非结构性碳水化合物与氮分配对美洲黑杨和青杨耐盐能力的影响

土壤盐渍化是阻碍林业发展的重要原因, 杨树(Populus spp.)是中国主要的人工林树种, 探究盐胁迫下植物的碳氮代谢特征与抗盐胁迫能力, 将有助于杨树人工林的可持续发展。该研究利用美洲黑杨(P. deltoides)和青杨(P. cathayana)两个物种, 采用去叶与不去叶处理, 在盐胁迫下研究两种杨树的抗逆性差异。研究发现, 盐胁迫下美洲黑杨的总生物量和光合能力均显著高于青杨。盐胁迫与去叶处理导致美洲黑杨叶绿素浓度和光系统II最大光量子效率显著高于青杨, 表明去叶对美洲黑杨影响较小, 但是加重了盐对青杨的毒害作用。美洲黑杨茎叶Na⁺浓度显著低于青杨, 表明美洲黑杨能够有效地限制Na⁺向地上部分运输。在盐胁迫条件下, 美洲黑杨茎和根比青杨能够维持更高浓度的淀粉、可溶性糖以及蔗糖, 前者较高的腺苷二磷酸葡萄糖焦磷酸化酶活性促进了光合产物向淀粉转换, 保证植物有充足的非结构性碳水化合物来参与渗透调节和维持其他生命活动, 而去叶使得青杨非结构性碳水化合物严重不足, 受盐胁迫影响更严重。盐胁迫下, 青杨分布在脂溶性蛋白(膜系统相关蛋白质)的氮浓度显著下降, 而NH₄⁺、谷氨酸脱氢酶活性与脯氨酸浓度显著升高。研究结果证明, 非结构性碳水化合物的积累、转化和分配是植物抗逆性的重要特征。     

Application of fluorophore-assisted carbohydrate electrophoresis to analysis of disaccharides and oligosaccharides derived from glycosaminoglycans

Various combinations of fluorescent dyes, polyacrylamide gels, and electrophoresis buffers were tested by fluorophore-assisted carbohydrate electrophoresis (FACE) for the purpose of analyzing sulfated and nonsulfated glycosaminoglycan (GAG) oligosaccharides in which disaccharides and low-molecular weight oligosaccharides were included. A nonionic fluorescent dye was found to be suitable for analyzing sulfated disaccharides derived from sulfated GAGs (e.g., chondroitin sulfate, dermatan sulfate) because sulfated disaccharides themselves had enough anionic potential for electrophoresis. The migration rates of chondroitin sulfate (CS) disaccharides in polyacrylamide gels were affected by the number of sulfate residues and the conformation of each disaccharide. When an anionic fluorescent dye, 8-aminonaphthalene-1,3,6-trisulfonic acid disodium salt (ANTS), was coupled with sulfated GAG oligosaccharides, nearly all of the conjugates migrated at the electrophoretic front due to the added anionic potential. Nonsulfated hyaluronan (HA) oligosaccharides (2-16 saccharides) were subjected to electrophoresis by coupling with a nonionic fluorescent dye, 2-aminoacridone (AMAC), but did not migrate in the order of their molecular size. Especially di-, tetra-, hexa-, and octasaccharides of HA migrated in the reverse order of their molecular size. HA/CS oligosaccharides were able to migrate in the order of their chain lengths by coupling with an anionic fluorescent dye in a nonborate condition.     

Seasonal Variation in the Chemical Composition of Tropical Australian Marine Macroalgae

The proximate chemical composition (ash, soluble carbohydrate, lipid and protein) was determined in 30 common species of tropical Australian marine macroalgae from Darwin Harbour (12^∘26′S, 130^∘51′E), in summer (hot and wet) and winter (cool and dry). There was a wide diversity of species in both seasons (19 species in summer and 20 species in winter). In most species, the major component was soluble carbohydrate (chlorophytes range 2.5–25.8% dry weight (dw), phaeophytes range 8.4–22.2% dw, rhodophytes range 18.7–39.2% dw) with significantly higher (p < 0.05) percentages only in winter season rhodophytes. Highest percentages of protein were found in rhodophytes collected in the summer (range 4.8–12.8% dw), with significantly lower percentages (p < 0.05) during winter. All species had lipid contents within the range 1.3–7.8% dw, with highest percentages in summer phaeophytes, but no significant differences between species or season. Most species had moderate to high ash contents (24.2–89.7% dw), with the highest percentages during summer. Compared with summer samples, macroalgae collected in winter had higher energy value and slightly lower percentages of inorganic matter. The variation of algal groups and chemical composition may influence the availability of the food source for the majority of herbivores, which in turn is likely to effect their ecology and community structure.     

C3 grasses have higher nutritional quality than C4 grasses under ambient and elevated atmospheric CO2

