Roles Of Alternative Pathway And Exogenous Hydrogen Peroxide In Salt Tolerance Of Nitraria Tangutorum Bobr.

Soil salinization seriously affects the growth and development of plant.It is important for us to study the salt-tolerance mechanism and the adjustment mechanism of halophytes under salt stress.And it has a great significance of salt-tolerant plants application to ecological restoration,and salt-tolerant crop breeding.Nitraria tangutorum Bobr.is a deciduous shrub belonging to the Nitraria genus in Nitrariaceae.It has excellent resistance to saline,drought,cold,barren environment,and it is the preferred vegetation for reconstructing saline-alkali land.In addition,N.tangutorum has high medicinal and economic value.N.tangutorum was used to study the roles of alternative pathway and exogenous hydrogen peroxide under salt stress.The results were showed as follows:（1）The respiration rate,alternative pathway respiration rate,SOD,CAT and APX activity of N.tangutorum Bobr.increased first and then decreased with the increase of salt concentration.However the relative water content,chlorophyll content,and POD,COX activities of the leaves decreased first,then increased and decreased at last.The maximum of respiration rate and alternative pathway respiration rate appeared under the 300 mmol·L^-11 NaCl stress,and the turning points of the other physiological indicators appeared under 200 mmol·L^-1 NaCl stress.It indicated that N.tangutorum Bobr.could adapt to low degree of salt stress by inducing alternative pathway capacity and regulating antioxidase activities,while more serious salt stress could inhibit the physiological metabolism of N.tangutorum Bobr.,resulting in low antioxidase activities,accumulation of ROS,and destruction of cell membrane integrity.（2）Under the salt stress,the trend of physiological indexes in leaves of N.tangutorum Bobr.were similar to that of NaCl with the pretreatment of SHAM.However,the relative water content,chlorophyll content,antioxidases,and COX enzyme activity of N.tangutorum Bobr.leaves were decreased when SHAM inhibited the alternative pathway.Compared to NaCl treatment,they had higher relative electrolyte leakgae,TBARS content,and ROS content.It promoted ROS accumulation in leaves and aggravated the damage of salt stress when the alternative pathway was inhibited.The results of the experiment showed that the operation of alternative pathway under salt stress help to increase the salt tolerance of N.tangutorum Bobr.（3）Under 200 mmol·L^-11 NaCl stress,when exogenous 1 mmol·L^-11 H₂O₂ pretreat the leaves of N.tangutorum,the leaf respiration rate,alternate pathway capaciety,V_alt/V,relative water content,chlorophyll content,and antioxidase activities and COX activity were higher than those of NaCl treatment,but relative electrolyte leakgae,TBARS content and ROS content were significantly decreased.In addition,after treated with H₂O₂ scavenger DMTU,the physiological indexes were lower than those of NaCl treatment.It further verifys that exogenous H₂O₂ can increase respiration rate,reduce lipid peroxidation and oxidative stress,and effectively enhances salt tolerance of N.tangutorum Bobr.