Nano-hematite promotes seed germination and stress resilience of maize: redox-mediated kick-start of respiratory metabolism

Successful seed germination is critical for agricultural production and ecosystem sustainability. Naturally occurring nano-minerals often coexist with seeds in the environment, yet their effects on seed germination remain largely unexplored. Here, we show that exposure to nano-hematite (α-Fe₂O₃) significantly promotes maize seed germination and resistance to multiple stresses (drought, cold, and salinity). Mechanistically, hematite at the nano-scale (∼200 nm) is internalized into seeds during germination and activate redox signaling, initiating early and vigorous mitochondrial respiration, as reflected by increased O₂ consumption rate and elevated ATP production (34.1%) compared to unexposed seeds. LC-MS/MS analysis revealed higher abundance of primary metabolites (sugars, amino acids, fatty acids) in seeds exposed to hematite, indicating boosted catabolism of storage reserves. This metabolic shift provides carbon skeletons to fuel energy metabolism, ultimately accelerating germination. X-ray photoelectron spectroscopy (XPS) detected oxygen vacancies (OVs) and Fe²⁺ on the surface of hematite. The Fe²⁺/hematite hybrid acts as a Fenton-like catalyst, decomposing H₂O₂ to generate hydroxyl radicals (·OH). RNA-Seq analysis further revealed that nano-hematite reprograms the seed transcriptome, differentially regulating genes involved in redox signaling, ROS-quenching, central carbon and nitrogen metabolism, sugar/amino acid/ion transport, and defense response. This coordinated transcriptional reprogramming collectively fuels germination and enhances the plant's adaptive capacity to adverse conditions. These findings expand our understanding of the role of naturally occurring nano-minerals on seed germination, with potential benefits for agricultural productivity and ecological sustainability, especially under a changing climate.