Molybdenum nanoparticle improved seed germination in Kale via regulating ROS homeostasis and metabolites accumulation under salinity stress

Seed germination is severely constrained by soil salinity, limiting crop establishment in salt-affected agricultural lands. This study investigated whether seed priming with molybdenum nanoparticles (Mo NPs) enhances germination and early seedling growth of kale (Brassica oleracea var. acephala) under NaCl stress compared with conventional bulk molybdate treatment. Seeds were primed with 100 mg L-¹ Mo NPs or bulk Na2MoO4 for 12 h, then germinated under 150 mM NaCl for 3 days. Physiological markers were measured at 24 and 72 h, while untargeted metabolomics was performed on 3-day-old radicles. Seedling performance was evaluated after 10 days of 150 mM NaCl in hydroponics. Salinity reduced germination by 45% and radicle fresh weight by 49.6% compared with control. Mo NPs priming increased germination by 18.8% and radicle fresh weight by 74.8% under salinity relative to bulk Mo treatment. Mo NPs -primed seeds maintained higher GA and melatonin contents, reduced ABA accumulation, and exhibited enhanced POD activity at 24 h. Metabolomics revealed sustained starch degradation (maltose, glucose-6-phosphate), TCA cycle intermediates (malate, isocitrate), and reduced GSSG/GSH ratio in Mo NPs +NaCl compared with NaCl alone. Proline accumulation shifted from suppression at 24 h to elevation at 72 h in Mo NPs-treated seeds. Seedlings from Mo NPs-primed seeds maintained higher shoot biomass, chlorophyll content, and photosystem II efficiency under prolonged salinity. We conclude that Mo NPs priming outperforms bulk molybdate by coordinating early antioxidant defense, hormonal balance, reserve mobilization, and metabolic flexibility, enabling kale seeds to overcome the salinity-induced germination reduction.