Ultrastructural localization of polysaccharides in the wall and septum of the basidiomycete Schizophyllum commune

Abstract

The location of polysaccharides in the wall and the septum of monokaryotic mycelium of Schizophyllum commune was determined using thin sections and shadowed preparations. Extraction procedures and staining, to detect periodate-sensitive polysaccharides, were used to localize wall polymers that had previously been identified by chemical analysis. Apart from a water-soluble β-1,3-β-1,6-linked glucan (mucilage) that surrounds the hyphae, the lateral wall has an outer layer consisting of relatively pure α-1,3-glucan (S-glucan). The inner layer consists of R-glucan, an alkali-insoluble polymer containing a large proportion of β-1,3-β-1,6-linked glucan, in which chitin microfibrils are embedded. Adjacent to the plasmalemma, these microfibrils are clearly visible but at the interface with the S-glucan layer they are completely embedded in R-glucan. The septum has a central plate mainly composed of randomly oriented chitin microfibrils, except at the septal swelling, where they are arranged circularly around the septal pore. The central plate is covered at both sides by a layer of R-glucan in which chitin microfibrils are embedded. R-Glucan and chitin only occur in the central part of the septal swelling. The main body of this structure is made up of a mucilaginous substance that may be similar to the water-soluble β-1,3-β-1,6-glucan that surrounds the hyphae. S-Glucan appears to be absent from the septum. At the junction of lateral wall and septum, chitin and R-glucan appear to be resistant to enzymatic treatment, which dissolves most of the other wall material, resulting in the appearance of septal rings.