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991.
Francine M. R. Hughes Mats Johansson Shaojun Xiong Elisabet Carlborg Dawn Hawkins Magnus Svedmark Adrian Hayes Alexander Goodall Keith S. Richards Christer Nilsson 《Plant Ecology》2010,208(1):77-92
River management practices have altered the hydrological regimes of many rivers and also altered the availability of regeneration
niches for riparian species. We investigated the impact of changed hydrological regimes on the sex ratios and the Spatial
Segregation of the Sexes (SSS) in the dioecious species Salix myrsinifolia Salisb.–phylicifolia L. and S. lapponum L. by studying the free-flowing Vindel River and the regulated Ume River in northern Sweden. We surveyed sex ratios of these
species in 12 river reaches on the Vindel River and in 17 reaches on the Ume River. In addition, we surveyed the sex and location
above mean river stage of 1,002 individuals across both river systems to investigate the SSS of both species. Cuttings were
collected from male and female individuals of S. myrsinifolia–phylicifolia from both rivers and subjected to four different water table regimes in a greenhouse experiment to investigate growth response
between the sexes. We found an M/F sex ratio in both river systems similar to the regional norm of 0.62 for S. myrsinifolia–phylicifolia and of 0.42 for S. lapponum. We found no evidence of SSS in either the free-flowing Vindel River or the regulated Ume River. In the greenhouse experiment,
hydrological regime had a significant effect on shoot and root dry weight and on root length. Significantly higher shoot dry
weights were found in females than in males and significantly different shoot and root dry weights were found between cuttings
taken from the two rivers. We concluded that changed hydrological regimes are likely to alter dimensions of the regeneration
niche and therefore to influence sex ratios and SSS at an early successional stage, making it difficult to find clear spatial
patterns once these species reach maturity and can be sexed. 相似文献
992.
Zhongqiang Li Dan Yu Wen Xiong Qiang Wang Manghui Tu 《Biodiversity and Conservation》2006,15(11):3401-3416
Assessments of biodiversity are time-consuming and require a high level of expert knowledge. A reduced set of taxonomic ranks
other than species has been proved to be useful for rapid and cost-effective assessment of biodiversity. However, few studies
have examined how well this method performs for aquatic plant group that of enormous ecological importance. We studied the
aquatic plant flora in the arid zone of China and examined whether the distribution of species α- and β-diversity could be
predicted well from genus-, and family-levels. Analyses of 3 years field data showed that significant and positive relations
exist between α-diversity of species and α-diversity of genera and family in both entire arid zone and five sub-zones. In
contrast, β-diversity at species level is difficult to predict from β-diversity indexes at higher taxonomic level. The results
indicate that higher-taxon α-diversity, especially at the generic level in our research, can be useful surrogates of species
α-diversity for aquatic plants conservation. 相似文献
993.
994.
Xiong Y Wiltsie J Woods A Guo J Pivnichny JV Tang W Bansal A Cummings RT Cunningham BR Friedlander AM Douglas CM Salowe SP Zaller DM Scolnick EM Schmatz DM Bartizal K Hermes JD MacCoss M Chapman KT 《Bioorganic & medicinal chemistry letters》2006,16(4):964-968
A potent and selective anthrax LF inhibitor 40, (2R)-2-[(4-fluoro-3-methylphenyl)sulfonylamino]-N-hydroxy-2-(tetrahydro-2H-pyran-4-yl)acetamide, was identified through SAR study of a high throughput screen lead. It has an IC50 of 54 nM in the enzyme assay and an IC50 of 210 nM in the macrophage cytotoxicity assay. Compound 40 is also effective in vivo in several animal model studies. 相似文献
995.
Wang YA Yu X Overman S Tsuboi M Thomas GJ Egelman EH 《Journal of molecular biology》2006,361(2):209-215
Many thin helical polymers, including bacterial pili and filamentous bacteriophage, have been seen as refractory to high-resolution studies by electron microscopy. Studies of the quaternary structure of such filaments have depended upon techniques such as modeling or X-ray fiber diffraction, given that direct visualization of the subunit organization has not been possible. We report the first image reconstruction of a filamentous virus, bacteriophage fd, by cryoelectron microscopy. Although these thin ( approximately 70 A in diameter) rather featureless filaments scatter weakly, we have been able to achieve a nominal resolution of approximately 8 A using an iterative helical reconstruction procedure. We show that two different conformations of the virus exist, and that in both states the subunits are packed differently than in conflicting models previously proposed on the basis of X-ray fiber diffraction or solid-state NMR studies. A significant fraction of the population of wild-type fd is either disordered or in multiple conformational states, while in the presence of the Y21M mutation, this heterogeneity is greatly reduced, consistent with previous observations. These results show that new computational approaches to helical reconstruction can greatly extend the ability to visualize heterogeneous protein polymers at a reasonably high resolution. 相似文献
996.
