Growth and osmoregulation of Boekelovia hooglandii in relation to salinity

The growth and osmoregulation of Boekelovia hooglandii Nicolai et Baas Becking (Chrysophyceae) was investigated as a function of salinity. This chromophyte microflagellate was found to be euryhaline and also to require sodium for growth. The optimum sodium chloride concentration for growth was 0.2–0.4 M, and growth was severely inhibited in media with sodium chloride concentrations above 1 M. Using gas chromatography – mass spectroscopy analysis of cell extracts, it was established that the alga contains D-mannitol, myo-inositol, as well as the inositol derivative, cyclohexanetetrol. The content of cyclohexanetetrol and mannitol increased with increased salinity, while the content of inositol remained almost constant. Potassium and magnesium were the major intracellular cations. However, the content of cations and amino acids showed only minor increases with salinity over a wide salinity range. The contents of cyclohexanetetrol and mannitol increased rapidly when cells were subjected to hypertonic shocks. It was concluded that B. hooglandii utilizes cyclohexanetetrol and mannitol as osmoregulatory substances. Key words: Boekelovia hooglandii, chromophyte, cyclohexanetetrol, euryhaline, D-mannitol, myo-inositol, osmoregulation, salinity.