OSMOTIC ADJUSTMENT IN MARINE EUKARYOTIC ALGAE: THE ROLE OF INORGANIC IONS, QUATERNARY AMMONIUM, TERTIARY SULPHONIUM AND CARBOHYDRATE SOLUTES

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Abstract
The effects of steady state salinities (150 to 700 mol m−3NaCl) on the growth rates and intracellular solutes of the prasinophyte algae Tetraselmis chui Butcher and Prasinocladus Kuckuck and the prymnesiophyte algae, Prymnesium parvum Carter and Ruttnera spectabilis Geitler, are described. Maximum growth rates were reached in media approximating to the NaCl concentration of oceanic waters (about 500 mol m−3). The following intracellular organic solutes paralleled the increases of external salinity: the tertiary sulphonium compound β-dimethylsulphoniopropionate (DMSP) in T. chui, Prasinocladus, P. parvum and R. spectabilis; the polyhydric alcohol, mannitol, in T. chui, Prasinocladus and R. spectabilis; the quaternary ammonium compounds (QACs), glycine betaine and homarine, in T. chui and Prasinocladus. QACs were not detected in P. parvum and R. spectabilis. An unknown polyol, which may be the cyclitol, 1,4/2,5 cyclohexanetetrol, was synthesized by P. parvum and R. spectabilis and in addition P. parvum contained significant concentrations of glucose. Sucrose was not detected in the algal extracts. Proline was an insignificant osmoticum in all the algae. Increases of the media NaCl concentration led to the uptake and accumulation of K+in T. chui and Prasinocladus, with smaller increases of Na+and Cl−. The intracellular K+concentrations in the prasinophyte algae were about five times greater than those of Na+. The inorganic cations Na+and K+, and their accompanying anions, and the organic solutes found could largely account for the osmotic balance of T. chui and Prasinocladus. The inorganic ions in P. parvum and R. spectabilis were not determined.