低温-秋水仙素诱导甜瓜多倍体研究

以刚展开子叶的甜瓜植株为材料,采用低温-秋水仙素处理,植株全部成活,通过检测气孔-叶绿体的变化情况,选出4株定植于营养箱内,采收全部植株所结果实,保留种子并测量.采收期过后,用嫩芽叶尖为材料,对3株甜瓜进行染色体计数检测,检出1个四倍体.结果表明:低温-秋水仙素处理可以有效降低秋水仙素的毒害作用,提高植株成活率.植株后期,有由四倍体回复到二倍体的现象,说明在植株生长后期倍性稳定性有所改变.     

Ebola virus entry requires the cholesterol transporter Niemann-Pick C1

Infections by the Ebola and Marburg filoviruses cause a rapidly fatal haemorrhagic fever in humans for which no approved antivirals are available. Filovirus entry is mediated by the viral spike glycoprotein (GP), which attaches viral particles to the cell surface, delivers them to endosomes and catalyses fusion between viral and endosomal membranes. Additional host factors in the endosomal compartment are probably required for viral membrane fusion; however, despite considerable efforts, these critical host factors have defied molecular identification. Here we describe a genome-wide haploid genetic screen in human cells to identify host factors required for Ebola virus entry. Our screen uncovered 67 mutations disrupting all six members of the homotypic fusion and vacuole protein-sorting (HOPS) multisubunit tethering complex, which is involved in the fusion of endosomes to lysosomes, and 39 independent mutations that disrupt the endo/lysosomal cholesterol transporter protein Niemann-Pick C1 (NPC1). Cells defective for the HOPS complex or NPC1 function, including primary fibroblasts derived from human Niemann-Pick type C1 disease patients, are resistant to infection by Ebola virus and Marburg virus, but remain fully susceptible to a suite of unrelated viruses. We show that membrane fusion mediated by filovirus glycoproteins and viral escape from the vesicular compartment require the NPC1 protein, independent of its known function in cholesterol transport. Our findings uncover unique features of the entry pathway used by filoviruses and indicate potential antiviral strategies to combat these deadly agents.     

Woody cover and hominin environments in the past 6 million years

The role of African savannahs in the evolution of early hominins has been debated for nearly a century. Resolution of this issue has been hindered by difficulty in quantifying the fraction of woody cover in the fossil record. Here we show that the fraction of woody cover in tropical ecosystems can be quantified using stable carbon isotopes in soils. Furthermore, we use fossil soils from hominin sites in the Awash and Omo-Turkana basins in eastern Africa to reconstruct the fraction of woody cover since the Late Miocene epoch (about 7 million years ago). (13)C/(12)C ratio data from 1,300 palaeosols at or adjacent to hominin sites dating to at least 6 million years ago show that woody cover was predominantly less than ～40% at most sites. These data point to the prevalence of open environments at the majority of hominin fossil sites in eastern Africa over the past 6 million years.     

Alternative stable states explain unpredictable biological control of Salvinia molesta in Kakadu

Suppression of the invasive plant Salvinia molesta by the salvinia weevil is an iconic example of successful biological control. However, in the billabongs (oxbow lakes) of Kakadu National Park, Australia, control is fitful and incomplete. By fitting a process-based nonlinear model to thirteen-year data sets from four billabongs, here we show that incomplete control can be explained by alternative stable states--one state in which salvinia is suppressed and the other in which salvinia escapes weevil control. The shifts between states are associated with annual flooding events. In some years, high water flow reduces weevil populations, allowing the shift from a controlled to an uncontrolled state; in other years, benign conditions for weevils promote the return shift to the controlled state. In most described ecological examples, transitions between alternative stable states are relatively rare, facilitated by slow-moving environmental changes, such as accumulated nutrient loading or climate change. The billabongs of Kakadu give a different manifestation of alternative stable states that generate complex and seemingly unpredictable dynamics. Because shifts between alternative stable states are stochastic, they present a potential management strategy to maximize effective biological control: when the domain of attraction to the state of salvinia control is approached, augmentation of the weevil population or reduction of the salvinia biomass may allow the lower state to trap the system.     

