Studies on the Ship-fouling Alga Enteromorpha I. Aspects of the Fine-structure and Biochemistry of Swimming and Newly Settled Zoospores

Certain aspects of the fine-structure and biochemistry of swimming and settled zoospores of Enteromorpha intestinalis are described in an attempt to elucidate the mechanism of attachment, in relation to the problem of tanker-fouling by this plant. The general disposition of the more important organelles is described and particular attention is paid to cytoplasmic vesicles within the swimming cell. The most important of these in the settlement process are believed to be (i) small vesicles situated peripherally at the extreme anterior end of the zoospore, (ii) larger vesicles with very electron-opaque contents which dominate the front half of the swimming cell, and (iii) small vesicles probably produced from the surface of the endoplasmic reticulum lying adjacent to the Golgi bodies. There is a lot of evidence that the larger vesicles and their contents are produced from the Golgi bodies, possibly in association with the adjacent endoplasmic reticulum. Newly settled zoospores rapidly lose the larger vesicles and secrete a fibrillar substance believed to be adhesive. Within 30 min of contact with a surface a thin cell wall is discernible between the plasmalemma and the adhesive material, and this continues to increase in thickness over the first hours of settlement. By the use of specific enzymes, notably α-amylase, trypsin, and pronase, the biochemical nature of the material within the larger vesicles has been investigated. The evidence points to it being largely proteinaceous in character, the vesicle content and secreted material being digested by proteolytic enzymes. Although α-amylase has no discernible effect on either the vesicle content or secreted substance, results presented in the succeeding paper indicate that this enzyme has a very marked influence on zoospore adhesion. All the evidence together points to the conclusion that a mucopolysaccharide adhesive substance is produced, probably by the Golgi region, consisting of protein and carbohydrate moieties. This is discussed in relation to the sites of synthesis of similar mucopolysaccharide/mucoprotein secretory materials in animal cells.