Cd), a toxic heavy metal, causes morpho-physiological changes in plants, ultimately reducing growth and productivity. Nanoparticle (NP)-mediated Cd-toxicity mitigation in plants is eco-friendly and cost-effective. However, the mechanisms underlying NP-Cd interactions in soybeans remain unclear. Therefore, this study aims to investigate the effects of foliar and soil treatments with zinc oxide NPs (ZnO-NPs) on soybeans under Cd stress using untargeted metabolomic profiling. ZnO-NPs were synthesized through a green process utilizing an orange peel extract. According to SEM, XRD, and TEM analysis, the green-synthesized ZnO-NPs exhibited a spherical morphology with moderate aggregation, a uniform size distribution (27-48 nm), and high elemental purity confirming successful synthesis and structural integrity. Soil and foliar applications with ZnO-NPs (100-1000 mgL-1) under Cd toxicity reduced Cd content, enhanced Zn content, and restored photosynthetic activity. Furthermore, Org(organic)-ZnO-NPs increased chlorophyll content and regulated antioxidant activity. Metabolomic analysis revealed 219 and 298 non-targeted metabolites in soybean leaves and roots under normal and Cd-stressed conditions, respectively. These metabolites belong to various classes, including glycerophospholipids, flavonoids, and prenolipids, and are essential in maintaining membrane stability and supporting plant defense mechanisms. Treatment with Org-ZnO-NPs restored 45.7 % (leaf) and 35.7 % (root) of Cd-disrupted metabolite accumulation to normal levels. Our findings show that green-synthesized ZnO-NPs effectively regulate heavy metal uptake, repair photosynthetic machinery damage, and restore metabolite levels disrupted by Cd toxicity, offering a sustainable strategy for remediating Cd-contaminated soils. Future research should aim to elucidate the molecular mechanisms of ZnO-NPs action and evaluate their efficacy through field-scale trials under diverse environmental conditions.

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