Effects of salinity changes on the growth of Dunaliella salina and its isozyme activities of glycerol-3-phosphate dehydrogenase.

Dunaliella salina could survive in media containing a wide range of NaCl concentrations ranging from about 0.05 M to saturation (around 5.5 M). Glycerol is an important osmolyte when Dunaliella survive in various salt environments, and G3pdh is a key enzyme in glycerol metabolism. The osmotic response of D. salina was investigated by studying its cell growth, glycerol content change, and isozyme activity of glycerol-3-phosphate dehydrogenase (G3pdh) in different salinities. Results showed that 2.0 M NaCl was the optimal salinity for the growth of D. salina, in which condition the highest glycerol content of 64.02 +/- 3.21 (mean +/- SD) microg/mL was detected. D. salina could rapidly increase or decrease glycerol contents to adapt to hypoosmotic or hyperosmotic environments. The glycerol content declined 52.05% when salinity was changed from 2.0 to 0.5 M NaCl, and the glycerol content increased 43.61% when salinity was increased from 2.0 to 5.0 M NaCl. In the isozyme electrophoresis assay two kinds of isozymes, G3pdh and superoxide dismutase (Sod), were detected synchronously. Interestingly, it was first found that there are five isozymes of G3pdh in D. salina. G3pdh-2 mainly takes effect in moderate to high salinities, whereas the other four isozymes take effect in low salinities, which may provide an important clue for future research on osmoregulation mechanisms.