Mechanism of nitric oxide enhancing NaCl tolerance of barley seedlings based on physiol-biochemical analysis and LC-MS metabolomics

Abstract Nitric oxide (NO) is involved in the abiotic stress of plants and enhanced NaCl tolerance of barley seedlings. However, the internal mechanism is unclear. In this study, the physiology and metabolomics characteristics of barley seedlings with the present of NO and its specific scavenger 2,4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) under NaCl stress were investigated to understand the key function of NO in NaCl tolerance. Results showed that sodium nitroprusside (SNP; a NO donor) alleviated the growth inhibition and oxidative damage caused by 60 mM of NaCl. The 0.2 mM SNP treated barley seedlings exhibited higher antioxidant enzymes activity, total phenolic content, antioxidant capacity, and free amino acids content. However, the 0.5 mM of cPTIO induced the opposite effects. Based on the results of metabolomics analysis, it was found that SNP enhanced glycolysis, galactose, fructose and mannose metabolism, as well as amino acids biosynthesis and tricarboxylic acid metabolisms in barley seedlings compared with NaCl stress. These results indicated that NO could induce barley seedlings tolerance to NaCl stress depending on its roles in enhancing phenolics accumulation, antioxidation enzymes activity, antioxidant capacity as well as accelerating the carbohydrate metabolism and amino acids biosynthesis.