Genetic Structure of the Ancestral Population of Modern Humans

Neutral DNA polymorphisms from an 8-kb segment of the dystrophin gene, previously ascertained in a worldwide sample (n= 250 chromosomes), were used to characterize the population ancestral to the present-day human groups. The ancestral state of each polymorphic site was determined by comparing human variants with their orthologous sites in the great apes. The ``age before fixation' of the underlying mutations was estimated from the frequencies of the new alleles and analyzed in the context of these polymorphisms' distribution among 13 populations from Africa, Europe, Asia, New Guinea, and the Americas (n= 860 chromosomes in total). Seventeen polymorphisms older tan 100,000–200,000 years, which contributed ∼90% to the overall nucleotide diversity, were common to all human groups. Polymorphisms endemic to human groups or continentally restricted were younger than 100,000–200,000 years. Africans (six populations) with 13 such sites stood out from the rest of the world (seven populations), where only 2 population-specific variants were observed. The similarity of the frequencies of the old polymorphisms in Africans and non-Africans suggested a similar profile of genetic variability in the population before the modern human's divergence. This ancestral population was characterized by an effective size of about 10,000 as estimated from the nucleotide diversity; this size may describe the number of breeding individuals over a long time during the Middle Pleistocene or reflect a speciation bottleneck from an initially larger population at the end of this period. Received: 3 February 1998 / Accepted: 9 February 1998     

不同施肥处理对‘赤霞珠’葡萄根际土壤养分和真菌群落的影响

【背景】宁夏贺兰山东麓葡萄产区忽视有机肥的施用,果树枝条焚烧污染环境,造成土壤养分缺失,土壤质量下降。【目的】为解决长期施用化肥对土壤造成的一系列问题,通过大田试验研究施肥及喷施不同浓度菌剂对土壤理化性质、真菌群落组成及多样性的影响,为酿酒葡萄可持续健康发展提供科学依据。【方法】以‘赤霞珠’葡萄根际土壤为试验对象,采用Illumina MiSeq高通量测序技术,测定并分析根际土壤理化性质、真菌群落组成和多样性在7个处理[常规施肥(CK)、蚯蚓粪+腐熟枝条+100倍菌剂(T1)、蚯蚓粪+腐熟枝条+200倍菌剂(T2)、蚯蚓粪+腐熟枝条+300倍菌剂(T3)、蚯蚓粪+未腐熟枝条+100倍菌剂(A1)、蚯蚓粪+未腐熟枝条+200倍菌剂(A2)和蚯蚓粪+未腐熟枝条+300倍菌剂(A3)]的变化。【结果】相较于CK,葡萄根际土壤理化性质差异明显,施肥处理增加了土壤有机质含量,土壤pH含量无明显变化,改良了土壤结构,活化了土壤有效养分。相较于CK,各处理真菌分类操作单元(operational taxonomic unit, OTU)数均降低,A2处理根际土壤丰富度及多样性均显著增加。真菌群落组成...     

Microtubules and cyclic amp in human leukocytes: on the order of things

We have shown previously that the β-adrenergic agonist isoproterenol (2μM) and the phosphodiesterase inhibitor isobutylmethylxanthine (1 mM) produce a much greater increase in cyclic AMP in human leukocytes that have been pretreated with colchicine (or with other agents that affect microtubule assembly) than in control leukocytes. The effects of colchicines were both time- and dose-dependant. These and other data suggested that the generation of cyclic AMP is normally restricted by an intact system of cytoplasmic microtubules. If so, then the same time and dose dependencies might apply to other colchicines-induced changes in leukocyte function. We have now assayed the distribution of concanavalin A (Con A)-receptor complexes on the leukocyte membrane, taking into account that leukocytes competent to assemble microtubules show a uniform distribution of surface- bound Con A whereas microtubule-deficient cells accumulate Con A in surface caps. We have found that the effect of colchicine on capping is also both time- and dose dependent, and that the dose-response relationships conform to those required to increase cyclic AMP levels. These findings provide further evidence that both colchicine-induced Con-A capping and colchicine- induced cyclic AMP generation depend upon the relaxation of constraints normally imposed by cytoplasmic microtubules upon the plasma membrane, which limit, respectively, lateral mobility of the lectin-receptor complexes, and expression of hormone-sensitive adenylate cyclase. Moreover, colchicine-induced Con-A cap formation is not affected even by very large changes in leukocyte cyclic AMP levels. Thus, elevated cyclic AMP levels do not appear to promote the dissolution of microtubules; rather, the dissolution of microtubules permits the generation of increased amounts of cyclic AMP.     

