Topochemical and Electron Microscopic Analyses on the Lignification of Individual Cell Wall Layers During Wood Formation and Secondary Changes

Abstract

The topochemical distribution of lignin and phenolic extractives in wood cell walls is determined on a cellular level by using scanning UV microspectro- photometry (UMSP) and transmission electron microscopy (TEM). These improved cellular analytical techniques enable direct imaging of the lignin distri- bution within individual cell wall layers during wood formation and secondary changes. The UMSP technique is based on the ultraviolet illumination of semithin transverse sections which can be related semiquantitatively to the concentration of lignin. Electron microscopy is variously used to obtain high-resolution information on the lignin distribution in wood cell walls which can be visualised by staining with potassium permanganate (KMnO4). By applying these improved techniques, (1) the topochemistry of lignification in developing xylem and wood tissue after wounding, (2) the topochemical detection of phenolic extractives, and (3) the lignin distribution in tropical bamboo species are presented and illustrated in detail. The described methods and presented results demonstrate that cellular UV microspec- trophotometry and electron microscopy are ideally suited to study the topochemical distribution of lignin and phenolic extractives on a subcellular level. In particular, the application of the UV-scanning technique enables a direct imaging of lignin distribution (geometrical resolution of 0.25 μm � 0.25 μm) and provides funda- mental information on the topochemistry of lignification. The techniques can be used for a wide range of applications in wood biology and wood topochemistry.