奇妙的植物细胞壁扩展素

通常,在植物茎或根顶端分生组织后面的细胞,可进行 1— 3个数量级的扩展或生长,这种扩展主要是指细胞壁和液泡的扩展。那么植物细胞的细胞壁为什么会发生扩展呢 ?植物生理学家曾为此做过大量的研究工作,最近发现了一种能使植物细胞壁扩展的奇妙物质,即扩展素 (Expansin)　　早在 20世纪 70年代初期,有人曾提出一个假说,即生长中的植物组织细胞,在酸性条件下的扩展或生长速度将大大超过中性条件。由此可以设想,生长激素可通过把质子泵入细胞壁而诱导生长。该论点认为细胞壁酸碱值 (pH)的减小可激活一种或多种细胞壁松驰酶,从而使…     

细胞壁在植物重金属耐性中的作用

植物细胞壁主要是由多糖、蛋白质和木质素等组成的一个复合体,广泛参与植物生长发育及对各种逆境胁迫的响应,是重金属离子进入细胞质的第一道屏障。本文主要综述了植物细胞壁主要成分,包括细胞壁多糖、细胞壁蛋白质和木质素,在响应重金属胁迫反应中的作用及其参与重金属耐性的机制,以期能对植物细胞壁在重金属耐性中的作用有更深入的了解。     

细胞壁在植物生殖生长中的作用

植物细胞壁在生殖生长中起着重要作用,如胼胝质壁启动大小孢子母细胞的分化途径,影响大小孢子的发生和发育,启动花粉萌发和花粉管伸长;固定或稳定胚胎的极性轴,维持胚胎分化状况等。     

植物激素在顶端优势中的作用

概述了有关植物激素在顶端优势中作用的各种不同假说及研究现状。     

细胞壁在植物胚胎发生中的作用

在植物的生长与发育过程中,细胞壁不仅在决定和维持细胞形态方面发挥了重要作用,而且还参与了对细胞生长与分化的调控,这种调控涉及一些细胞壁信号分子,尤其是一些细胞壁水解产物在细胞内和细胞间的转导。现对细胞壁在植物胚胎发生中的作用进行综述。     

膨胀素在植物生长发育中的作用

膨胀素是一类具有非水解活性的细胞壁松弛蛋白,参与植物生长发育过程中细胞壁的修饰。大多数植物中都发现有膨胀素基因家族成员存在,其功能涉及植物生长发育的各个方面,包括营养生长、形态发生、受精授粉、果实成熟等,并表现出高度的组织、器官和细胞特异性。本文综述膨胀素在种子萌发、叶的发育、根茎生长、花的发育等生长发育过程中的作用。     

植物细胞壁松弛因子

植物细胞壁的松弛是细胞伸长必需的一个生理过程,发生于植物生长发育的各个阶段。研究发现参与细胞壁松弛的因子有多种,主要包括膨胀素（expansin）、木葡聚糖内转糖苷酶/水解酶（XTH）、糖基水解酶和羟基自由基（·OH）四大类。本文主要对这些细胞壁松弛因子的结构特征、作用机制及其在植物生理过程中的作用等方面的研究进展进行综述。     

植物细胞壁松弛蛋白——膨胀素

膨胀素(expansin,也称作扩张素或扩张蛋白)是一种引起植物细胞壁松弛的蛋白质,在植物细胞伸展以及一系列涉及细胞壁修饰的生命活动中起着关键作用。膨胀素由多基因家族编码,目前的研究表明膨胀素超家族由4个基因亚家族构成。膨胀素存在于不同的种属植物中,并克隆了大量的扩张蛋白基因。综述了近年来国内外有关膨胀素基因和蛋白的结构特征及作用机制等方面的研究进展。     

