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排序方式: 共有277条查询结果,搜索用时 265 毫秒
71.
Md Sainur Samad Lars R. Bakken Shahid Nadeem Timothy J. Clough Cecile A. M. de Klein Karl G. Richards Gary J. Lanigan Sergio E. Morales 《PloS one》2016,11(3)
Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N2O and N2. It is known that N2O reduction to N2 is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N2O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N2O production index (IN2O) and N2O/(N2O+N2) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N2O+N2 μmol N/h/vial) were significantly associated with C mineralization (CO2 μmol/h/vial) measured both under oxic (r2 = 0.62, p = 0.0015) and anoxic (r2 = 0.89, p<0.0001) conditions. 相似文献
72.
Sedimentation characteristics of newly synthesized Epstein-Barr viral DNA in superinfected cells. 总被引:6,自引:5,他引:1
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Replicating Epstein-Barr virus (EBV) DNA molecules isolated from superinfected Raji cells were shown to consist of 80S to 65S and 58S (mature) molecules Pulse-chase experiments showed that radioactive label of DNAS molecules with the larger sedimentation coefficients was partially chased into 58S labeled forms. Formation of large concatemers of viral DNA could not be detected at any time after superinfection. The continuous presence of the 65S viral DNA intermediate throughout the replicative cycle combined with the observed inhibition of EBV DNA synthesis by addition of nontoxic levels of ethidium bromide to the superinfected cell culture led us to propose that EBV replication proceeds via a relaxed circular DNA intermediate. 相似文献
73.
Short-term exposure to high CO2 increases rates of photosynthesis and growth in soybeans, but with prolonged high CO2 exposure, these high rates are sometimes not maintained. Growth of soybean (Glycine max (L.) Merrill cv. Fiskeby V) seedlings kept for 25 days at atmospheres of 350 or 1000 μ/l CO2 was compared with growth of plants given 2, 4 or 6 day alternating exposure to high and low CO2 levels (13 days of total exposure to each level). Final dry weight of plants increased with number of days in high CO2 but leaf areas were not greatly affected. Thus dry weight gains per unit leaf area (net assimilation rates) were higher in high CO2 than in low CO2 throughout the entire period of the experiment and the pattern of exposure to high CO2 did not affect the rate of dry weight gain in high CO2 . 相似文献
74.
Synthesis of radiolabeled acetyl-coenzyme A from sodium acetate 总被引:3,自引:0,他引:3
The synthesis of high specific radioactivity [14C]-acetyl-Coenzyme A from [14C]sodium acetate, 2,6-dichlorobenzoic acid, 1,1'-carbonyldiimidazole, and CoA is reported. Starting with 1 mumol of [14C]sodium acetate, this method yields pure [14C]acetyl-CoA in yields approaching 40%. Chromatography on a reversed-phase ODS column was used to separate acetyl-CoA from Coenzyme A and side products. The acetylating agent is apparently a reaction intermediate, acetylimidazole. 相似文献
75.
Summary The photosynthetic response properties of individuals of Solanum dulcamara L. collected from sun and shade habitats were compared in controlled environments. Light-saturated photosynthetic rates and seven additional parameters associated with photosynthetic and growth performance were measured over a range of 12 environmental conditions that simulated natural habitat differences in light intensity, moisture availability and daily temperature amplitude. In contrast to previous studies, the results suggest there is no ecotypic differentiation with respect to the sun and shade environments from which the individuals were collected. It appears that all but one of the field-collected individuals are capable of successfully inhabiting the full range of light environments from which the species was collected. 相似文献
76.
A.‐M. Klein S. D. Hendrix Y. Clough A. Scofield C. Kremen 《Plant biology (Stuttgart, Germany)》2015,17(1):201-208
Pollination is critical to fruit production, but the interactions of pollination with plant resources on a plant's reproductive and vegetative features are largely overlooked. We examined the influences of pollination, irrigation and fertilisation on the performance of almond, Prunus dulcis, in northern California. We used a full‐factorial design to test for the effects of pollination limitation on fruit production and foliage variables of whole trees experiencing four resource treatments: (i) normal water and nutrients, (ii) reduced water, (iii) no nutrients, and (iv) reduced water and no nutrients. In each of these combinations, we applied three pollination treatments: hand‐cross pollination, open‐pollination and pollinator exclusion. Pollination strongly affected yield even under reduced water and no nutrient applications. Hand‐cross pollination resulted in over 50% fruit set with small kernels, while open‐pollinated flowers showed over 30% fruit set with moderate‐sized kernels. Pollinator‐excluded flowers had a maximum fruit set of 5%, with big and heavy kernels. Reduced water interacted with the open‐ and hand‐cross pollination treatments, reducing yield more than in the pollinator exclusion treatment. The number of kernels negatively influenced the number of leaves, and reduced water and no nutrient applications interacted with the pollination treatments. Overall, our results indicate that the influences of pollination on fruit tree yield interact with the plant availability of nutrients and water and that excess pollination can reduce fruit quality and the production of leaves for photosynthesis. Such information is critical to understand how pollination influences fruit tree performance. 相似文献
77.
