Evidence of accessory compounds in vessel walls of Sapelli heartwood (Entandrophragma cylindricum) obtained by transmission electron microscopy

Abstract

In a project on highly variable decay resistance of Sapelli heartwood, vessel walls were investigated by transmission electron microscopy. During processing, the specimens were either acetone dehydrated prior to embedding or directly embedded. It was found that the outer secondary wall of vessels in specimens with increased durability consists of several concentrically arranged sublayers. The inner secondary wall was distinctly stained with potassium permanganate only after direct embedding, those specimens dehydrated with acetone did not show this phenomenon. It can be supposed that acetone removes incrusting material from the inner secondary wall layer. On the other hand, less durable Sapelli heartwood specimens generally had no electron-dense inner secondary wall, independent of the type of processing. It is assumed that incrusting material in vessel walls plays an important role in restricting fungal attack.