Structure and differentiation of the cell wall of Phytophthora palmivora: cysts, hyphae and sporangia.

Abstract

Walls from cysts, hyphae and sporangia of Phytophthora palmivora consist chiefly (ca. 90% dry wt) of β-glucans with 1,3-, 1,4- and 1,6-links. The glucans are predominatly β-1,3-linked but there are significant differences in the relative proportion of 1,3-, 1,6- and 1,4-linked glucosyl residues among the three wall types. There are also differences in protein content, susceptibility to degradation by various β-glucanases, and surface texture. The isolated cyst wall consists solely of a thin fabric of long, tightly interwoven, randomly oriented microfibrils. Both inner and outer surfaces of the cyst wall are distinctly microfibrillar. The hyphal wall has two different textures; the internal surface is distinctly microfibrillar while the external surface is non-fibrillar. In a germinated cyst, there is a zone of demarcation where the microfibrils of the cyst wall disappear into the smooth outer texture of the germ tube wall. An exo-β-1,3-glucanase preferentially removed the amorphous material of the outer surface of the germ tube leaving exposed a continuous microfibrillar fabric from cyst to hyphal tube. Conceivably, the textural and structural differentiation of the cell wall may play a decisive role in cellular morphogenesis.