L da Silva Lopes RB Marques HB Fernandes S da Silva Pereira MC Ayres MH Chaves FR Almeida 《Journal of biomedical science》2012,19(1):68-6
ABSTRACT: BACKGROUND: The mechanisms of the antinociceptive activity of () epicatechin (EPI), a compound isolated from the hydroalcoholic fraction of Combreum leprosum Mart & Eicher. METHODS: were assessed in the model of chemical nociception induced by glutamate (20 mumol/paw). To evaluate the mechanisms involved, the animals , male Swiss mice (25-30 g), received EPI (50 mg/kg p.o.) after pretreatment with naloxone (2 mg/kg s.c. opioid antagonist), glibenclamide (2 mg/kg s.c. antagonist K + channels sensitive to ATP), ketanserin (0.3 mg/kg s.c. antagonist of receptor 5-HT2A), yoimbine (0.15 mg/kg s.c. alpha2 adrenergic receptor antagonist), pindolol (1 mg/kg s.c. 5-HT1a/1b receptor antagonist), atropine (0.1 mg/kg s.c. muscarinic antagonist) and caffeine (3 mg/kg s.c. adenosine receptor antagonist), ondansetron (0.5 mg/kg s.c. for 5-HT3 receptor) and L-arginine (600 mg/kg i.p.). RESULTS: The antinociceptive effect of EPI was reversed by pretreatment with naloxone and glibenclamide, ketanserin, yoimbine, atropine and pindolol, which demonstrates the involvement of opioid receptors and potassium channels sensitive to ATP, the serotoninergic (receptor 5HT1A and 5HT2A), adrenergic (receptor alpha 2) and cholinergic (muscarinic receptor) systems in the activities that were observed. The effects of EPI, however, were not reversed by pretreatment with caffeine, L-arginine or ondansetron, which shows that there is no involvement of 5HT3 receptors or the purinergic and nitrergic systems in the antinociceptive effect of EPI. In the Open Field and Rotarod test, EPI had no significant effect, which shows that there was no central nervous system depressant or muscle relaxant effect on the results. CONCLUSIONS: This study demonstrates that the antinociceptive activity of EPI in the glutamate model involves the participation of the opioid system, serotonin, adrenergic and cholinergic. 相似文献
78.
Patton DT Garden OA Pearce WP Clough LE Monk CR Leung E Rowan WC Sancho S Walker LS Vanhaesebroeck B Okkenhaug K 《Journal of immunology (Baltimore, Md. : 1950)》2006,177(10):6598-6602
CD4+CD25+Foxp3+ regulatory T cells (Tregs) contribute to the maintenance of peripheral tolerance by inhibiting the expansion and function of conventional T cells. Treg development and homeostasis are regulated by the Ag receptor, costimulatory receptors such as CD28 and CTLA-4, and cytokines such as IL-2, IL-10, and TGF-beta. Here we show that the proportions of Tregs in the spleen and lymph nodes of mice with inactive p110delta PI3K (p110deltaD910A/D910A) are reduced despite enhanced Treg selection in the thymus. p110deltaD910A/D910A CD4+CD25+Foxp3+ Tregs showed attenuated suppressor function in vitro and failed to secrete IL-10. In adoptive transfer experiments, p110deltaD910A/D910A T cells failed to protect against experimental colitis. The identification of p110delta as an intracellular signaling protein that regulates the activity of CD4+CD25+Foxp3+ Tregs may facilitate the further elucidation of the molecular mechanisms responsible for Treg-mediated suppression. 相似文献
79.
Stephen C. Jewett Lisa M. Clough Arny L. Blanchard William G. Ambrose Howard M. Feder Max K. Hoberg Alex V. Whiting 《Polar Biology》2009,32(11):1665-1680
Macrobenthos of the shallow (<10 m) nearshore marine waters of northern Kotzebue Sound was examined in 2002–2004 to (1) determine
nearshore community structure and (2) assess the influence of sewage disposal. A variable number of benthic stations were
sampled during three summers, with extensive effort at the disposal zone in 2003. The benthic community structure is similar
to other nearshore Arctic locations, and was similar to a previous benthic study done in 1986–1987. The potential of sewage
impact was assessed at the request of the community, because sewage is occasionally discharged into the Sound, in volumes
of up to 38 million liters, typically through the ice in early spring. Only minimal effects of disposal on the benthos were
evident and the effects could not be separated from the impacts of low salinity and relatively high water pigments. Low diversity
(H′) and species richness (d) and high biomass characterized stations in the sewage area. Parameters often associated with extreme sewage pollution, particularly
hypoxic and/or anoxic conditions and high abundance of opportunistic taxa, were not observed. Local traditional ecological
knowledge was solicited throughout the study, and was used to help define the area potentially affected by sewage disposal. 相似文献
80.