Surface-Engineered Manganese Nanozymes Direct Selective Tryptophan Oxidation to Reprogram Plant Root Architecture

Abstract

Tryptophan (Trp) oxidation is a key biochemical process influencing plant development and numerous biomedical pathways. Here, we investigate how manganese doping modulates the catalytic behavior of titanium dioxide nanoparticles toward selective Trp oxidation. Mn-doped TiO2 nanoparticles containing 5%, 10%, and 20% Mn were systematically examined, while structurally related metal oxides (pristine TiO2, MnO2, MnFe2O4, maghemite (γ-Fe2O3), and industrial Fe3O4) were included as reference materials to establish catalytic benchmarks. Whereas the reference oxides predominantly promoted nonspecific reactive oxygen species (ROS) generation or exhibited lower catalytic efficiency, Mn-doped TiO2 displayed highly tunable reactivity. Specifically, 5% Mn doping favored broad-spectrum photocatalytic ROS production, whereas increasing the Mn content to 20% transformed the material from a conventional photocatalyst into a highly selective nanozyme. The 20% Mn-doped TiO2 exhibited superior biomimetic catalytic activity and was therefore subjected to detailed mechanistic studies. Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) revealed highly selective, nanozyme-driven Trp oxidation pathways leading to the formation of auxin-mimicking metabolites. In vivo experiments using Arabidopsis thaliana demonstrated that the resulting metabolite cocktail significantly stimulated lateral root formation, indicating improved nutrient acquisition potential. Collectively, these findings establish Mn-doped TiO2 as a tunable catalytic platform capable of directing amino acid oxidation toward biologically relevant products and highlight its potential applications in agriculture and biomedicine.