Effect Of Polysaccharides From Grateloupia Filicina On Rice Seeds Under NaCl Stress

Rice?Oryza sativa L.?is a salt-sensitive crop which could be suppressed by salt stress.In China,nearly 20%rice is affected by salinization land which is the key factor to decrease yield.For seed germination,it is very important for the weak resistance in defending salt stress,which could depress rice growth and development.A large number of studies have shown that seaweed polysaccharides could be used as fertilizer to improve plant resistance,and molecular weight might have an influence on the effect but mechanisms are not clear.So,we chose the Grateloupia filicina from Rhodophyta to degrade different Mws polysaccharides and studied their effects for rice seeds under salt stress,which could provide more theory for environmentally friendly anti-salt additive and polysaccharides high value utilization.First,we compared the traditional heating degradation and microwave irradiation degradation method,and studied the degraded parameters such as temperature,pH,H₂O₂ concentration and microwave power.In this research,improving temperature?70 ^oC-90 ^oC?and decreasing pH?pH 3-pH 1?could accelerate degrading,but the effects of enhancing H₂O₂ concentration?1%-3%?and microwave power?300 W-900 W?were limited.Finally,polysaccharides with different Mws?LGFP-1:40.8 kDa,LGFP-2:22.6 kDa,LGFP-3:5.1 kDa,LGFP-4:3.0 kDa?were prepared.The chemical characterization and structure were tested.Briefly,the content of sugar,sulfate,and protein was 52.4%-65.1%,13.5%-26.1%and 0.17%-0.95%separately,and monosaccharide was mainly composed of galactose.The infrared spectrogram showed that the degradation did not destroy the main sugar structure,and the scanning electron microscopy showed the low molecular weight polysaccharide with more clearly loose texture.Therefore,different molecular weight polysaccharides were applied to rice seeds under salt stress,and chitosan and Enteromorpha polysaccharides were compared.Through seed germination quality,LGFP-1 was chosen for the high seed germination potential,root length and vigor index.Furthermore,optimum concentration was decided at 0.1 mg/mL for the best germination quality.Next,the effects on physiological and biochemical were studied and the result showed that LGFP-1 could significantly improve proline content and the activity of SOD and POD which could alleviate the osmotic and oxidative stress under salt stress.For further study on the mechanism,FITC was linked to LGFP-1 and the result from confocal laser scanning microscope showed polysaccharide could be absorbed by root and shoot with different distribution.From the microscope,the fluorescence was more obvious in root than shoot.It's easy to find FITC fluorescence was in root epidermis cells,and fluorescence in shoot was sparse,and there was no fluorescence in cotyledon.At the same time,the effect on anti-salt gene was studied.LGFP-1 could significantly increase OsCLC1,OsCLC2 and OsSOS1 expression,especially OsSOS1 that is responsible for the ion regionalization of salt resistant,which suggested LGFP-1could enhance rice seed anti-salt activity by regulating genes.