Prion propagation and toxicity in vivo occur in two distinct mechanistic phases

Mammalian prions cause fatal neurodegenerative conditions including Creutzfeldt-Jakob disease in humans and scrapie and bovine spongiform encephalopathy in animals. Prion infections are typically associated with remarkably prolonged but highly consistent incubation periods followed by a rapid clinical phase. The relationship between prion propagation, generation of neurotoxic species and clinical onset has remained obscure. Prion incubation periods in experimental animals are known to vary inversely with expression level of cellular prion protein. Here we demonstrate that prion propagation in brain proceeds via two distinct phases: a clinically silent exponential phase not rate-limited by prion protein concentration which rapidly reaches a maximal prion titre, followed by a distinct switch to a plateau phase. The latter determines time to clinical onset in a manner inversely proportional to prion protein concentration. These findings demonstrate an uncoupling of infectivity and toxicity. We suggest that prions themselves are not neurotoxic but catalyse the formation of such species from PrP(C). Production of neurotoxic species is triggered when prion propagation saturates, leading to a switch from autocatalytic production of infectivity (phase 1) to a toxic (phase 2) pathway.     

土地利用类型变化对城市大气边界层特征影响的数值模拟

利用ENVI和IDL,GIS以及上海市航片,将ARW-WRF中尺度模式中的下垫面土地利用类型数据中上海市部分做了修正:对照模式中24种土地类型分类,将原本定义为农作物耕地和草场,草地,灌木丛,以及沙土和淤泥的部分,根据实际情况改为城区和在建城区,扩大了城市的范围,获取城市建筑物高度信息以得到更精确地粗糙度数据,使其与实...     

Overexpression and export of Vibrio anguillarum metalloprotease in Escherichia coli

Vibrio anguillarum metalloprotease, an extracellular zinc metalloprotease involved in the virulence mechanism of Vibrio anguillarum, is synthesized from the empA gene as a 611-residue precursor and naturally secreted via Sec secretion pathway in Vibrio anguillarum. In this study, heterologous expression of the empA gene encoding metalloprotease and export of the recombinant metalloprotease in Escherichia coli were examined. The empA gene was subcloned into pBAD24 with arabinose promoter and sequenced. The sequence encoded a polypeptide (611 amino acids) consisting of four domains: a signal peptide, an N-terminal propeptide, a mature region and a C-terminal propeptide. The empA gene inserted in plasmid pBAD24 was overexpressed in TOP10 strain of E. coli after arabinose induction. The 36kDa polypeptide of the recombinant metalloprotease as the mature protease was further confirmed by SDS-PAGE and immunoblotting. It was found that recombinant metalloprotease with the EmpA activity and antigenicity was exported into the periplasm of Escherichia coli cells via Sec translocation pathway, whereas it was secreted into extracellular environments in V. anguillarum. The results imply that the expression, export and processing mechanism of the protein in E. coli are similar to those in V. anguillarum.     

带干扰Poisson风险模型的破产时间分析

现实生活中,保险公司发生破产行为的可能性是非常小的。对保险公司而言,他们更为关心的是公司需要多长时间会破产。运用鞅论的方法,分析了一类带干扰的Poisson风险模型资金盈余首次达到0的时间,并得到了它的矩母函数和期望。     

一种复杂系统研究方法——基于多智能体的整体建模仿真方法

本文在对一般复杂系统进行研究分析的基础上,针对目前国内外的研究现状,提出了一种研究复杂系统的新方法－基于多智能体的整体建模仿真方法,对这种方法的操作流程和步骤进行了详细的说明,并介绍了支撑这种方法的ＳＷＡＲＭ仿真平台,最后指出了这种建模仿真方法在军事和经济系统中的应用前景。