Grasses with the C₃ photosynthetic pathway are commonly considered to be more nutritious host plants than C₄ grasses, but the nutritional quality of C₃ grasses is also more greatly impacted by elevated atmospheric CO₂ than is that of C₄ grasses; C₃ grasses produce greater amounts of nonstructural carbohydrates and have greater declines in their nitrogen content than do C₄ grasses under elevated CO₂. Will C₃ grasses remain nutritionally superior to C₄ grasses under elevated CO₂ levels? We addressed this question by determining whether levels of protein in C₃ grasses decline to similar levels as in C₄ grasses, and whether total carbohydrate : protein ratios become similar in C₃ and C₄ grasses under elevated CO₂. In addition, we tested the hypothesis that, among the nonstructural carbohydrates in C₃ grasses, levels of fructan respond most strongly to elevated CO₂. Five C₃ and five C₄ grass species were grown from seed in outdoor open‐top chambers at ambient (370 ppm) or elevated (740 ppm) CO₂ for 2 months. As expected, a significant increase in sugars, starch and fructan in the C₃ grasses under elevated CO₂ was associated with a significant reduction in their protein levels, while protein levels in most C₄ grasses were little affected by elevated CO₂. However, this differential response of the two types of grasses was insufficient to reduce protein in C₃ grasses to the levels in C₄ grasses. Although levels of fructan in the C₃ grasses tripled under elevated CO₂, the amounts produced remained relatively low, both in absolute terms and as a fraction of the total nonstructural carbohydrates in the C₃ grasses. We conclude that C₃ grasses will generally remain more nutritious than C₄ grasses at elevated CO₂ concentrations, having higher levels of protein, nonstructural carbohydrates, and water, but lower levels of fiber and toughness, and lower total carbohydrate : protein ratios than C₄ grasses.     

Effect of Active Oxygen Radicals on Protein and Carbohydrate Moieties of Recombinant Human Erythropoietin

Our previous study showed that active oxygen radicals generated from a Fenton system and a xanthine plus xanthine oxidase system caused serious loss of in vivo bioactivity of recombinant human erythropoietin (EPO), a highly glycosylated protein. In the present study, we characterized the oxidative modifications to the protein and carbohydrate moiety of EPO, which lead to a reduction of its bioactivity. In vitro bioactivity was reduced when EPO was treated with oxygen radi cals generated from a Fenton system in the presence of 0.016 mM H₂0₂, and the reduction was directly proportional to the loss of in vivo bioactivity. SDS-PAGE analysis showed that dimer formation and degradation was observed under more severe conditions (Fenton reaction with 0.16 mM H₂0₂). The tryptophan destruction was detected at 0.016 mM H₂O₂ and well correlated with the loss of in vitro bioactivity, whereas loss of other amino acids were occurred under more severe conditions. Treatment with the Fenton system did not result in any specific damage on the carbohydrate moiety of EPO, except a reduction of sialic acid content under severe condition. These results suggest that active oxygen radicals mainly react with the protein moiety rather than the carbohydrate moiety of EPO. Destruction of tryptophan residues is the most sensitive marker of oxidative damage to EPO, suggesting the importance of tryptophan in the active EPO structure. Deglycosylation of EPO caused an increase of susceptibility to oxygen radicals compared to intact EPO. The role of oligosaccharides in EPO may be to protect the protein structure from active oxygen radicals.     

Impact of Chlorophorus caragana damage on nutrient contents of Caragana korshinskii

The amino acid, protein, carbohydrate, and mineral element contents and composition of the xylem, phloem, and leaves of healthy and insect-damaged Caragana korshinskii plants were analyzed to evaluate the changes in the nutrient content of C. korshinskii after damage by Chlorophorus caragana. The amino acid content decreased in the leaf and phloem but increased in the xylem in response to damage, while the protein content did not change in the leaf, increased in the xylem, and decreased in the phloem. The carbohydrate content increased slightly in the leaf but decreased in the xylem and phloem. The six mineral elements analyzed, namely, phosphorous, potassium, magnesium, zinc, manganese, and iron decreased in the xylem, phloem, and leaf. The present results may provide a basis for understanding the mechanisms underlying the effect of C. caragana on the loss of viability of C. korshinskii.     

Different regulation of leaf respiration between Spinacia oleracea, a sun species, and Alocasia odora, a shade species

Mature leaves of shade species exhibit lower respiratory rates than those of sun species. To elucidate the mechanism underlying different respiratory rates between sun and shade species, we examined respiratory properties of leaves in Spinacia oleracea L., a sun species, and Alocasia odora (Lodd.) Spach, a shade species, with special reference to changes in the respiratory rate throughout the night. In S. oleracea , rates of both CO₂ efflux and O₂ uptake decreased with time during the night, whereas in A. odora both rates were virtually constant at lower levels. The rates of O₂ uptake in S . oleracea increased upon addition of sucrose, and the rates attained were virtually identical throughout the night. However, the addition of an uncoupler [carbonyl cyanide p -(trifluoromethoxy)-phenylhydrazone; FCCP] did not alter the rates. In contrast, the rates of O₂ uptake in A. odora were enhanced by the addition of FCCP, but not by sucrose. The concentrations of carbohydrates in the tissue decreased throughout the night in both species and the ATP/ADP ratio was always greater in A. odora. These results indicate that, in S. oleracea , the availability of respiratory substrate determines the respiratory rate, while the low respiratory rate in A. odora is ascribed to its low demand for ATP.     

The effect of inorganic phosphate on the activity of bacterial ribokinase

Ribokinase and adenosine kinase are both members of the PfkB family of carbohydrate kinases. The activity of mammalian adenosine kinase was previously shown to be affected by pentavalent ions (PVI). We now present evidence that the catalytic activity of E. coli ribokinase is also affected by PVI, increasing both the velocity and affinity of the enzyme for d-ribose. The K_m for ribose decreased from 0.61 mM to 0.21, 0.25, and 0.33 mM in the presence of 20 mM phosphate, arsenate, and vanadate, respectively. The activity of ribokinase was stimulated in a hyperbolic fashion, with the maximum velocity increasing 23-fold, 13-fold, and 11-fold under the same conditions, respectively. Activity was also affected upon the addition of phosphoenolpyruvate, suggesting that phosphorylated metabolites could be involved in enzymatic control. The similar effect of PVI on distantly related enzymes suggests that a common mechanism for activity is shared among PfkB family members.