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981.
982.
Nuclear magnetic relaxation rates of H217O, 23Na+, and 25Mg2+ have been measured in aqueous hyaluronate solutions. The dependence on solution pH of the relaxation rates has been investigated, as well as the competition behavior of Na+ with Ca2+ and Mg2+. H217O and 23Na+ relaxation rates in chondroitin and hyaluronate solutions have been compared in the interval, 2 ? pH ? 12.5. The ion binding of hyaluronate can be fully accounted for by Coulomb interactions, with no need to involve chemical specificity. The hydration is only slighly pH dependent, and is comparable in magnitude to hydration of synthetic polyelectrolytes and monosaccharides. Ion-binding and hydration properties of hyaluronate and chondroitin are quite similar, except at elevated pH. At alkaline pH, an increase in charge density with pH is seen in hyaluronate and, to a much lesser degree, in chondroitin, possibly due to the titration of hydroxy groups. H217O data indicate an alkali-induced transition in both glycosaminoglycans. 相似文献
983.
Niche properties of Central European spiders: shading, moisture and the evolution of the habitat niche 总被引:4,自引:0,他引:4
Wiebke Entling Martin H. Schmidt Sven Bacher Roland Brandl Wolfgang Nentwig 《Global Ecology and Biogeography》2007,16(4):440-448
Aim Niche theory emphasizes the importance of environmental conditions for the distribution and abundance of species. Using a macroecological approach our study aimed at identifying the important environmental gradients for spiders. We generated numerical values of niche position and niche width. We also investigated relationships between these niche properties as well as the degree of phylogenetic conservatism in order to draw conclusions about the evolution of the habitat niche.
Location Central Europe: lowlands of Austria, Belgium, Germany, Luxembourg, the Netherlands and Switzerland.
Methods We analysed 244 published spider communities from 70 habitat types by correspondence analysis. The resulting community scores were used to test for correlations with habitat characteristics. Species scores were used to derive niche position (mean scores) and niche width (standard deviation of scores). To test for niche conservatism we estimated variance components across the taxonomic hierarchy.
Results The first two axes of the correspondence analysis were correlated with shading and moisture, respectively. Niche width had a hump-shaped relationship to both environmental gradients. β-diversity was strikingly higher in open habitats than in forests. Habitat niche conservatism was lower than phylogenetic conservatism in body size.
Main conclusions Environmental factors are important drivers for the β-diversity of spiders, especially across open habitats. This underlines the importance of preserving the whole range of moisture conditions in open habitats. Narrow niches of species occurring at the ends of both environmental gradients indicate that adaptations to extreme habitats lead to constraints in ecological flexibility. Nevertheless, the habitat niche of species seems to evolve much faster than morphological or physiological traits. 相似文献
Location Central Europe: lowlands of Austria, Belgium, Germany, Luxembourg, the Netherlands and Switzerland.
Methods We analysed 244 published spider communities from 70 habitat types by correspondence analysis. The resulting community scores were used to test for correlations with habitat characteristics. Species scores were used to derive niche position (mean scores) and niche width (standard deviation of scores). To test for niche conservatism we estimated variance components across the taxonomic hierarchy.
Results The first two axes of the correspondence analysis were correlated with shading and moisture, respectively. Niche width had a hump-shaped relationship to both environmental gradients. β-diversity was strikingly higher in open habitats than in forests. Habitat niche conservatism was lower than phylogenetic conservatism in body size.
Main conclusions Environmental factors are important drivers for the β-diversity of spiders, especially across open habitats. This underlines the importance of preserving the whole range of moisture conditions in open habitats. Narrow niches of species occurring at the ends of both environmental gradients indicate that adaptations to extreme habitats lead to constraints in ecological flexibility. Nevertheless, the habitat niche of species seems to evolve much faster than morphological or physiological traits. 相似文献
984.
