Small-sized selenium nanoparticles reduce the bioavailability of selenium in rice (Oryza sativa L.) by stimulating the formation of more iron plaque

Abstract

Nano-enabled agricultural technologies, particularly the application of small-sized selenium nanoparticles (Se NPs, <100 nm), demonstrate significant potential for stimulating crop growth and enhancing Se biofortification efficiency in dryland farming systems. However, the influence of Se NP size on bioavailability in flooded systems remains poorly understood. In this study, a rice (Oryza sativa L.) cultivation system was used to explore the relationship between the Se NP size (30 and 110 nm, 22 μm) and Se bioavailability under waterlogged conditions. Interestingly, 110 nm Se NPs significantly enhanced rice biomass, evidenced by a 19.4% increase in root fresh weight, and improved Se bioavailability in plants compared to both smaller (30 nm) and larger particles (2 μm). Mechanistically, smaller Se NPs (30 nm) appeared to enhance radial oxygen loss (ROL) and stimulate antioxidant enzyme activity (superoxide dismutase [SOD], peroxidase [POD], and catalase [CAT]). This physiological response promoted Fe(II) oxidation and subsequent iron plaque (IP) deposition on root surfaces, with DCB-extractable Fe levels showing a 29.1% increase compared to those of the 110 nm NP treatment group. The resulting increase in Se adsorption by the IP reduced Se translocation to aerial tissues, thereby decreasing its bioavailability in the smaller Se NP treatment group. Full life cycle experiments further confirmed that 110 nm Se NPs exhibited significantly higher Se accumulation in grains, an 85.3% increase compared to 30 nm NPs. These findings underscore the critical role of nanoparticle size and IP sequestration in determining Se bioavailability in rice grains. This study provides valuable insights for optimizing nano-Se fertilizers to improve Se biofortification in flooded agricultural systems.