Response Mechanism Of Lemna Minor To Cobalt And Nickel

In the present study,the floating aquatic plant Lemna minor which are widely distributed was chosen as the experimental materials and the heavy metal cobalt(Co)and nickel(Ni)were chosen as the stress factors.The technology of plant physiology and biochemistry,high performance liquid chromatography,Native-PAGE combined with Fourier transform-infrared spectroscopy(FTIR)were used to investigate the stress effects of Co and Ni on L.mior.1.The content of photosynthetic pigments,soluble sugar,soluble protein,superoxide anion(O2-),hydrogen peroxide(H2O2),free amino acids,organic acids and the change of antioxidant systems(antioxidative enzymes and antioxidants)and FTIR of L.minor exposed to Co(0,100,150 or 200 ?M)for 7 d were analyzed.The changes of enzyme activity which are related to citric acid metabolism after Co stress and the influence of exogenetic citric acid on the growth of L.minor were studied.The results showed that L.minor can largely accumulate Co.The content of Co in L.minor treated with 200 ?M Co was 5426.33 mg kg-1 dry weight(DW).O2-and H2O2 detected by histochemical staining were slightly increased under the stress of Co.The content of chlorophyll a(Ch1 a),chlorophyll b(Ch1 b)and carotenoid(Car)were slightly decreased.Co caused significant effects on antioxidant system and osmotic adjustment substances.The activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)and the content of ascorbic acid(AsA),soluble protein showed increasing trend.However,the activity of ascorbate peroxidase(APX)was inhibited apparently.The activity of glutathione reductase(GR)and the content of glutathione(GSH),soluble sugar were firstly increased and then decreased with the concentration of Co increasing.The isoenzymic spectrum analysis demonstrated that APX isozyme expression quantity was declined,while SOD,POD and CAT expression quantity were increased with increasing Co level.In the detected amino acids,all amino acids were firstly increased and then slightly decreased.The contents of citric acid,malic acid and oxalic acid were increased obviously in L.minor.The content of citric acid in L.minor treated with 200 ?MCo was increased to 16.87 fold compared to the control.The activity of citrate synthase,malate dehydrogenase and phosphoenolpyruvate carboxylase were increased obviously and the activity of isocitrate dehydrogenase was decreased.Moreover,exogenous application of citric acid promoted the growth of L.minor in all groups.FTIR results showed that the absorbance of bands near 1068,1387,1649,2924 and 3421 cm'1 were elevated.It is indicated that the synthesis of organic acids,amino acids,peptides and carbohydrates(such as polysaccharides,cellulose,hemicellulose)had been promoted under Co stress.2.The content of photosynthetic pigments,soluble sugar,soluble protein,O2-,H2O2,free amino acid,organic acid,fatty acid and the change of antioxidant systems and FTIR of L.minor exposed to Ni(0,100,150 or 200 ?M)for 7 day were analyzed.The results showed that L.minor can massively accumulate Ni,the content of Ni can rich to 2012 mg-kg-1 DW in L.minor treated with 200 ?M Ni.Treated with Ni inhibited the growth of L.minor and induced injury in L.minor.O2-and H2O2 were accumulated in L.minor with Ni concentration increasing.The content of Ch1 a,Ch1 b and Car were decreased continuously.Antioxidant system and substances of osmotic adjustment in L.minor changed in different-level.The activity of POD was persistently increased while the activities of CAT and APX were decreased with Ni concentration increasing.SOD and GR activity firstly were increased and then decreased.The result of isoenzymic spectrum analysis was consistent with that of enzyme activity analysis.The content of GSH and AsA were continuously increased.The content of soluble sugar and soluble protein were increased at the low concentration of Ni but then decreased at high concentration.The content of Thr,Val,Ile,Phe were obviously increased while the content of Asp was obviously decreased.The contents of citric acid,malic acid and oxalic acid were increased at first and then decreased.The results showed that the content of linolenic acid was decreased and the content of palmitic acid was increased in overall level.FTIR results showed that the absorbance of bands near 1068 and 3421 cm-1 were continuously slightly elevated.However,the absorbance of bands near 1387,1649,2924 cm-1 were decreased at high concentration.It is indicated that the synthesis of organic acids,amino acids,peptides and carbohydrates(such as polysaccharides,cellulose,hemicellulose)had been promoted at low concentration of Ni.However,the synthesis of these kinds of compounds had been inhibited at high concentration of Ni.