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排序方式: 共有88条查询结果,搜索用时 15 毫秒
31.
Kasper Reitzel Stephan Lotter Mirjam Dubke Sara Egemose Henning S. Jensen Frede Ø. Andersen 《Hydrobiologia》2013,703(1):189-202
Effects of chironomids on sediment–water exchange of nutrients and their impact on the efficiency of Phoslock® (a lanthanum (La) modified clay for phosphorus (P) removal in freshwater systems) were tested during a 35 days incubation experiment with sediment cores from a Danish eutrophic Lake. Four different sediment treatments with increased or natural densities of chironomids in combination with Phoslock® were used: (1) Control + (2) Chironomids + (3) Phoslock + (4) Chironomids & Phoslock. Nutrients in the overlying water were followed during the incubation period. The treatments with Phoslock reduced P in the overlying water significantly compared to the control treatment. In addition, the chironomids significantly increased sediment nitrate uptake as well as sediment ammonium release. After the incubation period, a sequential extraction of P and La was conducted. The Phoslock treatment led to a reduction of the iron-bound P pool in the sediment and a higher HCl-extractable P pool. Also, most La was recovered in the HCl extract, indicating that P became strongly bound to La in the Phoslock matrix. Sequential extraction of pure Phoslock demonstrated that the bentonite matrix of Phoslock contained redox sensitive iron, and that ammonium might be released from Phoslock, when dispersed in water. 相似文献
32.
In the high-arctic archipelago of Svalbard, the pink-footed goose (Anser brachyrhynchus) population has increased dramatically over the last decades. The population increase and the corresponding range expansion suggest a substantial increase in the potential for disturbance of the tundra caused by goose herbivory. In this study, we used surveys of pink-footed goose grubbing from two separate years (2007 and 2012) to examine the temporal changes in the prevalence of grubbing in central Spitsbergen. During this time period, the Svalbard-breeding pink-footed goose population had increased from 56,400 to 80,000 individuals. We compared grubbing prevalence between the 2 years, standardising the comparison by using a published model of habitat suitability for grubbing (Speed et al. in Ecosystems 12:349-359, 2009) as a covariate. Habitat suitability was a significant predictor of grubbing prevalence across both years, with higher grubbing probability in habitats predicted to be more suitable for grubbing. The probability of grubbing was on average 4 times higher in 2012 than in 2007. In 2007, all tundra habitats had a probability of <27 % of being grubbed whilst in 2012, there was a probability for being grubbed of more than 34 % in the least suitable habitat and around 59 % in the most suitable habitat. The increase in grubbing prevalence demonstrates a great need for monitoring the expanding pink-footed goose population and its impact on the tundra landscape. 相似文献
33.
J. E. Skjæraasen J. A. Devine J. A. Godiksen M. Fonn H. OtterÅ O. S. Kjesbu B. Norberg Ø. Langangen Ø. Karlsen 《Journal of fish biology》2017,90(1):109-128
Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre‐spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October–early November, at a leading cohort size (CL) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre‐spawning, but atretic re‐absorption of remnant oocytes containing yolk granules was found in all females immediately post‐spawning. As expected, concentrations of sex steroids, oestradiol‐17β (females), testosterone (both sexes) and 11‐ketotestosterone (both sexes), increased pre‐spawning before dropping post‐spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post‐ovulatory follicles were visible in histological sections from female gonads 9–11 months post‐spawning, but then disappeared. Spawning commenced around a CL of c. 750 µm (700–800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, LT = 60 cm). Spawning lasted from 13 February to 29 March. 相似文献
34.
Finn Ø. Winther 《Cell and tissue research》1971,121(4):499-506
Summary Guinea pigs were given horseradish peroxidase intracardially and its diffusion in the vascular stria was studied. The Peroxidase spred freely among the intermediate cells and the marginal cells, but was never found to have passed zones occupied by tight junctions. It is concluded that the zones of tight junctions bordering the vascular stria represent a diffusion barrier to horseradish peroxidase. 相似文献
35.
Molecular cloning of lupin leghemoglobin cDNA 总被引:3,自引:0,他引:3
Poly(A)+RNA isolated from root nodules of yellow lupin (Lupinus luteus, var. Ventus) has been used as a template for the construction of a cDNA library. The ds cDNA was synthesized and inserted into the Hind III site of plasmid pBR 322 using synthetic Hind III linkers. Clones containing sequences specific for nodules were selected by differential colony hybridization using32P-labeled cDNA synthesized either from nodule poly(A)+RNA or from poly(A)+RNA of uninfected root as probes. Among the recombinant plasmids, the cDNA gene for leghemoglobin was identified. The protein structure derived from its nucleotide sequence was consistent with known amino acid sequence of lupin Lb II. The cloned lupin Lb cDNA hybridized to poly(A)+RNA from nodules only, which is in accordance with the general concept, that leghemoglobin is expressed exclusively in nodules. 相似文献
36.
