新质源雄性不育烟草MS革新3号雄蕊发生的细胞学观察

雄性不育烟草MS革新3号的雄性败育时期发生在雄蕊原基分化后至孢原细胞形成前,在开放花朵中很少能见到退化的雄蕊,偶或有退化雄蕊的,也没有正常花药的形成,仅有退化花丝和畸形萎缩花药,花药内空无一物。与正常烟草(保持系)子房由2心皮组成不同,雄性不育烟草MS革新3号子房绝大多数都由3心皮组成。     

小麦生理型雄性不育系微丝骨架和胼胝质的变化与其相关基因的表达分析

【目的】研究生理型雄性不育小麦花粉细胞内微丝和胼胝质的结构及其相关基因的表达,并揭示其与生理型雄性不育的关系,为进一步研究化学杂交剂SQ-1诱导小麦生理型雄性不育的机理提供一定的理论依据。【方法】以化学杂交剂SQ-1诱导的生理型雄性不育系ms(A)-西农1376及对应正常可育系(A)-西农1376为试材,用TRITC-phalloidin标记细胞内微丝,苯胺蓝标记胼胝质,qRT-PCR技术分别对肌动蛋白解聚因子TaADF（Actin depolymerizing factor）、类葡聚糖合成酶TaGSL（Glucan synthase-like）进行差异表达分析。【结果】(1)在减数分裂前期Ⅰ、中期Ⅰ、后期Ⅰ这三个时期,生理型雄性不育系花粉细胞的微丝结构与可育系没有显著差异：前期Ⅰ,微丝分布于整个细胞质中,细胞核区域也可见少量微丝环绕细胞核;中期Ⅰ,微丝分布在细胞质中,在形成纺锤体部位染色更深,形成纺锤体微丝,由细胞两极发出的纺锤体微丝伸向赤道板;后期Ⅰ,在向两极移动的染色体的中间部位染色较深,微丝分布较多。(2)在早末期Ⅰ,与可育系相比,不育系花粉细胞没有形成清晰且明显可见的中国灯笼状成膜体微丝结构,且在细胞中线部位亦没有清晰可见的微丝累积。(3)晚末期Ⅰ,可育系花粉细胞在形成细胞板的部位是线性的、平滑的,成膜体微丝消失,而不育系花粉细胞在形成细胞板的部位形成了很大的缝隙,同时,可育系胼胝质在细胞板处的沉积比较平滑,而不育系胼胝质在细胞板处的沉积较可育系相比缺乏,并且是褶皱的、有裂纹的。(4)四分体时期,可育系花粉可见围绕细胞核的辐射状微丝,不育系花粉细胞中微丝呈模糊状态,并且不育系中胼胝质染色的整体荧光强度较可育系减弱。利用实时荧光定量PCR技术分析肌动蛋白解聚因子TaADF和类葡聚糖合成酶TaGSL在减数分裂期的相对表达量,结果发现,不育系中TaADF的相对表达量是可育系的4.28倍,由于TaADF表达量上调,加剧了细胞内微丝解聚,微丝结构受到破坏,同时不育系中TaGSL表达量下降,只有可育系的0.83倍,胼胝质的沉积也受到影响。【结论】TaADF在不育系中上调表达,破坏了细胞内微丝的正常结构,使微丝不能正常行使其功能,进而可能导致花药发育中与育性相关的某些代谢通路等受到影响。与此同时,微丝结构的破坏导致细胞板形成出现异常也可能是引起胼胝质在细胞板处沉积受到影响的一个重要原因。因此,微丝和胼胝质的异常变化与化学杂交剂SQ-1诱导的生理型雄性不育密切相关。     

Polarity and velocity of sliding filaments: control of direction by actin and of speed by myosin

Myosin filaments, which are responsible for a large repertoire of motile activities in muscle and nonmuscle cells, can translocate actin filaments both toward and away from their central bare zone. This bidirectional movement suggests that there is enough flexibility in the head portion of the tightly packed myosin molecules in the native myosin filaments to move actin filaments not only in the expected direction, but also in the direction opposite to that predicted by the regular structure of muscle--away from the center of the myosin filament.     

