拟南芥bHLH家族转录因子DYT1在花药发育过程中调控胼胝质降解(英文)

胼胝质的合成和降解是雄配子体减数分裂过程中的一个重要特征,对后期花粉成熟有重要作用.在此研究中,分离到了一个雄性不育突变体msl57,该突变体的绒毡层分化及胼胝质降解过程出现异常,导致花粉败育.图位克隆和遗传分析表明:MSl57基因与bHLI-I家族转录因子DYTI(At4g21330)是同一基因.因此,将ms157突变体改名为dyt1-2.反式激活作用实验揭示了DYTI的激活功能域位于基因的250 ～504bp之间.通过酵母双杂交实验发现DYT1蛋白在体内可以形成同源二聚体来执行其功能.RT-PCR及定量PCR分析表明胼胝质酶相关基因A6的表达在突变体背景下严重下调.因此,DVF1通过调控胼胝质的降解来影响花药发育过程.     

浑善达克沙漠化防治重点生态系统功能区防风固沙功能动态特征分析

浑善达克沙漠化防治重点生态系统功能区是位于内蒙古地区维护国家北方生态安全屏障的重要区域.本文基于气象、遥感数据,运用RWEQ(Revised Wind Erosion Equation)模型,定量分析了1990—2015年浑善达克防风固沙功能区生态系统结构与防风固沙功能的时空变化特征,揭示了生态系统结构变化对防风固沙服务功能的影响.结果表明:26年间各生态系统间转换强烈,以草地生态系统转出为主,2005年之前主要向农田生态系统和荒漠生态系统转变,2005年以后得益于生态建设工程的实施和禁牧封育等措施,主要向草地、森林生态系统转变.研究区以微度和轻度土壤侵蚀为主,风蚀情况整体好转.农田生态退耕、荒漠化程度减轻、草地质量提高等生态系统转换有益于提升防风固沙功能.同时,也揭示了该功能区内生态退耕对防风固沙服务功能的影响,两者呈显著负相关.     

语言自主性学习理论评述

人本主义心理学认为学习者具有发展潜能的能力和动力，研究者应促进其个性发展和潜能发挥；社会认知学派通过所构建的研究框架确定学习自主性程度，采用五个维度描述自主学习状态，认为自主学习能力习得是将外部学习技能内化为个人能力的过程；信息加工理论指出完整意义上的自主学习过程经历四个阶段，还构建了自主学习内在机制；元认知理论认为循序渐进的发展过程直接影响自主性学习能力的发展。对各理论学派教育哲学理念进行全面梳理，利于研究者借鉴其成果，从而提出本土化之理论。     

高技术指标：2007年度33国(地区)技术竞争力报告

文中的高技术指标（High Tech Indicators,HTI）为佐治亚理工大学发布的沿用多年的指标。数据对
比的时间段分别为1993年、1996年、1999年、2002/3年和2007年。论文给出了33个国家（地区）当前的竞争
力指标——技术排名(Technological Standing, TS), 同时提供了四个表征未来竞争力前景的主要指标——国家
发展取向指标(National Orientation, NO)、社会经济基础指标(Socio-Economic Infrastructure, SE)、技术基础指
标(Technological Infrastructure, TI)与生产能力指标(Productive Capacity, PC)。论文无意在高技术指标的结果上
多加笔墨,但是也的确注意到,中国已经取代美国占据了技术排名的首位。这一结果反映了高技术指标的特
点,更重要的是,它反映了中国过去15年的惊人发展速度。     

Haematopoietic stem cells do not asymmetrically segregate chromosomes or retain BrdU

Stem cells are proposed to segregate chromosomes asymmetrically during self-renewing divisions so that older ('immortal') DNA strands are retained in daughter stem cells whereas newly synthesized strands segregate to differentiating cells. Stem cells are also proposed to retain DNA labels, such as 5-bromo-2-deoxyuridine (BrdU), either because they segregate chromosomes asymmetrically or because they divide slowly. However, the purity of stem cells among BrdU-label-retaining cells has not been documented in any tissue, and the 'immortal strand hypothesis' has not been tested in a system with definitive stem cell markers. Here we tested these hypotheses in haematopoietic stem cells (HSCs), which can be highly purified using well characterized markers. We administered BrdU to newborn mice, mice treated with cyclophosphamide and granulocyte colony-stimulating factor, and normal adult mice for 4 to 10 days, followed by 70 days without BrdU. In each case, less than 6% of HSCs retained BrdU and less than 0.5% of all BrdU-retaining haematopoietic cells were HSCs, revealing that BrdU has poor specificity and poor sensitivity as an HSC marker. Sequential administration of 5-chloro-2-deoxyuridine and 5-iodo-2-deoxyuridine indicated that all HSCs segregate their chromosomes randomly. Division of individual HSCs in culture revealed no asymmetric segregation of the label. Thus, HSCs cannot be identified on the basis of BrdU-label retention and do not retain older DNA strands during division, indicating that these are not general properties of stem cells.     

Host specificity of Lepidoptera in tropical and temperate forests

For numerous taxa, species richness is much higher in tropical than in temperate zone habitats. A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecological specialization, resulting in a greater proportion of insect species occupying narrow niches within a community. We tested this hypothesis by comparing host specialization in larval Lepidoptera (moths and butterflies) at eight different New World forest sites ranging in latitude from 15 degrees S to 55 degrees N. Here we show that larval diets of tropical Lepidoptera are more specialized than those of their temperate forest counterparts: tropical species on average feed on fewer plant species, genera and families than do temperate caterpillars. This result holds true whether calculated per lepidopteran family or for a caterpillar assemblage as a whole. As a result, there is greater turnover in caterpillar species composition (greater beta diversity) between tree species in tropical faunas than in temperate faunas. We suggest that greater specialization in tropical faunas is the result of differences in trophic interactions; for example, there are more distinct plant secondary chemical profiles from one tree species to the next in tropical forests than in temperate forests as well as more diverse and chronic pressures from natural enemy communities.