Plant Cell Walls

Abstract

Common to all plant species, the cell wall is the tough outer coat that protects the plant cell. The cell wall is mostly carbohydrate‐based, comprising three major classes of polysaccharides: cellulose, hemicellulose and pectin. There are also important structural proteins as well as phenolic and aliphatic polymers. The cell wall provides mechanical strength to the plant body, allowing upright growth and structure formation, and also plays important roles in cellular processes such as cell expansion, tissue differentiation, intercellular communication, water movement and defence responses against pests or pathogens. Cell walls may even be involved in signal sensing during pattern formation in plant development.

Key Concepts

  • The cell wall is the outermost layer of the plant cell.
  • The cell wall consists essentially of three major types of carbohydrates – cellulose, hemicellulose and pectins – and proteins.
  • Some specialised cell wall types, for example woody cell walls also contain phenolic and aliphatic polymers in addition to carbohydrate polymers.
  • The cell wall is a dynamic structure whose composition changes during cell, tissue and plant development and in response to various stresses.
  • The cell wall provides mechanical strength to the plant body.
  • The cell wall plays important roles in processes such as cell expansion, tissue differentiation, intercellular communication, water movement and defence responses against pests or pathogens.

Keywords: cell wall; plant; polysaccharide; structure; function; cell surface; extracellular matrices

Figure 1. Model showing the arrangement of cellulose microfibrils in the walls of a plant cell. Microfibrils are inextensible, so this spiral‐like arrangement dictates that the cylindrical cell will expand predominantly in one dimension, as shown. Many of the cells in an elongating stem or root conform to this model.
Figure 2. Schematic models for pectic polymers. (a) Homogalacturonan can be extensively methyl‐esterified and acetylated. (b) Rhamnogalacturonan I has long arabinan and arabinogalactan side branches, which can be interlinked. (c) Rhamnogalacturonan II has highly complex side chains which show some limited variability between plant species.
Figure 3. Schematic structural models for xyloglucan (a) and xylan (b).
Figure 4. Mechanism of wall loosening caused by the activity of xyloglucan endo‐transglycosylase (XET).
Figure 5. Immunogold localisation of lignin in the secondary cell walls of poplar wood fibre cells. The image shows a cross section of a fibre cell wall which has been treated with a preparation of gold particles coupled with antibodies that recognise lignin. The gold particles are visible as black dots in the S1 and S2 layers of the secondary cell wall, indicating the presence of lignin there, but are absent from the primary wall and middle lamella between two neighbouring cells. Bar is 0.5 µm. Reproduced from Joseleau et al. 2004 © Springer.
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Further Reading

Morgan JL, Strumillo J and Zimmer J (2013) Crystallographic snapshot of cellulose synthesis and membrane translocation. Nature 493: 181–186.

Purushotham P, Cho SH, Díaz‐Moreno SM, et al. (2016) A single heterologously expressed plant cellulose synthase isoform is sufficient for cellulose microfibril formation in vitro. Proceedings of the National Academy of Sciences of the United States of America 113: 11360–11365.

Schuetz M, Benske A, Smith R, et al. (2014) Laccases direct lignification in the discrete secondary cell wall domains of protoxylem. Plant Physiology 166: 798–807.

Wolf S, Hematy K and Hofte H (2012) Growth control and cell wall signaling in plants. Annual Review of Plant Biology 63: 381–407.

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How to Cite close
Srivastava, Vaibhav, McKee, Lauren S, and Bulone, Vincent(Jul 2017) Plant Cell Walls. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001682.pub3]