Current alarm systems in intensive care units create a very high rate of false positive alarms because most of them simply compare physiological measurements to fixed thresholds. An improvement can be expected when the actual measurements are replaced by smoothed estimates of the underlying signal. However, classical filtering procedures are not appropriate for signal extraction, as standard assumptions, such as stationarity, do no hold here: the time series measured often show long periods without change, but also upward or downward trends, sudden shifts and numerous large measurement artefacts. Alternative approaches are needed to extract the relevant information from the data, i.e., the underlying signal of the monitored variables and the relevant patterns of change, such as abrupt shifts and trends. This article reviews recent research on filter-based online signal extraction methods designed for application in intensive care. 相似文献
985.
986.
Birgit Gielen Hans J. De Boeck Catherine M. H. M. Lemmens Roland Valcke Ivan Nijs Reinhart Ceulemans 《Physiologia plantarum》2005,125(1):52-63
Model ecosystems were grown in 12 sunlit, climate-controlled chambers to gain insight into the effects of elevated (+3°C) air temperature (Tair ) on temperate grasslands. In this study, the hypothesis of delayed senescence in response to elevated Tair was tested for Rumex acetosa L. and Plantago lanceolata L. During the autumn of the first treatment year, frequent measurements were made of leaf chlorophyll a (Chl a ) fluorescence transients. Chl fluorescence images of individual leaves as well as digital colour images of these ecosystems were captured. Chl fluorescence variables, such as the maximum quantum yield of primary photochemistry (Fv /Fm ), indicated a decreasing efficiency with time. Despite no treatment effect on Fv /Fm , other variables derived from the Chl fluorescence transients showed a strong trend towards a positive effect of a 3°C temperature increase on the photosynthetic performance of R. acetosa and P. lanceolata in the first year. After mid-September, the initial positive treatment effect disappeared for R. acetosa , strongly suggesting that leaf lifespan of this species was shortened by higher Tair . One possible explanation is more intense drought stress in the elevated compared to the ambient temperature treatments. Second-year measurements were possibly too limited in time to confirm this trend. These results show that temperate grassland species may take advantage of a future increase in Tair during autumn. This will ultimately depend on the species' degree of acclimation to a temperature change and on the resistance to drought stress. 相似文献
987.
The U3 Promoter and the nef Gene of Simian Immunodeficiency Virus (SIV) smmPBj1.9 Do Not Confer Acute Pathogenicity upon SIVagm 下载免费PDF全文
Stefan Wagener Matthias T. Dittmar Brigitte Beer Renate Knig Roland Plesker Stephen Norley Reinhard Kurth Klaus Cichutek 《Journal of virology》1998,72(4):3446-3450
Two chimeric proviruses comprising the U3 promoter and the nef gene of simian immunodeficiency virus (SIV) smmPBj1.9 in addition to other genomic regions of SIVagm3mc from African green monkeys (Cercopithecus aethiops) were constructed. The derived chimeric viruses (SIVagm3mc/SIVsmmPBj1.9) were both able to replicate in nonstimulated peripheral blood leukocytes from pig-tailed macaques (Macaca nemestrina), a biological property often correlated with acute pathogenicity. However, only one of the chimeric viruses was acutely pathogenic, inducing a rapid depletion of the peripheral CD4+ T cells in two infected pig-tailed macaques within 10 days after infection in a manner similar to infection with SIVsmmPBj1.9 itself. The other chimeric virus actively replicated during the first 8 weeks after experimental infection of two pig-tailed macaques but induced neither acute disease nor CD4+ T-cell depletion for 113 weeks after infection. Thus, the U3 promoter and the nef gene of SIVsmmPBj1.9 alone appear to be insufficient to confer acute pathogenicity to SIVagm3mc. 相似文献
988.
