Localization of specific monosaccharides in cells of the brown alga Padina gymnospora and the relation to heavy-metal accumulation

Summary.

The brown alga Padina gymnospora has been studied due to their ecological significance and biochemical characteristics, including its high capability of heavy-metal accumulation. It has been suggested that the fucans are among the main polysaccharides related to metal binding and precipitation in cell walls. The main purpose of this work was to determine the localization of specific monosaccharides in P. gymnospora cells. In this way, the lectins Ulex europaeus agglutinin and Canavalia ensiformis concanavalin A with specificity to α-L-fucose and to terminal residues of α-D-glucosyl and α-D-mannosyl, respectively, were applied in young individuals. These revealed a preferential distribution of α-L-fucose at cell walls near the external surface in cortical cells and near the plasmalemma in cortical and medullar cells. The distribution of α-L-fucose in cell walls indicates the distribution of sulfated polysaccharides (sulfated fucans) that colocalize with the heavy-metal granules (Zn and Cd) described in previous works. Therefore, our results suggest that α-L-fucose participates in the nucleation and immobilization of heavy metals in P. gymnospora cell walls. An intense labeling of U. europaeus agglutinin and a weak labeling of concanavalin A was also observed in physodes. X-ray microanalysis revealed the presence of zinc, sulfur, and calcium in physodes of algae collected in a heavy-metal-contaminated area. Besides the affinity between polyphenolic compounds and heavy metals, it is suggested that the mechanism of metal binding by physodes could be related to the presence of sulfated fucans.