Absorption Characteristics And Tolerance Mechanism Of Spirogyra To Lead

At present,heavy metal pollution is serious in major water systems in China,and some practical,economical and efficient technologies are urgently needed.Algae treatment of heavy metal polluted water is undoubtedly a good choice.In this paper,freshwater algae Spirogyra(Spirogyra.sp)was used to adsorb Pb in water,with different concentrations of Pb(0,0.5,1.0,2.5,5.0,7.5,10.0 mg/L)to cultivate Spirogyra and then determine Spirogyra growth and physiological indexes(RGR,soluble sugar,chlorophyll,MDA)change.It studied the Spirogyra to lead absorption ability and the subcellular distribution of lead in Spirogyra and chemical characteristics,and different times(1-7 d)Pb in the process of Spirogyra cells.The absorption characteristics of Pb were further analyzed by transmission electron microscope,TEM-EDX,FTIR and Freundlich isothermal adsorption model.The effects of different concentrations of Pb on the antioxidant enzyme activity(SOD,POD,CAT)and metal chelate(MT,PCs)of Spirogyra were studied to explore the tolerance mechanism of sponge to lead.The main results were as follows:1.Lead had certain influence on the growth of Spirogyra,showing that low concentration promotes growth,while high concentration inhibits growth.The relative growth rate(RGR)of Spirogyra treated with Pb less than 2.5mg/L was positive,while the RGR was negative when the concentration was higher.The effects on soluble sugar were shown as follows:0.5mg/L Pb increased soluble sugar content in Spirogyra,while Pb larger than 0.5mg/L inhibited soluble sugar,and Pb destroyed chlorophyll in Sptrogyra.When Pb concentration was higher than 5mg/L,MDA co:ntent increased significantly,and membrane lipid peroxidation of Spirogyra intensified.2.Spirogyra had a good enrichment and adsorption capacity for lead.In this experiment,the maximum adsorption capacity reached 2607.04mg/kg,and the maximum biological enrichment coefficient reached 475.38,belonging to the lead superaccumulator.As shown in the absorption process,lead ions were firstly absorbed by the cell wall in large quantities,and a small amount entered the cell interior,which is distributed in soluble components of the cell fluid.With the increase of treatment time,the proportion of lead absorbed by the cell wall decreased,and lead entering the cell interior was transferred from vacuoles to organelles and membranes.The distribution of lead subcells at different concentrations showed that a large amount of lead was found in cell walls(60%-69%),followed by organelles and membranes(20%-34%),and a small amount in soluble components of cell fluid(3%-20%).The Freundlich model could well explain the adsorption of lead by cell walls.3.TEM analysis showed that 7.5mg/L lead treatment caused damage to the structure of the Spirogyra membrane.EDX analysis showed that there were characteristic peaks of Pb in the cell membrane,organelles,vacuoles and other parts(weight percentage:45.72%-49.02%).4.Lead in Spirogyra existed in various chemical forms,mainly in the binding state of insoluble phosphoric acid(28%-63%)and oxalic acid(22%-38%).With the increase of lead concentration,the activity is higher,and the proportion of soluble inorganic lead and organic lead with greater toxicity increases.Cell wall fixation and chemical morphological transformation may be the important reasons for the high tolerance of Spirogyra cells.FTIR analysis showed that the main functional groups bound to lead ions were methyl and c-o polysaccharide skeletons.5.With the increase of lead concentration,SOD and POD activity first increased and then decreased.SOD activity was the highest when lead concentration was 5mg/L,and POD activity was the highest when lead eoncentration was lmg/L.CAT activity has been decreasing,possibly because Pb will destroy CAT enzyme structure.The proline content in Spirogyra was increasing.SOD,POD and proline may be the main measures for Spirogyra to deal with the peroxidation caused by lead poisoning.6.With the increase of lead concentration,the content of non-mercapto protein(NPT)and plant chelating peptide(PCs)in sponge first increased and then decreased.When the lead concentration was 2.5mg/L,the NPT content was the highest,which was 8.78 ? mol/g.PCs reached a maximum concentration of 4.09 ? mol/g at 5mg/L lead concentration.With the increase of lead concentration,MT content in cell fluid and organelle in Spirogyra increased,and MT content in cell wall first increased and then decreased,and MT content in cell fluid was the highest.