Carbohydrate-rich cell walls display complex designs, which together with the presence of phenolic polymers constitutes a barrier for microbes, fungi, and animals. Plant cell walls are composed of a small number of distinct chemical polymers tightly woven into a meshwork with specific 3D architectural organization, allowing the respective cell walls to perform various mechanical and biochemical functions. The mechanical functions include providing tensile strength to the plant body and formation of a physical barrier to harsh biotic and environmental insults. The biochemical functions include reorganization of cell wall components and possibly signal transduction in response to pathogen attack, environmental stresses, and during different developmental stages.
Plant cell walls are highly sophisticated fiber composite structures that have to fulfill a wide range of biological roles that are central to plant life. 2 Some cell wall components have supposedly ancient prokaryotic origins and others are present in extant descendents of the algal ancestors of land plants.
In general our current understanding of cell wall evolution is limited. Common to all land plants (embryophytes) though are carbohydrate-rich cell walls that provide support, act as defensive barriers, are conduits for information, and are a source of signaling molecules and developmental cues. Although cell walls display considerable variability in their fine structures, most are essentially highly complex fiber composites based upon a load-bearing network that is infiltrated with matrix polymers. In the primary walls of growing plant cells, cellulose microfibrils are tethered together by cross-linking glycans (also known as hemicelluloses) and this assembly is embedded in matrix polysaccharides and glycoproteins. In the secondary walls of woody tissues, the embedding material is the phenolic polymer lignin.