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  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A xyloglucan-derived pentasaccharide. Xyl2-Glc3, was shown by viscometry to promote the depolymerisation of xyloglucan by enzyme extracts from bean (Phaseolus vulgaris L. cv. Canadian Wonder) leaves and pea (Pisum sativum L. cv. Alaska) stems. Xyl2-Glc3 was also shown by a radiochemical assay to act as an acceptor substrate for xyloglucan endotransglycosylase activity (XET: EC 2.4.1.—) present in the same extracts. In both these assays, a heptasaccharide (Xyl3-Glc4) was more effective than Xyl2-Glc3 whereas two isomeric tetrasaccharides (Xyl1-Glc3) were essentially ineffective. The agreement in the structural requirements of the two assays suggests that they share a common basis; we therefore propose that the oligosaccharide-sensitive enzyme that depolymerises xyloglucan is XET rather than cellulase (EC 3.2.1.4). In the viscometric assay, the penta- and heptasaccharides would, according to our interpretation, compete with high molecular weight xyloglucan molecules as acceptor substrates for XET, leading to a decrease in the weight-average molecular weight of the xyloglucan and, therefore, to a decrease in viscosity.Our results indicate that oligosaccharides have to possess two α-d-xylose residues in order to act as acceptor substrates for XET. The non-reducing end of a high-molecular weight xyloglucan can also act as an acceptor substrate. Therefore, it is likely that exo-hydrolysis by α-d-xylosidase would destroy the ability of a polysaccharide to act as an acceptor, even though α-d-xylosidase may remove only a single xylose residue from each polysaccharide molecule.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Hemicellulosic polysaccharides from persimmon fruit (Diospyros kaki L.) pericarp were extracted from depectinated cell walls with 0.5, 1 and 4 M KOH at different stages of development: (I) maximal growth corresponding to the first sigmoidal growth phase; (II) cessation of growth corresponding to the lag between the first and the second sigmoidal phases; (III) maximal growth corresponding to the second sigmoidal phase; and (IV) cessation of growth when the fruit had reached its maximum size and the change in colour (green to red) had taken place. During fruit development the amount of total hemicelluloses per unit dry mass cell wall decreased twofold. Xyloglucan was present in the three hemicellulosic fractions, and also decreased with fruit age, although its amount relative to other hemicelluloses increased. The amount of xyloglucan was especially high in the hemicelluloses extracted with 4 M KOH, representing more than 50% at stages III and IV. The average molecular mass of xyloglucan increased from stage I through stage II (0.5 M hemicellulosic fraction) or through stage III (I and 4 M hemicellulosic fractions) and decreased after that. The xyloglucan endotransglycosylase (XET: EC 2.4.1.-) activity was measured as the incorporation of [3H]XXXGol (reduced xyloglucan heptasaccharide labelled at position 1 of the glucitol moiety) into partially purified persimmon fruit xyloglucan. XET specific activity increased greatly between stages I and II. The importance of this enzyme during fruit ripening is discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 75 (1989), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The plant growth promoter, auxin, may loosen the primary cell wall by increasing the activity of extracellular cellulases – a group of enzymes that cleave hemicellulose chains in the walls of both monocotyledons and dicotyledons. Evidence is reviewed that suggests that these hemicellulose chains tether adjacent microfibrils, and that by cleaving such chains the cellulases facilitate cell expansion. On the basis of this structural arrangement a mechanism for elastic and plastic wall extension is proposed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 433 (2005), S. 83-87 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Increasing the l-ascorbate (vitamin C) content of crops could in principle involve promoting its biosynthesis or inhibiting its degradation. Recent progress has revealed biosynthetic pathways for ascorbate, but the degradative pathways remain unclear. The elucidation of such ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Xyloglucan-oligosaccharides and cello-oligosaccharides, both of which are potential products of the action of cellulase on plant cell wail polysaccharides, inhibited acid-induced elongation in pea (Pisum sativum L. cv. Alaska) stem segments. Xyloglucan-derived nonasaccharide (XG9; Glc4-Xyl3)Gal-Fuc) and decasaccharide (XG10; Glc4-Xyl3-Gal2-Fue) inhibited acid-induced growth at 1.0 and 0.1 nM, respectively, whereas the heptasaccharide (XG7; Glc4-Xyl3) and octasaccharide (XG8; Glc4-Xyl3-Gal)2 which lack L-fucose, did not. XG9 at 1 nM inhibited acid-induced growth as effectively as it inhibits auxin-induced elongation. This suggests that XG9's effect as an inhibitor of auxin action is not mediated by a suppresion of H+-efflux, but rather that XG9 blocks some step that is common to the action of both auxin and H+ on growth. Cello-oligosaccharides (degree of polymerisation 4–7) also inhibited acid-induced growth at 10 nM; these are therefore a new class of possible oligosaccha-rin. The inhibitory effect of xyloglucan- and cellooligosaccharides on acid-induced growth was rapidly reversed by washing.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A revised system of abbreviated names is proposed for xyloglucan-derived oligosaccharides. Each (1→4)-linked β-d-glucosyl residue (and the reducing terminal d-glucose moiety) of the backbone is given a one-letter code according to its substituents. The name of the oligosaccharide consists of these code letters listed in sequence from non-reducing to reducing terminus of the backbone.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Planta 157 (1983), S. 111-123 
