Osmotic responses of Dunaliella to the changes of salinity

Some species in genus Dunaliella are unique in their remarkable abilities to accumulate large numbers of beta-carotene and thrive in media containing a wide range of NaCl concentrations ranging from about 0.05 M to saturation (around 5.5 M). The algae contain no rigid polysaccharide cell wall and thus have been found to be able to rapidly change their volume and shape in response to changes in the extracellular hypo- or hyper-osmotic pressure. In osmotic adjustment, the osmoregulatory response of Dunaliella functions to maintain osmotic balance at high salinities by synthesis and varying the intracellular concentration of glycerol. In this review, we describe the osmotic response process of Dunaliella under salinity stress, including the changes of cell volume, intracellular ions concentration, intracellular glycerol concentration, and the expression of some salt-induced genes. Some specific proteins and enzymes can be induced by different salinities in osmotic response process. In addition, we introduce the exogenous expression of salt-related genes of Dunaliella salina in plants and microorganisms for the purpose of confirming the functions of related genes, proteins, and enzymes. The aim of this review is to emphasize the importance of the studies on the mechanisms of osmotic adjustments of Dunaliella in order to develop its unique osmotic characteristics. It is prospected that future research should pay attention to the specific signal transduction pathway and the mechanism of osmoregulation, and to improve the salt tolerance of higher plants by using salt-tolerant genes of Dunaliella.