Wall Structure and spore Germination in Fusarium culmorum

Abstract

The conidial and germ-tube walls of Fusarium culmorum (W. G. Smith) Sacc. have been examined by various chemical and electron-microscope techniques. On the basis of these results and hypothesis is proposed for the organization of these walls. Microchemical tests indicate the presence of chitin in the walls and suggest that the mucilaginous layer around the conidium is mainly composed of xylan. Chemical analyses of isolated wall material confirm the presence of chitin constituents in the wall, and a rylan layer around the conidium. Furthermore, the wall contains a polypeptide moiety which has a different amino acid composition from the rest of the protein of the cell. Electron microscope studies of replicas and sections of conidia, germ tubes, and hyphae reveal a layered structure for the wall. The central layer is non-microfibrillar and is overlaid on both sides with a layer of randomly orientated microfibrils. The mucilaginous layer of the conidium obscures the microfibrillar structure beneath it unless the mucilage is removed by hydrolysis. The problem of hyphal growth is discussed on the basis of the structure of germ-tube tips and mature hyphae observed.