The Plasma Membrane and the Cell Wall

Plant cell walls are among the features that distinguish plants from animals. The cell wall contributes to internal cellular turgor pressure while offering protection to the cell from external threats. The cell wall is also flexible, and its content and structures are modulated according to growth and tropisms. A typical plant cell wall is primarily composed of carbohydrates synthesized either at the plasma membrane (PM) or in the trans-Golgi network: cellulose and callose are produced at the PM, whereas the matrix polysaccharides, i.e., pectins and hemicelluloses, are synthesized in the Golgi apparatus and are subsequently transported across the PM via exocytosis. The wall also contains enzymes and structural glycoproteins. The cell wall is formed by independent and coordinated mechanisms based on physical properties and self-assembly, as well as the action of cell wallmodifying enzymes. Thus, the plant cell wall physiology is dynamic and includes coordinated sugar synthesis, polymer assembly, trafficking, and modification.