新发现的植物细胞壁蛋白

分别从矮牵牛和菜豆基因文库中分离到的一种基因都编码富含甘氨酸的蛋白质(GRP),经免疫学方法证实,GRP为细胞壁蛋白。从玉米悬浮培养细胞中分离到富含苏氨酸与羟脯氨酸的糖蛋白(THRGP)和富含组氨酸与羟脯氨酸的糖蛋白(HHRGP)。氨基酸及中性糖的组成、分子形状、免疫特性等生化特点都表明THRGP和HHRGP是单子叶植物类型的细胞壁蛋白。     

The molecular basis of plant cell wall extension

In all terrestrial and aquatic plant species the primary cell wall is a dynamic structure, adjusted to fulfil a diversity of functions. However a universal property is its considerable mechanical and tensile strength, whilst being flexible enough to accommodate turgor and allow for cell elongation. The wall is a composite material consisting of a framework of cellulose microfibrils embedded in a matrix of non-cellulosic polysaccharides, interlaced with structural proteins and pectic polymers. The assembly and modification of these polymers within the growing cell wall has, until recently, been poorly understood. Advances in cytological and genetic techniques have thrown light on these processes and have led to the discovery of a number of wall-modifying enzymes which, either directly or indirectly, play a role in the molecular basis of cell wall expansion.     

Expansin(细胞壁松弛蛋白)的发展

Expansin是一种体外诱导分离的植物细胞壁伸展的蛋白,在修饰细胞壁基础上使细胞膨胀。Expansin的功能众多,除了促进细胞生长,还包括影响营养生长、形态发生、授粉受精、果实软化等,并表现出高度的组织、器官和细胞特异性。目前已经在多种植物及其他一些生物范围内对expansin及类expansin序列和蛋白质进行了研究,并对它们的作用机制进行了探索。     

Xyloglucan endotransglucosylase activity loosens a plant cell wall

BACKGROUND AND AIMS: Plant cells undergo cell expansion when a temporary imbalance between the hydraulic pressure of the vacuole and the extensibility of the cell wall makes the cell volume increase dramatically. The primary cell walls of most seed plants consist of cellulose microfibrils tethered mainly by xyloglucans and embedded in a highly hydrated pectin matrix. During cell expansion the wall stress is decreased by the highly controlled rearrangement of the load-bearing tethers in the wall so that the microfibrils can move relative to each other. Here the effect was studied of a purified recombinant xyloglucan endotransglucosylase/hydrolase (XTH) on the extension of isolated cell walls. METHODS: The epidermis of growing onion (Allium cepa) bulb scales is a one-cell-thick model tissue that is structurally and mechanically highly anisotropic. In constant load experiments, the effect of purified recombinant XTH proteins of Selaginella kraussiana on the extension of isolated onion epidermis was recorded. KEY RESULTS: Fluorescent xyloglucan endotransglucosylase (XET) assays demonstrate that exogeneous XTH can act on isolated onion epidermis cell walls. Furthermore, cell wall extension was significantly increased upon addition of XTH to the isolated epidermis, but only transverse to the net orientation of cellulose microfibrils. CONCLUSIONS: The results provide evidence that XTHs can act as cell wall-loosening enzymes.     

Dynamics of limiting cell wall porosity in plant suspension cultures

Changes in the limiting porosity of cell walls, i.e. the size limit for permeation of neutral molecules through the wall, were studied in several higher-plant cell-suspension cultures. For this purpose, samples of biomass fixed at different cultivation times were investigated using a method based on size-exclusion chromatography of polydisperse dextrans before and after equilibration with the extracted cell clusters. In suspension cultures of Chenopodium album L., Dioscorea deltoidea Wall. and Medicago sativa L., the mean size limit (MSL; critical Stokes' radius for exclusion of neutral polymers from half of the intracellular space) was found to vary between 2.4 and 3.8 nm. It decreased significantly during transition from the growth phase to the stationary phase. In the case of the C. album culture this change was found to be irrespective of whether sucrose in the medium was completely depleted at the end of the growth phase or not. The MSL was kept constant for long periods of the stationary phase if cell viability was maintained by repeated sucrose supplement. In a suspension strain of Triticum aestivum L., the MSL of cell wall permeation was comparatively small (1.75 nm) and remained constant during all cultivation phases. Relations between limiting porosity and cell wall growth, loss of pectic compounds to the medium, cross-linking activities and cell wall stiffening are discussed. Received: 19 December 1996 / Accepted: 23 April 1997     

