Effect Of Exogenous Nitric Oxide On The Growth Of Chlorella Vulgaris Under The Stress Of CTAC And Flu Combined Pollution System

When two or more contaminations with different properties or from different sourcescoexisted in the same environment medium, there are reciprocal interactions amongthem. These phenomena, which are ubiquitous in actual aquatic environment, have beencalled combined pollution. The research of combined pollution and its mechanism isone of the priority directions in environmental chemsitry at present. The toxicity ofcombined pollution generally displays a synergistic, additive or antagonistic effect. Dueto the high toxicity, synergistic effect of combined pollution has been foucsed byresearchers. Alleviating the toxicity of synergistic effect is crucial for controling theecological risk combined contaminants in aquatic systems. In recent years，Nitric oxide(NO) has been aroused people’s widespread attention for its unique physiologicalfunction. NO is an activity molecule which widely exists in the organism (includinganimals, plants and microorganism). NO can be synthesised by enzyme or non enzymecatalytic synthesis pathway in plants. Many researches showed that NO plays animportant role in regulating physiological process such as seed germination, growth,aging, respiration and resistance stress and so on.Based on the previous research of our group, this thesis investigated the effect ofSNP, an exogenous NO-donor, on the joint toxicity of binary mixtures of CTAC andFlu (CTAC/Flu), which are representatives of surfactants and Polycyclic aromatichydrocarbons (PAHs) respectively, in a unicellular green alga Chlorella vulgaris. Theeffect of SNP on the biomass, chlorophyll content, soluble protein content, levels ofMDA, H2O2and ROS, and the catalytic activities of antioxidant enzymes, includingSOD, POD and CAT have been investigated with Chlorella vulgaris in a96h exposureto CTAC/Flu. The results are listed as follows:(1) Under the combined pollution system of CTAC and Flu stress, compared toexogenous NO donor nitrosoglutathione (GSNO) andS-Nitroso-N-acetyl-DL-penicillamine (SNAP), Sodium Nitroprusside (SNP) has a moresignificant effect on the biomass of Chlorella vulgaris. Compared to the control group,the inhibition of biomass C. vulgaris was increased with addition of20μM SNP, whichshowed that the low concentration of SNP relieved the toxic effects by the compoundpollution system of CTAC and Flu in Chlorella vulgaris. On the contrary, the algalbiomass was reduced with the addition of100μM SNP, which showed that highconcentration of SNP increased the inhibition by the combined pollution system of CTAC and Flu in C. vulgaris.(2) SNP has a significant effect on the chlorophyll content (chlorophyll a, chlorophyllb and total chlorophyll) and soluble protein content under the stress of combinedpollution system of CTAC and Flu in C. vulgaris. With the addition of low SNP (20μM)in the combined pollution system of CTAC and Flu (100/2.5μg/L), algal chlorophyll a,chlorophyll b, total chlorophyll and soluble protein content increased from3.18,2.33,5.14and70.45mg/L to4.86,3.52,6.82and102.81mg/L, respectively. However withthe addition of high concentration of SNP (100μM), algal chlorophyll and solubleprotein dramatically decreased. These results showed that the improvement of resistingadversity ability of C. vulgaris by the addition of exogenous NO was related to thevariation of chlorophyll and soluble protein content.(3) SNP caused a significant effect on the activity of antioxidant enzyme and theactive of ROS in C. vulgaris under stress of the combined pollution system of CTACand Flu. The addtion of low concentration of SNP (20μM) can significantly reduce theaccumulation of malondialdehyde (MDA) in C. vulgaris, decrease the content of nitricoxide (NO), hydrogen peroxide (H2O2) and reactive oxygen species (ROS), but increasethe activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT).These showed that supplementation of low concentration of SNP reduced H2O2, ROSand MDA induction by CTAC/Flu through enhancing the activities of antioxidantenzymes, such as SOD, POD and CAT. On the contrary, high concentration of SNP(100μM) aggravated the peroxidation damage in C. vulgaris by the stress of combinedpollution system of CTAC and Flu. In conclusion, these results demonstrated that thedamage of surfactants and PAHs combined pollution in hydrobios can be alleviatedvia reducing the production of oxidizing substances with an exogenous supply of NOin a certain concentration range.