The cell wall is the outer coat that provides a tough protective casing of the plant cell. Decades of research efforts have contributed to our current understanding of cell wall structure and function. The cell wall is composed primarily of three major classes of polysaccharide: cellulose, hemicellulose and pectin, as well as structural proteins, and phenolic and aliphatic polymers. In addition to structural roles, the cell wall has a multitude of important functions in plants. For example, cell wall expansion and its regulation is the basis of cell and plant growth, the cell wall gives plant cells their characteristic shapes, and it is strongly involved in defence responses against pathogens and herbivores. Furthermore, recent studies indicate some novel and remarkable roles for the cell wall in sensing processes during pattern formation in plant development. This article provides a general summary of the current understanding of cell wall structure and function.

Key Concepts:

• Plant cell walls are crucial for plant morphology and development.
  
• The primary walls are generally deposited during cell growth, while secondary walls may re‐inforce the extracellular space after cells have ceased to grow.
  
• Three main polysaccharide classes may be discerned; cellulose, hemicelluloses and pectins.
  
• The polysaccharides form an intricate and crosslinked architecture.
  
• Several classes of cell wall structural proteins may be involved in scaffolding the deposition of cell wall material.
  
• Enzymatic cell wall proteins are involved in modifying the properties of the cell wall during and after its assembly.
  
• Cell wall modifications are a major regulatory mechanism of cell and plant growth.
  
• The dynamic adjustment of cell wall properties is a crucial part of plant defence responses against pathogens and herbivores and mechanical injury.
  
• Stress gradients in the cell wall are sensed by cells and may be a source of positional information during morphogenesis.