The Physiological, Biochemical Responses And Detoxification Of Scenedesmus Obliquus To Heavy Metals Lead And Chromium

Heavy metal pollution has become a global concerned environment problem. Microalgaeare sensitive to heavy metal stress and can uptake and transport a certain amount of heavy metals,which lead it to be an important biosource of water environmental monitoring and heavy metalpollution prevention.In this paper, Scenedesmus obliquus was cultured in the modified BG-11medium,and the physiological,biochemical response and detoxification effect of Scenedesmusobliquus to heavy metals had been researched:1.By the methods of dry weight,liquid oxygen electrode,XE-PAM and enzyme activitydetection kits, the influence of three heavy metals (Pb2+、Cr3+、Cr6+) on the growth,photosynthetic performance, and antioxidant system of S.obliquus were investigated. The resultsshowed that the IC50of Pb2+, Cr3+and Cr6+were82.94μmol·L-1,121.15μmol·L-1and23.65μmol·L-1, respectively. Under the stress of IC50, the oxygen evolution rates of JNU49weresignificantly inhibited from2rd to8th day under Pb2+stress, from1st to3rd day under the stressof Cr3+and Cr6+; however, the respiration rates were not obviously affected. Under the stress ofPb2+, Fv/Fm, Yield and rETR of PSⅡin S.obliquus were obviously lower than the control,while qP was higher than the control from1st to5th day, and then became lower than thecontrol from6th to8th day; photosynthetic performance of S.obliquus was less influenced by thestress of Cr3+and Cr6+than that of Pb2+. Under the stress of heavy metals, MDA content ofS.obliquus increased significantly, especially on3rd and4th day; the activity of SOD increased,obviously on3rd and4th day; while the activity of CAT and T-AOC of S.obliquus increasedslightly as well. This study suggested that biomass concentration, photosynthetic rate,chlorophyll fluorescence parameters and SOD activities of S.obliquus were sensitive to the stressof heavy metals, these parameters could be taken as the indicators when evaluating the detrimentof heavy metals stress towards microalgae.2. By the methods of ICP-MS,qPCR and HPLC and, the removal efficiency in three heavymetals (Pb2+、Cr3+、Cr6+), PCS gene expression and PCs content of S.obliquus weremeasured.The results showed that the removal rates of Pb2+, Cr3+and Cr6+were51.52%（Pb2+）、69.64%（Cr3+）and70.86%（Cr6+）when S.obliquus was cultured in the heavy-metal containing medium for96hours.Under heavy metal stress, PCS gene expression quantity of S.obliquus hadbeen elevated in diffirent levels.The increment of PCS expression quantity was Cr6+>Cr3+>Pb2+in the first24hours,and was Pb2+>Cr3+>Cr6+in the last48hours.The total PCs contentsincrement were also different when S.obliquus was under different metal stress, and the resultshowed Cr3+> Cr6+> Pb2+. The total PCs reached the maximum when the S.obliquus werecultured for24hours, and the maximum were298.05nmol-SH·g-1FW (Pb2+),2203.26nmol-SH g-1FW (Cr3+) and473.97nmol-SH·g-1FW(Cr6+), and which were1.88,13.91,2.99folds of the control, respectively. Furthermore,none of PC3was detected in S.obliquus.The above studies showed that detoxification efficiency of diffirence metals of S.obliquuswere also different. And S.obliquus showed better detoxification efficiency for Cr3+and Cr6+thanPb2+.The stress of Pb2+on S.obliquus was slow and long-term,and lots of cells were dead in thelater culture period.On the contrary, the stress of Cr3+and Cr6+on S.obliquus was fast andshort-term,and the growth tendency nearly returned to normal.In this study,the stress effect of Pb2+, Cr3+and Cr6+on S.obliquus and the detoxificationefficiency of S.obliquus were discussed, and these results could provide a theoretical basis for theexploitation of microalgae biomarkers and aquatic environment treatment for heavy metalspollution.