The relationship between xyloglucan endotransglycosylase and in-vitro cell wall extension in cucumber hypocotyls

It has been proposed that cell wall loosening during plant cell growth may be mediated by the endotransglycosylation of load-bearing polymers, specifically of xyloglucans, within the cell wall. A xyloglucan endotransglycosylase (XET) with such activity has recently been identified in several plant species. Two cell wall proteins capable of inducing the extension of plant cell walls have also recently been identified in cucumber hypocotyls. In this report we examine three questions: (1) Does XET induce the extension of isolated cell walls? (2) Do the extension-inducing proteins possess XET activity? (3) Is the activity of the extension-inducing proteins modulated by a xyloglucan nonasaccharide (Glc₄-Xyl₃-Gal₂)? We found that the soluble proteins from growing cucumber (cucumis sativum L.) hypocotyls contained high XET activity but did not induce wall extension. Highly purified wall-protein fractions from the same tissue had high extension-inducing activity but little or no XET activity. The XET activity was higher at pH 5.5 than at pH 4.5, while extension activity showed the opposite sensitivity to pH. Reconstituted wall extension was unaffected by the presence of a xyloglucan nonasaccharide (Glc₄-Xyl₃-Gal₂), an oligosaccharide previously shown to accelerate growth in pea stems and hypothesized to facilitate growth through an effect on XET-induced cell wall loosening. We conclude that XET activity alone is neither sufficient nor necessary for extension of isolated walls from cucumber hypocotyls.     

Narciclasine与植物激素的相互作用研究

主要研究了天然生物活性物质Narciclasine(NCS)与植物激素的相互作用。发现NCS对于IAA刺激小麦胚芽鞘伸长过程、GA3对大麦胚乳中α-淀粉两诱导作用及6-BA对离体萝卜子叶光下增大以及转绿过程的促进作用,均显示出一定的抑制作用,而且其抑制强度均随浓度的增加而增加。对于不同的生理过程,NCS表现出不同的抑制强度,其中对离体萝卜子叶光下转绿过程的抑制作用较强。对于离体子叶的光下增大和转绿过程,不同植物激素的表现不同,6-BA和GA3对离体子叶增大及光下转绿具有促进作用;ABA和NCS则显示出一定的抑制作用。     

A cell wall protein down-regulated by auxin suppresses cell expansion in Daucus carota (L.)

We investigated the function of the auxin-regulated cell wall gene DC 2.15, a member of a small gene family, present in Daucus carota (L.) and other plants. Cultured cells derived from carrot hypocotyls transformed by the DC 2.15 cDNA in antisense direction were ten-fold longer than wild-type cells, indicating a function of the corresponding protein in suppression of cell expansion. The analysis of carrot plants expressing the DC 2.15 gene in antisense direction showed that the corresponding protein and/or related proteins probably are involved in leaf and vascular bundle development. The antisense plants generally displayed a retarded growth phenotype and delayed greening in comparison to wild-type plants. The asymmetric architecture of the wild-type leaves was degenerated in the DC 2.15 antisense plants and the leaves showed a torsion within and along their major vein. The vascular bundles showed a lowered ratio of the phloem/xylem area in cross sections of the leaf middle vein whereas the bundle sheath and the cambium showed no obvious phenotype. Expression of a promoter-GUS construct was found primarily in vascular bundles of stems, leaves and in the nectar-producing flower discs. The observed pleiotropic antisense phenotype indicates, by loss of function, that one or several related cell wall proteins of this gene family are necessary to realize several complex developmental processes.