Ultrastructural changes during aging of wood cells

Abstract

Although most of the wood cells which are produced in the cambium die after the deposition of secondary wall thickening and lignification, the parenchymous cells contain living substances throughout the sapwood and are used for transportation and storage of metabolic materials. In the electron microscope dark globular particles of different sizes were traced from cambium to heartwood border in the parenchymous cells of pine. In the sapwood-heartwood transition zone the dark particles loose their globular shape and the dark content is deposited upon the parenchymous cell wall and therewith upon the membranes of the window-like pits. In this state the membranes are darkly colored so that it is assumed that the dark materials diffuse into the membranes. Dark deposits were observed within the compound middle lamella, in the chambers of bordered pits, and within the fiber lumina. From these observations it is concluded that the dark substances migrate through the middle lamella into the pit chambers and from there into the cell lumina. There is evidence that the decomposition of the globular particles as well as the diffusion of the dark substances into the cell walls begin in a region which is macroscopically considered to be part of the sapwood. Subsequent reactions in the deposition places result in the formation of typical heartwood substances.