传递细胞——物质短途运输中起作用的特化细胞

传递细胞广泛存在于植物界的各种群。传递细胞的分化主要与器官的发育程度以及转运物质的供应有关。当植物某个部位所需的运输速率远高于溶质正常跨膜运输速率时,在此部位就可能有传递细胞。传递细胞最基本的特征是细胞壁向内突起生长（壁内突）并与质膜共同形成壁膜器。壁内突从形态上可划分为2种类型：网状内突和肋状内突。大多数传递细胞壁内突的发育在沿着溶质流动的方向表现出极性。传递细胞的胞质一般比周围薄壁组织细胞浓,胞内富含线粒体和内膜分泌系统细胞器如内质网、高尔基体、小囊泡等。传递细胞在物质的短途运输中起作用。玉米胚乳传递细胞可能还具有防御病原微生物进入胚乳和胚的功能。本文就传递细胞的种类和特性、结构和功能、形成机制和诱导因素,以及基因表达调控等方面的研究进展做介绍。     

荞麦胚和胚乳的发育及贮藏营养物质的积累

荞麦原胚期,胚乳为游离核期。球形胚晚期,胚乳开始细胞化。心形胚期,胚囊中部形成一层“开放细胞”。鱼雷形胚期,胚囊中部有５－７层胚乳细胞。子叶弯曲胚期,胚乳全部形成胚乳细胞,具传递细胞特征的合点胚乳吸器形成。胚乳细胞的初始垂周壁来自于自由生长壁和胞质分裂形成的细胞板;初始平周壁由自由生长垂周壁分友相接形成,及有丝分裂的细胞板形成。开花后９ｄ,胚乳细胞积累淀粉,比胚细胞积累早６ｄ。开花后１５ｄ,胚乳最     

玉米胚乳传递细胞的结构观察研究

以玉米品种'登海11号'为材料,分别于授粉后8、10、15和20 d采集颖果,取所需部位并采用树脂包埋的方法及半薄和超薄切片技术,对玉米胚乳传递细胞进行了显微和超微结构观察.结果显示:(1)胚乳传递细胞的壁内突从外层向内层依次递减,溶质浓度逐步降低,形成了明显的溶质浓度梯度,有利于溶质的运输;(2)中层胚乳传递细胞和内层胚乳传递细胞的邻壁上存在胞间连丝或一些孔径较大的胞壁孔道,从而使溶质更快的进入内层胚乳传递细胞;(3)在壁内突周围存在许多线粒体.研究表明,玉米胚乳传递细胞的结构适合溶质运输.     

植物胚性愈伤诱导的机理及提高途径

对植物胚性愈伤诱导的研究结果进行综合分析,寻找植物胚性愈伤诱导参与的基因、诱导的机理、甲基化与提高植物胚性愈伤诱导途径之间的联系,探索提高植物胚性愈伤诱导几率的可能途径,为转化困难的植物的基因工程操作奠定基础。LBD (laterial organ boundaries domain)家族基因、伤口诱导脱分化蛋白WIND1 (wound induced dedifferentiation 1)、AP2/ERF转录因子BABYBOOM等参与了植物胚性愈伤诱导的过程;DNA甲基化在这个过程中也发挥了重要作用,植物胚性细胞通过PCG和PKL通路两种表观遗传途径促使胚性细胞保持胚性。这些研究结果表明,通过筛选距离合子胚最近的体细胞作为外植体,利用分子标记进行筛选具有胚性的细胞或组织作为外植体进行培养,在培养基中添加去甲基化的试剂等方法可能能够提高植物胚性愈伤诱导的比例,转化困难的农作物的基因工程育种有望得到显著改进。     

蔷薇科植物体细胞胚胎发生及影响因素研究进展

总结了近30年来蔷薇科植物体细胞胚胎发生及影响因素的研究进展。蔷薇科植物体胚发生多数是直接发生途径和间接发生途径同时存在,但以间接发生途径为主。合子胚作为外植体明显好于营养器官作为外植体。诱导体胚发生的植物生长素类调节剂以NAA、2,4-D为主,细胞分裂素类调节剂以6-BA为主,少数植物种类的体胚诱导需要添加KT。冷处理对蔷薇科植物的体胚分化有效。光照对蔷薇科植物的体胚发生没有显著的影响,有时光照会抑制体胚发生。今后应逐步开展对蔷薇科植物体细胞胚胎发生的生理、生化及分子机理的研究,这在蔷薇科植物的新品种培育、遗传改良、优良单株的离体扩殖等具有重要意义。     