Observations of extreme upwelling filaments in the southeast atlantic ocean

Cold oceanic water upwells along the western coastline of most major continents. The thermal front that demarcates the farthest seaward extent of this upwelled water is sometimes characterized by extensive whisps or cross-frontal filaments. These may play an important role in the functioning of the upwelling ecosystem as a whole. Satellite observations on filaments of the Benguela upwelling system show filaments that exceed 1000 kilometers in length. Two mechanisms that may produce the exceptional length of these filaments are interaction with Agulhas rings and the effect of intense berg winds.     

Alzheimer's disease: insolubility of partially purified paired helical filaments in sodium dodecyl sulfate and urea

A method is described for the partial purification of the paired helical filaments that accumulate progressively in human neurons in Alzheimer's disease (senile dementia). Paired helical filaments have unusual solubility characteristics, including insolubility in sodium dodecyl sulfate, urea, reducing agent, and guanidine, which prevent analysis of their molecular composition by gel electrophoresis. The paired helical filaments appear to contain covalent bonds other than disulfide, which cross-link individual filaments into a rigid intracellular polymer. Thus, paired helical filaments appear to represent an example in neurons of an insoluble cross-linked protein. Covalently cross-linked protein polymers occur in lens senile cataracts and in terminally differentiated skin keratinocytes, suggesting that there may be a common mechanism for remodeling some structural proteins during cell aging.     

杜仲叶橡胶丝网络结构的研究

除去非胶成分使纯粹的橡胶丝完全暴露出来，可得到杜仲全叶的胶丝网络体系。通过观察和比较，可见杜仲叶中的胶丝网络结构与叶脉的网络结构完全一致，证明胶丝是叶脉的组成部分。同时观察到杜仲叶缘锯齿的骨架主要由两股胶丝组成，胶丝网络的分枝形式为反向汇集型，叶尖附近的叶缘上排列着发育不平衡的锯齿结构     

Magnetosomes are cell membrane invaginations organized by the actin-like protein MamK

Magnetosomes are membranous bacterial organelles sharing many features of eukaryotic organelles. Using electron cryotomography, we found that magnetosomes are invaginations of the cell membrane flanked by a network of cytoskeletal filaments. The filaments appeared to be composed of MamK, a homolog of the bacterial actin-like protein MreB, which formed filaments in vivo. In a mamK deletion strain, the magnetosome-associated cytoskeleton was absent and individual magnetosomes were no longer organized into chains. Thus, it seems that prokaryotes can use cytoskeletal filaments to position organelles within the cell.     

Twisting motions of sunspot penumbral filaments

The penumbra of a sunspot is composed of numerous thin, radially extended, bright and dark filaments carrying outward gas flows (the Evershed flow). Using high-resolution images obtained by the Solar Optical Telescope aboard the solar physics satellite Hinode, we discovered a number of penumbral bright filaments revealing twisting motions about their axes. These twisting motions are observed only in penumbrae located in the direction perpendicular to the symmetry line connecting the sunspot center and the solar disk center, and the direction of the twist (that is, lateral motions of intensity fluctuation across filaments) is always from limb side to disk-center side. Thus, the twisting feature is not an actual twist or turn of filaments but a manifestation of dynamics of penumbral filaments with three-dimensional radiative transfer effects.     

Conducting polyaniline filaments in a mesoporous channel host

Conducting filaments of polyaniline have been prepared in the 3-nanometer-wide hexagonal channel system of the aluminosilicate MCM-41. Adsorption of aniline vapor into the dehydrated host, followed by reaction with peroxydisulfate, leads to encapsulated polyaniline filaments. Spectroscopic data show that the filaments are in the protonated emeraldine salt form, and chromatography indicates chain lengths of several hundred aniline rings. The filaments have significant conductivity while encapsulated in the channels, as measured by microwave absorption at 2.6 gigahertz. This demonstration of conjugated polymers with mobile charge carriers in nanometer channels represents a step toward the design of nanometer electronic devices.     

