首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Aims The impacts of future global warming of 1.5°C and 2°C on the productivity and carbon (C) storage of grasslands in China are not clear yet, although grasslands in China support ~45 million agricultural populations and more than 238 million livestock populations, and are sensitive to global warming.  相似文献   

2.
3.
We studied Holocene speleothems and tufa samples collected in numerous caves and rivers in the Dinaric Karst of Croatia, Slovenia, Bosnia and Herzegovina, as well as Serbia and Montenegro. Differences in the formation process of tufa and speleothems are discussed in the context of their isotopic composition (14C, 13C and 18O), as well as the chemistry of surface water (rivers, lakes) and drip water (in caves). The physical and chemical parameters monitored in the surface water (tufa precipitation) and drip water (speleothem precipitation) show that more stable conditions accompany speleothem rather than tufa formation. This is particularly obvious in the water temperature variations (2-22°C in surface water and 7-12°C in drip water) and in saturation index variation (3-11 in surface water and 1-6 in drip water). The range of 14C ages recorded by Holocene speleothems (∼12?000 yr) is wider by several thousands years than that of Holocene tufa samples (∼6000 yr). δ13C values for tufa samples range from −12‰ to −6‰ and for speleothem samples from −12‰ to +3‰ reflecting higher soil carbon and/or vegetation impact on the process of tufa than on speleothem formation. The differences in δ18O values of tufa and speleothem samples from different areas reflect different temperature conditions and differing isotopic composition in the water. The study shows that speleothems from the Dinaric Karst can be used as global palaeoclimatic records, whereas tufa records changes in the local palaeoenvironment.  相似文献   

4.
The in-situ inter- and intracellular localization patterns of phosphoenolpyruvate (PEP) and ribulose 1,5-bisphosphate (RuBP) carboxylases in green leaves of severalPanicum species were investigated using an indirect immunofluorescence technique. Four species were examined and compared:P. miliaceum (C4),P. bisulcatum (C3), andP. decipiens andP. milioides (C3–C4 intermediates which have Kranz-like leaf anatomy and reduced photorespiration). In the C4 Panicum, PEP carboxylase was located in the cytosol of the mesophyll cells and RuBP carboxylase was restricted to the bundle-sheath chloroplasts. In contrast, in the C3 Panicum species, PEP carboxylase was found throughout the leaf chlorenchyma, in both the cytosol and chloroplasts, and RuBP carboxylase was located in the chloroplasts. For the C3–C4 intermediate plants, the patterns depended on the species examined. ForP. decipiens, the in-situ localization of both carboxylases was similar to that described forP. bisulcatum and other C3 plants. However, inP. milioides, PEP carboxylase was found exclusively in the cytosol of the mesophyll cells, as inP. miliaceum and other C4 species, whereas RuBP carboxylase was distributed in both the mesophyll and bundle-sheath chloroplasts.Abbreviations PEP phosphoenolpyruvate - RuBP ribulose 1,5-bisphosphate  相似文献   

5.
6.
7.
8.
Summary The 13C values of whole body samples of the beetle Tribolium castaneum are closely correlated with the 13C values of the plant carbon in its diet. The correlation is always high for diets ranging from 100% C4 to 100% C3 plant material. The degree of correlation is independent of the growth rate of the animals.  相似文献   

9.
10.
Galbanic acid (GBA) is an active sesquiterpene coumarin derivative, with various medicinal benefits, including anticancer properties. However, the low solubility of GBA is the main limitation of its clinical applications. In this study, we used a nanosystem based on poly (D, l -lactide)–polyethylene glycol (PLA–PEG), for the delivery of GBA to C26 colon carcinoma cells. The physicochemical characteristics of nanoparticles (NPs) prepared by the emulsification–evaporation method were evaluated. MTT assay was used to compare the anticell proliferation of GBA and PLA–PEG–GBA against C26 cell lines. PLA–PEG-NPs with an average size of about 140 nm had an enhanced release of GBA at a pH of 5.5 compared with a pH of 7.4. Cytotoxicity studies showed that the IC 50 of the PLA–PEG–GBA NPs (8 µM) was significantly lower than free GBA (15 µM). In the in vivo study, PLA–PEG–GBA NPs exhibited remarkable efficacy and reduced in vivo toxicity in C26 colon carcinoma tumor-bearing female BALB/c mice. To study the antiangiogenesis effect of the NPs, tumor sections were stained with an anti CD34 antibody. The results show the CD34 (+) vessels were decreased in the GBA and PLA–PEG–GBA treated mice by more than 75% and 90%, respectively. These results suggest that the encapsulation of GBA into the PLA–PEG could potentially be used for the treatment of colorectal cancer.  相似文献   

