Effects Of Salt Stress On Chemical Structure And Biological Activity Of Nostoc Flagelliforme Extracellular Polysaccharide

Nostoc flagelliforme extracellular polysaccharide is an acidic heteropolysaccharide produced by the metabolism, and it has good economic value and medicinal value. Because of having salt tolerant protection mechanisms, the secretion of extracellular polysaccharide could significantly increase, the chemical structure and biological activity also changed in salt stress environment.This paper aims to explore the changes in structure and activity of Nostoc flagelliforme extracellular polysaccharide under salt stress, and provide a theoretical basis for Nostoc resilience mechanisms. The main contents include the changes of Nostoc flagelliforme cell morphology and the secretion of extracellular polysaccharide under different salt concentrations, and the effects of different salt concentration on chemical structure, antioxidant activity, antitumor activity, immune activity of extracellular polysaccharide.The main results were as follows:1.Nostoc cells under salt stress changed lighter and more yellow than control cells.The majority of cells congregated and surrounded by a transparent polysaccharide mucus layer. The secretion of extracellular polysaccharide increased by 27.6% and 45.0% when the concentration of NaCl were 0.1 and 0.3mol/L. Polysaccharide under different salt concentrations were extracted and purified, and the final polysaccharide content reached about 80%.2.IR spectroscopy showed that, NEPS,0.1M-YEPS and 0.3M-YEPS have obvious characteristic absorption peak of polysaccharides. Stretching vibration of hydroxyl and carboxyl groups of 0.1M-YEPS and 0.3M-YEPS significantly reduced or even disappeared.All of the polysaccharide under different salt concentrations showed low molecular weight. There were four glycosidic bond connections in 0.3M-YEPS that is-5) Ara (1-, Ara (1-,-3) Gal (1-and Gal (1-, and arabinose and galactose may be located on branches.3.Antioxidant analysis showed that salt stress can significantly increase the antioxidant capacity of Nostoc flagelliforme extracellular polysaccharide.The oxygen radical scavenging capacity of 0.1M-YEPS and 0.3M-YEPS were 2 times and 2.5 times than that of NEPS. The DPPH·and ABTS+·radical scavenging capacity of NEPS, 0.1M-YEPS and 0.3M-YEPS were enhanced, and showed a dose-response relationship.4.Extracellular polysaccharide under different salt concentrations could inhibit the proliferationin of tumor cells in a certain range of time and concentration,and showed a dose-dependent manner. The IC50 value of 0.3M-YEPS on HT-29 cells was 2.81mg/mL, but the inhibition rate of NEPS and O.1M-YEPS did not reach 50% in the range of experimental concentration; The IC50 value of O.1M-YEPS and 0.3M-YEPS on LoVo cells were 2.96mg/mL and 2.37mg/mL, the inhibition rate of NEPS did not reach 50% in the range either.So salt stress could increase the anti-tumor activity of Nostoc flagelliforme extracellular polysaccharide.5.The study of immune activity of extracellular polysaccharide under different salt concentrations showed that NEPS could not promote the proliferation of RAW264.7 cells,but 0.1M-YEPS and 0.3M-YEPS could promote it within a certain range of concentrations.The phagocytic capacity to neutral in red RAW264.7 cells were enhanced with 0.1M-YEPS and 0.3M-YEPS.Extracellular polysaccharide could increase the activity of SOD in RAW264.7 cells, and 0.3M-YEPS showed the highest activity, which indicated that salt stress can increase the immune activity of macrophage RAW264.7.