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排序方式: 共有367条查询结果,搜索用时 109 毫秒
361.
Punckt C Bölscher M Rotermund HH Mikhailov AS Organ L Budiansky N Scully JR Hudson JL 《Science (New York, N.Y.)》2004,305(5687):1133-1136
Stainless steels undergo a sharp rise in pitting corrosion rate as the potential, solution concentration, or temperature is changed only slightly. We report experiments using real-time microscopic in situ visualizations that resolve the nucleation and evolution of individual pits during the transition. They suggest that the sudden onset of corrosion is explained by an explosive autocatalytic growth in the number of metastable pits and that stabilization of individual pits takes place only later. This finding agrees with a theoretical approach treating the onset of pitting corrosion as a cooperative critical phenomenon resulting from interactions among metastable pits, and it extends perspectives on the control and prevention of corrosion onset. 相似文献
362.
Toth AL Varala K Newman TC Miguez FE Hutchison SK Willoughby DA Simons JF Egholm M Hunt JH Hudson ME Robinson GE 《Science (New York, N.Y.)》2007,318(5849):441-444
The presence of workers that forgo reproduction and care for their siblings is a defining feature of eusociality and a major challenge for evolutionary theory. It has been proposed that worker behavior evolved from maternal care behavior. We explored this idea by studying gene expression in the primitively eusocial wasp Polistes metricus. Because little genomic information existed for this species, we used 454 sequencing to generate 391,157 brain complementary DNA reads, resulting in robust hits to 3017 genes from the honey bee genome, from which we identified and assayed orthologs of 32 honey bee behaviorally related genes. Wasp brain gene expression in workers was more similar to that in foundresses, which show maternal care, than to that in queens and gynes, which do not. Insulin-related genes were among the differentially regulated genes, suggesting that the evolution of eusociality involved major nutritional and reproductive pathways. 相似文献
363.
364.
ROUGH SHEATH2: a Myb protein that represses knox homeobox genes in maize lateral organ primordia 总被引:1,自引:0,他引:1
The regulation of members of the knotted1-like homeobox (knox) gene family is required for the normal initiation and development of lateral organs. The maize rough sheath2 (rs2) gene, which encodes a Myb-domain protein, is expressed in lateral organ primordia and their initials. Mutations in the rs2 gene permit ectopic expression of knox genes in leaf and floral primordia, causing a variety of developmental defects. Ectopic KNOX protein accumulation in rs2 mutants occurs in a subset of the normal rs2-expressing cells. This variegated accumulation of KNOX proteins in rs2 mutants suggests that rs2 represses knox expression through epigenetic means. 相似文献
365.
366.
SJ Uhm MK Gupta ZC Das JH Kim C Park T Kim HT Lee 《Reproduction in domestic animals》2009,44(1):106-115
Retrovirus-mediated exogenous gene transfection of somatic cells is an efficient method to produce transgenic embryos by somatic cell nuclear transfer (SCNT). This study evaluated whether efficiency of transgenic embryos production, by SCNT using fibroblast cells transfected by retrovirus vector, is influenced by the introduced transgene and whether recloning could further improve its efficiency. Transgenic cloned embryos were produced by SCNT of porcine foetal fibroblast cells transfected by either LNβ-Z or LNβ-enhanced green fluorescent protein (EGFP) retrovirus vector and evaluated for their developmental ability in vitro . Blastomeres from four-cell stage porcine embryos, produced by SCNT of foetal fibroblast cells transfected with LNβ-EGFP retroviral vector, were subsequently recloned into enucleated metaphase II oocytes and evaluated for changes in chromatin configuration, in vitro embryo development and gene expression. Analysis of results showed that cleavage and blastocyst rates of porcine SCNT embryos, using LacZ (53.6 ± 6.4%; 12.0 ± 5.7%) or EGFP (57.5 ± 6.3%; 10.1 ± 4.1%) transfected fibroblasts, did not differ (p > 0.05) from those of non-transfected controls (60.9 ± 8.2%; 12.3 ± 4.0%). Recloning of blastomeres did not further improve the in vitro development rate. Interestingly, the nuclei of blastomere underwent slower remodelling process than somatic cell nuclei. Both cloned and recloned embryos showed 100% transgene expression and there were no evidence of mosaicism. In conclusion, our data shows that the efficiency of transgenic cloned embryos production by SCNT of somatic cells transfected with replication-defective retrovirus vector is not influenced by the transgene introduction into donor cells and recloning of four-cell stage blastomere could not further improve its efficiency. 相似文献
367.
Salmon of the Southeastern U.S.: Sucker migrations deliver resource subsidies to oligotrophic stream
Mack White Kit Wheeler Ryan R. Hudson Justin N. Murdock 《Ecology of Freshwater Fish》2023,32(1):181-194
The ability for migratory fishes to move commonly limiting resources such as nitrogen (N) and phosphorus (P) between discrete environments can have pronounced effects on recipient ecosystems. To further understand the geographic and taxonomic scope of migratory fish resource subsidies, we quantified N and P subsidies delivered by adfluvial suckers (Smallmouth Buffalo, Ictiobus bubalus) via excretion, eggs and carcasses to a small oligotrophic stream during their annual spawning migration. We also compared nutrient inputs from migrant buffalo with watershed nutrient export to assess the likelihood that delivered nutrients were ecologically important. We estimated that approximately 67,000 buffalo delivered 730 kg of N and 80 kg of P to Citico Creek as a result of excretion and egg subsidies across three migration waves. We estimated that carcasses delivered negligible amounts of N and P due to extremely low retention. The ratio of migrant inputs (Mw) to system export (Ew; Mw/Ew) varied amongst three migration waves and compounds (i.e. dissolved inorganic nitrogen, ammonium and soluble reactive phosphorus), with values for Mw/Ew ranging from 0.25 to 5.10, reflecting the potential of nutrient subsidies to exceed nutrients exported from the system under certain conditions. Our findings suggest that suckers have the potential to deliver large resource subsidies to their spawning habitats and that these subsidies may be ecologically important, thus warranting additional consideration of the functional relevance of nongame fishes and their migrations. 相似文献