豆科黄华属植物种子表面特征的研究

在扫描电镜下观察了豆科黄华属Thermopsis 18种植物种子的表面纹饰,发现 T．alpina,T.bar- bata,T．inflata,T．lupinoides,T. licentiana,T.smithiana和T．turkestanica的种子表面为粗网状,T californica,T.divaricarpa,T. macrophylla,T．mollis的种子表面为细网状,T.gracilis,T.montana,T. fabacea的种子表面为相对平滑型纹饰,T．alterniflora的种子表面为不规则条形,T．chinensis的种子表 面为粘膜状,T.rhombifolia的种子表面为条形及 T．viuosa的种子表面为碎屑状纹饰。结果表明黄华属的种子表面特征对属下类群的划分有一定意义,对澄清某些混乱的种有一定价值。     

榆科榉属模式的考证

长期以来,Zelkova crenata Spach被认为是榉属(Zelkova)的模式。作者基于国际植物命名法规中的模式指定原则,并通过有关文献的考证,确认Zelkova carpinifolia(Pall.) K. Koch为榉属的合法模式,而并非Z. crenata Spach或Z. carpinifolia(Pall.) Dipp.。     

内蒙古大兴安岭森林可燃物燃烧释放PM2.5中水溶性离子排放特性

研究森林可燃物燃烧释放的细颗粒物(PM_2.5)的排放因子对于揭示森林火灾对大气和生态系统的影响至关重要,而水溶性离子是细颗粒物的重要化学成分,对颗粒物的形成具有重要意义。利用自主设计的生物质燃烧系统,模拟内蒙古大兴安岭5种典型乔木(蒙古栎、白桦、兴安落叶松、黑桦、山杨)的3种组成部分(树干、树枝、树皮)及其地表死可燃物(凋落物层、半腐殖质层、腐殖质层)以及3种典型灌木(平榛、二色胡枝子、兴安杜鹃)树枝燃烧,采用ISC1100离子色谱分析仪测定2种燃烧状态(阴燃和明燃)下PM_2.5中水溶性离子(Na⁺、NH₄⁺、K⁺、Mg²⁺、Ca²⁺、F^-、Cl^-、NO₃^-、NO₂^-、SO₄^2-)的排放因子。结果表明:乔木所有组成部分及其地表死可燃物和灌木树枝燃烧所排放PM_2.5中检测到的水溶性离子,阴燃以K⁺、Cl^-和Na⁺为主要组分,明燃以K⁺、Cl^-和SO₄^2-为主要组分。不同燃烧状态下相同乔木树种及其地表死可燃物和相同灌木排放PM_2.5中检测到的水溶性离子总量均存在显著差异。灌木树枝在阴燃期间PM_2.5中水溶性无机离子的排放因子比明燃更高。乔木释放的PM_2.5中阳离子与阴离子的比率为1.26,地表死可燃物为1.12,灌木为2.0,表明颗粒物呈碱性。内蒙古大兴安岭的森林大火不会通过释放水溶性离子导致生态系统的酸化。     

Diet-induced obesity in rats leads to a decrease in sperm motility

Background  

Obesity is rapidly becoming a worldwide epidemic that affects children and adults. Some studies have shown a relationship between obesity and infertility, but until now it remains controversial. Thus, the aim of the present study was to investigate the effect of high-fat diet-induced obesity on male reproductive parameters.