Ultrastructure and composition of the cell walls of Sclerotinia sclerotiorum

The cell walls of Sclerotinia sclerotiorum (Lib.) de Bary have been examined by electron microscope, infrared and biochemical techniques. The rind walls of the sclerotia have a rough outer electron-dense layer which is absent from the other walls. The hyphal walls do not have definite layers, but the pseudo-parenchymatous walls possess a relatively thin electron-dense inner wall surrounded by a substantially thicker outer electron-transparent layer. Microfibrils, probably of chitin, are present in all walls. Whereas β-glucan and chitin are constituents of the hyphal walls, and of the pseudoparenchymatous and rind walls of the sclerotia, a melanin was found in the rind walls only. Enzyme studies with culture filtrates from two lytic soil micro-organisms suggested that the β-glucan was similar to laminarin, a β (1→3) glucan. In addition the presence of β ( 1→6) linkages was indicated in the pseudoparenchymatous walls. Acid-hydrolysis products of the pseudoparenchymatous and hyphal walls were similar and included amino-acids, amino-sugar and glucose with some mannose. Phenol oxidase was present in the rind cells and in an exudate from the sclerotial surfaces. The product of the activity of this enzyme on catechol differed from the melanin pigment of the rind walls.