人参“最佳叶片”结构和超微结构特征的研究

弱光（ＬＬ）下叶片的比叶重、叶厚度、单位叶面积叶肉细胞数目和叶肉细胞表面积都明显低于“最佳叶片”和强光（ＨＬ）下叶片。与ＨＬ叶片相比,“最佳叶片”不仅比叶重和叶厚度略高于ＨＬ叶片,同时,单位叶面积叶肉细胞数目和叶肉细胞表面积也明显高于ＨＬ叶片。“最佳叶片”在靠近上表皮形成一层类似栅栏状细胞。随着光照的增加,人参叶片吉绿体和叶绿体基粒变小,基粒片层系统减少,淀粉粒和质体球却明显增多。“最佳叶片”叶绿     

A virus-encoded "superantigen" in a retrovirus-induced immunodeficiency syndrome of mice.

The development of an immunodeficiency syndrome of mice caused by a replication-defective murine leukemia virus (MuLV) is paradoxically associated with a rapid activation and proliferation of CD4+ T cells that are dependent on the presence of B cells. The responses of normal spleen cells to B cell lines that express the defective virus indicated that these lines express a cell surface determinant that shares "superantigenic" properties with some microbial antigens and Mls-like self antigens. This antigen elicited a potent proliferative response that was dependent on the presence of CD4+ T cells and was associated with selective expansion of cells bearing V beta 5. This response was markedly inhibited by a monoclonal antibody specific for the MuLV gag-encoded p30 antigen.     

Constitutive display of cryptic translation products by MHC class I molecules

Major histocompatibility complex (MHC) class I molecules display tens of thousands of peptides on the cell surface, derived from virtually all endogenous proteins, for inspection by cytotoxic T cells (CTLs). We show that, in normal mouse cells, MHC I molecules present a peptide encoded in the 3' "untranslated" region. Despite its rarity, the peptide elicits CTL responses and induces self-tolerance, establishing that immune surveillance extends well beyond conventional polypeptides. Furthermore, translation of this cryptic peptide occurs by a previously unknown mechanism that decodes the CUG initiation codon as leucine rather than the canonical methionine.     

Transgenic mice with I-A on islet cells are normoglycemic but immunologically intolerant

Insulin-dependent diabetes mellitus (IDDM) is caused by a specific loss of the insulin-producing beta cells from pancreatic Langerhans islets. It has been proposed that aberrant expression of major histocompatibility complex (MHC) class II molecules on these cells could be a triggering factor for their autoimmune destruction. This proposal was tested in transgenic mice that express allogeneic or syngeneic class II molecules on the surface of islet cells at a level comparable with that normally found on resting B lymphocytes. These animals do not develop diabetes, nor is lymphocyte infiltration of the islets observed. This immunological inactivity does not result from tolerance to the "foreign" class II molecules.     

Bakers' yeast, a model for fungal biofilm formation

Biofilms are formed by the aggregation of microorganisms into multicellular structures that adhere to surfaces. Here we show that bakers' yeast Saccharomyces cerevisiae can initiate biofilm formation. When grown in low-glucose medium, the yeast cells adhered avidly to a number of plastic surfaces. On semi-solid (0.3% agar) medium they formed "mats": complex multicellular structures composed of yeast-form cells. Both attachment to plastic and mat formation require Flo11p, a member of a large family of fungal cell surface glycoproteins involved in adherence. The ability to study biofilm formation in a tractable genetic system may facilitate the identification of new targets for antifungal therapy.     

Disulfur monoxide: production by Desulfovibrio

Desulfovibrio desulfuricans growing on agar surfaces produces a gas that appears to be identical to "Schenk's sulfur monoxide," which was later identified as disulfur monoxide The gas stimulates surface growth of Desulfovibrio on an agar medium and is used by the cells as an electron donor for the reduction of benzyl viologen.     

Conserved eukaryotic fusogens can fuse viral envelopes to cells

Caenorhabditis elegans proteins AFF-1 and EFF-1 [C. elegans fusion family (CeFF) proteins] are essential for developmental cell-to-cell fusion and can merge insect cells. To study the structure and function of AFF-1, we constructed vesicular stomatitis virus (VSV) displaying AFF-1 on the viral envelope, substituting the native fusogen VSV glycoprotein. Electron microscopy and tomography revealed that AFF-1 formed distinct supercomplexes resembling pentameric and hexameric "flowers" on pseudoviruses. Viruses carrying AFF-1 infected mammalian cells only when CeFFs were on the target cell surface. Furthermore, we identified fusion family (FF) proteins within and beyond nematodes, and divergent members from the human parasitic nematode Trichinella spiralis and the chordate Branchiostoma floridae could also fuse mammalian cells. Thus, FF proteins are part of an ancient family of cellular fusogens that can promote fusion when expressed on a viral particle.     

