Identifying the conformational state of bi-liganded haemoglobin

While most researchers agree on the global features of cooperative ligand binding to haemoglobin (Hb), the internal mechanisms remain open to debate. This is not due to inaccurate measurements, but is rather a consequence of the cooperative ligand binding that decreases the equilibrium populations of the partially liganded states and makes observation of the transitions between these substates more difficult. For example, the equilibrium population of the doubly liganded tetramers is typically less than 5% of the total Hb. As a result many models with widely varying mechanisms may fit the oxygen equilibrium curve, but may not be consistent with observations of other parameters, such as ligand-binding kinetics or subunit association equilibria. The wide range of methods and models has led to divergent conclusions about the properties of specific substates. One notable debate concerns the properties of the doubly liganded forms. The simple two-state model predicts a shift in the allosteric equilibrium based on the number of ligands bound, but not on their distribution within the tetramer. From studies of dimer-tetramer equilibria of various pure and hybrid forms, it was concluded that a tetramer with two ligands bound on the same α β dimer (species 21, an asymmetric hybrid) shows an enhanced tetramer stability, similar to singly liganded Hb, relative to the other three types of doubly liganded tetramers which resemble the triply liganded forms [Ackers et al. (1992), Science 255: 54–63]. The implications of this model and the relevant experiments will be reviewed here. Received 27 April 1998; received after revision 17 July 1998; accepted 10 August 1998     

水滑石类有机无机杂化材料的合成与嫁接作用

以硝酸根型水滑石为前驱体,采用阴离子直接交换法制备了水杨酸根柱撑水滑石有机-无机杂化材料,在对样品进行结构表征的基础上,用DTA、IR和XRD等手段研究了主体层板和客体阴离子柱之间的相互作用.结果表明,有机阴离子插入水滑石层间,由于主客体相互作用,可使水滑石层的脱羟基温度和有机阴离子的燃烧分解温度得到较大幅度的提高.不同温度处理样品的XRD和IR研究表明,样品的热处理过程实质上是一个促进主客体相互作用的过程,即客体阴离子向主体层板的嫁接过程,其直接结果是形成氢键.通常,对嫁接温度的选择应是在样品的脱除层间水和羟基完全脱去的温度之间.     

西昌地区玉米杂交种单株产量与主要农艺性状相关性分析

对130个玉米杂交种的株高、百粒重、穗行数等12个农艺性状与单株产量进行了相关分析,结果表明,单株产量与穗重、行粒数、穗粗、百粒重、穗长均呈极显著正相关,相关系数分别为0.98403、0.70197、0.70007、0.65396、0.52793;而穗重与穗粗、行粒数、百粒重、穗长也呈极显著正相关。进一步通径分析表明,各性状对产量的直接效应依次为穗重>穗长>行粒数>穗轴粗>穗行数>穗位高>百粒重>穗粗>穗位叶宽。因此,在西昌地区玉米育种工作中,增大穗长和行粒数,提高穗位高和穗位叶宽,并注重其他性状的选择,是获得玉米高产的科学有效办法。     

Cationic Organic/Inorganic Hybrids and Their Swelling Properties

Specific properties of poly（dimethylsiloxanes）, such as low glass transition temperature, low surface energy, good insulating properties, biological and chemical inertness, high diffusion coefficient of gases, make them very attractive for practical applications in the daily life. However, there is a great interest last time in the preparation of ionic organic/inorganic materials with new properties for new applications. Quaternary ammonium salt（QAS） groups included in siloxane copolymers could induce new interesting properties such as： permanent fungicidal and bactericidal properties, which make them very attractive as materials for sanitary applications, improved selectivity coefficients of the gas-separation membranes, ion-exchange properties and so forth. So far, QAS groups have been located in the side chain.     

