Mechanistic understanding of iron oxide nanobiotransformation in Zea mays: a combined synchrotron-based, physiological and molecular approach

Abstract

The study investigates the nanobiotransformation dynamics and molecular level impact of iron oxide nanoparticles (nFe₃O₄) on Zea mays. Specifically, the impact of soil-applied nFe₃O₄ (500 mg kg⁻¹) or FeCl₃ (75 mg kg⁻¹) on Z. mays morphological, physiological, and transcriptional responses was investigated in a whole life cycle study. X-ray absorption spectroscopy (XAS) showed that the Fe local structure changed upon nanoscale Fe internalization, indicating potential nanoparticle biotransformation within the plant tissues. Neither of the Fe amendments induced significant plant morphological changes, although FeCl₃ reduced chlorophyll content (SPAD index 37.43 vs. 44.33) and stomatal transpiration (s cm⁻¹, 5.08 vs. 9.67) and increased lipid peroxidation (MDA content, μM, 7.01 vs. 3.26) compared with controls. Conversely, nFe₃O₄-treated plants exhibited milder physiological response as compared to FeCl₃-treated plants (SPAD index: 40.42 vs. 37.43; MDA content: 4.57 vs. 7.01 μM). Gene expression of selected biomarkers showed a 2- to 4-fold increase of glutathione reductase (gsr1) and mate1 xylem transporter, and a 2-fold decrease of proline responding (pro1) gene. These findings, together with iron intake quantification, suggest limited internalization and translocation of iron in the pristine nanometric form and that Fe³⁺ internalization was a function of the amount in the medium. Importantly, nFe₃O₄ provided a controlled and more precise method of iron release in planta. The combination of physical, chemical, and biological data to assess the potential of nFe₃O₄ as a nanofertilizer leads to novel insights on the potential impact of nano-enabled agriculture and nanobiofortification.