G R I C U L T U R A L S C I E N C E T E C H N O L O G Y

?A g r i c u l t u r a l S c i e n c e&T e ch n o·og y》是我国第一家农业科技综合类英文期刊,袁隆平主编,湖南省农业信息与工程研究所主办,安徽吴楚传媒股份有限公司提供编辑出版支持,2010年改为月刊,国际公开发行。国内统一刊号C N 4 3-1 4 2 2/S?国际标准刊号I S S N 1 0 0 9-4 4 2 9?该刊立足国内、面向世界,重点宣传国内农业科研实践、农业技术革新的成杲;报道国内农业科研及相关领域的最新进展;介绍国内特色资源、农业生产与经济发展状况。旨在提高我国农业科研的国际影响力,促进我国农业科技成果在全世界范围内的交流。     

Recognition of thymine adenine.base pairs by guanine in a pyrimidine triple helix motif

Oligonucleotide recognition offers a powerful chemical approach for the sequence-specific binding of double-helical DNA. In the pyrimidine-Hoogsteen model, a binding size of greater than 15 homopurine base pairs affords greater than 30 discrete sequence-specific hydrogen bonds to duplex DNA. Because pyrimidine oligonucleotides limit triple helix formation to homopurine tracts, it is desirable to determine whether oligonucleotides can be used to bind all four base pairs of DNA. A general solution would allow targeting of oligonucleotides (or their analogs) to any given sequence in the human genome. A study of 20 base triplets reveals that the triple helix can be extended from homopurine to mixed sequences. Guanine contained within a pyrimidine oligonucleotide specifically recognizes thymine.adenine base pairs in duplex DNA. Such specificity allows binding at mixed sites in DNA from simian virus 40 and human immunodeficiency virus.     

Keeping G proteins at bay: a complex between G protein-coupled receptor kinase 2 and Gbetagamma

The phosphorylation of heptahelical receptors by heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptor kinases (GRKs) is a universal regulatory mechanism that leads to desensitization of G protein signaling and to the activation of alternative signaling pathways. We determined the crystallographic structure of bovine GRK2 in complex with G protein beta1gamma2 subunits. Our results show how the three domains of GRK2-the RGS (regulator of G protein signaling) homology, protein kinase, and pleckstrin homology domains-integrate their respective activities and recruit the enzyme to the cell membrane in an orientation that not only facilitates receptor phosphorylation, but also allows for the simultaneous inhibition of signaling by Galpha and Gbetagamma subunits.     

肉苁蓉组织培养的研究

为了探讨用组织培养的方法生产肉苁蓉药用成分的可行性，以肉苁蓉的茎片段、花为外植体进行了组织培养试验。结果表明，茎片段、子房外植体在添加2，4－D的培养基上诱导的愈伤组织分别呈块状、颗粒状，都为白色；而在添加KT的培养基上诱导的愈伤组织都呈颗粒状，黄绿色，添加KT，NAA的MT培养基对肉苁蓉愈伤组织的诱导及其生长效果最好。愈伤组织在从外植体母体上分割继代培养前，使愈伤组织与培养基接触培养15d后，有利于愈伤组织的生长。     

武字号玉米改良自交系产量性状配合力分析

根据中国玉米杂交优势利用模式,就国内种质系的选育对武109自交系用含唐四系、旅系种质的自交系进行了改良研究和自交选系。结果表明,选育的自交系8126一般配合力高,在5.77万株/hm2下测配新组合大穗大粒,抗病抗倒,结实性好,高产稳产,开发前景较好。     

Structure of a gammadelta T cell receptor in complex with the nonclassical MHC T22

Gammadelta T cell receptors (TCRs), alphabeta TCRs, and antibodies are the three lineages of somatically recombined antigen receptors. The structural basis for ligand recognition is well defined for alphabeta TCR and antibodies but is lacking for gammadelta TCRs. We present the 3.4 A structure of the murine gammadelta TCR G8 bound to its major histocompatibility complex (MHC) class Ib ligand, T22. G8 predominantly uses germline-encoded residues of its delta chain complementarity-determining region 3 (CDR3) loop to bind T22 in an orientation substantially different from that seen in alphabeta TCR/peptide-MHC. That junctionally encoded G8 residues play an ancillary role in binding suggests a fusion of innate and adaptive recognition strategies.     