11.
The roundworm C. elegans is widely used as an aging model, with hundreds of genes identified that modulate aging (Kaeberlein et al., 2002. Mech. Ageing Dev. 123 , 1115–1119). The development and bodyplan of the 959 cells comprising the adult have been well described and established for more than 25 years ( Sulston & Horvitz, 1977 . Dev. Biol. 56 , 110–156; Sulston et al., 1983. Dev. Biol. 100 , 64–119.). However, morphological changes with age in this optically transparent animal are less well understood, with only a handful of studies investigating the pathobiology of aging. Age‐related changes in muscle ( Herndon et al., 2002 . Nature 419 , 808–814), neurons ( Herndon et al., 2002 ), intestine and yolk granules ( Garigan et al., 2002 . Genetics 161 , 1101–1112; Herndon et al., 2002 ), nuclear architecture ( Haithcock et al., 2005 . Proc. Natl Acad. Sci. USA 102 , 16690–16695), tail nuclei ( Golden et al., 2007 . Aging Cell 6 , 179–188), and the germline ( Golden et al., 2007 ) have been observed via a variety of traditional relatively low‐throughput methods. We report here a number of novel approaches to study the pathobiology of aging C. elegans. We combined histological staining of serial‐sectioned tissues, transmission electron microscopy, and confocal microscopy with 3D volumetric reconstructions and characterized age‐related morphological changes in multiple wild‐type individuals at different ages. This enabled us to identify several novel pathologies with age in the C. elegans intestine, including the loss of critical nuclei, the degradation of intestinal microvilli, changes in the size, shape, and cytoplasmic contents of the intestine, and altered morphologies caused by ingested bacteria. The three‐dimensional models we have created of tissues and cellular components from multiple individuals of different ages represent a unique resource to demonstrate global heterogeneity of a multicellular organism.  相似文献   

12.
Most methods of estimating chimpanzee population densities rely on nest counts. We tested the most frequently used techniques on a known chimpanzee community living in the rainforest of the Taï National Park, Côte d’Ivoire. The best density estimates are given by counts that assume groups of nests to be distributed randomly and that use the mean group size for homogenous habitat but the median for heterogenous habitats. Correction for real forest cover within the region should be made because chimpanzees make nests only in forested regions. This method gave the exact chimpanzee density for the Taï population, i.e. 1.7 nest builders/km2. For the nationwide survey, we first estimated the chimpanzee density for different types of habitat (e.g. intact primary forest: 1.64 chimpanzees/km2; degraded forests: 0.4 chimpanzees/km2; human encroached forests and mosaic habitats: 0.09 chimpanzees/km2). Second, we estimated the total forest cover of the country with satellite pictures. This gave an estimated chimpanzee population in Côte d’Ivoire of about 11,676 ± 1,168 individuals, which equals the number of spectators at a soccer game in an average European town. Sadly, only three National Parks may have chimpanzee populations large enough to be viable, whereas the rest are scattered and isolated small populations that are already threatened in their survival.  相似文献   

13.
In development, T cells first express their antigen receptors in the thymus, where they may undergo selection processes leading to major histocompatibility complex (MHC) restriction and tolerance. A high proportion of thymocytes are thought to fail this selection in some way and to be destined for intrathymic death. These cells are categorized as the cortical type since they constitute most of the cortical cells; they express both CD4 and CD8 antigens but only very low levels of MHC class I antigens. One suggested cause of thymocyte death is a failure to produce a functional T cell receptor (Tcr) due to errors in the rearrangements of germline DNA, resulting in V regions being absent or incorrectly spliced to the other segments of the transcribed gene. We have sequenced from the C region through to the V region of 14 rat Tcr chain clones isolated from thymocyte cDNA libraries. Of the 14, 13 have complete and correct rearrangements, whereas one was expressed from an unrearranged gene. Most of these clones are likely to be derived from the cortical population, for Northern blot analysis showed that these cells and total thymocytes expressed similar amounts of chain mRNA.Furthermore, the RNA from cortical-type cells contained a very similar ratio of full-length to truncated chain mRNA as did activated thymocytes and mature T lymphocytes. The data imply that defective chain gene rearrangement is not a major cause of failure in the selection of thymocytes. The sequences of the rat Tcr and chain constant regions are also reported.  相似文献   

