Silicon nanoparticles and potassium silicate enhance salt tolerance by modulating ABA biosynthesis and flavonoid metabolism in chrysanthemum (Chrysanthemum × morifolium (Ramat.) Hemsl.)

Salinity stress severely limits the growth, productivity, and ornamental quality of chrysanthemum ( Chrysanthemum x morifolium (Ramat.) Hemsl.), necessitating sustainable strategies to improve stress tolerance. Although silicon (Si) is known to enhance plant resilience under abiotic stress, the comparative effectiveness and underlying mechanisms of soluble silicon and silicon nanoparticles (SiNPs) remain poorly understood. Here, we provide the first integrated comparative analysis of effects observed with supplementation of potassium silicate and SiNPs in mitigating 150 mM NaCl-induced salinity stress in chrysanthemum, with emphasis on antioxidant regulation, metabolite reprogramming, and stress-responsive gene expression. Hereafter, potassium silicate (K₂SiO₃) represents the soluble Si treatment, whereas silicon nanoparticles are designated as SiNPs. Silicon nanoparticles were characterized using Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD), revealing predominantly spherical, impurity-free nanoparticles ranging from 40-55 nm. Salinity stress caused severe oxidative damage, evidenced by increased malondialdehyde accumulation, whereas silicon supplementation significantly enhanced antioxidant defense. Activities of superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (POD) were elevated under combined salinity and Si treatments, with potassium silicate conferring more sustained protection during prolonged stress. Untargeted LC-MS/MS-based metabolomic profiling identified 195 differentially accumulated metabolites across treatments. Approximately 37% of metabolites were upregulated under salinity stress combined with Si, with marked enrichment of flavonoids, osmolytes, amino acids, and organic acids associated with reactive oxygen species (ROS) scavenging and stress adaptation. Gene expression analysis further revealed strong induction of CmNCED3A and CmCAT , indicating ABA-biosynthesis-associated and antioxidant transcriptional responses. Collectively, potassium silicate and SiNPs enhanced salinity tolerance through coordinated antioxidant defense, metabolic reprogramming, and stress-responsive gene expression.