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51.
52.
Elodie A. Courtois Clément Stahl Joke Van den Berge Laëtitia Bréchet Leandro Van Langenhove Andreas Richter Ifigenia Urbina Jennifer L. Soong Josep Peñuelas Ivan A. Janssens 《Ecosystems》2018,21(7):1445-1458
The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO2, methane—CH4 and nitrous oxide—N2O) remains poorly understood in highly complex ecosystems such as tropical forests. We used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana Shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in these nutrient-poor tropical soils. Surprisingly, none of the three GHG flux rates differed with topographical position. CO2 effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH4 fluxes were best explained by variation in SWC, with soils acting as a sink under drier conditions and as a source under wetter conditions. Unexpectedly, our study areas were generally sinks for N2O and N2O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This first study describing the spatial variation of soil fluxes of the three main GHGs measured simultaneously in forests of the Guiana Shield lays the foundation for specific studies of the processes underlying the observed patterns. 相似文献
53.
Regulators of complement activity mediate inhibitory mechanisms through a common C3b‐binding mode 下载免费PDF全文
Federico Forneris Jin Wu Xiaoguang Xue Daniel Ricklin Zhuoer Lin Georgia Sfyroera Apostolia Tzekou Elena Volokhina Joke CM Granneman Richard Hauhart Paula Bertram M Kathryn Liszewski John P Atkinson John D Lambris Piet Gros 《The EMBO journal》2016,35(10):1133-1149
Regulators of complement activation (RCA) inhibit complement‐induced immune responses on healthy host tissues. We present crystal structures of human RCA (MCP, DAF, and CR1) and a smallpox virus homolog (SPICE) bound to complement component C3b. Our structural data reveal that up to four consecutive homologous CCP domains (i–iv), responsible for inhibition, bind in the same orientation and extended arrangement at a shared binding platform on C3b. Large sequence variations in CCP domains explain the diverse C3b‐binding patterns, with limited or no contribution of some individual domains, while all regulators show extensive contacts with C3b for the domains at the third site. A variation of ~100° rotation around the longitudinal axis is observed for domains binding at the fourth site on C3b, without affecting the overall binding mode. The data suggest a common evolutionary origin for both inhibitory mechanisms, called decay acceleration and cofactor activity, with variable C3b binding through domains at sites ii, iii, and iv, and provide a framework for understanding RCA disease‐related mutations and immune evasion. 相似文献
54.
Jan Hendrik Reinders Philip G. De Groot Mervin D. Gonsalves Joke Zandbergen Cornelia Loesberg Jan A. Van Mourik 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1984,804(3):361-369
Von Willebrand protein was synthesized and secreted by human endothelial cells in culture. Ca2+ ionophore A23187 and phorbol myristate acetate stimulated the release of Von Willebrand protein from the cultured cells. Stimulated release was accompanied by the disappearance of rod-like structures from the cultured endothelial cells immunostained for Von Willebrand protein, suggesting the existence of a storage organelle for Von Willebrand protein in these cells (Loesberg, C., Gonsalves, M.D., Zandbergen, J., Willems, C., Van Aken, W.G., Stel, H.V., Van Mourik, J.A. and De Groot, P.G. (1983) Biochim. Biophys. Acta 763, 160–168). Cultured human endothelial cells were fractionated on a density gradient of colloidal silica. Von Willebrand protein was found in two organelle populations: a buoyant one sedimenting with a variety of cell organelle marker enzymes, including those of the Golgi apparatus, mitochondria, lysosomes, peroxisomes, endoplasmic reticulum and plasma membrane fragments (peak density of this fraction: 1.08 g·ml?1), and a dense one with a peak density of 1.12 g·ml?1. The dense organelles containing Von Willebrand protein were apparently free of other organelles. Stimulating Von Willebrand protein release with phorbol myristate acetate or Ca2+ ionophore A23187 resulted in a decrease or even complete disappearance of Von Willebrand protein from the high-density organelle fraction, implying a role of this organelle in the stimulus-induced release of Von Willebrand protein. The Von Willebrand protein content of the buoyant fraction was lowered to some extent or did not change upon incubation of the cells with ionophore A23187 and phorbol myristate acetate. Restoration of Von Willebrand protein content of the dense organelle fraction after stimulation occurred within 2 days; this was accompanied by recurrence of immunostaining of rod-shaped structures in cells and an increase in cellular Von Willebrand protein. The excretion of restored Von Willebrand protein could be stimulated again. 相似文献
55.
Abstract The buoyancy regulation in light-limited cultures of the gas vacuolate cyanobacterium Microcystis aeruginosa AK1 was studied at three temperatures, 15, 20 and 28°C. At the two highest temperatures the organism remained buoyant during the entire light period, whereas at the lowest temperature the buoyancy was reduced at the start of the light period. With this temperature the buoyancy was lost during the light period. This reduced buoyancy was caused by an increase in ballast and a decrease in the gas vesicle volume. Buoyancy changes during a transient state with slow changes in temperatures, i.e., 1°C per day, were caused by changes in polysaccharide ballast. The gas vesicle volume showed no significant change during the transient state.
The maximal photosynthetic rate was dependent upon the growth and incubation temperature, whereas the light harvesting efficiency was independent of the temperature. The results are discussed in an ecological context. 相似文献
The maximal photosynthetic rate was dependent upon the growth and incubation temperature, whereas the light harvesting efficiency was independent of the temperature. The results are discussed in an ecological context. 相似文献
56.
