Effects Of Pb Stress On The Growth And Physiological Characteristics Of Endophyte Symbiont Of Melica Transsilvanica

With the rapid development of global industry,heavy metal pollution is increasingly serious.A large number of studies indicate that plant microbial symbiosis can enhance host plants’ adsorption capacity and tolerance to heavy metals,and improve the remediation ability of soil heavy metal pollution.Melica transsilvanica is a perennial gramineous plant,which is only distributed in the northern slope of Tianshan Mountains and the arid shrub in Xinjiang,China,can be systematically infected by endophytic fungi and the plant is particularly flourishing on both sides of the highway.Melica transsilvanica seeds with the endophytic fungi(E+)and endophytic fungi free(E-)were used as the materials in this study,aiming to illustrate the changes of heavy metals on E+、E-seed germination,plant growth physiology and heavy metals content in plants;identify the symbiont can improve the tolerance to heavy metals.The results of this study will provides theoretical basis and basic information for using symbiotic to enhance the tolerance of heavy metals in plants effectively and prevention heavy metals pollution.The main results are as follows:1.Different concentrations of lead,cadmium,mercury and arsenic were used to stress the Melica transsilvanica seeds,in order to study the effect of heavy metal stress on the germination and plant growth.The results showed that Pb concentration of 5 mg/L,Cd concentration of less than 60 mg/L and Hg concentration of less than 50 mg/L are all promoted the germination rate of the seeds,while other concentrations are an exception.When Pb concentration was 800-1200 mg/L,Cd concentration was 9 and 150 mg/L,As concentration was 1 mg/L,E+seeds germination index was significantly higher than E-(P<0.05).The seeds with endophytic fungi were more tolerant to Pb stress than to Cd,Hg and As stress.2.Pot experiment was used to study the effect of Pb Stress on the growth characterisic of E+and E-,the results show that when the Pb concentration reaches 1500mg/L,compared with the control,the fresh weight of the root decreased by 82.5%(P<0.05);When the Pb Stress was 2000 mg/L,the total root length,root surface area and root diameter of E+were significantly higher than that of E-(P<0.05);When the Pb Stress was 1000 and 2000 mg/L,the Pb content in E+root was significantly higher than that in E-(P<0.05).the presence of endophytic fungi can alleviate the inhibition of Pb on the root system and the toxicity of Pb on the plant.3.Using pot experiment to investigate the effects of Pb stress on the Physiological Characteristics of Melica transsilvanica.The results indicated that Pb Stress was 2000 mg/L,MDA content of E+was significantly lower than E-(P<0.05).The activities of POD,SOD and CAT in the leaves of E+were significantly increased by 96.83%,25.66%and 42.55%compared with E-at Pb content less than 200mg/L.In conclution,Endophytic fungi can alleviate the damage caused by heavy metal stress and enhance the tolerance to Pb.