14.
Feeding of benzoic acid-[7-14C], benzaldehyde-[7-14C] and cinnamic acid-[3-14C] to Ephedra distachya resulted in efficient incorporations of 14C into the α-carbon atom of the side chain of l-ephedrine. Thus ephedrine was shown to be biosynthesized by the condensation of a C6C1 portion which is derived from phenylalanine via cinnamate and an unidentified C2-N fragment.  相似文献   

15.
Summary Sperm whale apomyoglobin was expressed to high levels on minimal media and isotopically labeled with 13C and 15N nuclei. The isotopically labeled apoprotein was purified to homogeneity in a single step by reversed-phase chromatography and reconstituted with hemin and carbon monoxide gas for NMR analysis. Sequence-specific backbone 1HN, 15N and 13C as well as side-chain 13C resonance assignments have been made for over 90% of the amino acids in the carbon monoxide complex of the protein. Resonance assignments were made by analysis of a series of 3D triple resonance spectra measured on the uniformly labeled sample. These assignments will provide the basis for analyzing the effects of point site mutations on the structure, stability and dynamics of the protein in solution.  相似文献   

16.
17.
The stable carbon and oxygen isotope ratios in cellulose of C3 and C4 plants growing on the surface of a montane peat bog in the Nilgiri hills, southern India, were measured. The mean monthly δ13C values in cellulose of both C3 and C4 plants are found to be significantly related to rainfall, while the δ18O values are sensitive to changes in maximum temperature and relative humidity of the region. Further, higher δ18O values were observed in C4 plants compared to C3 plants, suggesting that C4 plants are probably less sensitive to relative humidity as compared to C3 plants and are able to photosynthesize even during drier conditions. The plant isotope-climate correlations thus established can be used for reconstructing the past temperature and rainfall conditions of the tropics from the isotopic ratios of peat deposits, derived from a mixture of C3 and C4 plants in the region.  相似文献   

18.
J. E. Reed  R. Chollet 《Planta》1985,166(4):439-445
The concentrations of 17 nucleotides and three nucleosides have been determined in a batch suspension culture of Datura innoxia using a new procedure for extraction, purification and high-performance liquid chromatography separation of these compounds. The nucleotide pools change appreciably in the different phases of growth. These changes indicate the preparation for and initiation of cell proliferation, and reflect metabolic events during cell division, cell elongation and starvation. The main components of the nucleotide pool are uracil nucleotides, with uridine 5-diphosphate sugars as the predominant fraction, and the adenine nucleotides. Although their concentrations vary by a factor of more than 6 the ratio of the uracil to adenine nucleotides is kept fairly constant during growth. The energy charge is maintained at a rather high value. The correlation of these events with nutrient uptake and macromolecular synthesis by the batch culture is presented in the following paper.Abbreviations Glc glucose - GlcNAc 2-acetamido-2-deoxy-d-glucose - HPLC high performance liquid chromatography - UDP uridine 5-diphosphate  相似文献   

19.
20.
Smoking is a risk factor for insulin resistance and metabolic syndrome. However, mechanisms responsible for smoking-induced insulin resistance are unclear. We examined the combined effect of nicotine, a toxic substance in tobacco smoke, and palmitate in the serum physiological concentration range on tumor necrosis factor-α (TNF-α) expression and impairment of glucose uptake in C2C12 myotubes, since smokers do not have increased serum free fatty acid (FFA) concentrations with insulin resistance compared to nonsmokers. C2C12 myotubes were incubated for 24 h with nicotine (1 μmol/l) in the presence or absence of palmitate (200 μmol/l). RT-PCR and Western blotting showed increased TNF-α expression in C2C12 myotubes treated with nicotine in the presence of palmitate. Furthermore, stimulation with nicotine in the presence of palmitate enhanced the production of reactive oxygen species (ROS) and activated the protein kinase C-nuclear factor-κB (PKC-NF-κB) pathway, as detected by dihydroethidium staining and Western blotting, respectively. Consequently, the translocation of GLUT4 to the plasma membrane as well as insulin-stimulated Akt phosphorylation was impaired, and glucose uptake to the myocytes was blocked. In addition, the production of ROS was suppressed by 4-hydroxy-TEMPO, and inhibition of GLUT4 translocation to the plasma membrane was canceled. These results suggest that in C2C12 myotubes, nicotine in the presence of palmitate enhanced the production of ROS and the expression of TNF-α through the PKC-NF-κB pathway; suppressed GLUT4 translocation to the plasma membrane; and impaired glucose uptake to cells. This pathway represents a possible mechanism by which smoking induces insulin resistance in the body.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号