Effect of nitric oxide on seed germination and seedling growth of Astragalus adsurgens under NaCl stress

The aim of this study was to clarify the physiological regulatory function of exogenous nitric oxide (NO) during Astragalus adsurgens seed germination and seedling growth. A. adsurgens was treated with different concentrations of sodium nitroprusside SNP solution as an NO donor under 0.3% NaCl stress and physiological indexes of seed germination and seedling growth were tested. The results showed that under the NaCl stress condition, SNP promoted seed germination and relieved damage at the seedling stage, at concentrations up to 200 μmoL·L-1. However, at the higher concentration of 300 μmoL·L-1, SNP inhibited seed germination and seedling growth. Damage to A. adsurgens seeds caused by 0.3% NaCl stress was significantly alleviated in the presence of 60 μmol·L-1 SNP. With SNP treatment under NaCl stress, the seed germination percentage, germination potential, germination index, vigour index, and radicle length were 22.6%, 54.5%, 58.20%, 112.00%, and 43.70%, respectively, as compared with controls subjected to NaCl stress without SNP treatment. These values were close to or slightly higher than those of untreated controls (without NaCl stress or SNP). Treatment with 120 μmol·L-1SNP significantly reduced the damage to the A. adsurgens seedlings under 0.3% NaCl stress. The chlorophyll content, superoxide dismutase, catalase, and peroxidase activities of A. adsurgens seedling leaves increased by 208.91%, 117.57%, 40.24%, and 89.95%, respectively, while the concentration of malondialdehyde decreased by 32.55%. In conclusion, our experiments demonstrated that an appropriate concentration of exogenous NO could improve seed germination, promote the synthesis of chlorophyll by seedlings, reduce the malondialdehyde content, relieve lipid peroxidation and protect the integrity of the chloroplast membrane, increase superoxide dismutase, catalase, and peroxidase activities, inhibit the accumulation of free radicals and peroxides, and accelerate the growth of seedlings. These physiological processes lowered the harm to A. adsurgens seedlings under salt stress conditions