Response Of Nostoc Flagellifome To UV Radiation

Response of Nostoc flagelliforme to ultraviolet radiation was studied in this thesis.In order to explore the self-protection mechanism of Nostoc flagelliforme underultraviolet stress, we used the simulated UV radiation to treat the liquid suspensioncultured Nostoc flagelliforme cells and studied a range of physiological andbiochemical characteristics changes of Nostoc flagelliforme under UV-B radiation. Inthis thesis, we mainly studied the following aspects:First of all, The experimental results revealed the impacts of UV radiation on thephysiological characteristics of Nostoc flagelliforme from cell structure and metabolicpoints of view. After irradiating by UV-B radiation under5W/m2for different time, thecells size became smaller and the exopolysaccharides parcel layer was thicker, thethylakoids became loose and the whole carboxylase body scattered, not only declinedin the number but also smaller in size. Phycocyanin particles moved to the cells centerand phycobilisomes became smaller. Within the first12h of UV-B radiation, thechlorophyll a content increased near40%, though followed by a rapid decrease, thefinal chlorophyll a content was only10%less than the control after48h of radiation.The content of carotenoids increased about120%during the first12h, while thephycocyanin content declined slightly, which was less than1%, but sharply decreasewas observed from the12to48h. UV-B radiation caused the reduction of the totalcarbohydrate in Nostoc flagelliforme cells. The cells total carbohydrate contentdecreased around15%in12h, but slight change during12-48h was observed. At thesame time, the exopolysaccharides concentration increased17%after48h of UV-Bradiation. The protein and lipid amount decreased about60%and50%after irradiatedby UV-B for12and24h, respectively, while MDA content was still increasing. AfterUV-B radiation treatment, some amino acids such as Cys, Tyr, Phe, Met and Leureduced but others including Glu, Val, Gly, Ile, Pro and His increased. The UV-Bradiation induced growth inhibition of reovery culturing cells, however, logarithmicphase of cells growth could be observed after culturing.Secondly, we studied the response of photoprotective compounds andexopolysaccharides of Nostoc flagelliforme to UV-B radiation. The results showed thatUV-B radiation had obvious promoting effects on scytonemin and oligosaccharide-linked mycosporine-like amino acids (OS-MAAs) production. The scytonemin content increased103.9%after48h of exposure to1W/m2and164.0%at5W/m2. Theincrease of OS-MAAs content was145.4%and114.5%after12h at5W/m2and48hat1W/m2. HPLC analysis of total MAAs showed that composition of MAAs in liquidsuspension-cultured N.flagelliforme cells was different from that in natural colonies.The induction of MAAs under UV-B appeared to be uneven. The change of theradiation intensity caused the rise or fall of some MAAs concentration, and someMAAs were disappeared or emerged. After12h at5W/m2and36h at1W/m2UV-Bradiation, the carotenoids content increased near121.7%and139.3%. Prolineconcentration increased almost1.3times more than the control in12h under5W/m2UV-B radiation, although significantly decreased latter. During the recovery culturingperiods, short time of UV-B irradiated cells secreted more exopolysaccharides than thelong time UV-B irradiated. The increase of exopolysaccharides content was10%and42.8%of the cells irradiated for3and6h. The crude exopolysaccharides wereextracted. The UV and IR spectroscopy, apparent morphology reveled thatcharacteristics of the crude exopolysaccharides had changed. The ability of scavengingsuperoxide anion radical has been greatly improved.Finally, the crude exopolysaccharides were isolated and purified, two mainexopolysaccharides (NFPS1and NFPS2) were obtained. The physical and chemicalproperties of each polysaccharide were analysed. Results showed that NFPS1was ananalogue of the original N.flagelliforme exopolysaccharides, both had similarities insurface morphology, UV and IR spectroscopy, thermal stability, the relevant chemicalproperties, and monosaccharide composition. NFPS2, a suspected glycoproteincompounds with simple monosaccharide composition, has not been reported previously.In free radical scavenging test, the labor division of NFPS1and NFPS2was obvious.NFPS1scavenged more superoxide anion radicals than NFPS2, the clearance rate of0.05g/L NFPS1even reached over90%, while NFPS2had good ability of scavenginghydroxyl radical, which showed scavenging rate nearly60%at the concentration of0.05g/L.