Pascale Hubert Roland Greimers Elizabeth Franzen-Detrooz Jean Doyen Pierre Delanaye Jacques Boniver Philippe Delvenne 《Cancer immunology, immunotherapy : CII》1998,47(2):81-89
Dendritic cells (DC) are the most efficient antigen presenting cells. The clinical use of DC as vectors for antitumor and
anti-infectious disease immunotherapy has been limited by their low level and accessibility in normal tissue. Substantial
numbers of DC can be generated from peripheral blood cultured in the presence of interleukin-4 (IL-4) and granulocyte/macrophage-colony-stimulating
factor (GM-CSF). We showed in this study that substantial numbers of DC can be obtained from the peripheral blood of patients
with (pre)neoplastic lesions of the uterine cervix. The procedure required relatively small blood samples (10 ml) and the
presence of 100 U/ml IL-4 and 800 U/ml GM-CSF in the culture medium. There was no significant difference in the morphology,
yield, phenotype and function of generated DC between patients with cervical (pre)neoplastic lesions and healthy individuals.
When the hematopoietic factor Flt3 ligand (Flt3L, 40 ng/ml) was added, there was an average increase in the DC population
of 26% compared to cultures with GM-CSF and IL-4 alone. Approximately 1.2 × 106 cells with the characteristics of dendritic cells could be obtained when Flt3L was included in the medium. The addition of
Flt3L did not modify the phenotypic profile of DC (HLA-DR+, CD1a+, CD4+, CD54+, CD80+, CD86+, CD40+, CD3− and CD14−). In addition, Flt3L generated functional DC capable of stimulating the proliferation of alloreactive T cells. These results
suggest that Flt3L, in association with GM-CSF and IL-4, provides an advantageous tool for the large-scale generation of DC
and that an immunotherapy based on the use of DC generated in vitro is possible in patients with (pre)neoplastic lesions of
the uterine cervix.
Received: 8 January 1998 / Accepted: 30 April 1998 相似文献
989.
The iron requirement of four strains of lactobacilli (L. acidophilus, L. delbrueckii subsp. bulgaricus, L. plantarum, and L. pentosus) was studied in a synthetic medium under aerobic or anaerobic conditions. Effects of iron salt and iron-chelated compounds
were tested on bacterial growth in manganese-free or -supplemented media. No significant growth stimulation was observed in
any condition. These results support the absolute manganese requirement for optimum growth of lactobacilli and the needless
incorporation of iron in growth media.
Received: 5 November 1997 / Accepted: 20 January 1998 相似文献
990.
Roland Abi Nahed Guillaume Martinez Jessica Escoffier Sandra Yassine Thomas Karaouzène Jean-Pascal Hograindleur John Turk George Kokotos Pierre F. Ray Serge Bottari Gérard Lambeau Sylviane Hennebicq Christophe Arnoult 《The Journal of biological chemistry》2016,291(6):3076-3089
Phospholipase A2 (PLA2) activity has been shown to be involved in the sperm acrosome reaction (AR), but the molecular identity of PLA2 isoforms has remained elusive. Here, we have tested the role of two intracellular (iPLA2β and cytosolic PLA2α) and one secreted (group X) PLA2s in spontaneous and progesterone (P4)-induced AR by using a set of specific inhibitors and knock-out mice. iPLA2β is critical for spontaneous AR, whereas both iPLA2β and group X secreted PLA2 are involved in P4-induced AR. Cytosolic PLA2α is dispensable in both types of AR. P4-induced AR spreads over 30 min in the mouse, and kinetic analyses suggest the presence of different sperm subpopulations, using distinct PLA2 pathways to achieve AR. At low P4 concentration (2 μm), sperm undergoing early AR (0–5 min post-P4) rely on iPLA2β, whereas sperm undergoing late AR (20–30 min post-P4) rely on group X secreted PLA2. Moreover, the role of PLA2s in AR depends on P4 concentration, with the PLA2s being key actors at low physiological P4 concentrations (≤2 μm) but not at higher P4 concentrations (∼10 μm). 相似文献