利用扫描电镜原位拉伸研究竹材增韧机制

为了阐明竹材优良韧性的力学原理,以毛竹为研究对象,使用扫描电镜联用原位加载设备观察了竹材薄片纵向拉伸过程的裂纹扩展规律,并对断裂表面进行了组织水平、细胞水平、亚细胞水平的多尺度显微观察。结果表明:竹材纵向拉伸断裂裂纹拓展一般呈阶梯型展开。维管束与基本组织之间、竹纤维与薄壁组织细胞之间、纤维和薄壁细胞的壁层之间均有明显的分层现象,表明竹材断裂过程中存在从组织到细胞,乃至亚细胞水平的多级弱界面。这些弱界面可以有效阻碍裂纹扩展,增加断裂消耗功,从而显著增强竹材的韧性。      

牛卵丘－卵母细胞复合体体外成熟前后超微结构

实验用透射电镜技术研究了牛卵立－卵母细胞复合体（ＣＯＣ）体外成熟前后卵母细胞、卵丘细胞及它们之间联系的结构特征．体外培养前,卵母细胞微绒毛数量较少,有的伸入秀明带中;各种细胞器集中分布于皮质区,形成“细胞器带”;核膜可打褶,核仁致密化．卵母细胞与卵丘细胞间及卵丘细胞之间形成间隙连接;卵丘细胞中线粒体致密、形态多样．成熟培养后．微绒毛增多．卵周隙形成;高尔基复合体消失,脂滴伴随着线粒体内迁．少数线粒体转变为幼稚型,皮质区形成“细胞器游离带’;皮质颗粒开始沿质膜下呈线状排列,但有的仍成团分布;排出第一极体处无微绒毛．中期赤道板附近无细胞器;卵丘细胞间及卵丘细胞与卵母细胞间联系中止;卵丘细胞中线粒体转变为幼稚型．     

Protein, DNA, and virus crystallography with a focused imaging proportional counter

A set of programs has been developed for rapid collection of x-ray intensity data from protein and virus crystals with a commercially available two-dimensional focused geometry electronic detector. The detector is compact and portable, with unusually high spatial resolution comparable to that used in oscillation photography. It has allowed x-ray data collection on weakly diffracting crystals with large unit cells, as well as more conventional "diffractometer-quality" crystals. The quality of the data is compared with that from oscillation photography and automated diffractometry in the range of unit cells from 96.3 to 383.2 angstroms. Isomorphous and anomalous difference Pattersons, based on detector data, are shown for a variable surface glycoprotein mercury derivative and for a repressor-DNA bromine derivative, which has been solved at 7 angstroms with detector data only.     

牛卵丘－卵母细胞复合体体外成熟前后超微结构

实验用透射电镜技术研究了牛卵立－卵母细胞复合体（ＣＯＣ）体外成熟前后卵母细胞、卵丘细胞及它们之间联系的结构特征．体外培养前,卵母细胞微绒毛数量较少,有的伸入秀明带中;各种细胞器集中分布于皮质区,形成“细胞器带”;核膜可打褶,核仁致密化．卵母细胞与卵丘细胞间及卵丘细胞之间形成间隙连接;卵丘细胞中线粒体致密、形态多样．成熟培养后．微绒毛增多．卵周隙形成;高尔基复合体消失,脂滴伴随着线粒体内迁．少数线粒体转变为幼稚型,皮质区形成“细胞器游离带’;皮质颗粒开始沿质膜下呈线状排列,但有的仍成团分布;排出第一极体处无微绒毛．中期赤道板附近无细胞器;卵丘细胞间及卵丘细胞与卵母细胞间联系中止;卵丘细胞中线粒体转变为幼稚型．     

变色沙蜥鳞片显微皮纹结构和功能

对隶属鬣蜥科、沙蜥属的变色沙蜥鳞片扫描电镜下超微结构的观察，发现了类似“钉状”感受器的结构，与壁虎科和美洲鬣蜥科中的类似。感受器分布在全身各处的鳞片中，以头背部鳞片上数量众多。所有的鳞片表面结构类似，鳞片上的角皮层细胞表面平坦，没有明显的微饰物结构，除了头背部的鳞片呈多角形细胞样。考虑到干燥环境下生活的种类附着污物不是主要的问题，而主要选择是减少反光，显微皮纹特征很好的符合这一假说。     

Salt transport organelle in Artemia salenis (brine shrimp)

The branchiae of Artemia adapted to triple-strength sea water (105 per mil salinity) were studied with the electron microscope. The epithelial lining of the metepipodite segment possesses organelles composed of stacks of disc-shaped mitochondria interlaced with flattened extensions of a canalicular system that in turn communicates with the plasma-bound surface of the cells. The distance between the canalicular and mitochondrial membranes is small and quite constant. The marked similarity to "mitochondrial pumps" in the anal papillae of tosquito larvae suggests that the organelle is concerned with salt transport.     

