Study On Effects And Assessments Of NaCl Stress On Seed Germination And Physiological And Biochemical Of Seedling Of Herbages

Herbages growing is an effective way to modify the saline land,and assessment of salt tolerance is the important foundation of screening,utilizing and popularizing germplasms of high quality herbages. It plays an important role in modifying and utilizing coastal salinization soil. In this study, 5 leguminous herbages such as Melilotus albus L.,Medicago stiva L.,Astragalus sinicus L.,Astragalus adsurgens Pall. and Coronilla variable L. were employed to analyze as test materials. Using 9 salt concentration gradients that was 0.0%(CK),0.2%,0.4%,0.6%,0.8%,1.0%,1.2%,1.4% and 1.6%,we made salt stress treatment to 5 herbages seeds in two stages that was seed germination and seedling growth. With determining some physiological and biochemical indexes,including relative germination rate,relative germination potential,salt tolerance index,seedling growth potential,relative water content,cell membrane permeability,Chlorophyll content,free proline content,MDA content,soluble sugar content and protective enzyme activity and so on, observing a series of physiological and biochemical response on salt stress treatment,and evaluating comprehensively,the order of salt tolerance could be obtained.The results showed that:(1) The sensitive concentration of of NaCl stress for 5 tested herbages were different.Low salt concentration (0.2%,0.4% and 0.6%) had promoting effect on seed germination of herbages.The relative germination rate of Melilotus albus,Medicago stiva and Astragalus adsurgens were higher than that in the control group.With the increase of salt concentration,relative germination rate and relative germination potential showed apparent downtrend.When the salt concentration was higher than 0.8%,relative germination rate and relative germination potential of tested herbages decreased a lot. When the salt concentration was 1.6%,relative germination rate and relative germination potential of tested herbages decreased to less than 72% and 70% respectively.Both showed significantly and extremely significant correlation with salt concentrations.(2) Low salt stress concentration had promotion effect on seedling growth of herbages.Between 0.2% and 0.8% salt concentrations,the seedling growth potential of 5 herbages were all higher than those in the control group.With the increase of salt concentration,seedling growth potential and salt tolerance index had the same change tendency as first increasing and then decreasing.(3) With the increase of salt concentration,the leaf relative water content of 5 herbages decreased,cell membrane permeability increased;Chlorophyll content,Chlorophyll a content and Chlorophyll b content showed similar changes on salt stress,the trend was first increasing and then decreasing.When the salt concentration was higher than 0.4%,the change of Chlorophyll content mainly attributed to the change of Chlorophyll a content. Chlorophyll a content showed significantly and extremely significant correlation with salt concentrations.The correlation between Chlorophyll b content and salt concentration were different relaying on the varieties of herbages.(4) The MDA content and soluble sugar content of 5 herbages varied according to varieties of herbages and salt concentration,both showed increasing at low salt concentration(less than 0.4%),and then decreasing significantly with the increasing of salt concentration.At the low salt concentration(0.2% and 0.4%),soluble sugar content of Melilotus albus,Astragalus adsurgens,Medicago stiva and Astragalus sinicus were higher than that in the control group,but Coronilla variable did not change significantly;different herbages had obviously different soluble sugar content, MDA content and soluble sugar content all showed extremely negatively significant correlation with salt concentrations.(5) The change of free proline content and three kinds of protective enzyme activity in 5 herbages showed first increasing and then decreasing trend with the increase of salt concentration.The change of free proline content showed different trends in different herbages,free proline content in Melilotus albus and Astragalus adsurgens were higher than that in the control group. When the salt concentration was higher than 1.0%, SOD activity of Medicago stiva,Coronilla variable and Astragalus sinicus decreased obviously,and SOD activity of Melilotus albus and Astragalus adsurgens had only small range of decreasing with the increase of salt concentration.When the salt concentration was 0.4%, POD activity and CAT activity appeared peak value,and with the increase of salt concentration,they decreased obviously.(6) Using principal component analysis to assess the index of salt tolerance,it showed that on the germination stage of herbages,the assessment index of salt tolerance of herbages seeds were relative germination rate,relative germination potential,salt tolerance indexand seedling growth potential;on the seedling growth stage of herbages,the first choice to assess salt tolerance were free proline content,Chlorophyll content,SOD activity and soluble sugar content.(7) Using membership function to assess comprehensively 5 herbages,it showed that the sequence of salt tolerance on the germination stage of herbages was Medicago stiva>Astragalus adsurgens > Melilotus albus > Coronilla variable > Astragalus sinicus;on the seedling growth stage of herbages,it was Melilotus albus>Astragalus adsurgens>Coronilla variable>Medicago stiva>Astragalus sinicus;on the two stages of growing, it was Melilotus albus>Astragalus adsurgens> Medicago stiva>Coronilla variable>Astragalus sinicus. Melilotus albus and Astragalus adsurgens could be planted on mild and moderate salinization land, Medicago stiva and Coronilla variable could be planted on mild or potential salinization land, Astragalus sinicus could not be tolerant of saline and alkaline,it could only be planted on potential salinization land.