DUNALIELLA-SALINA - A MODEL SYSTEM FOR STUDYING THE RESPONSE OF PLANT-CELLS TO STRESS

This review focuses on the biochemical and physiological response of the halotolerant green alga. Dunaliella salina, to conditions of stress. It is now well established that in response to stress, cells of Dunaliella salina var. bardawil show increased glycerol production, massive beta-carotene accumulation and enhanced abscisic acid metabolism. In this respect, cellular responses are regulatory and seem to depend on a diversity of mechanisms which may be linked to a modification of the abscisic acid balance. Dunaliella lacks a rigid cell wall and the cellular contents are enclosed by an elastic plasma membrane that permits rapid cell volume changes in response to extracellular changes in osmolarity. Based on the 'stretch activated ion channels model' reviewed recently by Kirst (1990) we propose the following cascade of responses: volume change/distortion of plasmalemma-->change in pH-->redistribution of abscisic acid-->inhibition of H+-ATPase-[increased abscisic acid levels]-->opening of Ca2+ channels-->influx of Ca2+-->rise in cytosolic Ca2+-->[increased abscisic acid levels]-effect on metabolism (activity of enzymes).