An ultrastructural study of the relationship between rhizoids of Polysiphonia lanosa (L.) Tandy (Rhodophyceae) and tissue of Ascophyllum nodosum (L.) Le Jolis (Phaeophyceae)

Abstract

Rhizoids of Polysiphonia lanosa (L.) Tandy were found to digest their way into the host, Ascophyllum nodosum (L.) Le Jolis. The endoplasmic reticulum and vacuole membranes of host cells broke down early in digestion, while plastid and mitochondrial membranes appeared in negative instead of positive contrast. These changes sometimes took place before the rhizoid touched the cell. Digestion was generally complete and much A. nodosum wall material was incorporated into the outer rhizoid wall, although remnants of the pit-fields persisted within or immediately about the rhizoid. Secondary complex rhizoids appeared to incorporate one or more host cells which were digested in contact with the intrusive rhizoid protoplast. These observations are interpreted in light of ultrastructural studies of the relationships between other algal and fungal parasites and their hosts.