Cell Wall

8 Key excerpts on "Cell Wall"

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  eBook - ePub

  Fungi and Lignocellulosic Biomass

  • Christian P. Kubicek(Author)
  • 2012(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Chapter 1 The Plant Biomass 1.1 The Structure of Plant Cell Wall

  When we talk of plant biomass in terms of its use for biofuel and other biorefineries, we mostly mean the plant Cell Wall that makes up for more than 50% of the plants dry weight. This most outside located structure of the plant cell is also its most distinguishing feature, and because of its rigidity an essential component for their sedentary lifestyle. This rigidity also provides the strength to withstand mechanical stress and forms and maintains the plants shape. Despite this rigidity, nevertheless, the Cell Wall is a dynamic and metabolically active entity that plays crucial roles in growth, differentiation, and cell-to-cell communication and acts as a pressure vessel that prevents overexpansion when water enters the cell (Raven et al., 1999).

  Plant Cell Walls typically consist of three layers: the “primary Cell Wall” (a rather thin but continuously extending layer that is produced by growing cells), the “secondary Cell Wall” (a thick layer that is formed inside the primary Cell Wall after termination of cell growth), and the “middle lamella” (the outermost layer that forms an interface between secondary walls of adjacent plant cells and glues them together) (Figure 1.1 ).

  Figure 1.1 Organization of the different layers of the plant Cell Wall.

  Figure 1.2 Schematic diagram of the three-dimensional arrangement of the main polymers in the primary plant Cell Wall. The top sheet represents the middle lamella, the bottom sheet represents the plasma membrane; and the area in between represents the primary Cell Wall. Bright gray threads symbolize pectin, dark gray rectangular lines indicate hemicelluloses, small globes indicate soluble proteins, and the gray tubes indicate the cellulose microfibrils.

  The primary Cell Wall consists of the polysaccharides cellulose, hemicellulose, and pectin (Rose et al., 2004). The cellulose thereby aggregates to microfibrils that are covalently linked to hemicellulosic chains and form a cellulose—hemicellulose network that is embedded in the pectin matrix. The secondary wall is formed in some plants between the plant cell and primary wall when either a maximum size or a critical point in development has been reached and makes the plant cells rigid. It is made up from cellulose, hemicelluloses (mostly xylan), and lignin. The latter is a complex polymer of aromatic aldehydes that fills the spaces between cellulose, hemicellulose, and pectin components of the Cell Wall. Because of its hydrophobic nature, it drives out water and so strengthens the wall. In wood, three layers of the secondary Cell Wall, referred to as the S1 , S2 , and S3 lamellae, are found that result from different arrangements of the cellulose microfibrils (Mauseth, 1988; Figure 1.1 ). The first outermost layer—the S1 lamella—has both left- and right-handed microfibril helices; in contrast, the S2 (middle) and S3 (innermost) lamellae only comprise a single helix of microfibrils, although with opposite handedness to each other. During formation of the secondary Cell Wall, lignification takes place in the S1 and S2 but not S3 lamellae and also in the primary wall and middle lamella (Levy and Staehlin, 1992; Reiter, 2002; Popper, 2008). This arrangement allows the cellulose microfibrils to become embedded and fixed within the lignin, similar to steel rods that become embedded in concrete (Figure 1.2

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  eBook - ePub

  Methods in Cell Wall Cytochemistry

  • K V Krishnamurthy(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Chapter

  Cell Wall — Morphology and Chemical Composition

  1

  Contents 1.1    Morphology 1.2    Chemical Composition 1.2.1    Carbohydrates 1.2.1.1    Cellulose 1.2.1.2    Callose and Other 1, 3 β-Glucans 1.2.1.3    Chitin 1.2.1.4    Pectins 1.2.1.5    Hemicelluloses 1.2.1.6    Alginic Acid 1.2.1.7    Sulphated Polysaccharides 1.2.2    Glycoproteins 1.2.2.1    Structural Proteins 1.2.2.2    Enzymes 1.2.3    Lipids and Related Substances 1.2.3.1    Cutin 1.2.3.2    Suberins 1.2.3.3    Waxes 1.2.3.4    Sporopollenin 1.2.3.5    Pollenkitt 1.2.3.6    Tryphine 1.2.4    Lignins and Other Phenolic Substances 1.2.4.1    Lignins 1.2.4.2    Phenolic Acids and Amides 1.2.5    Mineral Substances 1.2.5.1    Silica 1.2.5.2    Calcium 1.2.5.3    Boron

  1.1    Morphology

  The Cell Wall is unique to plants and envelops the protoplast. Its presence or absence serves as a criterion to find out whether a given taxon is a plant or an animal. This characteristic is more reliable than the presence or absence of chlorophyll, as plant cells can change into a heterotrophic way of life by losing chlorophyll. As Frey-Wyssling and Mühlethaler1 had remarked, the plant Cell Walls historically played a special role in so far as they gave rise to the origin of the name “cell” itself. When Robert Hooke,2 in 1667, discovered cells in bottle cork, he observed only Cell Walls which formed compartmented structures similar to the ones seen in a honeycomb. Had the cell not been discovered through its Cell Walls in a plant structure, but in an animal such as in a protozoan, it would scarcely have been called “cell”: the discipline “cytology” would not have been named that way either.

