Immunocytochemical localization of the extracellular polysaccharide alginic acid in the brown seaweed, Fucus distichus.

Abstract

Fluorescent and peroxidase-labeled antibody techniques were employed to localize alginate, which is one component in the complex extracellular acidic polysaccharide situation of the brown seaweed, Fucus distichus. The alginate antigen was extracted and characterized by a variety of methods. It had a low degree of polymerization and a mannuronic acid to guluronic acid ratio of 2.2. No contaminants were detected. The specificity of rabbit antisera was tested by immunodiffusion. Antisera reacted with alginate and fractions of alginate but not with other brown algal polysaccharides. When cryostat sections of Fucus proved unsuitable, 1-µ sections embedded in glycol methacrylate were used for indirect fluorescent or peroxidase antibody staining. Highly sulfated extracellular polysaccharides and intracellular phenolic compounds were implicated in nonspecific staining. Texture artifacts were caused by solubility of alginates and other polysaccharides from embedded sections. Alginate was localized in variable patterns in all cell walls and some matrix regions. The applicability of the methods is discussed.