Physiological Responses Of Danshen (Salvia Miltiorrhiza Bge.Var.Zhongjiang) To Salt Stress And Its Alleviation Effect Via Exogenous GA3 Addition

Salt tolerance of medicinal plant Salvia miltiorrhiza?var.Zhongjiang?was tesed through sand culture experiment in the greenhouse of Nanjing Agricultural University.The aim of the experiment is to study the growth status,osmotic regulation substances and antioxidant enzymes activity as well as ion distribution of the plant under salt-stressed conditions.Additionally we wondered if GA3 addition could alleviate plant injury induced by salt stress.The medicinal plant Salvia miltiorrhiza seedlings were cultured in 0?Control?,25,50,75 and 100 mM NaCl mM solutions for given time,and then two different concentrations of GA3?30 and 50 mg L-1?were applied.The main results are listed as follows:1.Low NaCl did not lead to plant substantial damage of the plant,showing no significant changes in physiological index;meanwhile low NaCl concentration could ensure better growth of the plant in their seedling stage.When salt concentration was up to 75 mM,Salvia miltiorrhiza Bunge seedlings appeared to be much more stressed,as the result of growth inhibition,decreasing chlorophyll Chl-b content,and increasing cell permeability.However,GA3 significantly alleviated growth inhibition induced by severe salt stress,this was mainly due to increasing Sp content in the plant leaves.2.Low NaCl concentration can activate active oxygen scavenging system in salvia miltiorrhiza earlier salt stress stage.CAT and SOD activities were significantly increased under salt stress as compared with the control.In 75mM NaCl treatment,SOD activity was mardedly higher CAT activity,indicating SOD played a more important role in scavenging reactive oxygen species then CAT;while ROS scavenging capacity was relatively weak under such concentration of salt stress.Results all showed that exogenous GA3 could not only significantly improve POD,CAT,SOD activity in the salvia miltiorrhiza seedling leaves,but reduce the content of MDA content in the plant leaves,which effectively alleviated the salt stress.3.Salt stress resulted in divergences on ion distribution in salvia miltiorrhiza seedlings In the low salt treatment,Na⁺ was mainly accumulated in the roots;whereas Na⁺ graduately transferred from roots to stems and leaves with increasing salt stress concentration.Under salt stress,the inorganic cations,such as K⁺,Ca²⁺ and Mg²⁺ was greatly accumulated.Salvia miltiorrhiza improved its salt tolerance mainly through increasing K⁺/Na⁺ ratio,so as to maintain the normal growth of Salvia miltiorrhiza under salt stress.Exogenous GA3 application could improve Na⁺ and K⁺ accumulation the roots.To effectively avoid Na+toxicity to shoot,K⁺ absorption was much higher in shoots than in roots.GA3 addition also increased Ca²⁺ uptake and storage capacity both in plant organs,which played a important role in ensuring cell stability and nutrients banlance.Ca²⁺ played a viture role in maintaining the normal growth of Salvia miltiorrhiza in their seedling stage.4.Exogenous GA3 addition could effectively hampered the decrease of Pn under salt stress.In the 50-100 range of mM,Pn was significantly increased ascompared with the control.GA3 can also increase Tr,and decrease Ci,which improved theutilization ratio of CO₂ cells.Under high salt stress,seedling cell wall,cell membrane of chloroplasts and mitochondria morphology of leaf Salvia miltiorrhiza were damaged to the great extent.However,exogenous GA3 addition improved the membrane morphology,stroma of chloroplast grana lamellae,morphology and structure of mitochondria under salt stress.Thus,a conclusion could be drawn that the exogenous GA3 addition could maintain a relatively good photosynthesis of leaf Salvia miltiorrhiza in their seedling stage under salt stress.