Water-soluble galactan sulfates: low Mw-agarans in the carrageenan matrix of red seaweed cell walls

JOSÉ M. ESTEVEZ; MARINA CIANCIA; ALBERTO S. CEREZO

Asilomar, California

Otro; Plant Cell Wall Biosynthesis Meeting; 2005

Plant Cell Wall Biosynthesis Research Network

Water ?Soluble Galactan Sulfates:Low Mw-Agarans the Carrageenan Matrix of Red Seaweed Cell Wall Jose M Estevez1,2 ; Marina Ciancia1,; Alberto S Cerezo1 1Departamento of organic Chemistry, University of  Buenos Aires, Argentina;2 Carnegie Institucion, Departement of Plant Biology, Stanford Usa. The most abundant water soluble polysaccharides in red seaweeds are sulfated galactans (carrageenans and agarans), which have physiological significance in mechanical stress resistance, hydration, ionic and osmotic regulation of the seaweeds in marine environments. Carrageenans are sulfated galactans with alternating 3-linked beta-D-galactose and 4-linked (3,6-anhydro-) alpha-D-galactose units; while in agarans the 4 linked alfa-units belong to the L-series. The red seaweeds Kappaphycus alvarezii (Solieraceae) and Gymnogongrus torulosus (Phyllophoraceae) are classified as carrageenophtes. Analyses of galactan complexes of low and medium mw in both seaweeds showed a similar scheme, with major amounst of carrageenans of de kappa-family with some differences for each seaweed, but also significant quantities of  agarans. In G torulosus the radio of carrageenan: agaran structures in 1:0,5, showing the highest amonunst of agarans for carrageenophyte seaweed found until now. The agaran structures fot both seaweeds differ considerably from the agarose regularity. Carrageenans of high Mw are extracted together with low Mw agarans or galactan DL-hybrids, showing that these galactans are not always biosynthesized by monophyletic groups of red algae, but they are also present in paraphyletic or polyphyletic groupings (i.e agarophyte red seaweed). This fact could be a consequence of the multiple origin of each type of cell wall polysaccharides along the red algal evolution. Accordingly, the chemical structure of these products within the red seaweeds seems to be a stable chemotaxonomic character, useful for the characterization al genera or family level, but it is highly variable at ordinal or higher groupings.