The salt relations of Dunaliella
Dunaliella tertiolecta (marine) and D. viridis (halophilic) were each trained by serial transfer to growth at salt concentrations previously regarded as the other's domain. D. viridis then had a salt optimum at 1.0–1.5 M sodium chloride whereas that for D. tertiolecta was less than 0–2 M. Nevertheless D. tertiolecta grew faster than the halophil at all salt concentrations up to 3.5 M, the highest at which they were compared.
Both species accumulate glycerol, which is necessary for growth at elevated salinities and which responds in its content to water activity (a w ) rather than specifically to salt concentration. Variation in glycerol content is a metabolic process which occurs in the dark from accumulated starch as well as photosynthetically. Regulation of glycerol content by a w does not require protein synthesis. The NADP-specific glycerol dehydrogenase of each of the algae is likely to be directly involved in the regulation of glycerol content. Kinetic studies, together with those described in an earlier publication, show that the enzyme has regulatory properties, and that both glycerol and dihydroxyacetone act as effectors as well as reactants. A mechanism of the reaction is tentatively proposed.
Key wordsAlga Compatible solute Dunaliella Glycerol Halophil Marine Osmoregulation Salt relations
Unable to display preview. Download preview PDF.
- Aitken, D. M., Brown, A. D.: Properties of halophil nicotinamide-adenine dinucleotide phosphate-specific isocitrate dehydrogenase. True Michaelis constants, reaction mechanisms and molecular weights Biochem. J. 130, 645–662 (1972)Google Scholar
- Anand, J. C., Brown, A. D.: Growth rate patterns of the so-called osmophilic and non-osmophilic yeasts in solutions of polyethylene glycol. J. gen. Microbiol. 52, 205–212 (1968)Google Scholar
- Ben-Amotz, A.: Adaptation of the uncellular alga Dunaliella parva to a saline environment. J. Phycol. 11 50–54 (1975)Google Scholar
- Ben-Amotz, A., Avron, M.: The role of glycerol in the osmotic regulation of the halophilic alga Dunaliella parva. Plant Physiol. 51, 875–878 (1973a)Google Scholar
- Ben-Amotz, A., Avron, M.: NADP specific dihydroxyacetone reductase from Dunaliella parva. FEBS Letters 29, 153–155 (1973b)Google Scholar
- Borowitzka, L. J., Brown, A. D.: The salt relations of marine and halophilic species of the unicellular green alga, Dunaliella. The role of glycerol as a compatible solute. Arch. Microbiol. 96, 37–52 (1974)Google Scholar
- Brock, T. D.: Salinity and the ecology of Dunaliella from Great Salt Lake. I. gen. Microbiol. 89, 285–292 (1975)Google Scholar
- Brown, A. D.: Microbial water stress. Bact. Rev. 40, 803–846 (1976)Google Scholar
- Brown, A. D.: Compatible solutes and extreme water stress in eucaryotic microorganisms. Advanc. Microbial Physiol. 17, (in press, 1977)Google Scholar
- Craigie, J. S., McLachlan, J.: Glycerol as a photosynthetic product in Dunaliella tertiolecta Butcher. Canad. J. Bot. 42, 777–778 (1964)Google Scholar
- Johnson, M. K., Johnson, E. J., MacElroy, R. D., Speer, H. L., Bruff, B. S.: Effects of salts on the halophilic alga Dunaliella viridis. J. Bact. 95, 1461–1468 (1968)Google Scholar
- Wegmann, K.: Osmotic regulation of photosynthetic glycerol production in Dunaliella. Biochim. biophys. Acta (Amst.) 234, 317–323 (1971)Google Scholar