被子植物生殖器官中的传递细胞

传递细胞（ｔｒａｎｓｆｅｒｃｅｌｌ）是一类特殊的薄壁细胞,其特征是细胞壁向内突起生长,形成壁内突的结构,质膜紧贴细胞壁生长,从而使质膜的表面积大大增加,扩大了原生质体表面积与体积之比,有利于细胞吸收和分泌某些物质,在细胞物质的短途运输中起重要作用。超微结构研究表明,传递细胞的细胞核较大,细胞质浓,并富含线粒体、高尔基体等细胞器。传递细胞在被子植物生殖器官中普遍存在,对于这些器官完成其功能起到重要作用。下面简单介绍生殖器官各结构中存在的传递细胞及其功能。１　花柱的通道细胞开放型花柱具有花柱道,花柱…     

无融合生殖与柑橘多胚现象的研究进展

植物无融合生殖是指植物的胚珠组织不经历正常的减数分裂和受精作用,而直接进行胚发育形成种子的无性生殖方式。无融合生殖植物完全继承了母体的全部基因型,因而具有独特研究与育种意义。芸香科柑橘属植物具有独特的多胚现象,其珠心组织能够发育成不定胚(称为珠心胚)进行无融合生殖。文中介绍了柑橘类植物的珠心胚生殖现象、细胞学和遗传学研究进展。珠心胚现象虽然对柑橘杂交后代获得有较大影响,但在生产上可产生性状整齐一致的后代,可以培育无病毒苗木。     

豇豆胚胎发育早期的胚柄及胚乳中的传递细胞

在豇豆早期的胚胎发育中,随着胚柄和胚乳在结构上的分化,可以看到在特定部位上形成传递细胞特有的壁内突。在原胚早期,只在胚周围和合点处的胚囊周界壁上存在壁内突。在原胚后期,胚柄的基部细胞的侧壁以及与母体相邻的端壁都发育壁内突。这个时期与珠心冠和内珠被相邻的胚乳细胞的外切向壁上也开始发生内突。胚柄在胚分化时期明显地分化为基部区域和颈部区域。壁内突只发生在基部区域的细胞中。在原胚后期,胚周围形成细胞胚乳的鞘。这部分的胚乳,在种于发育时期,细胞的数目和大小都只稍有增加。当胚乳细胞形成以后,细胞很快变为彼此分离,与珠被组织直接相邻的胚乳细胞的壁发生明显的内突。胚分化和胚轴延长时期,在液体胚乳的区域,在向珠柄那一面的周界壁上,出现特别发达的壁内突。     

植物体内的传递细胞

早在1884年,Fischer在考虑叶肉组织细胞的光合产物是如何运输到小叶脉问题时,就曾猜想过叶子的小叶脉中,可能有某种特殊的细胞来起着它的传递作用。当时他称这种细胞为“中间细胞”。后来,有了一些这方面的报道,但并没引起人们的注意。一直到本世纪六十年代后期,由于运用了超薄切片技术和电子显微镜的观察,才又发现了这些运输代谢产物、细胞壁结构非常特殊的细胞,当时就称之为传递细胞(transfer cell)。起初人们认为传递细胞主要集中叶的木质部和韧皮部,特别是叶小脉的维管组织中。后来研究发现,这种细胞在植物体内分布却十分广泛。除了植物的叶以外,节、鳞片、苞片、小苞片、子叶、胚囊等都发现有这类细胞存在。近年来,国内学者又报道了蒜的花茎中也存在着这类细胞。     

植物组织培养中的胚状体

植物的胚胎发生是从合子开始的。但是,在自然界中,有些植物除合子胚外,还可以从胚囊的其它分子产生胚,如助细胞胚、反足细胞胚;甚至从珠心组织细胞产生胚,即不定胚。总之,被称为“胚”的结构,都限于有性生殖和胚珠的范围內。     

巨噬细胞胆固醇转运相关蛋白研究进展

动脉粥样斑块中泡沫细胞的形成与巨噬细胞胆固醇的转运密切相关,巨噬细胞胆固醇转运是胆固醇逆转运中的一个重要过程,它可清除外周组织过多的胆固醇,对维持细胞内胆固醇稳定、延缓动脉粥样硬化的发生发展有着重要意义.这个过程涉及到许多转运相关蛋白的作用,如三磷酸腺苷结合盒转运体A1/G1、载脂蛋白A-Ⅰ、胆固醇脂转运蛋白、卵磷脂胆固醇酰基转移酶等.本文就巨噬细胞胆固醇转运过程中相关蛋白的作用做一综述,以期为动脉粥样硬化相关疾病的防治研究提供新的思路.     

