Salicylic Acid and Spermidine Priming Boosts Rice Resistance to Potassium Deficiency-Induced Oxidative Stress

Potassium (K) deficiency is a widespread nutritional stress that significantly limits rice productivity by impairing growth and physiological functions. To address this challenge, we hypothesized that seed priming with salicylic acid (SA) or spermidine (SPD) could enhance seedling performance and stress tolerance under low-K conditions. This study evaluated the physiological, biochemical, and molecular responses of rice seedlings primed with SA and SPD when grown under potassium-deficient conditions. Both priming treatments significantly improved nutrient uptake and biomass accumulation, with shoot dry weight increasing by 36.9% under SA and 42.8% under SPD, and root dry weight increasing by 56% and 50%, respectively, compared with Water-K primed stressed seedlings. SA and SPD also reduced cell membrane damage, consistent with their role in mitigating oxidative stress. Notably, leaf malondialdehyde (MDA) levels reduced by 10.6% under SA and 10.9% under SPD, while root hydrogen peroxide (H₂O₂) levels reduced by 7.6% and 21%, respectively. In vitro assays demonstrated that SPD selectively scavenged superoxide radicals (O₂⁻) in dose-dependent manner, although it did not directly reduce H₂O₂ levels, suggesting a specific ROS-scavenging role. At the molecular level, priming particularly with SPD strongly upregulated genes associated with polyamine biosynthesis, including arginine decarboxylase (OsADC1), spermidine synthase (OsSPDS1 and OsSPDS3), and S-adenosylmethionine decarboxylase (OsSAMDC2). Overall, SPD priming conferred greater physiological and molecular benefits than SA, promoting enhanced seedling growth, improved ion homeostasis, and stronger stress resilience under K deficiency. These findings highlight seed priming SPD as a promising strategy to boost rice performance in low-K environments and support sustainable nutrient management.