    ISSN: 1432-2048
    Keywords: Cell wall (primary) ; Ferulic acid ; Pectic polysaccharide ; Phenolic coupling (oxidative) ; Polisaccharide, feruloylated ; Spinacia (cell walls)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Primary cell walls from exponentially growing cell-suspension cultures of spinach contained ferulic acid and p-coumaric acid esterified with galactopyranose and arabinopyranose residues of polysaccharides. The feruloylated polysaccharides behaved in exactly the same way as total cell-wall pectin with respect to (1) extraction with chelating agents, (2) extraction by trans-elimination degradation, (3) extraction with mild acid, and (4) electrophoretic separation into acidic and neutral species. Partial digestion of cell walls with Driselase, under conditions which specifically inhibited galactanase and galactosidases yielded galactose-containing feruloyl tri- to pentasaccharides, in all of which the feruloyl group was on the non-reducing terminus. Larger feruloyl oligosaccharides were also found, some of which were acidic. Partial acid-hydrolysis of cell walls gave a homologous series of feruloyl oligosaccharides, probably with the structure Feruloyl-arabinopyranose-(arabinofuranose)n-arabinose where n=0–7. Evidence is presented that the arabinose chain was unbranched, with the feruloyl group on the nonreducing terminus. It is suggested that acidic and neutral pectins carry ferulic acid on the non-reducing termini of the neutral arabinose- and/or galactose-containing domains. The pectins carry approximately one feruloyl residue per 60 sugar residues. Possible rôles of feruloyl pectin in the regulation of cell expansion, in disease resistance, and in the initiation of lignification are discussed.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-2048
    Keywords: Cell wall (expansion, enzymes) ; Cucumis (cell wall expansion) ; Enzyme (cell wall) ; Protein (cell wall extension inducing) ; Xyloglucan endotransglycosylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-2048
    Keywords: Key words: Cell wall signalling ; Endotransglycosylase action ; Oligosaccharin ; Pisum stem (cell expansion) ; Xylem (translocation) ; Xyloglucan oligosaccharide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. When [glucitol-3H]XXFGol (a NaB3H4-reduced xyloglucan nonasaccharide) was applied to excised shoots of pea (Pisum sativum L. cv. Progress) at the base of the epicotyl, it inhibited growth in the elongation zone, 4–5 cm distal. Experiments were conducted to discover whether such 3H-oligosaccharides are translocated intact over this distance, or whether an intercellular second messenger would have to be postulated. After 24 h, 3H from [glucitol-3H]XXFGol and [glucitol-3H]XXXGol showed U-shaped distributions, with most 3H at the base and apex of the stem. Radioactivity from [fucosyl-3H]XXFG and [xylosyl-3H]XXFG also moved acropetally, but did not concentrate at the apex, possibly owing to removal from the transpiration stream of fucose and xylose formed by partial hydrolysis of XXFG en route. When 10−7 M [glucitol-3H]XXFGol was supplied, about 14 fmol ·  seedling–1 of apparently intact [3H]XXFGol was extractable from the elongation zone after 24 h. Larger amounts of degradation products were extractable (including free [3H]glucitol) and some wall-bound 3H-hemicellulose was present (presumably formed by the oligosaccharides acting as acceptor substrates for transglycosylation). We conclude that biologically active oligosaccharides of xyloglucan can move through the stem acropetally and that they are maintained at low steady-state concentrations by both hydrolysis and transglycosylation.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Planta 171 (1987), S. 205-211 
    ISSN: 1432-2048
    Keywords: Cell wall ; Ferulic acid ; Pectic arabinogalactan ; Polysaccharide ; Secretion (polysaccharide) ; Spinacia (cell wall)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The pectic polysaccharides of spinach cell walls carry feruloyl groups on arabinose and galactose residues. The following experiments were designed to discover whether the arabinose residues are feruloylated intra-or extracellularly. Cultured spinach cells started to incorporate exogenous [3H]arabinose into polymers at a linear rate after a lag period of approx. 3–4 min, although radioactive polysaccharides and extensin did not start to appear outside the plasmalemma until after an approx. 25-min lag. In the same cells, polysaccharide-bound feruloyl-[3H]arabinose units starded to accumulate radioactivity at a linear rate after a lag period of approx. 4–5 min. Therefore, arabinose residues of polysaccharides began to be feruloylated while still intracellular. The rate of formation of polysaccharide-bound feruloyl-[3H]arabinose units did not appreciably increase after 25 min, showing that any additional extracellular feruloylation of the polysaccharide was relatively slow. This conclusion was supported by two different types of pulse-chase experiments, one of which was designed to detect feruloylation of polysaccharides up to 6 d after synthesis.
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