Ferrous ions inhibit Cu uptake and accumulation via inducing iron plaque and regulating the metabolism of rice plants exposed to CuO nanoparticles

Ferrous ions (Fe2+) in the rhizosphere play an indispensable role in the interaction between plants and nanoparticles (NPs). Here, we investigated the effect of Fe2+ (3 mM) on the dynamic adsorption, uptake and accumulation of CuO NPs (100 mg L-1) by rice plants using mu-XRF combined with metabolomics. The results show that the Cu content adsorbed by roots at 72 h was reduced by 71% compared to that at 6 h with the formation of sufficient amorphous iron plaque induced by Fe2+, which was consistent with the inverse changes of Fe and Cu intensities in mu-XRF mappings. Furthermore, the absorbed Cu contents in the roots and shoots were dramatically reduced by 90.3% and 47.2% compared to those exposed to only NPs at 72 h, respectively, due to the presence of Fe2+. The supply of Fe2+ triggered the decline in Cu contents of the roots and shoots from 6 h to 72 h by up to 81.5% and 41.3%. Metabolomics analysis indicates that Fe2+ markedly downregulated abundant organic acids and amino acids with respect to the control and NP treatment, but significantly upregulated fatty acids compared to the NP treatment, thus lessening the Cu accumulation in rice. This study provides new ideas for alleviating the stress caused by NPs in plants.

Automated summary

The addition of Fe2+ (3 mM) was found to reduce the adsorption of CuO NPs (100 mg L-1) by rice plants, leading to a decrease in Cu uptake and accumulation in roots and shoots. Fe2+ induced the formation of iron plaque and altered metabolite levels, resulting in less Cu accumulation in rice plants exposed to NPs.