sekundærveggen

The secondary cell wall is a rigid layer that forms inside the primary cell wall of plant cells, and in some algae and fungi. It is deposited after the cell has stopped expanding, providing structural support and protection. Unlike the primary cell wall, which is thin and flexible, the secondary cell wall is considerably thicker and more rigid. Its composition is primarily cellulose, but it also contains significant amounts of lignin, a complex polymer that confers great strength and resistance to decay and compression. Other components may include hemicellulose. The deposition of the secondary cell wall often occurs in distinct layers, which can have different orientations of cellulose microfibrils, further contributing to its mechanical properties. This layered structure is particularly evident in tracheary elements of the xylem, where it forms characteristic patterns like annular, helical, scalariform, or reticulate thickenings that help prevent the collapse of these water-conducting cells under negative pressure. The presence and composition of the secondary cell wall are crucial for the development of woody tissues and the overall structural integrity of plants.