Effect Of Bacillus Subtilis QM3 On Lead Stress Of Wheat Roots

Heavy metal Pb seriously affect plant growth and development,it leads to a serious decline in agricultural crop yield,this has become an urgent problem,and bioremediation are getting more and more attention.It is very important to screen a strain that can not only reduce the lead pollution of heavy metals,but promote the growth of crops.Bacillus subtilis is a kind of biocontrol bacteria,it can not only promote the growth of plants but alleviate the heavy metal stress on plant,different strains has different mitigation effects.This paper took wheat as the experimental material,to study the effects of different concentrations of B.subtilis QM3 on the physical and chemical characteristics and the root tip cell morphology of wheat roots under Pb2+stress conditions,so as to provide theoretical basis for the study of the application of the new agricultural application in the mitigation of heavy metal stress in plants and the development of microorganisms.The main results and conlusions were as follows:(1)Heavy metal Pb had inhibitory effect on the growth of wheat roots.Pb stress can significantly reduce the root length,root surface area,root volume and root projection area,the inhibition increased with the increase of Pb2+concentration.Under Lead stress,B.subtilis QM3 had significantly promoted various indexes of wheat root,when Pb2+was 500 mg/L,107CFU/mL B.subtilis QM3 bacterial solution could respectively increase the root length,root surface area,rootvolume and root area by 43.37%,42.28%,237.80%,286.06%(p<0.05).(2)Pb stress made wheat root show a tendency that biomass and root activity increased first and then decreased,under the Pb2+of50mg/L both biomass and root activity reached the maximum,and the inhibition increased with the increase of Pb2+concentration,B.subtilis QM3 can promote wheat root biomass and increase root vigor of the wheat root under the Pb stress,when Pb2+was 250 mg/L,107CFU/mL B.subtilis QM3 bacterial solution could respectively increase the biomass and root activity by 6.87% and 99.93%(p<0.05).(3)The content of soluble sugar、soluble protein、Pro、MDA and the relative permeability of cell membrane(conductivity)were increased by Pb2+in wheat root.In low Pb concentration,different concentration B.subtilis QM3 could significantly reduce the content of the above substances in root and reduce the relative permeability of cell membrane,when Pb2+was 500 mg/L,107CFU/mL B.subtilis QM3 bacterial solution could reduce the relative permeability of cell membrane by 13.82%(p<0.05).(4)Under Pb2+stress,the activity of SOD、CAT、APX、POD of wheat root increased first and then decreased.B.subtilis QM3 could obviously increase the activity of SOD、CAT、APX、POD of wheat root under low Pb stress,when the concentration of Pb2+was 500 mg/L,107CFU/mL B.subtilis QM3 bacterial liquid could respectively increase the SOD、CAT、APX、POD by 5.38%,83.46%,44.17%,10.11%(p<0.05).(5)The content of GSH and AsA were first increased and then decreased by Pb2+in wheat root.When Pb2+concentration were 50、250、2000mg/L,B.subtilis QM3 could obviously increase the contentof GSH(P<0.05);at low Pb2+concentration,the treatment of B.subtilis QM3 could significantly increase the content of As A(p<0.05).(6)With the increase of Pb concentration,the thickness and width of the epidermal decreased first and then increased.when under low Pb stress,the cell morphology of the B.subtilis QM3 treatment group was more complete than the sterile water treatment group,while in the middle and high lead concentration,the cell morphology of the sterile water treatment group was more complete than B.subtilis QM3 treatment group;Under sterile water treatment,the thickness of cortex increased first and then decreased.Under B.subtilis QM3 treatment,when Pb2+concentration were 0、50、500mg/L,the root cortex thickness was less than the sterile water treatment group;when Pb2+concentration was 2000mg/L,107CFU/ml B.subtilis QM3 treatment group cortical thickness is greater than that of the control group,however,108、 106CFU/ml B.subtilis QM3 treatment group cortical thickness is lower than that of the control group.