Maternal LAMP/p55gagHIV-1 DNA immunization induces in utero priming and a long-lasting immune response in vaccinated neonates

Infants born to HIV-infected mothers are at high risk of becoming infected during gestation or the breastfeeding period. A search is thus warranted for vaccine formulations that will prevent mother-to-child HIV transmission. The LAMP/gag DNA chimeric vaccine encodes the HIV-1 p55gag fused to the lysosome-associated membrane protein-1 (LAMP-1) and has been shown to enhance anti-Gag antibody (Ab) and cellular immune responses in adult and neonatal mice; such a vaccine represents a new concept in antigen presentation. In this study, we evaluated the effect of LAMP/gag DNA immunization on neonates either before conception or during pregnancy. LAMP/gag immunization of BALB/c mice before conception by the intradermal route led to the transfer of anti-Gag IgG1 Ab through the placenta and via breastfeeding. Furthermore, there were an increased percentage of CD4+CD25+Foxp3+T cells in the spleens of neonates. When offspring were immunized with LAMP/gag DNA, the anti-Gag Ab response and the Gag-specific IFN-γ-secreting cells were decreased. Inhibition of anti-Gag Ab production and cellular responses were not observed six months after immunization, indicating that maternal immunization did not interfere with the long-lasting memory response in offspring. Injection of purified IgG in conjunction with LAMP/gag DNA immunization decreased humoral and cytotoxic T-cell responses. LAMP/gag DNA immunization by intradermal injection prior to conception promoted the transfer of Ab, leading to a diminished response to Gag without interfering with the development of anti-Gag T- and B-cell memory. Finally, we assessed responses after one intravenous injection of LAMP/gag DNA during the last five days of pregnancy. The intravenous injection led to in utero immunization. In conclusion, DNA vaccine enconding LAMP-1 with Gag and other HIV-1 antigens should be considered in the development of a protective vaccine for the maternal/fetal and newborn periods.     

Enhancement of heat transfer in red cell suspensions in vitro experiments

New data on laminar heat convection with red cell suspensions have been gathered for both heating and cooling. When compared to data for the suspending medium alone, it is apparent that the red cells enhance laminar heat transfer when Pe greater than 4. This is probably due to particle movements. These new data disagree with earlier studies which indicated no enhancement of heat transfer for blood cell suspensions. The data do agree with previous correlations for enhanced thermal transport in sheared suspensions.     

The mechanism of anion transport across human red blood cell membranes as revealed with a fluorescent substrate: I. Kinetic properties of NBD-taurine transfer in symmetric conditions

Summary The molecular mechanism of anion exchange across the human red blood cell membrane was assessed with the fluorescent substrate analog NBD-taurine and the method of continuous monitoring of transport by fluorescence. The efflux of NBD-taurine was studied under a variety of experimental conditions such as temperature, pH and anion composition of cells and media. The temperature profile of NBD-taurine transfer from Cl-loaded cells into Cl media resembled that of Cl self-exchange, whereas that of NBD-taurine transfer from sulfate-loaded cells into sulfate media resembled that of sulfate self-exchange. Although the pH profiles of NBD-taurine transfer from Cl-loaded cells into Cl media and that of Cl self-exchange resembled each other, the analogous transfer with sulfate replacing Cl was markedly different. These and other data were analyzed and found to be consistent with a model which comprises the following: (a) a H⁺-titratable group in the carrier mechanism; (b) alteration of transport sites between the two sides of the membrane (i.e., ping-pong kinetics); and (c) transmembrane distribution of transport sites which is modulated by pH. It is shown that NBD-taurine transfer represents a tracer flux of a fluorescent substrate which gives a measure for the presence of monovalent transport sites at the inner surface of the membrane. The latter is markedly affected by the relative concentrations of anions and H⁺ on both sides of the red blood cell membrane.     

