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排序方式: 共有193条查询结果,搜索用时 15 毫秒
51.
Chang JT Palanivel VR Kinjyo I Schambach F Intlekofer AM Banerjee A Longworth SA Vinup KE Mrass P Oliaro J Killeen N Orange JS Russell SM Weninger W Reiner SL 《Science (New York, N.Y.)》2007,315(5819):1687-1691
A hallmark of mammalian immunity is the heterogeneity of cell fate that exists among pathogen-experienced lymphocytes. We show that a dividing T lymphocyte initially responding to a microbe exhibits unequal partitioning of proteins that mediate signaling, cell fate specification, and asymmetric cell division. Asymmetric segregation of determinants appears to be coordinated by prolonged interaction between the T cell and its antigen-presenting cell before division. Additionally, the first two daughter T cells displayed phenotypic and functional indicators of being differentially fated toward effector and memory lineages. These results suggest a mechanism by which a single lymphocyte can apportion diverse cell fates necessary for adaptive immunity. 相似文献
52.
Colchicine-inhibited cilia regeneration: explanation for lack of effect in tris buffer medium 总被引:1,自引:0,他引:1
In Stentor coeruleus growth of new, daughter ciliates and experimentaly inducled regeneration of oral membranellar cilia are reversibly inhibited by low, nontoxic concentrations of colchicine. However, if the clulture medium containing colchicine (or Colcemid) is made up in tris(hydroxymethyl)aminomethane buffer, growth of ciliated daughters and regeneration of oral cilia proceed normally. The evidence suggests that the mechanism of this reversal of the effects of colchicine (or Colcemid) is due to a chemical reaction between tris(hydroxymethyl)-aminomethane (or its hydrochloride, or both) and colchicine (or Colcemid), wihich reduces the effective concentration of these mitotic spindle inhibitors reaching the stentors. 相似文献
53.
Isolated chromaffin cells from adrenal medulla contain primarily monoamine oxidase B 总被引:6,自引:0,他引:6
Cultured chromaffin cells from bovine adrenal medulla were found to contain primarily the B form of monoamine oxidase. This monoamine oxidase B enzyme was somewhat distinct from B enzymes from other sources, in that noradrenaline was a much poorer substrate than serotonin. Nonetheless, studies with selective inhibitors of the A form (clorgyline) and the B form [(-)-deprenyl] confirmed that chromaffin cell monoamine oxidase was the B form. The observation that chromaffin cell monoamine oxidase has poor affinity for catecholamines is consistent with physiological needs that require the cell to synthesize and store large amounts of catecholamines. 相似文献
54.
A variety of mammalian and avian tissues N- and O-methylate indoleamines and phenylethylamines, with methyltetrahydrofolic acid as the methyl donor. Because it is considerably more efficient than S-adenosylmethionine, methyltetrahydrofolic acid may be the natural methyl donor in this reaction. With methyltetrahydrofolic acid, serotonin is O-methylated to 5-methoxytryptamine, a novel indoleamine in mammalian brain. 相似文献
55.
Banerjee SK 《Science (New York, N.Y.)》2001,291(5509):1714-1715
56.
57.
Inheritance of resistance to the fruit borer, Heliothis armigera Hübner in tomato was studied in TWO interspecific crosses. L. hirsutum f. gLabratum‘B 6013′. a fruit borer-resistant parent, was crossed with two susceptible L. esculentum varieties ‘HS 101’ and. ‘HS 102′. Six generations of two crosses were evaluated for percentage fruit: infestation (on a number basis) and the estimates of the gene effects were derived from the generation mean using a three parameter model A preponderance of additive gene effects was found for this trait. Heritability in the narrow sense was observed to be high indicating the fixable nature of the character. 相似文献
58.
The significance of microbial biomass sulphur in soil 总被引:2,自引:0,他引:2
The soil microbial biomass S fraction of total organic S in soil is considered to be relatively labile and the most active S pool for S turnover in soil. Its significance has been demonstrated in studies of S deficiency in agronomic situations and in those of S pollution from high atmospheric inputs. The utility of the CHCl3 fumigation-extraction technique for the measurement of microbial S has been proved for a range of soils and conditions. The various methodologies currently available are discussed, including the need for determination of the conversion (K
s) factor. Microbial S values, summarized from the available literature, ranged from 3 to 300 g S g-1 dry weight soil. They were generally greater in grassland than in arable systems, though the greatest values were obtained in the few examples from forest and peatland soil systems. Microbial S values showed direct relationships with both microbial C and with total soil organic S. Again, there were significant differences between arable and grassland systems. The effect of factors such as organic and inorganic inputs as well as soil physical conditions on microbial S are described. Microbial S turnover rates were estimated from seasonal, 35S-labelling and modelling studies. These rates varied between an approximately annual turnover rate in undisturbed soils up to 80 year-1 following the addition of readily available substrates. Prospective future research areas are also outlined. 相似文献
59.
Volatilization of NH3 from soil is a major N-loss mechanism that reduces the efficiency of applied N fertilizers, and causes environmental pollution. Strategies are needed to reduce the loss. The influences of dicyandiamide (DCD), farmyard manure (FYM) and irrigation on NH3 volatilization from an alluvial soil in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system was studied using the acid trap method. The loss of NH3 in the rice-wheat system ranged from 38.6 kg N ha-1 from the unfertilized soil to 69.0 kg N ha-1 in the treatment with urea+DCD. Substitution of 50% N provided through urea by FYM reduced NH3-N volatilization by 10% in rice and wheat as compared to the urea treatment. Application of DCD increased NH3 volatilization in wheat by 7% but in rice it had no effect. The irrigation level had no effect on NH3 volatilization in rice but fewer irrigations with fewer splits of N in wheat resulted in higher NH3 volatilization. Application of DCD and FYM with urea had similar effects on grain yield and N uptake by rice and wheat as that of the urea treatment. The study showed that integrated use of organic manure and chemical fertilizer has the potential to reduce the loss of N due to volatilization and thereby minimize environmental pollution. Nitrification inhibitors, which are reported to be useful in increasing the N-use efficiency by reducing the leaching and denitrification losses of N, however, may increase N loss due to volatilization. 相似文献
60.