Priming with reactive oxygen species-generating magnesium oxide nanoparticles promotes pepper seed germination by regulating redox and hormonal homeostasis

Seed germination is a critical process that determines plant establishment and is frequently constrained by environmental stresses. Nanopriming has emerged as a promising strategy to enhance seed performance. In this study, we investigated the effects and mechanisms of magnesium oxide nanoparticles (MgONPs) priming on pepper seed germination. Physicochemical characterization revealed that MgONPs possess high surface reactivity and selectively generate superoxide anion (O₂ • ⁻) and singlet oxygen (¹O₂), while producing no detectable hydroxyl radical ( • OH). Physiological and transcriptomic analyses demonstrated that MgONPs priming significantly enhanced seed vigor, germination rate, and uniformity under both normal and stress conditions. These improvements were accompanied by increased α‑amylase activity and soluble sugar content, indicating improved reserve mobilization. Transcriptomic analysis and hormone profiling indicated that MgONPs priming induced coordinated hormonal reprogramming in pepper seeds. Specifically, MgONPs priming led to downregulation of gibberellin catabolism by inducing the expression of GA2ox genes, and to a reduction in abscisic acid (ABA) content. Moreover, we found that MgONPs priming shifted auxin (IAA) homeostasis from active free IAA to inactive IAA‑amino acid conjugates via upregulation of GH3 genes. Co‑application with ROS scavengers abolished both the ROS burst and all associated beneficial physiological and hormonal effects, supporting a model in which ROS act as key upstream signals. Collectively, our findings suggest that MgONPs as an effective nanopriming agent, and propose a novel mechanism by which MgONPs‑generated ROS may act as a central regulator, reestablishing hormonal and metabolic homeostasis to promote seed germination.