Two different morphotypes of freshwater Cladophora surera (Cladophorales, Chlorophyta) produce similar sulfated cell wall polysaccharides

The Cladophoraceae (Cladophorales) includes branched (Cladophora) and unbranched (Chaetomorpha and Rhizoclonium) filamentous species, living in marine and freshwater environments. Species-level taxonomy is impeded by considerable morphological plasticity, related to environmental conditions, and switches between branched and unbranched morphologies have been reported within species. In this work, it was shown that Cladophora surera, a species widely distributed in streams in the Pampa Plains of Argentina, appears in two different morphotypes, branched and unbranched filaments. Phylogenetic analysis indicated that they correspond to the same species. The presence of these morphotypes could not be related with season or water flow. Moreover, under the same culture conditions it was possible to develop the branched morphotype from the unbranched one. The general structure of sulfated galactoxyloarabinans biosynthesized by the branched morphotype of this alga were studied previously. In this work, these sulfated 4-linked pyranosic arabinans were studied in relation to morphotype and season. It was shown that differences in structure of the water-soluble polysaccharides between samples could not be related to the morphotype but depend on the season. A detailed study by principal components analysis (PCA) of variables related with the main structural features showed clear differences between sulfated polysaccharides extracted from algae collected in spring, compared to those collected in other seasons. Structural analysis by chemical and spectroscopic methods of these sulfated arabinans collected in the different seasons are reported and discussed.