草棉、瑟伯氏棉花粉在陆地棉柱头上的萌发及其花粉管的生长

以陆地棉作母本,分别与草棉、瑟伯氏棉杂交,陆地棉自交作对照,采用扫描电镜、荧光显微技术观察花粉萌发与花粉管的生长。结果是:自交对照的花粉在授粉后30分钟开始萌发,而两个异种的花粉与陆地棉柱头接触后1小时才开始萌发。异种花粉管在陆地棉花柱中生长时,出现膨大、分叉、扭曲折叠和花粉管尖而细长等异常现象。这些异常现象出现的时间是,陆地棉×草棉是在授粉后12-21小时,而陆地×瑟伯氏棉则是在授粉后6-12小时。进入子房的异种花粉管大多数先后停滞下来,不能进入胚珠,异常生长的主要表现是尖端膨大。     

栽培大豆、野生大豆和半野生大豆酯酶同工酶的研究

本文采用聚丙烯酰胺凝胶电泳法，分析了栽培大豆、野生大豆和半野生大豆的酯酶同工酶．结果表明，栽培大豆幼苗期的酯酶同工酶共出现了１７条酶带。栽培大豆和野生大豆既有共同的酶带，又有各自独特的酶带，是亲缘关系较近的两个种。半野生大豆有类似野生大豆的酶谱，表现了野生种的特点．不同进化类型的大豆酯酶同工酶有明显不同。随着进化程度增高，酶带数目有增多的趋势．研究表明，大豆幼苗酯酶同工酶酶谱比较稳定，酶带明确，具有较为明显的种的专一性，可以做为大豆分类学和研究大豆进化关系的一个生化指标。     

Helix geometry, hydration, and G.A mismatch in a B-DNA decamer

The DNA double helix is not a regular, featureless barberpole molecule. Different base sequences have their own special signature, in the way that they influence groove width, helical twist, bending, and mechanical rigidity or resistance to bending. These special features probably help other molecules such as repressors to read and recognize one base sequence in preference to another. Single crystal x-ray structure analysis is beginning to show us the various structures possible in the B-DNA family. The DNA decamer C-C-A-A-G-A-T-T-G-G appears to be a better model for mixed-sequence B-DNA than was the earlier C-G-C-G-A-A-T-T-C-G-C-G, which is more akin to regions of poly(dA).poly(dT). The G.A mismatch base pairs at the center of the decamer are in the anti-anti conformation about their bonds from base to sugar, in agreement with nuclear magnetic resonance evidence on this and other sequences, and in contrast to the anti-syn geometry reported for G.A pairs in C-G-C-G-A-A-T-T-A-G-C-G. The ordered spine of hydration seen earlier in the narrow-grooved dodecamer has its counterpart, in this wide-grooved decamer, in two strings of water molecules lining the walls of the minor groove, bridging from purine N3 or pyrimidine O2, to the following sugar O4'. The same strings of hydration are present in the phosphorothioate analog of G-C-G-C-G-C. Unlike the spine, which is broken up by the intrusion of amine groups at guanines, these water strings are found in general, mixed-sequence DNA because they can pass by unimpeded to either side of a guanine N2 amine. The spine and strings are perceived as two extremes of a general pattern of hydration of the minor groove, which probably is the dominant factor in making B-DNA the preferred form at high hydration.     

