Secondary cell wall

Secondary cell wall is a structure found in many plant cells, located between the plasma membrane and the primary cell wall. This layer is typically more rigid and thicker than the primary cell wall due to its composition, which is designed to provide additional support and protection to the cell. The secondary cell wall is a significant feature in the cells of wood and bark, contributing to the strength and durability of these materials.

Composition

The secondary cell wall is primarily composed of cellulose, hemicellulose, and lignin. Cellulose provides the wall with tensile strength, hemicellulose acts as a matrix that embeds the cellulose fibers, and lignin confers rigidity and resistance against microbial attack and physical damage.

Cellulose

Cellulose is a long-chain polysaccharide that forms microfibrils, which are the main structural components of both primary and secondary cell walls. In the secondary cell wall, cellulose microfibrils are more densely packed than in the primary cell wall, contributing to its greater strength.

Hemicellulose

Hemicellulose in the secondary cell wall binds closely to cellulose, forming a network that helps to stabilize and strengthen the wall structure. Unlike cellulose, hemicellulose consists of shorter chains and has a branched structure.

Lignin

Lignin is a complex polymer that fills the spaces between cellulose and hemicellulose in the secondary cell wall. It is highly hydrophobic, which helps to waterproof the cell wall, reducing the loss of water and providing a barrier against pathogen invasion.

Function

The primary function of the secondary cell wall is to provide structural support to the plant, allowing it to grow taller and withstand environmental stresses such as wind and gravity. Additionally, the presence of lignin makes the secondary cell wall an effective barrier against pathogens and pests.

Formation

The formation of the secondary cell wall occurs after the cell has stopped expanding. It involves the deposition of cellulose, hemicellulose, and lignin in a specific and highly regulated manner. The process is controlled by a variety of genes and proteins that coordinate the synthesis and deposition of the wall's components.

Significance in Plants

The secondary cell wall plays a crucial role in the life of a plant. It not only provides structural integrity but also contributes to the plant's water conduction system, particularly in xylem vessels and tracheids, where it helps to facilitate the efficient transport of water and nutrients.

Economic Importance

Materials rich in secondary cell walls, such as wood and bark, are of significant economic importance. They are used in a wide range of applications, from construction materials and paper production to biofuel generation.