Ultrastructural studies of spore walls of Acaulospora morrowiae and A. scrobiculata

Abstract

Morphological and ultrastructural studies were used to determine spore wall structure in two Acaulospora species: A. morrowiae and A. scrobiculata. The spore wall of A. morrowiae is divided in three zones (A, B, C), each of which in broken spores separate into layers. Many features, such as a series of regularly distributed fibrillar layers of arched-appearing fibrils were clearly distinguishable. In A. scrobiculata, two zones were distinct in the wall: an outer zone, ornamented with deep round-bottomed depressions which extended into several of the arched-like layers, and an inner zone formed by three distinct layers. The first layer of the inner zone had a radial arrangement of fibrils; the two other layers were formed apparently by amorphous material. Arched and radial fibrils have been found in spores of other Glomales but not in those of other groups of fungi. Spores of Acaulospora are similar to those of certain other glomalean fungi. These and other data indicate the uniqueness of spore walls in the Glomales.