Effect of nitrogen concentration on fructan and fructan metabolizing enzymes in young chicory plants (Cichorium intybus) 总被引:2,自引:0,他引:2
Witloof chicory seeds ( Cichorium intybus L. var. foliosum cv. Flash) were sown in acid-washed vermiculite in a controlled environment growth chamber. Plants received a nitrogen poor ("N-poor": 0.2 m M NH4 NO3 ) but otherwise complete medium, or a nitrogen rich ("N-rich": 2 m M NH4 NO3 ) medium. After 1 month of growth the fructan concentration in the "N-poor" plants was about five times higher and also the activity of sucrose:sucrose 1-fructosyl transferase (1-SST; EC 2.4.1.99) was twice as high as in "N-rich" plants. The activities of the catabolic enzymes fructan 1-exohydrolase (1-FEH; EC 3.2.1.80) and acid invertase (EC 3.2.1.26) were higher in the "N-rich" plants where significant energy was invested in root and leaf growth. After one month of growth, part of the "N-poor" plants were switched to the "N-rich" medium. One day after this switch, a sharp decrease in sucrose and glucose concentration was observed in the roots. During the following days, both the activities of 1-SST and fructan:fructan 1-fructosyl transferase (1-FFT; EC 2.4.1.100) decreased and the 1-FEH and invertase activities increased. These changes were correlated with a decrease in fructan concentration. Ten days after the switch, glucose and sucrose concentrations increased again and fructan synthesis resumed. During this period 1-SST activity increased and 1-FEH activity decreased. Apparently 1-SST, 1-FFT and 1-FEH simultaneously control fructan in young chicory roots. The rather unexpected finding that 1-FEH activity, which was believed to occur only in older material, can be induced in very young roots indicates that this enzyme can be induced at any physiological stage. 相似文献
57.
Jan B. W. J. Cornelissen Joke W. B. van der Giessen Katsuhisa Takumi Peter F. M. Teunis Henk J. Wisselink 《PloS one》2014,9(9)
High numbers of Toxoplasma gondii oocysts in the environment are a risk factor to humans. The environmental contamination might be reduced by vaccinating the definitive host, cats. An experimental challenge model is necessary to quantitatively assess the efficacy of a vaccine or drug treatment. Previous studies have indicated that bradyzoites are highly infectious for cats. To infect cats, tissue cysts were isolated from the brains of mice infected with oocysts of T. gondii M4 strain, and bradyzoites were released by pepsin digestion. Free bradyzoites were counted and graded doses (1000, 100, 50, 10), and 250 intact tissue cysts were inoculated orally into three cats each. Oocysts shed by these five groups of cats were collected from faeces by flotation techniques, counted microscopically and estimated by real time PCR. Additionally, the number of T. gondii in heart, tongue and brains were estimated, and serology for anti T. gondii antibodies was performed. A Beta-Poisson dose-response model was used to estimate the infectivity of single bradyzoites and linear regression was used to determine the relation between inoculated dose and numbers of oocyst shed. We found that real time PCR was more sensitive than microscopic detection of oocysts, and oocysts were detected by PCR in faeces of cats fed 10 bradyzoites but by microscopic examination. Real time PCR may only detect fragments of T. gondii DNA without the presence of oocysts in low doses. Prevalence of tissue cysts of T. gondii in tongue, heart and brains, and anti T. gondii antibody concentrations were all found to depend on the inoculated bradyzoite dose. The combination of the experimental challenge model and the dose response analysis provides a suitable reference for quantifying the potential reduction in human health risk due to a treatment of domestic cats by vaccination or by therapeutic drug application. 相似文献
58.
Joke A. Putseys Liesbeth J. Derde Lieve Lamberts Hans Goesaert Jan A. Delcour 《Carbohydrate polymers》2009,78(4):854-861
When amylose was synthesized using potato phosphorylase in the presence of amylose complexing lipids, monodisperse populations of amylose–lipid complexes were formed. Enzyme dosage and glucose-1-phosphate (glc-1-P)/primer ratio influenced the reaction rate of the enzymic synthesis, presumably by changing the balance between amylose synthesis and amylose–lipid complexation and precipitation, and impacted the molecular weight of the complexes. Lipid characteristics affected the dissociation properties and amylose chain lengths of the amylose–lipid complexes presumably by determining the minimal amylose chain length necessary for complexation and precipitation. Tailor made short chain amylose–lipid complexes can hence be produced by choosing the appropriate reaction conditions. We propose a synthesis mechanism in which the primer is elongated until an amylose chain is obtained which is of sufficient length to complex a first lipid. Further chain extension then occurs, together with subsequent complexation until the complex becomes insoluble and precipitates. 相似文献
59.
Virgil E. C. J. Schijns Christel M. H. Wierda Thomas W. Vahlenkamp Marian C. Horzinek Raoul J. de Groot 《Immunogenetics》1995,42(5):440-441
The nueclotide sequence data reported in this paper have been submitted to the EMBL nucleotide databse and have been assigned the accession number X86972 相似文献
60.
Geert-Jan de Klerk Wim van der Krieken Joke C. de Jong 《In vitro cellular & developmental biology. Plant》1999,35(3):189-199
Summary Considerable progress has recently been made in understanding adventitious root formation using physiological studies. It
is recognized that rooting is a process consisting of distinct phases, each with its own requirements. In this review, the
successive phases in the rooting process are described and the possible roles of wounding-related compounds, auxin, ethylene
and phenolic compounds during these specific phases are discussed. Recent results are assisting the development of advanced
rooting treatments. Molecular studies on rooting are underway and will be essential in revealing the mechanisms underlying
adventitious root formation. 相似文献