PlantWall-06-2page(1) - Plant Cell Walls All Plant Cells...

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1 Plant Cell Walls All Plant Cells are surrounded by an extracellular matrix known as the Cell Wall a polysaccharide-rich matrix that surrounds all plant cells plays multiple roles in plant growth, development and defense responses there are two types of wall: primary & secondary
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2 Primary Wall first wall laid down surrounds growing cells surrounds meristematic cells cells in succulent tissues found at the junction of cells and at the outer edges of secondary walls composed of ~ 90% carbohydrate and 10% protein Secondary walls surround cells that differentiate to form specialized functions (i.e. wood cells, xylem cells) have altered polysaccharide composition often are lignified from Katherine Esau, Anatomy of Seed Plants, 1977 Cross section of Nelumbo nucifera petiole showing primary cell wall 90% polysaccharide 10% protein Polysaccharides are the main components of the primary plant cell wall
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3 Walls from round and elongated carrot suspension cultured cells. (Fast-freeze, deep-etch, rotary-shadowed replicas; McCann et al., 1993, J. Cell Science 106:1347 ) Three classes of polysaccharides make up the primary wall Cellulose Hemicellulose Pectin Composition of primary cell walls of suspension-cultured sycamore cells Wall Component Mass % of Cell Wall Pectic polysaccharides 34 Hemicellulose 24 Cellulose 23 Protein 19 McNeil et al., 1979, Fortschritte der Chemie organischer Naturstoffe, Volume 37, 191.
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4 Primary walls can be divided into two types: Type I primary walls (all flower plants except the grass family) Cellulose Hemicellulose (xyloglucan) Pectin (~22-35%) (homogalacturonan, HGA; Rhamnogalacturonan I, RG-I; Rhamnogalacturonan II; RG-II) Type II primary walls (the grass family, Poaceae ): Cellulose Hemicellulose (glucuronoarabinoxylan) Pectin (~10%) (HGA, RG-I, RG-II) Model of Primary Plant Cell Wall Carpita & Gibeaut (1993) Plant J. 3: 1-30
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5 Malcolm O’Neill, CCRC Schematic Model of Plant Primary Cell Wall Synthesis CELLULOSE World’s most abundant biopolymer Polymer of β 1-,4-linked glucose Individual glucan chains associate via H-bonds to form microfibrils that are largely crystalline. Cellulose I (the type of cellulose found in nature), glucan chains are aligned parallel to each other Length of the glucan chains varies depending upon the organism from DP ~2000 to up to DP ~15,000 Size of microfibril also varies depending upon the organism and can range from the elementary fibril (~ 36 glucan chains) up to very large fibrils (> 200 chains) found in cellulosic algae As plant cells mature from 1º to 2 º walls, cellulose can be found as associates of macrofibrils or bundles
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6 academic.brooklyn.cuny.edu/ biology/bio4fv/pag ...
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7 www.emc.maricopa.edu/. ../ BIOBK/BioBookCHEM2.html www.emc.maricopa.edu/. ../ BIOBK/BioBookCHEM2.html Cellulose gives tensile strength to the wall. In planta
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This note was uploaded on 12/03/2011 for the course BCMB 8020 taught by Professor Staff during the Fall '08 term at University of Georgia Athens.

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PlantWall-06-2page(1) - Plant Cell Walls All Plant Cells...

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