Structure of a transcribing T7 RNA polymerase initiation complex

The structure of a T7 RNA polymerase (T7 RNAP) initiation complex captured transcribing a trinucleotide of RNA from a 17-base pair promoter DNA containing a 5-nucleotide single-strand template extension was determined at a resolution of 2.4 angstroms. Binding of the upstream duplex portion of the promoter occurs in the same manner as that in the open promoter complex, but the single-stranded template is repositioned to place the +4 base at the catalytic active site. Thus, synthesis of RNA in the initiation phase leads to accumulation or "scrunching" of the template in the enclosed active site pocket of T7 RNAP. Only three base pairs of heteroduplex are formed before the RNA peels off the template.     

Structure and stability of X.G.C mismatches in the third strand of intramolecular triplexes

Intramolecular DNA triplexes that contain eight base triplets formed from the folding of a single DNA strand tolerate a single X.G.C mismatch in the third strand at acidic pH. The structure and relative stability of all four triplets that are possible involving a G.C Watson-Crick base pair were determined with one- and two-dimensional proton nuclear magnetic resonance techniques. Triplexes containing A.G.C, G.G.C, or T.G.C triplets were less stable than the corresponding parent molecule containing a C.G.C triplet. However, all mismatched bases formed specific hydrogen bonds in the major groove of the double helix. The relative effect of these mismatches on the stability of the triplex differs from the effect assayed (under different conditions) by two-dimensional gel electrophoresis and DNA cleavage with oligonucleotide EDTA.Fe(II).     

陆地棉×旱地棉F1代的性状遗传及细胞学研究

对陆地棉与旱地棉的杂种F,代及其亲本性状进行了调查,结果表明,杂交一代的性状表现有双亲性状,如株型、花冠大小等.有中间性状,也有超亲性状。如花萼齿数。对陆地棉与旱地棉的杂种F1代的花粉母细胞染色体的观察研究表明.陆地棉与旱地棉的杂种F1代不育的根本原因在于减数分裂中期染色体不能正常配对.引起部分染色体滞后及染色体习:=均衡分配,从而产生出多分孢子与微核,形成败育花粉,最终导致杂种不育。     

A complex with chromatin modifiers that occupies E2F- and Myc-responsive genes in G0 cells

E2F-6 contributes to gene silencing in a manner independent of retinoblastoma protein family members. To better elucidate the molecular mechanism of repression by E2F-6, we have purified the factor from cultured cells. E2F-6 is found in a multimeric protein complex that contains Mga and Max, and thus the complex can bind not only to the E2F-binding site but also to Myc- and Brachyury-binding sites. Moreover, the complex contains chromatin modifiers such as a novel histone methyltransferase that modifies lysine 9 of histone H3, HP1gamma, and Polycomb group (PcG) proteins. The E2F-6 complex preferentially occupies target promoters in G0 cells rather than in G1 cells. These data suggest that these chromatin modifiers contribute to silencing of E2F- and Myc-responsive genes in quiescent cells.     

掌叶大黄与河套大黄化学成分的比较研究

[目的]对陇东地区产的掌叶大黄（Rheumpalmatum L．）与河套大黄（RheumhotaoenseC．Y．ChengetC．T．Kao）根及根茎的化学成分进行研究。[方法]采用超声70％甲醇浸提法和硅胶柱色谱分离纯化,根据理化性质和波谱数据鉴定结构。[结果]从掌叶大黄与河套大黄根及根茎的70％甲醇提取物中共同分离鉴定出9种化合物,分别为：没食子酸（I）、大黄酸（Ⅱ）、大黄素（Ⅲ）、芦荟大黄素（Ⅳ）、芦荟大黄素．8．葡萄糖甙（Ⅴ）、大黄酚（Ⅵ）、大黄素甲醚（Ⅶ）、番泻甙A（Ⅷ）、番泻甙B（Ⅸ）。除此之外,从河套大黄的根中又分离出1种化合物——土大黄甙。[结论]河套大黄不能代替掌叶大黄作药用。