| Leymus chinensis (Trin.) Tzvel is a perennial rhizomatous Gramineae grass, it possesses some biological character such as high productivity, resistance to drought and salt stress, and it is dominant specie in the east of Eurasia steppe zone. It is also one of the major fine quality forage grass in the north of china. L. chinensis has much nutrient substance, and it can promote the growth of domestic animals in summer and autumn, so it is the fundamental forage grass in Mongolian Plateau. There are two ecotypes for L. chinensis according to leaf colour, the gray green type (GG) and the yellow green type (YG). The GG type is distributed in an extensive range of environmental conditions, including chernozem soil, forest brown soil, meadow and harsh saline soil, where soil pH can be more than 12; while the YG type can only found on mild saline meadow and chestnut soil. The intra-specific differences between the two types have received much attention in recent years, and the geographic demography, gas exchange and genetic diversity of the two type grasses have been well documented.The main products of plant photosynthesis are carbohydrates. Carbohydrate is one of the fundamental components of cell backbone, and important nutrient substance of plant growth. Plant often utilize sucrose, starch, galactose, maltose and glucose as carbon resource. Meanwhile, carbohydrate is a suitable solute, some small saccharides are very soluble in water and nontoxic at high concentrations, in this way, resistance to cold stress of some plants may be reinforced. Small molecular weight carbohydrate, such as sucrose and other oligosaccharides, is proved to be effective cryoprotectant. Water soluble carbohydrates are nontoxic to cell and have no inhibitory effect on metabolism, so moderate accumulation of water soluble carbohydrates can ensure normal cell turgor and metabolism under salt stress. Moreover, some flowering plants store fructans as reserve carbohydrates, and these reserve carbohydrates can ensure the carbon and energy supply for plant growth, furthermore, the reserve carbohydrate can promote plants to sprout, grow and reproduce when environment is well. The carbohydrate plays an important role in plant growth and development. Whereas the reports about the relationship between water-soluble polysaccharide structure and tolerance to abiotic stress of L. chinensis are little, so comparison research on physico-chemical property of two ecotype L. chinensis (GG and GY), e.g., monosaccharide composition, molecular weight distribution, degree of branching and extent of branching by side-chain substituents, has great significance to understand the mechanism of resistance to salt of two natural L. chinensis. The objectives of this research are to structurally characterize the molecular weight distribution, sugar composition and linkage form of polysaccharides from two L. chinensis growing in different salinification soil of the same steppe and determine any correlations between polysaccharide structure changes and tolerance of salt. Comparisons of polysaccharide changes of two L. chinensis may improve our understanding of intra-specific differences of resistance to salt between the two types. Neutral and alkaline salt stress were performed on seedlings of L. chinensis. The height, number, water content and content of sugar of the seedlings were tested after harvesting, moreover, the influence on growth and development of L. chinensis after neutral and alkaline salt stress treatment were discussed. Then the relationship between carbohydrate metabolism and salinity and alkalinity tolerance of L. chinensis were further understood through the research on water-soluble polysaccharide structure of two L. chinensis. we obtained the following results.(1) The mixed neutral salt was composed of NaCl:Na2SO4 = 9:1 (molar ratio), and the mixed alkaline salt consisted of NaHCO3:Na2CO3 = 9:1 (molar ratio), thus, total ion concentration of the two group mixtures was equal, meanwhile, each group included six concentration gradient, they were 60, 120, 180, 240, 300 and 360 mM. Hoagland nutrient solution was used as control. The stress effect of neutral salt and alkaline salt on the growth of L. chinensis was investigated in various proportions. The seedlings of L. chinensis were harvested after treating for seven days. The plant height, number and content of water were all tested and calculated, then all plants were separated into two parts, root and shoot. The homogenized dried samples powder of root and shoot were used to analyze the changes of soluble polysaccharide contents.The results showed that, comparing with L. chinensis before treatment, the increasing extent of seedlings after treating with neutral salt at 120 mM and 180 mM was larger than that of seedlings at 60 mM and 240 mM, moreover, increasing extent of seedlings at 240 mM was little. When the concentration increased up to 300 mM and 360 mM, the height of L. chinensis unexpectedly less than before, and this was because that some of plants had died under these two concentrations, the height of young seedlings was metered. As for seedlings treated with alkaline salt, the increasing extent was relatively high at 60 mM, while the seedlings growed little at 180 mM and 240 mM. By the same token, the height of the seedlings was also lower than that before alkaline treatment at 300 mM and 360 mM. It was concluded that the alkaline salt stress was more poisonous than neutral salt treatment.When the neutral salt concentration increased from 60 mM to 300 mM, the number of plants added, but the increasing extent was obviously low; the numbers of stressed L. chinensis seedlings had almost no change at 360 mM. When the alkaline salt concentration increased from 60 mM to 180 mM, the number of seedlings added, too, and the increment was small. It should be noted that the numbers of L. chinensis seedlings under alkaline salt stress increased little at 240 mM, and the number of plants was even lower than before when treating with 300 mM and 360 