Synergistic effects of <sc>L</sc>-arginine and nitric oxide in alleviating nickel-induced phytotoxicity: reducing oxidative damage and enhancing antioxidant defense in rice.

Nickel (Ni) stress severely impairs rice growth and productivity by disrupting physiological functions and inducing oxidative damage. This study investigated the individual and combined effects of nitric oxide (NO) and L -arginine (L -Arg) in mitigating Ni toxicity in rice (Oryza sativa L.). Ni exposure reduced plant biomass, chlorophyll content, photosynthesis, water use efficiency (WUE), and membrane stability, and increased Ni uptake, reactive oxygen species (ROS), malondialdehyde (MDA), electrolyte leakage (EL), and methylglyoxal (MG). Antioxidant enzyme activities and osmolyte levels were also altered. Foliar application of NO or L -Arg partially alleviated these effects, but the combined treatment (NO+L -Arg) provided superior protection. Co-treated plants showed improved growth, chlorophyll content, gas exchange, relative water content (RWC), and leaf water potential. Oxidative stress markers (H2 O2 , MDA, EL, and MG) were reduced, whereas antioxidant enzyme and glyoxalase system activities were stabilized. Soluble sugar and glycine betaine (GB) levels were optimized, and Ni accumulation in tissues was significantly decreased. Notably, the combined treatment enhanced expression of stress-related and metal detoxification genes (OsMTP1 , OsPCS5 , HSP70 , and OsZIP1 ). These findings highlight the synergistic role of NO andL -Arg in enhancing rice tolerance to Ni stress and suggest its potential as a sustainable strategy for improving crop resilience in contaminated soils.