Comparative physiological and metabolomic analyses reveal that Fe 3 O 4 and ZnO nanoparticles alleviate Cd toxicity in tobacco

Background Heavy metals repress tobacco growth and quality, and engineered nanomaterials have been used for sustainable agriculture. However, the underlying mechanism of nanoparticle-mediated cadmium (Cd) toxicity in tobacco remains elusive. Results Herein, we investigated the effects of Fe 3 O 4 and ZnO nanoparticles (NPs) on Cd stress in tobacco cultivar ‘Yunyan 87’ ( Nicotiana tabacum ). Cd severely repressed tobacco growth, whereas foliar spraying with Fe 3 O 4 and ZnO NPs promoted plant growth, as indicated by enhancing plant height, root length, shoot and root fresh weight under Cd toxicity. Moreover, Fe 3 O 4 and ZnO NPs increased, including Zn, K and Mn contents, in the roots and/or leaves and facilitated seedling growth under Cd stress. Metabolomics analysis showed that 150 and 76 metabolites were differentially accumulated in roots and leaves under Cd stress, respectively. These metabolites were significantly enriched in the biosynthesis of amino acids, nicotinate and nicotinamide metabolism, arginine and proline metabolism, and flavone and flavonol biosynthesis. Interestingly, Fe 3 O 4 and ZnO NPs restored 50% and 47% in the roots, while they restored 70% and 63% in the leaves to normal levels, thereby facilitating plant growth. Correlation analysis further indicated that these metabolites, including proline, 6-hydroxynicotinic acid, farrerol and quercetin-3- O -sophoroside, were significantly correlated with plant growth. Conclusions These results collectively indicate that metal nanoparticles can serve as plant growth regulators and provide insights into using them for improving crops in heavy metal-contaminated areas. Graphical Abstract