光对美洲蛙肌肉纤维衍射强度的分布研究

肌原纤维是由粗丝和细丝重迭而成的Ａ带和只含细丝的Ⅰ带组成，形成了天然光栅，因此可用光学方法探讨肌原纤维分子结构及其动力学问题。试验表明，单色光通过美洲蛙肌原纤维后，衍射光左右两端为非对称性，且左右条纹锋值间隔随肌原纤维节长度增大而减小。肌肉运动有张有弛，于是肌原纤维长度有变异，共变异与非对称有关。当肌原纤维长度增加时，左右两端强度差异变大，而相对应条纹的锋值间隔距离变小。这一现象与布拉格方程和折射     

Coupled, circumferential motions of the cell wall synthesis machinery and MreB filaments in B. subtilis

Rod-shaped bacteria elongate by the action of cell wall synthesis complexes linked to underlying dynamic MreB filaments. To understand how the movements of these filaments relate to cell wall synthesis, we characterized the dynamics of MreB and the cell wall elongation machinery using high-precision particle tracking in Bacillus subtilis. We found that MreB and the elongation machinery moved circumferentially around the cell, perpendicular to its length, with nearby synthesis complexes and MreB filaments moving independently in both directions. Inhibition of cell wall synthesis by various methods blocked the movement of MreB. Thus, bacteria elongate by the uncoordinated, circumferential movements of synthetic complexes that insert radial hoops of new peptidoglycan during their transit, possibly driving the motion of the underlying MreB filaments.     

萱藻丝状体诱导培养及采苗研究

对萱藻Scytosiphon lomentaria丝状体诱导培养及采苗进行了研究。在室内培养条件下,从萱藻盘状孢子体上获得了丝状体并游离培养成直径为1～2cm的藻团,采用将丝状体切碎的方法获得大量盘状孢子体,盘状孢子体经生长后在10℃和15℃下形成单室孢子囊并放出游孢子,以维尼纶绳为附着基进行孢子采集,置于10℃下培养35d后获得藻体长度为0．5～1.0cm的萱藻幼苗。结果表明：盘状孢子体在藻体直径达到100μm后开始形成丝状体,20℃下丝状体形成的时间早、数量多,生长速度快,切碎后的丝状体在20℃下5d后开始形成盘状体,20d后其形成率达到100％;15℃下10d后形成盘状体,20d后其形成率为65％;10℃下12d后才形成盘状体,20d后的形成率仅为40％。     

Elastic behavior of cross-linked and bundled actin networks

Networks of cross-linked and bundled actin filaments are ubiquitous in the cellular cytoskeleton, but their elasticity remains poorly understood. We show that these networks exhibit exceptional elastic behavior that reflects the mechanical properties of individual filaments. There are two distinct regimes of elasticity, one reflecting bending of single filaments and a second reflecting stretching of entropic fluctuations of filament length. The mechanical stiffness can vary by several decades with small changes in cross-link concentration, and can increase markedly upon application of external stress. We parameterize the full range of behavior in a state diagram and elucidate its origin with a robust model.     

Self-assembled silica-carbonate structures and detection of ancient microfossils

We have synthesized inorganic micron-sized filaments, whose microstucture consists of silica-coated nanometer-sized carbonate crystals, arranged with strong orientational order. They exhibit noncrystallographic, curved, helical morphologies, reminiscent of biological forms. The filaments are similar to supposed cyanobacterial microfossils from the Precambrian Warrawoona chert formation in Western Australia, reputed to be the oldest terrestrial microfossils. Simple organic hydrocarbons, whose sources may also be abiotic and indeed inorganic, readily condense onto these filaments and subsequently polymerize under gentle heating to yield kerogenous products. Our results demonstrate that abiotic and morphologically complex microstructures that are identical to currently accepted biogenic materials can be synthesized inorganically.     

