Transmission electron microscope observations of brown rot caused by Fomitopsis pinicola with respect to osmiophilic particles

Abstract

Changes in pinewood tracheids during decay by the brown rot fungus Fomitopsis pinicola were observed in the transmission electron microscope for a cultivation period of 80 days. It was found that F. pinicola normally caused degradation of carbohydrates over the entire cell wall with the cell wall contours maintained, but more rarely was capable of a complete degradation of the cell walls including the middle lamella and the cell corners. This indicates that some hyphae may have a ligninolytic enzyme system. The occurrence of osmiophilic particles in the protoplasm of hyphae and in wood cell walls was observed from early decay stages. They were randomly distributed in the wood and their distribution, being an indicator of carbohydrate depolymerization, permits this type of decay to be observed in the transmission electron microscope. The origin and function of the osmiophilic particles is discussed with respect to what is known about the enzymes of wood decay. Furthermore, the curve of weight loss is discussed in connection with earlier findings concerning wood decay and with the appearance of the osmiophilic particles.