  By virtue of its strategic position and structural organization, the Cell Wall or the extracellular matrix is meant to give shape or rigidity as well as protection and support to cells and tissues. It is also involved in the dimensional changes of the cells as these changes inevitably lead to changes in wall structure. The interaction between cell shape, cell growth rate, wall structure, and wall mechanics is influenced in large part by changes in biochemical processes inside the cell and vice versa. The other functions of the Cell Wall include control of intercellular transport, protection against other organisms, recognition and cell signalling, and storage of food reserves.3 It is at the heart of many key events in the life of a cell and the organism of which the cell is a part. In other words, “if the Cell Wall has something to do with the cell, it is equally true that the cell has something to do with the Cell Wall”.4

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  eBook - ePub

  Plant Biotechnology and Transgenic Plants

  • Kirsi-Marja Oksman-Caldentey, Wolfgang H. Barz(Authors)
  • 2002(Publication Date)
  • CRC Press

    (Publisher)

  It was concluded that the Cell Wall must have important functional roles, e.g., in cell-cell communication, transport of metabolites, differentiation, and development. To indicate this new appreciation of the Cell Wall as a dynamic and regulatory extracellular organelle, some authors prefer to call it an extracellular matrix. The growing realization that this matrix forms an integral and essential part of the plant cell may eventually even lead us to abandon the term extracellular in favor of, e.g., pericellular. In spite of these considerations, plant Cell Walls do play important static structural roles. First, they have to bear the turgor pressure, which results in enormous tangentially oriented stress forces in the Cell Wall plane (2). This stress is taken up by the fibrillar component in the Cell Wall, namely the cellulose microfibrils, which are interconnected and held in place by hemicelluloses. Second, the Cell Wall has to take up the pressure exerted on a plant cell by the surrounding tissue. This pressure is taken up by the matrix in which the fibrils are embedded, made up of polysaccharides containing uronic acids, namely pectins and glucuronoarabinoxylans, or—more precisely—by the water molecules held in the Cell Walls by these negatively charged polymers. In extreme cases, this water is replaced by the incorporation of lignin, a heavily cross-linked three-dimensional polyphenolic network able to withstand very high pressures. FIGURE 1 In vivo roles and ex vivo uses of plant Cell Walls and their components. Cell Walls fulfill many roles—both structural and functional— in the life of a plant, and different components are responsible for the different roles. Biotechnology may aim at improving these in vivo roles according to human interest, e.g., increasing resistance of crop plants against pathogens (HR, hypersensitive reaction)

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  eBook - ePub

  Plant Cells and their Organelles

  • William V. Dashek, Gurbachan S. Miglani(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  CHAPTER 9 Plant Cell Walls

  James E. Bidlack1 and William V. Dashek2

  1

  Department of Biology, University of Central Oklahoma, Edmond, OK, USA

  2

  Retired Faculty, Adult Degree Program, Mary Baldwin College, Staunton, VA, USA

  Introduction

  Constituents of the plant Cell Wall (CW) are among the most abundant biological molecules on earth and the functions of the CW are diverse. The CW provides mechanical strength, maintains cell shape, controls cell expansion, regulates transport, provides protection, functions in signaling processes, and stores food reserves (Brett and Waldron, 1990). The CW has even been referred to as a cell organelle (Mauseth, 1988), and more information is needed to have a complete understanding of how CW structure and function are integrated.

  Structure

  There are two types of CWs: primary and secondary (Hayashi, 2006; Albersheim et al., 2010). Primary CWs (Figure 9.1 a and b) are thin, elastic, and permit cell expansion while providing strength (Rose, 2003). Cells that possess only primary walls can lose their specialized form, divide, and subsequently differentiate into new cells (Evert, 2006). In some instances, cells possessing primary walls can exhibit thickenings and layering, for example, certain collenchyma cells (Bidlack and Jansky, 2014). The middle lamella is an area of union between adjacent cells’ primary walls. Secondary walls are thick, often consisting of layers and deposited when cell expansion is complete (Carpita et al., 2001). Examples of cells possessing secondary walls are xylem fibers, tracheids, vessel elements, and sclereids (see Chapter 1 ). These cell types possess lignified, spiral, scalariform, reticulate, or pitted walls (Figure 9.2 ).

