Iron nanoparticles mitigate lead toxicity through transcriptional modulation of metal responsive genes, glutathione metabolism and ABC transporters

The lack of localization pattern of iron nanoparticles (FeNPs), lead (Pb), and their complex interaction in high and low levels of Pb tolerance among varieties limit the advancement of nanotechnology-based tools for sustainable agriculture. In this study, we investigated the impact of foliar-applied FeNPs, their entry through stomata and trichomes within a 40-min interval, and their defensive role to mitigate Pb stress in two tobacco varieties. We found optimized photosynthetic efficiency, biomass indices (29–69%), stomatal length (4.6–14.1 μm), and ultrastructural integrity. Alongside this, we observed FeNPs-mediated decrease in Pb content, Pb bioaccumulation, Pb translocation, Pb localization, and cell death in both tobacco varieties, notably the higher Pb-tolerant variety (Haiyan-204), through fluorescence microscope, scanning electron microscope, atomic absorption spectroscopy, transmission electron microscope, and confocal laser scanning microscope. Transmission electron micrographs showed Pb localization mainly in the cell wall, tonoplast, and nucleus, while FeNPs were dispersed over the entire cell. Moreover, we observed association between decreased Pb stress and transcriptional reprogramming of ABC transporters, glutathione metabolism, plant hormone signal transduction, and the MAPK signaling pathway. The GO enrichment analysis highlighted link between FeNPs and response to biological processes mainly defense, ABA, and Jasmonic acid, and cellular processes specifically plasma membrane and chloroplast. Alongside this, genes involved in lead ion transport, metal ion binding, sequestering and detoxification were screened by analyzing GO functions. Our findings signify the nano-phytoremediation framework with future implications to build metal-tolerant species as a comprehensive and everlasting approach to address the environmental risk posed by heavy metals.