Sulfated Polysaccharides in the Freshwater Green Macroalga Cladophora surera Not Linked to Salinity Adaptation

Abstract

The presence of sulfated polysaccharides in cell walls of seaweeds is considered to be a consequence of the physiological adaptation to the high salinity of the marine environment. Recently, it was found that sulfated polysaccharides were present in certain freshwater Cladophora species and some vascular plants. Cladophora (Ulvophyceae, Chlorophyta) is one of the largest genera of green algae that are able to grow in both, seas and freshwater courses. Previous studies carried out on the water-soluble polysaccharides of the marine species C. falklandica established the presence of sulfated xylogalactoarabinans constituted by a backbone of 4-linked β-L-arabinopyranose units partially sulfated mainly on C3 and also on C2 with partial glycosylation, mostly on C2, with terminal β-D-xylopyranose or β-D-galactofuranose units. Besides, minor amounts of 3-, 6- and/or 3,6-linked β-D-galactan structures, with galactose in the pyranosic form were detected. In this work, the main water soluble cell wall polysaccharides from the freshwater alga Cladophora surera were characterized. It was found that this green alga biosynthesizes sulfated polysaccharides, with a structure similar to those found in marine species of this genus. Calibration of molecular clock with fossil data suggests that colonization of freshwater environments occurred during the Miocene by its ancestor. Therefore, the presence of sulfated polysaccharides in the freshwater green macroalga C. surera could be, in this case, an adaptation to transient desiccation and changes in ionic strength. Retention of sulfated polysaccharides at the cell walls may represent a snapshot of an evolutionary event, and, thus constitutes an excellent model for further studies on the mechanisms of sulfation on cell wall polysaccharides and environmental stress co-evolution.

Diversity of Sulfated Polysaccharides From Cell Walls of Coenocytic Green Algae and Their Structural Relationships in View of Green Algal Evolution

“…It is important to note, that the configuration of C-1-C-4 of α- l -arabinopyranose is the same as that of β- d -galactopyranose, and the configuration of C-1-C-4 of β- l -arabinopyranose is the same as that of α- d -galactopyranose ( Supplementary Figure S1 ), so the anomeric signals reported by these authors should correspond to the β-anomer of l -arabinopyranose. It is thus reasonable to believe that their experimental results are in agreement with structures proposed by Percival and coworkers ( Hirst et al, 1965 ; Johnson and Perival, 1969 ; Bourne et al, 1970 ) and Arata et al (2016 ; 2017a ).…”

“…In most, if not in all, cases, small amounts of other monosaccharide constituents suggest that there could be some other polysaccharides, minor constituents of the cell wall, the nature of which remains elusive. For example, when the sulfated polysaccharide systems from Cladophora falklandica and C. surera were studied, minor amounts of rhamnose were detected ( Arata et al, 2016 ; Arata et al, 2017a ). It is not known if it is derived from a rhamnan present in minor amounts, or if it is a minor constituent of the major water soluble polysaccharides obtained from these algae.…”

“…Similar polysaccharide structures were found for the freshwater Cladophora surera , although only traces of galactose in the furanosic form were detected. The presence of sulfated polysaccharides in a freshwater green macroalga of the Cladophorales could be, in this case, an adaptation to transient desiccation and changes in ionic strength of its environment ( Arata et al, 2017a ).…”

“…In addition, Surayot et al (2016) proposed for the water soluble polysaccharides from Cladophora glomerata , another freshwater alga phylogenetically very close to C. surera ( Arata et al, 2017a ), a backbone of 4-linked α- l -arabinopyranose units, with galactose and xylose residues as branches and sulfate groups linked to C-2 of the arabinose units. They also reported terminal arabinofuranose units.…”

“…For marine organisms, as seaweeds, marine invertebrates and sea grasses, sulfated polysaccharides are supposed to be a physiological adaptation to the high ionic strength of the marine environment ( Kloareg and Quatrano, 1988 ; Aquino et al, 2005 ; Pomin and Mourao, 2008 ). In addition, they are believed to have important support and protective functions, for example through moisture retention capacity that enhances desiccation resistance ( Kloareg and Quatrano, 1988 ; Arata et al, 2017a ). They may also be involved in cell interaction and adhesion, and form a protective barrier against pathogens ( Vavilala and D´Souza, 2015 ; Udayan et al, 2017 ).…”