水稻籼粳杂交F_1植株育性与花粉育性的关系

以2个广亲和品种(轮回422,02428)分别与籼、粳稻配组及粳/籼、籼/粳、粳/粳配组,检测了杂种F1代的结实率及镜检亲本F1代的花粉活性.试验结果表明:除测49外,亲本花粉可育性均较高,杂种F1代的花粉育性因亲本不同而有所差异,以广亲和品种与籼、粳稻配组所得的杂种F1代的花粉可育性最高;籼粳杂种F1代的花粉败育率与植株不结实率的相关系数达0.8380.     

水稻籼粳杂交F1植株育性与花粉育性的关系

以2个广亲和品种(轮回422，02428)分别与籼、粳稻配组及粳/籼、籼/粳、粳/粳配组，检测了杂种F1代的结实率及镜检亲本F1代的花粉活性.试验结果表明：除测49外，亲本花粉可育性均较高，杂种F1代的花粉育性因亲本不同而有所差异，以广亲和品种与籼、粳稻配组所得的杂种F1代的花粉可育性最高；籼粳杂种F1代的花粉败育率与植株不结实率的相关系数达0.838 0.     

猕猴桃种间体细胞杂种的抗寒性遗传的初步分析

中华猕猴桃（Actinitia chinesis）与狗枣猕猴桃（A.kolomidta）各间体细胞杂种无性系试管苗叶片在20,10,4,0和－15℃温度处理理,叶片细胞的电导率、脯氨酸质量分数ω和丙二醛质量摩尔浓度b具有不同的变化,结合叶片厚度测量数据,进行聚类分析的结果表明：种间体细胞杂种无性系CK6和CK13的抗寒性弱,趋向于中华猕猴桃;而无性系CK11和CK8的抗寒性强,趋向于狗枣猕猴桃。     

不同栽培技术对彩色马蹄莲生长的影响

本文研究了不同栽培基质、施肥量和赤霉素浓度对彩色马蹄莲生长的影响。通过测定不同栽培技术处理后彩色马蹄莲株高生长、开花数、开花期、开花质量的变化,为彩色马蹄莲栽培提供理论和技术依据。结果表明：彩色马蹄莲基质要求排水良好、肥料充足,生长需肥不易太多,施肥过多反而容易引起植株腐烂;赤霉素处理以GA3浓度为300mg／L植株生...     

Microwave absorption properties of SiC@SiO2@Fe3O4 hybrids in the 2–18 GHz range

To enhance the microwave absorption performance of silicon carbide nanowires (SiCNWs), SiO2 nanoshells with a thickness of approximately 2 nm and Fe3O4 nanoparticles were grown on the surface of SiCNWs to form SiC@SiO2@Fe3O4 hybrids. The microwave absorption performance of the SiC@SiO2@Fe3O4 hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO2@Fe3O4 hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO2 to iron(III) acetylacetonate mass ratio of 1:3,themicrowave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of?39.58 dB at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe3O4 nanoparticles coated on SiC@SiO2 nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation.     

Evolutionary analysis of allotetraploid hybrids of red crucian carp × common carp, based on ISSR, AFLP molecular markers and cloning of cyclins genes

The allotetraploid hybrids of red crucian carp x common carp are the first reported artificially cultured polyploid fish with bisexual fertility and stable inheritance in vertebrate. Using ISSR and AFLP markers and the cyclins genes, the genomes and cyclin gene sequence changes were analyzed between the allotetraploid hybrids and their parents. The results indicated that the allotetraploids inherited many genetic characteristics from their parents and the genetic characteristics were stable after 15 generations. However, the allotetraploids had a closer genetic relationship with their original female parents and represented a bias toward the maternal progenitor. DNA fingerprinting analysis showed that the allotetraploids had undergone sequences deletion from their original parents and that the deleted sequences were mostly from the male parent＇s genome. Some non-parental bands were found in the allotetraploid hybrids. Sequences analysis of the cyclin A1 and B1 genes showed nonsynonymous substitutions of single nucleotides in codons that were different from their original parents, leading to non-parental amino acid loci. We speculate that the non-additivity in the allotetraploids, compared with their progenitors, could be an adjustment to the genomic shock from heterozygosity and polyploidy, allowing maintenance of genetic stability.