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171.
Crawford DJ Ruiz E Stuessy TF Tepe E Aqeveque P Gonzalez F Jensen RJ Anderson GJ Bernardello G Baeza CM Swenson U Silva O M 《American journal of botany》2001,88(12):2195-2203
The level and apportionment of allozyme diversity were determined for 29 endemic (and 1 native) species from the Juan Fernández Islands, Chile. Mean diversities at the species level (H(es) = 0.065) are low but comparable to those measured for other insular endemics in the Pacific. A high mean proportion (0.338) of species-level diversity resides among populations. Diversity statistics were compared for species in different ecological-life history trait categories and abundance classes. Species occurring in large populations and those present in scattered small populations have higher diversities than species occurring in one or two populations. Although not significant with the conservative statistical test employed, lower diversity was found in highly selfing species as compared to animal- or wind-pollinated species. The apportionment of genetic diversity within and among populations (G(ST) values) is not significantly different for any of the species categories. Of particular interest is the lack of difference between animal- and wind-pollinated species because previous analyses of large data sets showed higher differentiation between populations of animal- than wind-pollinated species. Historical factors, both ecological and phylogenetic in nature, can influence the level and apportionment of diversity within insular endemics, and thus ecological correlates of diversity seen in many continental species may not apply to endemics. The results have several conservation implications. The preservation of large populations or several small populations is important for conserving diversity within species because when species are reduced to one or two populations, allozyme diversity is sharply reduced. High mean G(ST) values for the species examined illustrate the need for conserving as many populations as possible, either in the wild or in the garden, to preserve maximal diversity within species. Effective conservation strategies require empirical knowledge of each species. 相似文献
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174.
White J Crawford F Fremont D Marrack P Kappler J 《Journal of immunology (Baltimore, Md. : 1950)》1999,162(5):2671-2676
Soluble forms of the mouse MHC class I molecule, Dd, were produced in which the peptide binding groove was uniformly occupied by peptides attached via a covalent flexible peptide linker to the N terminus of the associated beta2-microglobulin. The MHC heavy chain and beta2-microglobulin were firmly associated, and the molecules displayed an Ab epitope requiring proper occupancy of the peptide binding groove. Soluble Dd containing a covalent version of a well-characterized Dd-binding peptide from HIV stimulated a T cell hybridoma specific for this combination. Furthermore, a tetravalent version of this molecule bound specifically with apparent high avidity to this hybridoma. 相似文献
175.
Chylomicrons labeled with [3H]cholesterol and [14C]triglyceride fatty acids were lipolyzed by hepatic lipase (HL) in vitro and then injected intravenously into normal mice fed low- or high-fat diets, and into apolipoprotein (apo) E-deficient mice. In normal mice fed the high-fat diet and injected with non-lipolyzed chylomicrons, the plasma clearance and hepatic uptake of the resulting [3H]cholesterol-labeled remnants was markedly inhibited. In contrast, chylomicrons lipolyzed by HL were taken up equally rapidly by the livers of mice fed the low- and high-fat diets. The removal of non-lipolyzed chylomicrons lacking apoE from the plasma of apoE-deficient mice was inhibited, but not the removal of chylomicrons lipolyzed by HL. Pre-injection of lactoferrin into normal mice inhibited the plasma clearance of both non-lipolyzed chylomicrons and chylomicrons lipolyzed by HL. The removal of HL from the surface of the lipolyzed particles by proteolytic digestion did not affect their rapid uptake, indicating that the hepatic recognition of the lipoproteins was not mediated by HL. These observations support previous findings that phospholipolysis of chylomicrons by hepatic lipase generates remnant particles that are rapidly cleared from circulation by the liver. They also support the concept that chylomicron remnants can be taken up by the liver by an apolipoprotein E-independent mechanism. We hypothesize that this mechanism is modulated by the remnant phospholipids and that it may involve their interaction with a phospholipid-binding receptor on the surface of hepatocytes such as the class B scavenger receptor BI. 相似文献
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177.
The supplementary eye field (SEF) is a region within medial frontal cortex that integrates complex visuospatial information and controls eye-head gaze shifts. Here, we test if the SEF encodes desired gaze directions in a simple retinal (eye-centered) frame, such as the superior colliculus, or in some other, more complex frame. We electrically stimulated 55 SEF sites in two head-unrestrained monkeys to evoke 3D eye-head gaze shifts and then mathematically rotated these trajectories into various reference frames. Each stimulation site specified a specific spatial goal when plotted in its intrinsic frame. These intrinsic frames varied site by site, in a continuum from eye-, to head-, to space/body-centered coding schemes. This variety of coding schemes provides the SEF with a unique potential for implementing arbitrary reference frame transformations. 相似文献
178.
Extensive manufacturing of explosives in the last century has resulted in widespread contamination of soils and waters. Decommissioning and cleanup of these materials has also led to concerns about the explosive hazards associated with residual energetics still present on the surfaces of ordnance and explosives scrap. Typically, open burning or detonation is used to decontaminate ordinance and explosive scrap. Here the use of an anaerobic microbiological system applied as a bioslurry to decontaminate energetics from the surfaces of metal scrap is described. Decontamination of model metal scrap artificially contaminated with 2,4,6-trinitrotoluene and of decommissioned mortar rounds still containing explosives residue was examined. A portable ion mobility spectrometer was employed for the detection of residual explosives residues on the surfaces of the scrap. The mixed microbial populations of the bioslurries effectively decontaminated both the scrap and the mortar rounds. Use of the ion mobility spectrometer was an extremely sensitive field screening method for assessing decontamination and is a method by which minimally trained personnel can declare scrap clean with a high level of certainty. 相似文献
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180.
Lumbers ER Yu ZY Crawford EN 《American journal of physiology. Regulatory, integrative and comparative physiology》2003,285(4):R908-R916
Fetal behavior, renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), and heart rate (HR) were studied 1-3 days after surgery in seven fetal sheep (aged 127-136 days). Five behavioral states were defined from chart recordings of electrocortical (electrocorticographic; ECoG) activity and eye, limb, and breathing movements. Most records were of high-voltage ECoG (HV) or low-voltage (LV) ECoG with breathing (LVB); 6.7 +/- 1.7% were LV ECoG with no breathing (LV0). RSNA was lower in LV0 (P < 0.001) and greater in LVB than in HV (P < 0.05). MAP was lower in both LV states than in HV and when the fetuses went from LV to HV (P < 0.001 to P < 0.03). HR was highest in HV (P < 0.001). In HV and LVB and when the fetus went from LV to HV, MAP and HR were inversely related (P = 0.012-0.003). In LVB and from LV to HV there were direct relationships between MAP and RSNA (P = 0.0014, P = 0.08), and when the fetus went from LV to HV there was also an inverse relationship between HR and RSNA (P = 0.02). Thus fetal RSNA, MAP, and HR are affected by behavioral state as is fetal cardiovascular control. The increase in RSNA during fetal breathing showed that there was an altered level of fetal RSNA associated with fetal breathing activity. 相似文献