Stable Isotope Ratios as a Tool for Assessing Changes in Carbon and Nutrient Sources in Antarctic Terrestrial Ecosystems

Samples of an angiosperm species, nine lichen species and a terrestrial alga, were collected from a variety of Antarctic terrestrial habitats, and were analysed for C and N stable isotope composition. Collections were made along natural gradients, the marine gradient, running from the sea coast inland and the moisture gradient, determined by melt water and precipitation runoff, and running towards the sea coast. Considerable variation in stable isotope ratios was found; δ¹³C values ranged between −16 and −32‰ and δ¹⁵N values between −23 and +23‰ The variation in stable carbon isotope ratios could be attributed in part to species specific differences, but differences in water availability also played a role, as was shown for the terrestrial alga Prasiola crispa and the lichen species Usnea antarctica. The differences in the isotope ratios of nitrogen could be retraced to the origin of nitrogen: marine or terrestrial. The nitrogen stable isotope ratios were influenced by both the marine gradient from the sea inland and the melt water and precipitation flow running in the opposite direction, towards the sea. This was shown for the lichen species Turgidosculum complicatulum and the angiosperm species Deschampsia antarctica. The variation in the C and N stable isotope ratios can be used to determine sources and pathways of N and changes in the water availability in Antarctic terrestrial ecosystems. Contrary to earlier reports the use of stable N isotope ratios is possible in this case because of the relative simplicity of the structure of the Antarctic terrestrial ecosystems.     

Use of isotopic signatures to assess the food web in a tropical shallow marine ecosystem of Southeastern Brazil

A dual isotope approach was used to assess the relative importance of terrestrial vegetation detritus and other primary producers in the trophic web of Flamengo Sound (Ubatuba, SP), SE Brazil, surrounded by the Atlantic Rain Forest. Primary producers showed distinct C signatures and the observed values suggest that little terrestrial or bulk sediment organic matter enter the food web of the sound. Suspended particulate organic matter (POM, supports the bulk of the consumers, with some contribution by macroalgae . Consumers C values ranged from −17.4 to . At least three trophic levels were detectable in the food web. The N value of POM was , while that of sediment and detritus was . The N values of suspension feeding benthic invertebrates were 8.2–, deposit feeders 8.3–, and carnivores 10.7–. Values for fishes were for detritivore, 11.4– for benthic feeders, 12.4– for zooplanktivores, and for piscivores/benthic invertebrate feeders. Squid mean value was . There is a reasonable agreement between feeding habits information from the literature and N values from this study. In the sound, the first and second trophic steps seem to be about 1– higher than those of similar organisms studied in temperate waters and this may reflect an input of allochtonous anthropogenic nitrogen enriched in ¹⁵N from human activities.     

Ectomycorrhizal colonization slows root decomposition: the post-mortem fungal legacy

The amount of carbon plants allocate to mycorrhizal symbionts exceeds that emitted by human activity annually. Senescent ectomycorrhizal roots represent a large input of carbon into soils, but their fate remains unknown. Here, we present the surprising result that, despite much higher nitrogen concentrations, roots colonized by ectomycorrhizal (EM) fungi lost only one-third as much carbon as non-mycorrhizal roots after 2 years of decomposition in a piñon pine ( Pinus edulis ) woodland. Experimentally excluding live mycorrhizal hyphae from litter, we found that live mycorrhizal hyphae may alter nitrogen dynamics, but the afterlife (litter-mediated) effects of EM fungi outweigh the influences of live fungi on root decomposition. Our findings indicate that a shift in plant allocation to mycorrhizal fungi could promote carbon accumulation in soil by this pathway. Furthermore, EM litters could directly contribute to the process of stable soil organic matter formation, a mechanism that has eluded soil scientists.     

血清GDF-15、FGF21与非酒精性脂肪性肝病患者肝纤维化和代谢综合征的关系研究

摘要 目的：研究血清生长分化因子15（GDF-15）、成纤维细胞生长因子21（FGF21）与非酒精性脂肪性肝病（NAFLD）患者肝纤维化和代谢综合征（MS）的关系。方法：选取我院2019年1月～2021年2月收治的102例NAFLD患者记作研究组。另选取同期健康体检志愿者100例作为对照组。比较两组血清GDF-15、FGF21与肝纤维化指标水平，并采用Pearson相关性分析明确血清GDF-15、FGF21与肝纤维化指标水平的关系。此外，将研究组患者按照是否并发MS分为MS组以及非MS组，比较MS组以及非MS组血清GDF-15、FGF21水平以及基线资料。采用多因素Logistic回归分析NAFLD并发MS的影响因素。结果：研究组血清GDF-15、FGF21水平高于对照组（均P＜0.05）。研究组血清透明质酸（HA）、层粘连蛋白（LN）、Ⅲ型前胶原（PCⅢ）以及Ⅳ型胶原（ⅣC）水平高于对照组（均P＜0.05）。经Pearson相关性分析发现，血清GDF-15、FGF21水平与血清HA、LN、PCⅢ、ⅣC水平均呈正相关关系（均P＜0.05）。经单因素分析发现，血清天冬氨酸氨基转移酶（AST）、丙氨酸氨基转移酶（ALT）、GDF-15、FGF21水平以及体质量指数、空腹血糖（FPG）、餐后2小时血糖（2hPG）、收缩压（SBP）、舒张压（DBP）、甘油三酯（TG）均和MS有关（均P＜0.05）。经多因素Logistic回归分析发现，血清AST、ALT升高是NAFLD并发MS的保护因素，而体质量指数、GDF-15、FGF21、FPG、2hPG、SBP、DBP、TG升高均是NAFLD并发MS的危险因素（均P＜0.05）。结论：血清GDF-15、FGF21与NAFLD患者肝纤维化以及MS均密切相关，可作为预测NAFLD患者肝纤维化以及MS的辅助性生物学指标。     

