Microtubules and the Control of Wood Formation

Abstract

Cell walls are reinforced by cellulose microfibrils, which resist cell expansion in response to turgor pressure. The orientation of cellulose microfibrils in the primary walls of cambial derivatives determines the direction of cell expansion, thereby controlling the shape and size of secondary xylem cells in trees. In addition, the texture of the secondary wall, in particular the orientation of cellulose microfibrils in the middle layer of the secondary wall (S2 layer), is closely related to the physical properties of secondary xylem cells. Thus, the orientation of cellulose microfibrils in the secondary walls determines the mechanical properties of wood. In addition, the secondary xylem cells form modifications of the cell wall, such as pits and perforations, by the localized deposition of cellulose microfibrils. These pits and perforations provide a pathway for liquid flow between secondary xylem cells. Thus, the ability to control the orientation and localization of cellulose microfibrils in the secondary wall might allow us to change the quality of wood and its products. There is considerable evidence that the dynamics of cortical microtubules are closely related to the orientation and localization of newly deposited cellulose microfibrils in the differentiating secondary xylem cells. Thus, manipulation of cortical microtubules would allow control of the texture of cell wall, with a consequent improvement of wood quality.