Assembly mechanism of the contractile ring for cytokinesis by fission yeast

Animals and fungi assemble a contractile ring of actin filaments and the motor protein myosin to separate into individual daughter cells during cytokinesis. We used fluorescence microscopy of live fission yeast cells to observe that membrane-bound nodes containing myosin were broadly distributed around the cell equator and assembled into a contractile ring through stochastic motions, after a meshwork of dynamic actin filaments appeared. Analysis of node motions and numerical simulations supported a mechanism whereby transient connections are established when myosins in one node capture and exert force on actin filaments growing from other nodes.     

Differential transmission of actin motion within focal adhesions

Cell migration requires the transmission of motion generated in the actin cytoskeleton to the extracellular environment through a complex assembly of proteins in focal adhesions. We developed correlational fluorescent speckle microscopy to measure the coupling of focal-adhesion proteins to actin filaments. Different classes of focal-adhesion structural and regulatory molecules exhibited varying degrees of correlated motions with actin filaments, indicating hierarchical transmission of actin motion through focal adhesions. Interactions between vinculin, talin, and actin filaments appear to constitute a slippage interface between the cytoskeleton and integrins, generating a molecular clutch that is regulated during the morphodynamic transitions of cell migration.     

Direct redox regulation of F-actin assembly and disassembly by Mical

Different types of cell behavior, including growth, motility, and navigation, require actin proteins to assemble into filaments. Here, we describe a biochemical process that was able to disassemble actin filaments and limit their reassembly. Actin was a specific substrate of the multidomain oxidation-reduction enzyme, Mical, a poorly understood actin disassembly factor that directly responds to Semaphorin/Plexin extracellular repulsive cues. Actin filament subunits were directly modified by Mical on their conserved pointed-end, which is critical for filament assembly. Mical posttranslationally oxidized the methionine 44 residue within the D-loop of actin, simultaneously severing filaments and decreasing polymerization. This mechanism underlying actin cytoskeletal collapse may have broad physiological and pathological ramifications.     

Acetyl coenzyme A carboxylase: filamentous nature of the animal enzymes

Acetyl coenzyme A carboxylases purified from several animal tissues exist as enzymatically active polymeric filaments of high molecular weight and have simillar electron microscopic, hydrodynamic, and catalytic properties. These filaments reversibly dissociate into inactive protomers of uniform size. Their re-assembly into catalytically active filaments is promoted by the presence of an allosteric activator.     

Single-molecule speckle analysis of actin filament turnover in lamellipodia

Lamellipodia are thin, veil-like extensions at the edge of cells that contain a dynamic array of actin filaments. We describe an approach for analyzing spatial regulation of actin polymerization and depolymerization in vivo in which we tracked single molecules of actin fused to the green fluorescent protein. Polymerization and the lifetime of actin filaments in lamellipodia were measured with high spatial precision. Basal polymerization and depolymerization occurred throughout lamellipodia with largely constant kinetics, and polymerization was promoted within one micron of the lamellipodium tip. Most of the actin filaments in the lamellipodium were generated by polymerization away from the tip.     

Isolation of filaments from brain

A method is presented for the isolation of filaments of 90-angstrom diameter from the white matter of bovine brain by first floating the myelinated axons in a centrifugal field and then fractionating the axons on a series of density gradients. This results in a fraction that contains two types of bundles of filaments but few other constituents. The filaments are stable over a wide range of temperatures and at both low and high ionic strength. Their density and their resistance to digestion by ribonuclease and deoxyribonuclease indicate that they are primarily protein. The molecular weight of the subunit is approximately 60,000. The protein does not comigrate with microtubule protein and does not bind cholcicine or nucleotides.