Plant cells encase themselves within a complex polysaccharide wall, which constitutes the raw material that is used to manufacture textiles, paper, lumber, films, thickeners and other products. The plant cell wall is also the primary source of cellulose, the most abundant and useful biopolymer on the Earth. The cell wall not only strengthens the plant body, but also has key roles in plant growth, cell differentiation, intercellular communication, water movement and defence. Recent discoveries have uncovered how plant cells synthesize wall polysaccharides, assemble them into a strong fibrous network and regulate wall expansion during cell growth.

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Growth of the plant cell wall

Pectin structure and biosynthesis

Pectins: structure, biosynthesis, and oligogalacturonide-related signaling.

Biofilms probably comprise the normal environment for most microbial cells in many natural and artificial habitats, and as such are complex associations of cells, extracellular products and detritus either trapped within the biofilm or released from cells which have lysed as the biofilm ages (Christensen, 1989). The main ‘cement ’ for all these cells and products is the mixture of polysaccharides secreted by the cells established within the biofilm. Probably the nearest analogy is processed food, in which a mixture of macromolecules of all types interact in variousways to form a recognizable structure. Within such a structure, cells, water, ions and soluble low-and high-molecular-mass products are trapped. In many biofilms, as in food, the hydrated polysaccharides may be in a semi-solid state. The major component in the biofilm matrix is water – up to 97% (Zhang et al., 1998), and the characteristics of the solvent are determined by the solutes dissolved in it. The exact structure of any biofilm is probably a unique feature of the environment in which it develops. As pointed out by Stoodley et al. (1999a), nutritional and physical conditions greatly affect the nature of laboratory biofilms and this is equally true for other types. Wimpenny & Colasanti (1997) have also suggested that biofilm structure is largely determined by the concentration of substrate. They further postulated that such differences also validate at least three conceptual models of biofilms – heterogeneous mosaics, structures penetrated by water channels, and dense confluent biofilms.

/pdf/biofilm-exopolysaccharides-a-strong-and-sticky-framework-2l41wpcyze.pdf

Biofilm exopolysaccharides: a strong and sticky framework.

Three subfamilies of grasses, the Ehrhartoideae, Panicoideae and Pooideae, provide the bulk of human nutrition and are poised to become major sources of renewable energy. Here we describe the genome sequence of the wild grass Brachypodium distachyon (Brachypodium), which is, to our knowledge, the first member of the Pooideae subfamily to be sequenced. Comparison of the Brachypodium, rice and sorghum genomes shows a precise history of genome evolution across a broad diversity of the grasses, and establishes a template for analysis of the large genomes of economically important pooid grasses such as wheat. The high-quality genome sequence, coupled with ease of cultivation and transformation, small size and rapid life cycle, will help Brachypodium reach its potential as an important model system for developing new energy and food crops.

/pdf/genome-sequencing-and-analysis-of-the-model-grass-5dln1jkes2.pdf

Genome sequencing and analysis of the model grass Brachypodium distachyon

▪ Abstract Rhamnogalacturonan II (RG-II) is a structurally complex pectic polysaccharide that was first identified in 1978 as a quantitatively minor component of suspension-cultured sycamore cell walls. Subsequent studies have shown that RG-II is present in the primary walls of angiosperms, gymnosperms, lycophytes, and pteridophytes and that its glycosyl sequence is conserved in all vascular plants examined to date. This is remarkable because RG-II is composed of at least 12 different glycosyl residues linked together by more than 20 different glycosidic linkages. However, only a few of the genes and proteins required for RG-II biosynthesis have been identified. The demonstration that RG-II exists in primary walls as a dimer that is covalently cross-linked by a borate diester was a major advance in our understanding of the structure and function of this pectic polysaccharide. Dimer formation results in the cross-linking of the two homogalacturonan chains upon which the RG-II molecules are constructed and ...

RHAMNOGALACTURONAN II: Structure and Function of a Borate Cross-Linked Cell Wall Pectic Polysaccharide

Turgor-driven plant cell growth depends on wall structure. Two allelic l-fucose-deficient Arabidopsis thaliana mutants (mur1-1 and 1-2) are dwarfed and their rosette leaves do not grow normally. mur1 leaf cell walls contain normal amounts of the cell wall pectic polysaccharide rhamnogalacturonan II (RG-II), but only half exists as a borate cross-linked dimer. The altered structure of mur1 RG-II reduces the rate of formation and stability of this cross-link. Exogenous aqueous borate rescues the defect. The reduced cross-linking of RG-II in dwarf mur1 plants indicates that plant growth depends on wall pectic polysaccharide organization.

http://science.sciencemag.org/content/sci/294/5543/846.full.pdf

Requirement of Borate Cross-Linking of Cell Wall Rhamnogalacturonan II for Arabidopsis Growth

Rhamnogalacturonan-II, a Pectic Polysaccharide in the Walls of Growing Plant Cell, Forms a Dimer That Is Covalently Cross-linked by a Borate Ester IN VITRO CONDITIONS FOR THE FORMATION AND HYDROLYSIS OF THE DIMER

The walls of suspension-cultured Chenopodium album L. cells grown continually for more than 1 year on B-deficient medium contained monomeric rhamnogalacturonan II (mRG-II) but not the borate ester cross-linked RG II dimer (dRG-II-B). The walls of these cells had an increased size limit for dextran permeation, which is a measure of wall pore size. Adding boric acid to growing B-deficient cells resulted in B binding to the wall, the formation of dRG-II-B from mRG-II, and a reduction in wall pore size within 10 min. The wall pore size of denatured B-grown cells was increased by treatment at pH ≤ 2.0 or by treatment with Ca 2+ -chelating agents. The acid-mediated increase in wall pore size was prevented by boric acid alone at pH 2.0 and by boric acid together with Ca 2+ , but not by Na + or Mg 2+ ions at pH 1.5. The Ca 2+ -chelator-mediated increase in pore size was partially reduced by boric acid. Our results suggest that B-mediated cross-linking of RG-II in the walls of living plant cells generates a pectin network with a decreased size exclusion limit for polymers. The formation, stability, and possible functions of a borate ester cross-linked pectic network in the primary walls of nongraminaceous plant cells are discussed.

The Pore Size of Non-Graminaceous Plant Cell Walls Is Rapidly Decreased by Borate Ester Cross-Linking of the Pectic Polysaccharide Rhamnogalacturonan II.

Malcolm A. O'Neill

Papers

Pectins: structure, biosynthesis, and oligogalacturonide-related signaling.

RHAMNOGALACTURONAN II: Structure and Function of a Borate Cross-Linked Cell Wall Pectic Polysaccharide

Requirement of Borate Cross-Linking of Cell Wall Rhamnogalacturonan II for Arabidopsis Growth

Rhamnogalacturonan-II, a Pectic Polysaccharide in the Walls of Growing Plant Cell, Forms a Dimer That Is Covalently Cross-linked by a Borate Ester IN VITRO CONDITIONS FOR THE FORMATION AND HYDROLYSIS OF THE DIMER

The Pore Size of Non-Graminaceous Plant Cell Walls Is Rapidly Decreased by Borate Ester Cross-Linking of the Pectic Polysaccharide Rhamnogalacturonan II.