  Figure 9.1

  (a) Electron micrograph of two adjoining plant cells with an intervening primary wall.

  From: Courtesy of J. Mayfield. (b) Model of the primary Cell Wall.

  From: https://en.wikipedia.org/wiki/Cell_wall .

  Figure 9.2

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  eBook - ePub

  Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals

  • Charles E. Wyman(Author)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  The thickness of the walls in xylem and fiber tissues is due to the formation of an extensive secondary Cell Wall as the cell matures. The sequence of events in the development of these cells is that after the cells have ceased growing by elongation, they begin to deposit a multilamellar secondary Cell Wall toward the cell lumen side of the primary Cell Wall [16]. At some point during and following secondary wall formation, the entire wall is infused with lignin monolignols [17]. The lignin polymerizes into the spaces in the existing wall and, consequently, significantly lowers its porosity [18]. Finally, the cell dies and its contents are absorbed, leaving a rigid water-impermeable cell-wall barrier. The biomass conversion perspective of the plant Cell Wall is, by necessity, heavily skewed toward the thick, lignified, secondary Cell Walls. These are the walls that harbor most of the mass and therefore most of the structural sugars in biomass. Unfortunately, they are also the most recalcitrant.

  Chemically, the plant Cell Wall is understood to be composed of cellulose, hemicelluloses, pectins, proteins, and often lignin. However, it is the complex intermingling of cross-linked layers brought together largely by self-assembly and template-assembly processes that create the complexity and resilience of the plant Cell Wall. The complex macromolecular architecture of the Cell Wall is a result of the self-ordering properties of cell-wall polymers generating a high degree of structural organization and complexity [19]. Three themes that govern the architectural plan of the plant Cell Wall are: (1) fibrous structural units embedded in an amorphous matrix; (2) covalent and non-covalent cross-linking; and (3) a polylamellate construction [20].

  The plant Cell Wall is sometimes envisioned as three intermingled networks that are extensively restructured during development. One is a protein network formed by the various classes of glycoproteins that contribute a scaffold to initial cell plate [21]. This network organizes cell plate membranes and the incorporation of initial cell-wall components as they are delivered to the cell plate by Golgi-derived vesicles. This original scaffold gets extensively remodeled and recycled during cell growth and maturation. While the protein network is not usually considered a significant contributor to recalcitrance, its role in establishing a template for cell-wall construction is still important. The second network is the pectic polysaccharide network. In the primary Cell Wall, the pectin network is credited with dictating key structural and mechanical properties of the wall including water content and porosity [22]. Again, this network is remodeled during growth and development and is usually not of critical concern for biomass conversion because the pectic polysaccharides are not especially recalcitrant to hydrolysis and extraction by pretreatment.

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  eBook - ePub

  Plant Biochemistry

  • Caroline Bowsher, Alyson Tobin(Authors)
  • 2021(Publication Date)
  • Garland Science

    (Publisher)

  Juncus and other rushes form aerenchyma, a spongy mass of stellar-shaped cells surrounded by extensive air spaces. Some cells, known collectively as motor cells, have walls that are selectively strengthened so that when they go through cycles of high turgidity (induced by high internal solutes) and low turgidity (induced by lowering internal solutes), the cells expand and contract in specific directions, much like hydraulic rams. The simplest examples are guard cells, whose expansion springs open the stomata on a leaf surface. More complex pistons serve to power nastic movements of plant leaves (leaf folding at night, unfolding at dawn) while others serve to spring traps in carnivorous plants. Adjustments to cell division planes and developing cell shapes lead to the formation of the whole range of plant organ shapes that are found in nature, from leaves and flowers to stems and tubers.

  Cell Walls Contain Microfibrils Embedded in a Complex Matrix

  Primary walls contain microfibrils of cellulose embedded in a matrix of hemicellulose and pectins (Chapter 7 ). The matrix contains a highly hydrated gel, so the water phase is a significant fraction of the Cell Wall’s fresh weight. The microfibrils provide strength and resist wall stretching along their length, so the wall expands at right angles to the preferred microfibril orientation. In cylindrical cells, microfibrils run around the cell in hoops or spirals in the side walls, resisting increases in cell diameter, so the cells grow mainly in length.

