Effects Of Ultraviolet-B (UV-B) Radiation On The Membrane System And DNA Of Nostoc Flagelliforme Cell

Liquid suspension cultivation of Nostoc flagelliforme cells under artificialsimulation of Ultraviolet-B (UV-B) radiation was studied in this thesis. In order toexplore the response of Nostoc flagelliforme cells to UV-B radiation, the effects ofmembrane system and DNA of Nostoc flagelliforme cells under UV-B radiation wasinvestigated. The main results were summarized as follows:(1) In order to research the impact of ultraviolet-B (UV-B) radiation on reactiveoxygen species(ROS) metabolism, the changes of reactive oxygen species(ROS)content, lipid peroxidation and antioxidant enzyme activitives of Nostoc flagelliformecells were determined. The results indicated that the contents of superoxide anion (·O2-)and hydrogen peroxide (H2O2) of Nostoc flagelliforme cells under low intensity (1W/m2) and high intensity (5W/m2) UV-B treatment increased，and the maximumof·O2-production reached under UV-B treatment for6h，that were480.62and510.34nmol·g-1DW, respectively. The H2O2content increased at all times and reached210.24å'Œ229.89nmol·g-1DW under UV-B treatment for48h.The malondialdehyde (MDA)content under UV-B radiation for48h attained0.085and0.147μmol g-1DW,whichwere251.70%and413.72%of the control;The membrane permeability of Nostocflagelliforme cells increased. The activities of superoxide dismutase (SOD) and catalase(CAT) reached the maximum at12h at both intensities. The ascorbate peroxidase (APX)activity increased in the early radiation（0-6h），then APX activity was unstable underlow intensity UV-B treatment and declined rapidly under high intensity UV-B treatment.(2) Nostoc flagelliforme cells membrane become partially distorted by UV-Bradiation treatment; The content of glycolipid and phospholipid decreased, beause theenzymes involved in lipid synthesis were destroyed by UV stress, which can lead to thesynthesis of glycolipid and phospholipid were blocked; The content of Nostocflagelliforme cells membrane protein eg.33kDa increased and protein eg.58kDa,114kDa were overproduced under UV-B radiation; Besides, the unsaturated fatty acidscontent of Nostoc flagelliforme cells were increased under UV-B radiation, whichcontributed to Nostoc flagelliforme cells for photosynthesis, unsaturated fatty acids canadjust the tolerance of cyanobacteria to UV stress, and help Nostoc flagelliforme cells tosurvive in the UV stress environment.(3) The effect of UV-B radiation on Nostoc flagelliforme cells DNA was studied with CTAB extract DNA method, the results were as follows: through the comparison ofvarious cell disruption methods, which the liquid nitrogen grinding method was best tobreak cells and extracted DNA with high purity, not easily degradable. Therefore, usingliquid nitrogen grinding to break cells, CTAB method to extract DNA, and DNAagarose gel electrophoresis to study the impact of UV-B radiation on Nostocflagelliforme cells DNA. The results showed that UV irradiation on Nostocflagelliforme cells DNA damage was not obvious under low intensity (1W/m2) for ashort time,and degradated for a long time; High-intensity UV-B irradiation could makeNostoc flagelliforme cells DNA completely degradated; UV-B radiation could causeNostoc flagelliforme cells DNA strand breaks; The fluorometric analysis of Nostocflagelliforme cells DNA unwinding (FADU) assay indicated that Nostoc flagelliformecells DNA strand breaks were related with radiation intensity and radiation time-related,but not directly proportional. The same intensity of UV-B treatment, the more seriousthe DNA strand breaks,the longer the time;The same time,with different UV-Btreatment intensity, DNA strand breaks were not significant.