Effects Of Exogenous Salicylic Acid On ROS Metabolism And AsA-GSH Cycle In Nitraria Tangutorum Bobr. Under Salt Stress

Nitraria tangutorum Bobr.is a deciduous shrub belonging to the Nitraria genus in Nitrariaceae.It has strong resistance in the saline,arid,cold,barren and other adversity environment,in addition,N.tangutorum has a wealth of nutrition and high medicinal value,which is the economic and ecological benefits of both tree species and salt and the excellent plant resources for alkali to transform and use.N.tangutorum was used to study the the regulation of different concentrations exogenous SA on membrane lipid peroxidation,reactive oxygen species metabolism and ascorbate-glutathione（As A-GSH）antioxidant circulation system during salt stress.The results were showed as follows:（1）The relative water content of leaves decreased with NaCl concentration,after exogenous SA,the relative water content of leaves increased first and then decreased with the increase of SA concentration,when treated with 100 mmol·L-1 NaCl and SA was 0.5 mmol·L-1 which reached the highest value,while NaCl concentration ≥ 200 mmol·L-1 and the concentration of SA was 1.0mmol·L-1 reached the highest value.With the increase of NaCl concentration chlorophyll content decreased significantly,when the NaCl concentration reached 400 mmol·L-1,the chlorophyll content was significantly lower than that of other salt treatment groups,with the increase of SA concentration when treated with 100 mmol·L-1 NaCl,chlorophyll content increased,the increase of SA concentration in other salt treatments increased first and then decreased.（2）Under the salt stress,the cell membrane system was damaged,with the increase of NaCl concentration,the content of reactive oxygen species increased,malondialdehyde（MDA）accumulated,membrane lipid peroxidation increased,intracellular electrolyte extravasation.The concentration of SA（≤ 1.0 mmol·L-1）could decrease the content of superoxide anion radical(O₂^·-)and hydrogen peroxide（H₂O₂）in the leaves of N.tangutorum,and reduce the accumulation of MDA,which indicated that exogenous SA could reduce salt damage and the resulting oxidative stress.（3）The activities of superoxide dismutase（SOD）,catalase（CAT）and peroxidase（POD）in the leaves of N.tangutorum were significantly increased after the treatment with exogenous SA,and the activities of SOD and CAT increased significantly.The activity of SOD and CAT increased first and then decreased,and reached the highest value when the concentration of SA was 1.0mmol·L-1,the POD activity was higher than that of NaCl concentration ≤ 300 mmol·L-1.With theincrease in SA concentration.Exogenous SA promoted the formation of ascorbic acid（As A）and glutathione（GSH）in As A-GSH cycle under salt stress,and the best effect was alleviated at 1.0mmol·L-1,at the same time,the activity of key enzymes of ascorbate peroxidase（APX）,dehydroascorbate reductase（DHAR）,monodehydroascorbate reductase（MDHAR）and glutathione reductase（GR）were increased.APX,GR activity increased first and then decreased with the increase of salt concentration and SA concentration,DHAR activity and MDHAR activity were decreased and increased with increasing concentration of SA at 400 mmol·L-1 and 100 mmol·L-1NaCl,The MDHAR activity increased with the increase of SA concentration and then decreased with the increase of DHAR concentration,The results indicated that SA could effectively improve the efficiency of AsA-GSH and enhance the scavenging effect on reactive oxygen species.