  Secondary walls are similar, but they contain a higher density of microfibrils and hence a higher cellulose content and a lower matrix water content than primary walls. The microfibrils may be laid down in a series of distinct layers that can be distinguished by microscopy. The matrix may be modified, for example, by the deposition of suberin, which renders it impermeable to water flows. In xylem and some other cells, lignin is deposited in the matrix and becomes highly cross-linked to the microfibrils, adding considerably to the mechanical strength of the wall (see Chapter 7

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  eBook - ePub

  Annual Plant Reviews, Plant Polysaccharides

  Biosynthesis and Bioengineering

  • Peter Ulvskov(Author)
  • 2010(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  We are on the verge of a rapid expansion in our understanding of the cell biology of the complex sets of polysaccharides that comprise plant Cell Walls. As we develop tools to map Cell Wall microheterogeneity we can perceive their considerable molecular complexity and diversity. Current major gaps in our knowledge of Cell Walls in relation to growth and development include systematic knowledge of the precise configurations and interactions of polysaccharides within the diverse Cell Walls of a growing organ, the functions of individual polysaccharides within a specific wall composites and also how the structural variants of the polysaccharide classes variedly influence Cell Wall architectures and properties. Inherent in all these studies will be the elucidation of regulatory and controlling mechanisms supporting the assembly of functionally specific wall architectures. At the level of organs, major gaps in knowledge include how cell and tissue wall architectures are integrated into the generation of organ mechanical properties and the nature of the involvement of Cell Walls in responses to diverse environmental and mechanical impacts.

  Acknowledgements

  JPK acknowledges funding support from the United Kingdom’s Biotechnology and Biological Sciences Research Council and Department of Trade and Industry and the European Union research framework programmes.

  Note Manuscript received September 2009 References

  Agarwal, U.P. (2006) Raman imaging to investigate ultrastructure and composition of plant Cell Walls: Distribution of lignin and cellulose in black spruce wood (Picea mariana ). Planta , 224, 1141–1153.

  Baluska, F., Salaj, J., Mathur, J., et al. (2000) Root hair formation: F-actin-dependent tip growth is initiated by local assembly of profiling-supported F-actin meshworks accumulated within expansin-enriched bulges. Developmental Biology , 227, 618–632.

  Barron, C., Parker, M.L., Mills, E.N.C., Rouau, X., Wilson, R.H. (2005) FTIR imaging of wheat endosperm Cell Walls in situ reveals compositional and architectural heterogeneity related to grain hardness. Planta , 220, 667–677.

  Be ová-Kákošová, A., Digonnet, C., Goubet, F., et al. (2006) Galactoglucomannans increase cell population density and alter the protoxylem/metaxylem tracheary element ration in xylogenic cultures of Zinnia . Plant Physiology , 142, 696–709.

  Blake, A.W., Marcus, S.E., Copeland, J.E., Blackburn, R.S., Knox, J.P. (2008) In-situ analysis of Cell Wall polymers associated with phloem fibre cells in stems of hemp, Cannabis sativa L. Planta

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  eBook - ePub

  Forest Products and Wood Science

  An Introduction

  • Rubin Shmulsky, P. David Jones(Authors)
  • 2018(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  The precise structure of pectin is not completely understood. In a process that may take several days to several weeks to complete, the cell enlarges and the Cell Wall gradually thickens as biopolymers produced within the cells are progressively added to the inside (lumen side) of the wall (Figure 3.4). Eventually, the protoplasm that fills the cell is lost and the cell has a thickened wall, consisting of primary and secondary wall layers, and a hollow center (Figure 3.4 d). Successive arrangements of biopolymer assemblies are responsible for the gradual thickening of a Cell Wall. But what are these biopolymers ? They are the three distinct types of macromolecule described earlier: cellulose, hemicellulose, and lignin. FIGURE 3.4. Stages in development of a wood cell. Longitudinal cells in cross‐section: (a) new cell has only ultrathin primary wall (P); (b, c) cell enlarges and then wall thickens as secondary wall (S) forms to inside of the primary wall; (d) wall continues to thicken with buildup of deposits. The buildup of biopolymers on the inner surfaces of the Cell Wall is not haphazard; it occurs in a very precise fashion. Cellulose, for example, is not incorporated into the Cell Wall as individual molecules but rather as intricately arranged clusters of molecules. The long‐chain cellulose molecules are synthesized from anhydroglucose (actually glucose attached to a mononucleotide) in many specific locations at the inner surface of the Cell Wall itself. As these chains lengthen, they aggregate laterally in a well‐defined way with their immediate neighbors, which are also growing, to form crystalline domains in a unit cell configuration (Figure 3.5). The cellulose crystal lattice is held together by intermolecular and dipolar interactions primarily in the form of hydrogen bonds; this arrangement is so stable that the individual chains cannot be dissolved in common solvents such as water or acetone

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