Physiological Mechanisms Of Ryegrass Seed Germination And Seedling Growth In Response To Salt Stress

Ryegrass belongs to the family gramineous,which can be divided into annual ryegrass(Lolium multiflorum Lam)and perennial ryegrass(Lolium perenne L.).Both of the ryegrass is important forage and lawn grasses in China.Ryegrass is suitable for growing in warm and humid environments,and has strong resistance to the salt,alkali and barren stresses.Although the two ryegrasses have similarities in biological characteristics,there are still some differences in stress resistance,and the specific mechanisms are not clear.Seed germination and seedling growth are the most important stages for plants to survive in saline environment.Therefore,we used annual ryegrass and perennial ryegrass as experimental materials.Firstly,we studied the response of two ryegrass seeds to salt stress at different temperatures during germination stage,and then analyzed the response mechanisms of two ryegrass seedlings to salt stress from the perspective of physio logical and proteomics,which provided a theoretical basis for the study of stress resistance physiology of ryegrass.The main results of this experiment are as follows:(1)Under salt stress,the germination percentages of both ryegrass seeds reached highest under high temperature(annual ryegrass reached the highest in 20-30?,perennial ryegrass reached highest in 20-30 and 25-35?).Germination percentages of annual and perennial ryegrass seeds decreased significantly with increasing salinity.When the temperature was 10-20?,germination percentages of the two ryegrass seeds were more significantly affected by salt stress.The results also showed that annual and perennial ryegrass seeds had the highest recovery germination percentages under 400 mM salt stress,and the germination percentage of annual ryegrass seeds was higher than,perennial seed(the highest recovery germination of annual ryegrass seeds can reach 72.53%and the perennial ryegrass seeds can reach 63.3%).In addition,low temperature significantly reduced the recovery percentage rate of two ryegrass seeds.(2)Salt stress inhibited physiological parameters of annual and perennial ryegrass seedlings.With the increasing of salt stress,the biomass of two ryegrass seedlings decreased significantly.Compared with the control,the fresh weight of the two ryegrass under the 200 mM salt stress decreased by 51%and 63%,respectively.Photo synthetic pigment contents(Chl a,Chl b and Car)were also inhibited,and the content in perennial ryegrass was significantly higher than annual ryegrass.Moreover,salt stress also affected chlorophyll fluorescence parameters of the two ryegrass species(Fv/Fm??PS??NPQ?qp).Salt stress significantly increased the contents of Na+,Ca2+and Mg2+ in annual and perennial ryegrass seedlings,and also inhibited the absorption of K+,compared with the control,the K+content in the leaves of two ryegrass under high salt stress was inhibited by 31.8%and 20.8%,respectively.Furthermore,the contents of MDA,pro line and soluble sugar in annual and perennial ryegrass seedlings also increased,and their contents in perennial ryegrass were significantly higher than those in annual ryegrass.The POD,CAT,SOD and APX activities of the two ryegrass seedlings were significantly increased under salt stress.(3)We selected annual and perennial ryegrass leaves under 200 mM salt stress to be used for proteomic analysis.The results showed that 78 differentially accumulated proteins were identified in the leaves of two ryegrass species.Among them,37 kinds of proteins abundances were changed in annual ryegrass(8 proteins were up-regulated and 29 proteins were down-regulated)and 41 were changed in perennial ryegrass(6 proteins were up-regulated and 35 proteins were down-regulated).Most of them are involved in carbohydrate energy metabolism,photosynthesis,stress defense,amino acid metabolism and protein fate,which may play an important role in the adaptation of annual and perennial ryegrass to salt stress.(4)Through the functional analysis of annual and perennial ryegrass,we found that salt stress inhibited the glycolysis pathways of two ryegrass and the basic metabolic pathways such as TCA cycle,while some proteins related to Calvin cycle were down-regulated in annual ryegrass leaves.Some proteins associated with Calvin cycle were down-regulated in the leaves of annual ryegrass,but up-regulated in perennial ryegrass,indicating that the damage of photo synthetic electron transport by salt stress was alleviated.The results also found that under salt stress,the expression of germin-like protein related to stress defense in the leaves of annual ryegrass was down-regulated,but there was no significant change in the protein of perennial ryegrass leaves.However,the 14-3-3 protein family which related to signal transduction,was down-regulated in perennial ryegrass.In addition,protein spots associated with protein fate are also affected by salt stress.These results provide a theoretical basis for comparing the salt tolerance mechanism and metabolic regulation of annual and perennial ryegrass leaves.