Variations in the structure of neutral sugar chains in the pectic polysaccharides of morphologically different carrot calli and correlations with the size of cell clusters

Carrot (Daucus carota L.) embryogenic callus (EC) loses its embryogenic competence and becomes nonembryogenic callus (NC) during long-term culture. With the loss of embryogenic competence, the cell clusters become smaller and the extent of intercellular attachments is reduced. Pectic fractions prepared from EC and NC were separated into two subfractions by gel filtration. A difference in sugar composition between EC and NC was found only in the high-molecular-mass (ca. 1300 kDa) subfraction, and the ratio of the amount of arabinose to that of galactose (Ara/Gal) was strongly and positively correlated with the size of cell clusters in several different cultures. From the results of sugar-composition and methylation analyses, and the results of treatment with exo-arabinanase, models of the neutral sugar chains of pectins from EC and NC are proposed. Both neutral sugar chains are composed of three regions. The basal region is composed of linearly linked arabinan 5-Ara_f> moieties in both types of callus. The middle galactan region is composed of 6-linked galactose, some of which branches at the 3 and 4 positions, and this region is larger and more frequently branched in NC than in EC. Finally, the terminal arabinan region is composed of 5-linked arabinose, branched at the 3 position, and the size of the terminal arabinan is larger in EC than in NC. The significance of the neutral sugar chains of pectins in the interaction of cell wall components and intercellular attachment is discussed.Abbreviations Ara/Gal ratio (w/w) of the amount of arabinose to that of galactose - EC embryogenic callus - NC non-embryogenic callus - T-Ara_f terminal arabinose The authors are grateful to Dr. Naoto Shibuya of the National Institute of Agrobiological Resources for his gift of exo-arabinanase.     

The sporophyte-gametophyte junction in the moss Acaulon muticum (Pottiaceae): EARLY STAGES OF DEVELOPMENT

The sporophyte-gametophyte junction in Acaulon muticum is composed of the sporophyte foot, the surrounding gametophyte vaginula, and an intervening placental space. At an early stage of development the foot has a large basal cell, characterized by extensive wall ingrowths beginning at the lowermost tip of the basal cell and extending along its tangential walls. Sporophyte cells in contact with the basal cell develop ingrowths on their outer tangential walls and on radial walls in contact with the basal cell. All sporophyte cells at this stage are characterized by numerous mitochondria, strands of endoplasmic reticulum, and dictyosomes, particularly in the cytoplasm adjacent to areas of extensive wall development. Plastids typically contain abundant starch reserves. As development proceeds, wall ingrowths become more extensive on all walls in the sporophyte foot but are never found on the upper wall of the basal cell in contact with the remainder of the sporophyte. Plastids in the foot contain fewer starch reserves later in development. Wall ingrowths are not visible in the cells of the gametophyte vaginula until well after extensive development has occurred in the sporophyte foot. Stacks or layers of endoplasmic reticulum are characteristic of the cells of the gametophyte vaginula, along with numerous mitochondria, dictyosomes, and well-developed plastids. Starch reserves typically are less abundant in cells of the gametophyte. The early development of extensive wall elaborations in the cells of the sporophyte foot, and particularly in the basal cell, may favor the rapid movement of water and nutrients from the gametophyte into the sporophyte at a time when rapid development in this minute, ephemeral moss is critical.     

Growth kinetics of a bacteriophage in continuous culture

Lytic coliphage Qbeta was grown in continuously cultured host bacteria using a cascade of stirred flow reactors. The apparatus was constructed so that the steady stream of exponentially growing bacterial cells passing through the stirred flow reactors served to prevent coevolution brought about by host-parasite interactions. Wall growth was the primary cause for deviation from ideal continuous culture conditions and is largely dependent on the surface structure of the host bacteria. Using an Escherichia coli strain deficient in adhesive type I pili expression, the desynchronization of single burst events could easily be followed over the course of four infection latency periods. Computer simulations based on a two-stage model for the Qbeta infection cycle were in perfect agreement with the experimental data. Applications of the optimized system to strategies of molecular evolution are discussed. (c) 1996 John Wiley & Sons, Inc.     

水稻伸长生长的数学模型

水稻地上部诸器官的伸长生长,可以分为3个阶段和两个过渡期．器官在前期的凹型曲线生长为加速生长（定为第1阶段）,中期的直线生长为等速生长（第2阶段）,后期的凸型曲线生长为减速生长（第3阶段）;每两个阶段临界处均存在特殊的生长过程,前面的定为第1过渡期,做变加速生长,后面的定为第2过渡期,做变减速生长.组成器官的各个细胞的伸长生长,也可以分为前期凹型曲线阶段、中期的直线阶段以及这两个阶段临界处的过渡期.运用类比原理推断;细胞在凹型曲线阶段,其原生质的膨压大于壁压,而且这两个压差始终维持稳定,这就使细胞做等加速生长;细胞经过过渡期的变加速生长过渡到直线生长阶段,在这个阶段中,膨压大小与壁压相等,这就使细胞以过渡期最末的生长速度做等速生长;最后壁压大于膨压,而且这两个相差压会阻止细胞的“惯性”生长直至停止生长,其结果产生减速生长．     

真菌细胞溶壁酶的产酶培养和应用效果

从土样中分离的７１株木霉（Ｔｒｉｃｈｏｄｅｒｍａ ｓｐ．）筛选出一株分解几丁质和葡聚糖能力较强的菌株。该菌株在麸皮、稻草粉、硫酸铵和诱导物为主成份的固体培养基上,经过２５℃、８４ｈ的培养,产生较高的真菌细胞溶壁酶,能溶解酵母、毛霉、黑曲霉及食用菌等丝状菌丝体的细胞壁,形成原生质体,经选用酵母、毛霉等进行原生质体再生,效果较优。     

