Formation of extracellular sulphated polysaccharide mucilage on the salt tolerant Characeae Lamprothamnium

The aim of this study was to examine the formation and the distribution of extracelluar sulphated polysaccharide (SP) mucilage on Lamprothamnium cells as a function of growth medium salinity. Six Lamprothamnium species were gathered from nine locations in South Australia, Victoria and NSW. The salinity of the original habitats varied from 2 to 41 g/L. Alcian Blue staining at low pH was employed to measure the coverage of SP on the thalli. The basal (older) internodes generally exhibited SP coverage between 80 and 100% (in one case 5%) regardless of salinity. In young (apical) internodes the SP coverage was lower, between 2 and 90%, again independent of salinity. Controlled salinity experiments confirmed that all cells developed SP cover with time, even cells in 0 and very low salinities. The rate of SP development on basal internodes increased with salinity. Similar trends could be seen in apical internodes, but the overall rate was slower, possibly influenced by cell development. A temporary loss of SP mucilage was observed upon planting cuttings at low salinities and low external sulphate concentrations. The SP mucilage was found on all the surveyed Lamprothamnium species. The SP coverage increased with cell age irrespective of growth medium salinity. The results are discussed with reference to the evolution of salt tolerance and the role of SP in different plant groups.