Structure and dynamics in solution of the complex of Lactobacillus casei dihydrofolate reductase with the new lipophilic antifolate drug trimetrexate

We have determined the three-dimensional solution structure of the complex of Lactobacillus casei dihydrofolate reductase and the anticancer drug trimetrexate. Two thousand seventy distance, 345 dihedral angle, and 144 hydrogen bond restraints were obtained from analysis of multidimensional NMR spectra recorded for complexes containing 15N-labeled protein. Simulated annealing calculations produced a family of 22 structures fully consistent with the constraints. Several intermolecular protein-ligand NOEs were obtained by using a novel approach monitoring temperature effects of NOE signals resulting from dynamic processes in the bound ligand. At low temperature (5 degrees C) the trimethoxy ring of bound trimetrexate is flipping sufficiently slowly to give narrow signals in slow exchange, which give good NOE cross peaks. At higher temperature these broaden and their NOE cross peaks disappear thus allowing the signals in the lower-temperature spectrum to be identified as NOEs involving ligand protons. The binding site for trimetrexate is well defined and this was compared with the binding sites in related complexes formed with methotrexate and trimethoprim. No major conformational differences were detected between the different complexes. The 2,4-diaminopyrimidine-containing moieties in the three drugs bind essentially in the same binding pocket and the remaining parts of their molecules adapt their conformations such that they can make effective van der Waals interactions with essentially the same set of hydrophobic amino acids, the side-chain orientations and local conformations of which are not greatly changed in the different complexes (similar chi1 and chi2 values).     

Assignment of cytosine N3 resonances in nucleic acids via intrabase three-bond coupling to amino protons

Coherences were observed between ¹⁵N3 of cytosine and its trans amino proton (H42) using a modified gradient-based heteronuclear single quantum coherence (HSQC) pulse sequence optimized for three-bond proton-nitrogen couplings. The method is demonstrated with a 22-nucleotide RNA fragment of the P5abc region of a group I intron uniformly labeled with ¹⁵N. Use of intraresidue ¹⁵ N3-amino proton couplings to assign cytosine ¹⁵ N3 signals complements the recently proposed J_NN HNN COSY [Dingley, A.J. and Grzesiek, S. (1998) J. Am. Chem. Soc., 120, 8293–8297] method of identifying hydrogen-bonded base pairs in RNA.     

Assessing potential bias in the determination of rotational correlation times of proteins by NMR relaxation

The various factors that influence the reliable and efficient determination of the correlation time describing molecular reorientation of proteins by NMR relaxation methods are examined. Nuclear Overhauser effects, spin-lattice, and spin-spin relaxation parameters of 15N NMR relaxation in ubiquitin have been determined at 17.6, 14.1, 11.7 and 9.4 Tesla. This unusually broad set of relaxation parameters has allowed the examination of the influence of chemical shift anisotropy, the functional form of the model-free spectral density, and the reliability of determined spin- spin relaxation parameters on the characterization of global tumbling of the protein. Treating the 15N chemical shift anisotropy (CSA) as an adjustable parameter, a consensus value of –170 ± 15ppm for the breadth of the chemical shift tensor and a global isotropic correlation time of 4.1ns are found when using the model-free spectral density to fit T1 and NOE data from all fields. The inclusion of T2 relaxation parameters in the determination of the global correlation time results in its increase to 4.6ns. This apparent inconsistency may explain a large portion of the discrepancy often found between NMR- and fluorescence-derived m values for proteins. The near identity of observed T2 and T1 values suggests that contributions from slow motions are not the origin of the apparent inconsistency with obtained T1 and NOE data. Various considerations suggest that the origin of this apparent discrepancy may reside in a contribution to the spectral density at zero frequency that is not represented by the simple model-free formalism in addition to the usual experimental difficulties associated with the measurement of these relaxation parameters. Finally, an axially symmetric diffusion tensor for ubiquitin is obtained using exclusively T1 and NOE data. A recommendation is reached on the types and combinations of relaxation data that can be used to reliably determine m values. It is also noted that the reliable determination of m values from 15N T1 and NOE relaxation parameters will become increasingly difficult as m increases.     

Difference in response of NK cell activity in newborns and adult to IL-2, IL-12 and IL-15

The killing activity of cord blood mononuclear cells (cMNC) against cytomegalovirus (CMV)-uninfected and -infected fibroblasts was comparable to that of adult peripheral blood mononuclear cells (aPBMC). The killing activity of cMNC against K562 cells was significantly lower compared with that of aPBMC. Treatment of cMNC and aPBMC with interleukin-2 (IL-2), IL-12 or IL-15 significantly enhanced killing activity against K562 cells and CMV-uninfected and -infected cells. By comparison of cMNC with aPBMC, killing activity against the K562 cells of cMNC was augmented to the level of aPBMC when cultured with IL-2, IL-12 or IL-15. The killing activity of cMNC against CMV-uninfected and -infected fibroblasts did not increase to the level of adult PBMC by treatment with IL-2, IL-12 or IL-15. These data suggest that cord blood contains a functionally different NK cell subpopulation than that among adult NK cells.