Nucellar projection transfer cells in the developing wheat grain

Summary Transfer cells in the nucellar projection of wheat grains at 25 ±3 days after anthesis have been examined using light and electron microscopy. Within the nucellar tissue, a sequential increase in non-polarized wall ingrowth differentiation and cytoplasmic density was evident. Cells located near the pigment strand were the least differentiated. The degree of differentiation increased progressively in cells further removed from the pigment strand and the cells bordering the endosperm cavity had degenerated. Four stages of transfer cell development were identified at the light microscope level. Wall ingrowth differentiation followed a sequence from a papillate form through increased branching (antler-shaped ingrowths) which ultimately anastomosed to form a complex labyrinth. The final stage of wall ingrowth differentiation was compression which resulted in massive ingrowths. In parallel with wall ingrowth deposition cytoplasmic density increased. During wall deposition, paramural and multivesicular bodies were prominent and were in close association with the wall ingrowths. The degeneration phase involved infilling of cytoplasmic islets within the wall ingrowths. This was accompanied by complete loss of the protoplast. The significance of this transfer cell development for sucrose efflux to the endosperm cavity was assessed by computing potential sucrose fluxes across the plasma membrane surface areas of the nucellar projection cells. Transfer cell development amplified the total plasma membrane surface area by 22 fold. The potential sucrose flux, when compared with maximal rates of facilitated membrane transport of sugars, indicated spare capacity for sucrose efflux to the endosperm cavity. Indeed, when the total flux was partitioned between the nucellar projection cells at the three stages of transfer cell development, the fully differentiated stage III cells located proximally to the endosperm cavity alone exhibited spare transport capacity. Stage II cells could accommodate the total rate of sucrose transfer, but stage I cells could not. It is concluded that the nucellar projection tissue of wheat provides a unique opportunity to study transfer cell development and the functional role of these cells in supporting sucrose transport.Abbreviations CSPMSA cross sectional plasma membrane surface area - LPMSA longitudinal plasma membrane surface area - PTS tri-sodium 3-hydroxy-5,8,10-pyrenetrisulfonate     

Lag in adaptation to lactose as a probe to the timing of permease incorporation into the cell membrane.

If bacteria are incapable of forming and incorporating proteins into the cytoplasmic membranes in all phases of the cell cycle, then not all cells from an asynchronous culture should be capable of growth when switched to a new carbon and energy source whose metabolism requires new membrane function. The transfer of an inducible culture to low lactose provides such a situation since the cells cannot grow unless galactoside permease can function to concentrate the lactose internally. From such experiments, it was concluded that the Y gene product of the lac operon is synthesized, incorporated, and can start functioning in active transport, at any time throughout the bulk of the cell cycle. Not only were the lags before growth re-ensued much shorter than would be expected if the membrane transport capability could only be developed in a small portion of the cycle, but brief pulses of a gratuitous inducer shortened the lags much further. Three types of Escherichia coli ML 30 culture were studied: cells that had exhausted the limiting glucose; cells taken directly from glucose-limited chemostats; and a washed suspension of highly catabolite repressed cells from cultures grown in high levels of glucose and gluconate. The growth studies reported here were performed on-line with a minicomputer. They represent at least an order of magnitude increase in accuracy in estimating growth parameters over previous instrumentation.     

花生不同生育期小叶脉转移细胞形态变化和ATP酶活性定位的研究

迄今已在上千种高等植物中看到具有胞壁内突生长的转移细胞,认为它是一种输送溶质的细胞,在源库二端行使光合产物的垭距离运输。转移细胞质膜上具有较强的ATP酶活性,在发育成熟的转移细胞质膜上ATP酶活     

Intercellular exchange of proteins: The immune cell habit of sharing

The recent recognition of new types of cell-cell communication pathways challenges classic theories of cell autonomy. Evidence of functional “proteome mixing” among interacting cells, particularly immune cells, supports the notion that no cell is an island, and that even these “unsplittable” units are actually non-autonomous. We summarize various mechanisms of intercellular transfer of proteins—trans-endocytosis, trogocytosis, exosomal transport, shuttle through nanotubes, and cell-contact-dependent intercellular transfer of intracellular proteins including oncogenic Ras. These phenomena suggest exciting new possibilities for proteome research, focusing on system-level proteomics that characterize cell contents and functions in the context of intercellular protein transfer.     

Cytoplasm and organelle transfer between mesenchymal multipotent stromal cells and renal tubular cells in co-culture

Cell-to-cell interactions of human mesenchymal multipotent stromal cells (MMSC) and rat renal tubular cells (RTC) were explored under conditions of co-cultivation. We observed formation of different types of intercellular contacts, including so called tunneling nanotubes. These contacts were shown to be able to provide transfer of cell's contents, including organelles. We documented intercellular exchange with fluorescent probes specific to cytosol, plasmalemma and mitochondria. Initial transport of cellular components was revealed after 3 h of co-culturing, and occurred in two directions—both direct and retrograde as referred to RTC. However, transport of probes toward MMSC was more efficient. One significant result of such transport was appearance of renal-specific Tamm-Horsfall protein in MMSC, indicating induction of their differentiation into kidney tubular cells. We conclude that transfer of cellular compartments between renal and stem cells could provide differentiation of MMSC when transplanted into kidney and result in therapeutic benefits in renal failure.