Solute Regulation in the Euryhaline Marine AlgaEnteromorpha prolifera(O. F. Müll) J. Ag.

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Abstract
Young, A. J., Collins, J. C. and Russell, G. 1987. Solute regulation in the euryhaline marine alga Enteromorpha prolifera (O. F. M€ll) J. Ag.—J. exp. Bot. 38: 1298–1308. The physiological basis for salt tolerance has been studied in the euryhaline alga Enteromorpha prolifera. Levels of inorganic ions and organic (compatible) solutes have been measured. K+ makes the major contribution towards the internal osmotic potential of the cell, while Cl− and, in particular, Na+ contents are low. Levels of the organic solute β-dimethylsulphonio-propionate (DMSP) are high but are fairly insensitive to changes in the external salinity. Levels of amino-acids, calcium, phosphate and sulphate contribute relatively little towards the internal osmotic potential of the alga. As salinity is altered there are marked changes in the tissue water content and volume. These changes directly affect the concentration of the osmotic solutes within the cell. In dilute seawaters there is an increase in turgor as there is little change in the internal solute content of the cell compared to values in normal sea water. Inorganic ions, in particular K+, and organic solutes are accumulated in concentrated seawaters, although concentrations greater than 2·00 × seawater result in a reduction in the internal osmotic potential of the cell, mainly through loss of K+.