Spin-State-Selective Excitation (S3E), which forexample selectively excites amide proton resonances corresponding toexclusively either the or the spin state of the covalentlybound 15N atom is employed for E.COSY-type extraction ofheteronuclear J coupling constants. Instead of having one spectrum with twopeaks (corresponding to the or spin state of15N), S3E generates two spectra, each with onlyone peak for each 15N nucleus. These two spectra are generatedfrom the same data set, so that there is no reduction in sensitivitycompared to conventional 1JNH-resolved methods.Another interesting feature in comparison with conventional methods is that1JNH can be suppressed during the evolutionperiod, meaning that no heteronuclear multiplet structure is visible in the1 frequency dimension. The S3E pulsesequence element is combined with NOESY for measurement of3JN-H and JN-Hcoupling constants in either a hetero- or a homonuclear correlated version.Experimental confirmation is obtained using the protein RAP 17-;97(N-terminal domain of 2-macroglobulin ReceptorAssociated Protein). 相似文献
37.
Elsebet Ø. Nielsen Marianne Aarslew-Jensen Nils Henrik Diemer Povl Krogsgaard-Larsen Arne Schousboe 《Neurochemical research》1989,14(4):321-326
The release ofd-[3H]aspartate (used as a tracer for endogenous glutamate and aspartate) was studied at high K+ (100 mM) and under ischemia in rats implanted with 0.3 mm diameter dialysis tubing through the hippocampus. The effect on thed-[3H]aspartate release of the two -aminobutyric acid (GABA) agonists 4,5,6,7-tetrahydroisoxazolo[5,4-c]-pyridin-3-ol (THIP) and (±)--(p-chlorophenyl)GABA (baclofen), which specifically activate GABAA and GABAB receptors, respectively, was studied. Initial experiments employing HPLC analysis showed a coincident increase in the amounts of glutamate, aspartate and the amount of radioactivity following introduction of K+ (100 mM) or a period of ischemia suggesting that thed-[3H]aspartate labels the transmitter pools of the two amino acids under the present experimental conditions. The presence of 10 mM baclofen or 10 mM THIP in the perfusion medium did not inhibit ischemia inducedd-[3H]aspartate release. On the contrary, 10 mM baclofen alone (but not 0.1 or 1 mM) in the perfusion medium induced release ofd-[3H]aspartate in a calcium dependent manner, whereas 10 mM THIP had no significant releasing effect.Special issue dedicated to Dr. Elling Kvamme 相似文献
38.
T cell clones (CD4+CD8–TCRαβ+γδ–) derived from bone marrow transplant recipients were stimulated with phytohaemagglutinin (PHA) +interleukin-2 (IL-2) in the
presence of irradiated (50 Gy) peripheral blood mononuclear cells (PBMC) derived from acute leukaemia patients(leukaemic PBMC
containing more than 95% blast cells). Leukaemic PBMC could function as accessory cells during mitogenic T cell activation
resulting in both T cell proliferation and a broad T cell cytokine response [IL-3, IL-4, IL-10, granulocyte/macrophage-colony-stimulating
factor (GM-CSF) tumour necrosis factor α (TNFα) and interferon γ (IFNγ) secretion]. Blockade of IL-1 effects by adding IL-1
receptor antagonist together with PHA+IL-2+leukaemia blasts increased T cell proliferation, whereas IL-6-neutralizing antibodies
did not alter T cell proliferation. A qualitatively similar T cell cytokine response and a similar cytokine profile (highest
levels detected for GM-CSF and IFNγ) were detected when normal polyclonal T cell lines were stimulated with PHA in the presence
of non-irradiated leukaemic PBMC. When leukaemic PBMC derived from 18 acute myelogenous leukaemia patients were cultured with
PHA and cells from a polyclonal T cell line, increased concentrations of the T cell cytokines IFNγ and IL-4 were detected
for all patients. We conclude that T cell activation resulting in proliferation and a broad cytokine response can take place
in the presence of excess acute myelogenous leukaemia blasts.
Received: 30 November 1995 / Accepted: 9 January 1996 相似文献
39.
40.
Kine Ø. Hanssen Gunnar Cervin Rozenn Trepos Julie Petitbois Tor Haug Espen Hansen Jeanette H. Andersen Henrik Pavia Claire Hellio Johan Svenson 《Marine biotechnology (New York, N.Y.)》2014,16(6):684-694
The inhibition of marine biofouling by the bromotyrosine derivative ianthelline, isolated from the Arctic marine sponge Stryphnus fortis, is described. All major stages of the fouling process are investigated. The effect of ianthelline on adhesion and growth of marine bacteria and microalgae is tested to investigate its influence on the initial microfouling process comparing with the known marine antifoulant barettin as a reference. Macrofouling is studied via barnacle (Balanus improvisus) settlement assays and blue mussel (Mytilus edulis) phenoloxidase inhibition. Ianthelline is shown to inhibit both marine micro- and macrofoulers with a pronounced effect on marine bacteria (minimum inhibitory concentration (MIC) values 0.1–10 μg/mL) and barnacle larval settlement (IC50?=?3.0 μg/mL). Moderate effects are recorded on M. edulis (IC50?=?45.2 μg/mL) and microalgae, where growth is more affected than surface adhesion. The effect of ianthelline is also investigated against human pathogenic bacteria. Ianthelline displayed low micromolar MIC values against several bacterial strains, both Gram positive and Gram negative, down to 2.5 μg/mL. In summary, the effect of ianthelline on 20 different representative marine antifouling organisms and seven human pathogenic bacterial strains is presented. 相似文献