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51.
The Plasmodium falciparum apical membrane antigen 1 (AMA1) is a leading candidate for a malaria vaccine. Here, within-population analyses of alleles from 50 Thai P. falciparum isolates yield significant evidence for balancing selection on polymorphisms within the disulfide-bonded domains I and III of the surface accessible ectodomain of AMA1, a result very similar to that seen previously in a Nigerian population. Studying the frequency of nucleotide polymorphisms in both populations shows that the between-population component of variance (F(ST)) is significantly lower in domains I and III compared to the intervening domain II and compared to 11 unlinked microsatellite loci. A nucleotide site-by-site analysis shows that sites with exceptionally high or low F(ST) values cluster significantly into serial runs, with four runs of low values in domain I and one in domain III. These runs may map the sequences that are consistently under the strongest balancing selection from naturally acquired immune responses. 相似文献
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Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO2 总被引:1,自引:0,他引:1
Morgan JA Pataki DE Körner C Clark H Del Grosso SJ Grünzweig JM Knapp AK Mosier AR Newton PC Niklaus PA Nippert JB Nowak RS Parton WJ Polley HW Shaw MR 《Oecologia》2004,140(1):11-25
Atmospheric CO2 enrichment may stimulate plant growth directly through (1) enhanced photosynthesis or indirectly, through (2) reduced plant water consumption and hence slower soil moisture depletion, or the combination of both. Herein we describe gas exchange, plant biomass and species responses of five native or semi-native temperate and Mediterranean grasslands and three semi-arid systems to CO2 enrichment, with an emphasis on water relations. Increasing CO2 led to decreased leaf conductance for water vapor, improved plant water status, altered seasonal evapotranspiration dynamics, and in most cases, periodic increases in soil water content. The extent, timing and duration of these responses varied among ecosystems, species and years. Across the grasslands of the Kansas tallgrass prairie, Colorado shortgrass steppe and Swiss calcareous grassland, increases in aboveground biomass from CO2 enrichment were relatively greater in dry years. In contrast, CO2-induced aboveground biomass increases in the Texas C3/C4 grassland and the New Zealand pasture seemed little or only marginally influenced by yearly variation in soil water, while plant growth in the Mojave Desert was stimulated by CO2 in a relatively wet year. Mediterranean grasslands sometimes failed to respond to CO2-related increased late-season water, whereas semiarid Negev grassland assemblages profited. Vegetative and reproductive responses to CO2 were highly varied among species and ecosystems, and did not generally follow any predictable pattern in regard to functional groups. Results suggest that the indirect effects of CO2 on plant and soil water relations may contribute substantially to experimentally induced CO2-effects, and also reflect local humidity conditions. For landscape scale predictions, this analysis calls for a clear distinction between biomass responses due to direct CO2 effects on photosynthesis and those indirect CO2 effects via soil moisture as documented here. 相似文献
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Polley H. Wayne; Johnson Hyrum B.; Mayeux Herman S.; Malone Stephen R. 《Annals of botany》1993,71(4):347-356
Two cultivars of wheat (Triticum aestivum L.), 'Yaqui 54' and'Seri M82', were grown along a gradient of daytime carbon dioxideconcentrations ([CO2]) from near 350-200 µmol CO2 mol-1air in a 38 m long controlled environment chamber. Carbon dioxidefluxes and evapotranspiration were measured for stands (plantsand soil) in five consecutive 7·6-m lengths of the chamberto determined potential effects of the glacial/interglacialincrease in atmospheric [CO2] on C3 plants. Growth rates andleaf areas of individual plants and net assimilation per unitleaf area and daily (24-h) net CO2 accumulation of wheat standsrose with increasing [CO2]. Daytime net assimilation (PD, mmolCO2 m-2 soil surface area) and water use efficiency of wheatstands increased and the daily total of photosynthetic photonflux density required by stands for positive CO2 accumulation(light compensation point) declined at higher [CO2]. Nighttimerespiration (RN, mmol CO2 m-2 soil surface) of wheat, measuredat 369-397 µmol mol-1 CO2, apparently was not alteredby growth at different daytime [CO2], but RN /PD of stands declinedlinearly as daytime [CO2] and PD increased. The responses ofwheat to [CO2], if representative of other C3 species, suggestthat the 75-100% increase in [CO2] since glaciation and the30% increase since 1800 reduced the minimum light and waterrequirements for growth and increased the productivity of C3plants.Copyright 1993, 1999 Academic Press Atmospheric carbon dioxide, carbon accumulation, evapotranspiration, light compensation point, net assimilation, respiration, Triticum aestivum, water use efficiency, wheat 相似文献
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Weinzweig N Chin G Polley J Charbel F Shownkeen H Debrun G 《Plastic and reconstructive surgery》2000,105(7):2433-2439
Management of complex and relentless large arteriovenous malformations with long term control and acceptable aesthetic results can be accomplished. This outcome requires selective intra-arterial embolization, judicious surgical resection, composite reconstruction with free tissue transfer, other ancillary procedures, or both, and careful serial follow-up examinations to rule out recurrent or persistent disease. 相似文献
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R Simões WB Feitosa CM Mendes AC Nicacio FRO de Barros 《Biotechnic & histochemistry》2013,88(3):79-83
Sperm chromatin integrity is essential for accurate transmission of male genetic information, and normal sperm chromatin structure is important for fertilization. Protamine is a nuclear protein that plays a key role in sperm DNA integrity, because it is responsible for sperm DNA stability and packing until the paternal genome is delivered into the oocyte during fertilization. Our aim was to investigate protamine deficiency in sperm cells of Bos indicus bulls (Nelore) using chromomycin A3 (CMA3) staining. Frozen semen from 14 bulls were thawed, then fixed in Carnoy's solution. Smears were prepared and analyzed by microscopy. As a positive control of CMA3 staining, sperm from one bull was subjected to deprotamination of nuclei. The percentage of CMA3-positive bovine sperm did not vary among batches. Only two bulls showed a higher percentage of CMA3-positive sperm cells compared to the others. CMA3 is a simple and useful tool for detecting sperm protamine deficiency in bulls. 相似文献