RESEARCH PAPER Formation of extracellular sulphated polysaccharide mucilage on the salt tolerant Characeae Lamprothamnium Dr. Kaire Torn 1 , Mary J. Beilby 2 , Michelle T. Casanova 3 and Sabah Al Khazaaly 2 1 Estonian Marine Institute, University of Tartu, Tallinn, Estonia 2 School of Physics, Department of Biophysics, University of NSW, NSW, Australia 3 University of Ballarat, Centre for Environmental Management, Mt Helen, Royal Botanic Gardens Melbourne, Westmere, Australia 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. Received: June 7, 2013 Revised: October 31, 2013 Accepted: December 9, 2013 Keywords: Characeae / Extracellular mucilage / Lamprothamnium / Salt tolerance / Sulphated polysaccharides 1 Introduction Flowers et al. [1] estimate that less than 1% of angiosperms are salt tolerant and that this ability might have been lost and regained several times in many plant families over 470 million years of evolution of plants on land. Extant Family Characeae are closely related to ancestors of land plants [2, 3] and provide a good electrophysiological model for land plant cells [4]. The Characeae are found in many, diverse aquatic habitats. Over 300 described species include both rapid colo- nizers and temporary water body pioneers, as well as those preferring more stable environmental conditions and habitats. Species from the genus Lamprothamnium stand out because of their ability to tolerate a very broad range of salinities, as well as fluctuations in salinity. Lamprothamnium can grow in brackish to hypersaline water bodies, in which the salinity can decrease through rainfall and freshwater inputs, or increase with evapora- tion and sea spray [5]. Lamprothamnium sp. has been observed to bear oogonia in salinities exceeding those of seawater [6]. Correspondence: Dr. Kaire Torn, Estonian Marine Institute, University of Tartu, Mäealuse 14, Tallinn 12618, Estonia E-mail: kaire.torn@ut.ee Abbreviations: SP, sulphated polysaccharide International Review of Hydrobiology 2014, 98,1–9 DOI 10.1002/iroh.201301666 © 2014 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim 1