997.
Zhang W Swanson R Xiong Y Richard B Olson ST 《The Journal of biological chemistry》2006,281(49):37302-37310
The anticoagulant serpin antithrombin acquires a potent antiangiogenic activity upon undergoing conformational alterations to cleaved or latent forms. Here we show that antithrombin antiangiogenic activity is mediated at least in part through the ability of the conformationally altered serpin to block the proangiogenic growth factors fibroblast growth factor (FGF)-2 and vascular endothelial growth factor (VEGF) from forming signaling competent ternary complexes with their protein receptors and heparan sulfate co-receptors on endothelial cells. Cleaved and latent but not native forms of antithrombin blocked the formation of FGF-2-FGF receptor-1 ectodomain-heparin ternary complexes, and the dimerization of these complexes in solution and similarly inhibited the formation of FGF-2-heparin binary complexes and their dimerization. Only antiangiogenic forms of antithrombin likewise inhibited (125)I-FGF-2 binding to its low affinity heparan sulfate co-receptor and blocked FGF receptor-1 autophosphorylation and p42/44 MAP kinase phosphorylation in cultured human umbilical vein endothelial cells (HUVECs). Moreover, treatment of HUVECs with heparinase III to specifically eliminate the FGF-2 heparan sulfate co-receptor suppressed the ability of antiangiogenic antithrombin to inhibit growth factor-stimulated proliferation. Antiangiogenic antithrombin inhibited full-length VEGF(165) stimulation of HUVEC proliferation but did not affect the stimulation of cells by the heparin-binding domain-deleted VEGF(121). Taken together, these results demonstrate that antiangiogenic forms of antithrombin block the proangiogenic effects of FGF-2 and VEGF on endothelial cells by competing with the growth factors for binding the heparan sulfate co-receptor, which mediates growth factor-receptor interactions. Moreover, the inability of native antithrombin to bind this co-receptor implies that native and conformationally altered forms of antithrombin differentially bind proangiogenic heparan sulfate domains. 相似文献
998.
Binding of insulin to the insulin receptor initiates a cascade of protein phosphorylation and effector recruitment events leading to the activation of multiple distinct signaling pathways. Previous studies suggested that the diversity and specificity of insulin signal transduction are accomplished by both subcellular localization of receptor and the selective activation of downstream signaling molecules. The small GTPase Rab5 is a key regulator of endocytosis. Three Rab5 isoforms (Rab5a, -5b, and -5c) have been identified. Here we exploited the RNA interference technique to specifically knock down individual Rab5 isoforms to determine the cellular function of Rab5 in distinct insulin signaling pathways. Small interference RNA against a single Rab5 isoform had no effect on protein kinase B (PKB)/Akt or MAPK activation by insulin in NIH3T3 cells overexpressing human insulin receptor. However, simultaneous knockdown of all three Rab5 isoforms dramatically attenuated PKB/Akt activation by insulin without affecting MAPK activation. This inhibition of PKB/Akt activation was because of the impaired interaction between insulin receptor substrate 1 and the p85alpha subunit of phosphatidylinositol 3-kinase. These results indicate a requirement of Rab5 in presenting p85 to insulin receptor substrate 1. Additional evidence supporting a role for Rab5 was suggested by studies with GAPex-5, a vps9 domain containing exchange factor. Down-regulation of GAPex-5 impaired insulin-stimulated PKB/Akt activation. Collectively, this study indicates the involvement of Rab5 in insulin signaling. 相似文献
999.
1000.
目的观察体外培养条件下的牛眼小梁细胞(bovine trabecular meshwork cell,BTMC)是否表达水通道蛋白-1(Aquaporin-1,AQP-1)。方法采用免疫组织化学方法检测AQP-1在BTMC上的表达,并进行半定量分析。结果正常BTMC可见AQP-1蛋白表达,其灰度值为:167.94±1.18;阴性对照为:195.64±1.62,统计学分析其差异具有显著性(P<0.05)。结论在体外培养条件下,BTMC表达AQP-1,这有助于在体外条件下研究房水流出阻力、并探讨青光眼的药物治疗。 相似文献