Sulfated polysaccharides (SP) are highly anionic compounds found in vertebrates, invertebrates and algae. Recently we reported the occurrence of sulfated galactans (SG) in the cell wall of marine angiosperms (seagrass), but not in terrestrial or sweet water vascular plants (Aquino et al, Glycobiology, vol 15:1:11,2005). Unpublished results concerning different species of seagrasses (Ruppia maritima, Halodule wrightti and Halophila decipiens) suggested that the presence of SG is a convergent evolutional adaptation to inhabit the marine environment with a high osmotic pressure. In an attempt to elucidate further questions of the seagrass physiology and to determine whether the presence of SG in seagrasses is associated with the environment NaCl concentration, we decided to study plants exposed to different salinities. We extracted and analyzed SP from the leaves and root system of 3 species of seagrasses. Surprisingly, samples of the same species, but collected from environments with different salinities, differ in their SG contents. Thus, samples of R.maritima extracted from an environment with a salinity of 36% showed higher concentration of highly sulfated SG than the sample from a salinity of 15%. The same pattern is observed for the specie H. wrightii. Plants from a 49% salinity contained higher concentrations and highly sulfated SG than the plants from a 36% salinity. A curious observation is that the highly sulfated SG is present exclusively in the root system, which is responsible for the nutrient absorption and gas transport. Overall, these results corroborate the proposition that the presence of SGs in seagrasses is related to the NaCl concentration. Most of this SP is on the root system, which is the part of the plant more exposed to osmotic pressures, than on the leaves.

Financial Support: CNPq and FAPERJ.