mM alkaline salt, it was because that some seedlings had died under these concentration. These results also strengthened the conclusion that alkaline salt stress was more poisonous than neutral salt on L. chinensis growth.For neutral salt stress, the water content of seedlings was reduced gradually as the salt concentration increasing, and the decrease extent was relatively small; at the same time, the water content of the seedlings treated with alkaline salt was reduced, too, further, the reducing extent was larger than that of neutral salt stress when alkaline salt concentration ranging from 60 mM to 300 mM.The percent contents of sugars in the dried root and shoot powder of L. chinensis treated with neutral salt and alkaline salt were calculated after analyzing with HPLC technology. The results indicated that the change tendency of polysaccharide was relatively obvious, while mannitose had little change, as for sucrose, glucose and fructose, the contents of them changed little. In conclusion, the polysaccharide might play an important role in salt tolerance of L. chinensis.(2) There are two L. chinensis ecotypes in steppe, the yellow green type (YG) and the gray green type (GG). Water soluble polysaccharides of YG and GG were extracted and fractionated to neutral and acid component, respectively, then monosaccharide composition of them was tested. The results showed that Man content of neutral and acid polysaccharides isolated from GG was higher than that of YG, while Glc content was lower than that of YG, this indicated that Man and Glc concerned with tolerance to salt stress of L. chinensis.(3) 13C-NMR analysis was performed for neutral polysaccharide of YG (Huang-N-6B) and GG (Hui-N-6B), respectively. The results showed that Huang-N-6B and Hui-N-6B were all composed of five monosaccharides, they were Glc, Gal, Ara, Man and Xyl. The monosaccharide residues of Huang-N-6B were mainly composed by 1, 4-linkage, there was no substituent group at position C-6 of Huang-N-6B, meanwhile, there were 3~5 methyl monosaccharides in the whole molecular, moreover, there was no reducing end, and there was methyl glycoside in the end residue of Huang-N-6B. Glc of Huang-N-6B had the 1, 4-linkage as the main connection way,α-Gal was the 1, 3-linkage, Xyl was the 1, 2-linkage. The monosaccharide linkage of Hui-N-6B were similar with Huang-N-6B, however,α-Gal andβ-Glc were reducing end in Hui-N-6B, and there were substituent groups at posotion C-6. Comparing with Huang-N-6B, the peaks of 62.85, 66.53 and 78.40 ppm suggested that the existance of 1, 4-α-Manp.Treating L. chinensis seedlings with incorporated neutral and alkaline salt, respectively. The results showed that effect of alkaline salt on height, number and water content of L. chinensis was more obvious than neutral salt, this demonstrated that toxic effect of alkaline salt was larger than neutral salt. Sugar concent of treated L. chinensis was also detected, and the conclusion was that polysaccharide isolated from the aerial and underground parts of L. chinensis react relatively obviously, however, other monosaccharide and oligosaccharide content changed little. The polysaccharide structure analysis showed that Man content of neutral and acid polysaccharide isolated from GG was higher than that of YG, while Glc content was lower than that of YG. The neurtral polysaccharides of GG and YG were further purified to give Hui-N-6B and Huang-N-6B, respectively, and structure comparison of Hui-N-6B and Huang-N-6B indicated that 13C-NMR spectrogram of Hui-N-6B had obvious Man chemical shift peak than Huang-N-6B, the conclusion was consistent with monosaccharide composition. These results indicated that Man and Glc of L. chinensis polysaccharide were relative to salt resistance. The relationship between polysaccharide structure and tolerance to salt stress of L. chinensis was analyzed, and the results were important to seed breeding of L. chinensis and other halotolerant plants. Glycoalkaloids, nitrogen containing secondary metabolites found in some Solanaceae and Liliaceae species. Glycoalkaloids is composed of aglycone and carbohydrate moiety. Extensive research have been performed on biological activities of glycoalkaloids. Glycoalkaloids possess antifungal, antitumor, insecticidal, and molluscicidal activities which were derived mainly from their abilities to disrupt membranes and to inhibit acetylcholinesterase. The researchers tried to find the action mechanism and evolutionary reason of glycoalkaloids. The Solanum plants eggplant (Solanum melongena L.) and potato (Solanum tuberosum L.) all contain two main glycoalkaloids, and the synergism of paired glycoalkaloids extracted from the same plant has been studied, but the synergistic phytotoxic effect of them are little.The phytotoxic effect of four glycoalkaloids and two 6-O-sulfated glycoalkaloid derivatives were evaluated by testing their inhibition of cucumber root growth. The bioassays were performed using both the single compounds and equal-molar mixtures, respectively. Cucumber root growth was reduced by chaconine (C), solanine (S), solamargine (SM) and solasonine (SS) with IC50 values of 260 (C), 380 (S), 530 (SM), and 610μM (SS). The inhibitory effect was concentration-dependent. 6-O-sulfated chaconine and 6-O-sulfated solamargine had no inhibitory effects, which indicated that the carbohydrate moieties played an important role in inhibiting cucumber root growth. The equal-molar mixtures of paired glycoalkaloids, both chaconine/solanine and solamargine/solasonine, produced synergistic effects on inhibiting cucumber root growth. By contrast, the mixtures of unpaired glycoalkaloids from different plants had no obviously synergistic effects. The growth inhibited plant roots lacked hairs, which implied that the inhibition was perhaps at the level of root hair growth. These results supported the hypothesis that two glycoalkaloids were synthesized at the same time and interacted synergistically to protect plants.
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