Subunits of forming pollen exine and Ubisch bodies as seen in freeze substitutedLedebouria socialis Roth (Hyacinthaceae)

Summary High-pressure freezing/freeze substitution/TEM was employed to investigate anthers of the monocotyledonous angiospermLedebouria socialis Roth (Hyacinthaceae) during early tetrad stage. The initials of the outer sporopollenous pollen wall stratum (=sexine) and of the homologous tapetal products (=Ubisch bodies) are composed of highly regular subunits: clustered globules with a constant diameter of approximately 28 nm. The clusters develop within diffuse accumulations of electron-dense material. This process, interpreted as sporopollenin polymerization, does not necessarily depend on the presence of membrane-bound enzymes. Immunogold labeling with JIM 5 and JIM 7 antibodies revealed that the primexine as well as the dissolving tapetal cell walls, the sites of sexine and Ubisch body formation, respectively, contain un-esterified and methyl-esterified pectins.Abbreviations E-PTA ethanolic phosphotungstic acid - PA periodic acid - UA/Pb uranyl acetate/lead     

Aspects of morphogenesis and function of diatom cell walls with implications for taxonomy

Summary Aspects of morphogenesis and morphology of diatom cell walls are reviewed to highlight functional correlations between wall structures and three-dimensional cytoplasmic activities during the cell cycle. Morphogenesis of the siliceous valve within the silica deposition vesicle is discussed in the light of the dependency on a precisely orchestrated moulding machinery, involving the cytoskeleton, mitochondria, endoplasmic reticulum, spacer vesicles produced by the Golgi apparatus, and the plasmalemma, in combination with adhesion of the cells to parts of the parental wall and localized plasmolyses. Sensitivity of morphogenetic events to fluctuations of external factors has implications for taxonomy.Abbreviations CF cleavage furrows - cPL cleavage plasmalemma - GB girdle bands - LP labiate process - LPA labiate process apparatus - MC microtubule center - mLP macro labiate process - MT microtubule - MTOC microtubules organizing center - PL plasmalemma - SDV silica deposition vesicle - SL SDV membrane - SpV spacer vesicles Dedicated to Professor Peter Sitte on the occasion of his 65th birthday     

Cholesteric-like crystal analogs in glucuronoxylan-rich cell wall composites: Experimental approach of acellular re-assembly from native cellulosic suspension

Summary Many plant cell walls are constructed according to a helicoidal pattern that is analog to a cholesteric liquid crystal order. This raises the question whether the wall assembly passes through a true but temporary liquid crystal state. The paper focuses on experiments performed from aqueous suspensions of extracted quince slime, i.e., a cellulose/glucuronoxylan wall composite that presents a helicoidal order when observed in situ, within the enlarged periplasm of the seed epidermal cells. Experiments carried out in acellular conditions showed that a spontaneous reassociation into a helicoidal order can be obtained from totally dispersed suspensions. The ultrastructural aspect of the reassembled mucilage suspension was different according to the resin used (LR White or nanoplast, a water-soluble melamin resin). It was always typically polydomain, and when an order was visible it was cholesteric-like and similar to the in situ native organization. Transition states with many imperfections expressed the difficulty of the system to reassemble in the absence of constraining surfaces. The possible intervention of glucuronoxylan (GX) in the ordered assembly of the microfibrils was checked by: (1) progressive extraction of GX by trifluoroacetic acid (TFA). The extraction was associated to a control of the fraction by analysis of uronic acid contents and observation at the electron microscope level. Extraction of GX provoked the formation of a flocculent mass, the flocculation being more intense when the TFA was more concentrated; (2) progressive change of pH in order to analyze the influence of pH on flocculation. Low pH (ca. pH 3) led also to a flocculation of the suspension, but the floc was reversibly lost after dialysis against distilled water. The results indicate the antifloc role of the GX due to the anionic charges carried by the side-chains. However, the function of GX as helper twisting agent in the cholesteric-like reassembly must not be ruled out.     

Domain conservation in several volvocalean cell wall proteins

Based on our previous work demonstrating that (SerPro)_x epitopes are common to extensin-like cell wall proteins in Chlamydomonas reinhardtii, we looked for similar proteins in the distantly related species C. eugametos. Using a polyclonal antiserum against a (SerPro)₁₀ oligopeptide, we found distinct sets of stage-specific polypeptides immunoprecipitated from in vitro translations of C. eugametos RNA. Screening of a C. eugametos cDNA expression library with the antiserum led to the isolation of a cDNA (WP6) encoding a (SerPro)_x-rich multidomain wall protein. Analysis of a similarly selected cDNA (VSP-3) from a C. reinhardtii cDNA expression library revealed that it also coded for a (SerPro)_x-rich multidomain wall protein. The C-terminal rod domains of VSP-3 and WP6 are highly homologous, while the N-terminal domains are dissimilar; however, the N-terminal domain of VSP-3 is homologous to the globular domain of a cell wall protein from Volvox carteri. Exon shuffling might be responsible for this example of domain conservation over 350 million years of volvocalean cell wall protein evolution.     

A putative catabolite-repressed cell wall protein from the mycoparasitic fungus Trichoderma harzianum

A cDNA clone encoding a putative cell wall protein (Qid3) was isolated from a library prepared from chitin-induced mRNA in cultures of the mycoparasitic fungus Trichoderma harzianum. The predicted 14 kDa protein shows a potential signal peptide, several hydrophobic domains and certain motifs that are structurally similar to proline-rich and glycine-rich plant cell wall proteins. Expression of the qid3 gene is derepressed in the absence of glucose. When introduced in yeast, qid3 expression causes cell division arrest into cytokinesis and cell separation, probably due to its cell wall localization.