Polysaccharide-Stabilized Selenium Nanoparticles Derived from Phellinus igniarius Regulate Growth and Metabolic Reprogramming in Rice

polysaccharide-stabilized selenium nanoparticles (SH-SeNPs). These ~90 nm nanoparticles exhibited excellent stability and enhanced antioxidant capacity compared with native polysaccharides. Foliar application significantly promoted the early growth and biomass of rice without inducing oxidative stress. Specifically, treatment with 5 mg/L SH-SeNPs increased the root length from 5.22 ± 0.78 cm (control) to 5.91 ± 0.50 cm, while the 45 mg/L treatment increased the shoot length from 1.63 ± 0.27 to 1.89 ± 0.35 cm during germination. Mechanistically, SH-SeNPs maintained redox homeostasis through selective enzymatic regulation. Metabolomic analysis indicated a potential strategic metabolic reprogramming: SH-SeNPs appeared to induce the diversion of carbon-nitrogen flux from free amino acids toward the shikimate and phenylpropanoid pathways. This proposed "efficient defense-robust growth" balance suggests that SH-SeNPs may act not merely as a nutrient source but also as a metabolic regulator. These findings provide insights into the mechanisms through which polysaccharide-stabilized SeNPs regulate growth and metabolism in rice during early growth stages, highlighting their potential as nano-biostimulants for seedling establishment.