大豆花柱和柱头的显微结构观察

以无限型开花大豆品种东农434(Glycine max L.Merr.cv.Dongnong434)为试验材料,利用光学显微镜、透射电子显微镜和扫描电子显微镜观察大豆花柱和柱头结构。结果表明,大豆柱头属于湿柱头,成熟的柱头表面由两种类型的乳突构成,在柱头上有一层表膜;柱头细胞内有丰富的细胞器,液泡内沉积有电子致密的贮藏物质。大豆花柱属于中空花柱,花柱成倒"J"形,靠近柱头部分发生弯曲,花柱基部表皮有气孔和表皮毛。花柱中央为花柱道,其周围分布有一层特殊的通道细胞。成熟花柱细胞中含有丰富的多糖类物质。     

A new way to keep immune cells in check

To avoid being attacked by the immune system, normal cells carry proteins on their surfaces that mark them as "self." Until now, researchers have identified only one type of self marker: so-called class I major histocompatibility complex proteins. Now, on page 2051, a team reports that macrophages, the immune system's scavenger cells, recognize a different inhibitory signal--a protein called CD47. The findings also shed light on the role of CD47, a surface protein present on basically every cell type--and long a molecule in search of a function.     

Scissors-grip model for DNA recognition by a family of leucine zipper proteins

C/EBP is a sequence-specific DNA binding protein that regulates gene expression in certain mammalian cells. The region of the C/EBP polypeptide required for specific recognition of DNA is related in amino acid sequence to other regulatory proteins, including the Fos and Jun transforming proteins. It has been proposed that these proteins bind DNA via a bipartite structural motif, consisting of a dimerization interface termed the "leucine zipper" and a DNA contact surface termed the "basic region." An evaluation of the properties of conserved amino acids within the basic region of 11 deduced protein sequences, coupled with the observation that they are located at an invariant distance from the leucine zipper, has led to the formulation of a "scissors-grip" model for DNA binding. The architectural features of this model are well suited for interaction with directly abutted, dyadsymmetric DNA sequences. Data supportive of the model were obtained with chemical probes of protein: DNA complexes.     

土壤湿度估计的理想同化试验研究

通过使用集合Kalman滤波,建立基于不同离散化方法的同化土壤湿度的理想试验。通过设置不同的初始状态,以集合预报的形式建立了openloop和模拟的理想＂真值＂,并将来自不同离散化方法得到的理想＂真值＂集合生成多模型集合预报的理想＂真值＂。分别使用单个的离散化方法同化来自各自理想＂真值＂和多模型集合预报的理想＂真值＂,来检验通过同化表层土壤湿度后对整个湿度廓线的改进能力。结果表明,由于不同的离散化方法建立的土壤层之间的相关性不同,不同的离散化方法通过同化表层土壤湿度后土壤湿度廓线均有改进,但是改进的效率不同;当使用多模型的集合预报时,能够更有效地吸收观测,比任何单个模型的同化效果都要好。     

Creating long-lived superhydrophobic polymer surfaces through mechanically assembled monolayers

We show that elastomeric surfaces can be tailored using "mechanically assembled monolayers" (MAMs), structures that are fabricated by combining self-assembly of surface grafting molecules with mechanical manipulation of the grafting points in the underlying elastic surface. The versatility of this surface modification method is demonstrated by fabricating MAMs with semifluorinated (SF) molecules. These SF-MAMs have superior nonwetting and barrier properties in that they are "superhydrophobic" and nonpermeable. We also establish that these material characteristics do not deteriorate even after prolonged exposure to water, which usually causes surface reconstruction in conventionally prepared SF self-assembled monolayers.     

我国四大名园水体的水面理景手法和理论研究

以＂避暑山庄＂、＂清漪园＂、＂拙政园＂、＂留园＂的水体理景为研究对象,重点研究了我国四大名园水体的水面理景处理手法和相关理论。其中＂避暑山庄＂水体立意为表现江南水乡情调,水面处理手法采用师法江南水乡特点的水网密布,洲岛环水,星罗棋布,以洲、岛、堤、桥为划分水面的手法,来表现江南水乡水面的基本自然特征。＂清漪园＂水体立意为略师西湖其意而融己所长,水面处理手法采用两断＂西堤＂及支堤分隔水面,并赋予皇家御苑＂仙苑＂和＂天人感应＂的思想内涵。＂拙政园＂和＂留园＂水体更注重通过＂一勺代水＂的水面处理手法达到＂一勺则江湖万里＂来表现立意,让人联想到的水体空间有＂纳千顷之汪洋＂的意境。该研究可在风景园林设计师设计处理水面时提供借鉴和参考。     

食蚊鱼白内障的研究初报

采用定期观察方法,了解食蚊鱼白内障的发生过程以及由此导致的外部形态和行为的变化情况。研究的食蚊鱼群体的白内障有较高的发生率,白内障鱼一般体色晦暗,经常浮于水面缓慢游动;其摄食和生长也受较大影响。食蚊鱼白内障大多是双眼同时发生的,眼球可见不同程度的浑浊。从外观形态区分,食蚊鱼白内障主要有两种类型,一种是绕核性白内障,另一种无法看到晶状体形状,表现为整个眼球的不透明。对病鱼的眼球等进行组织病理观察,发现病理变化部位主要在晶体,所有病例的晶状体纤维都出现病理变化,最普遍的是晶状体皮质区纤维不同程度变性或断裂;晶状体上皮细胞有脱落、增生等。食蚊鱼白内障为鱼类白内障研究提供良好材料。