| This paper aims to explore the changes in physiological and biochemicalcharacteristics of Nostoc flagelliforme under salt stress, and provide a theoretical basisand data support to Nostoc resources protection and resilience mechanisms. Cellmorphology, submicroscopic structure, cells growth status, photosynthetic pigments,polysaccharides, proteins, proline, salinty-induced lipid peroxidation and thecorresponding antioxidant activity changes were discussed in this study. Moreover,Nostoc flagelliforme cells grown unde salt stress were studied with regard topurification and the physico-chemical characterization of the extracellularpolysacchaarides (EPS) secreted in a liquid suspension culture. The main results wereshown as follows:1. Obvious changes displayed in cell morphology. Filament homogonium weredisintegrated and shorten into trichomes or unicells. The majority of cells werecongregated and surrounded by a transparent polysaccharide mucus layer.Theamplification and redistribution of the thylakoids within the salt-adapted cells involvethe reorganization of the photosynthetic unit and the redistribution of pigments. Withthe changes in thylakoids menbrane system, cell inclusions including cyanophycin,carboxysomes, glycogen granules, polyphosphate granules, poly-β-hydroxybutyrategranules and bigger gas vaculous were also triggered by salt stress. Accumulation andconsumption of endogenous energy storage material became the dominant in cellsmetabolism.2. The growth rate of Nostoc flagelliforme signigicantly inhibited in salt stress.Aninitial lag phase was observed before a new steady state growth was established. thephotosynthetic pigments composition in Nostoc flagelliforme are unchanged butdescreasing in level as a increasing concentration of NaCl. Content of chlorophyll a andphycocyanin decreased while that of carotenoids increased under salt stress. Salt stressenhanced the synthesis of extracellular polysaccharide. Osmotic adjustment substancessuch as intracellular soluble suger,proline and protein increased in salinty culture. Dueto the salinty-induced lipid peroxidation, permeability of plasma membrane and MDAcontents increased. Anti-peroxidase defense system played an important role inantioxidant mechanism of Nostoc flagelliforme. 3. The crude exoploysaccharide(EPS) was extracted from Nostoc flagelliformegrown under salt stress. Precipitated by ethanol after deproteinization. Two portions ofpolysaccharides(NFEPS-A and NFEPS-B) were prepared after separation on DEAEion-exchange cellulose column chromatography. Two portions of refinedpolysaccharides(NFEPS-A1and NFEPS-A2) were prepared after purification onSephadex G-100column chromatography. According to polyacrylamide gelelectrophoresis, each of the two polysaccharides was a single composition.4. White powder was got from pure polysaccharide NFEPS–A2by freeze-dried. Itis soluble in water but insoluble in organic solvents suche as acetone, chloroform,dimethyl sulfoxide. Moreover, the EPS does not contain starch and amino acids, withoutshorter side chains or fewer branches. It also does not contain reducing aldehyde orketone. The scanning electron microscope(SEM) analysis indicated that the EPSpossessed a porous structure and rough surface. It is non-sulfated polysaccharides, freeof protein and nuclear acid. The IR spectral analysis showed that there wereintramolecular hydrogen bond and intermolecular hydrogen bond in NFEPS-A2. Inaddition, the existences of stretching vibration of the carbon-hydrogen and deformationvibration of hydroxyl group and characteristic absorption of mannose pyranose werealso demonstrated. Its monosaccharide composition was determined by GC-MS toconsist of D-glucose, D-xylose, D-fructose, D-galactose, arabinose, the Tarot sugar,allose, etc. The removal efficiency hydroxyl radical (OH) and superoxide anion radical(O2-) were46.79%and40%respectively. The free radicals scavenging effect ofexopolysaccharide secreted by Nostoc flagelliforme grown under salt stress wasstronger than that of normal Nostoc flagelliforme. |
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