A THREE-DIMENSIONAL COMPUTER MODEL OF THE TRACHEID CELL WALL AS A TOOL FOR INTERPRETATION OF WOOD CELL WALL ULTRASTRUCTURE

Abstract

Three-dimensional computer models were used to simulate transmission electron micrographs in order to determine the effects of changes in microfibril orientation and arrangement on the appearance of ultrastructural images based on thin sections. It is shown that the tangential fibrillar texture commonly associated with wood cell walls results not from individual microfibrils arranged in tangential lamellae but from overlapping of adjacent microfibrils irrespective of their arrangement. The tangential lamellae observed in transmission electron micrographs of wood cell walls do not necessarily reflect the underlying nanostructure of the wall. Tangential textures can occur irrespective of the arrangement of microfibrils in tangential, radial or random patterns as a direct result of the helical organisation of the cell wall. Comparison between model images and high resolution micrographs suggests that microfibrils are arranged randomly in weakly defined clusters, with perhaps varying amounts of tangential or radial organisation.