Plasma membrane electron transport coupled to Na+ extrusion in the halotolerant alga Dunaliella

The halotolerant alga Dunaliella adapts to exceptionally high salinity and maintains low [Na+](in) at hypersaline solutions, suggesting that it posses ses efficient mechanisms for regulating intracellular Na+. In this work we examined the possibility that Na+ export in Dunaliella is linked to a plasm a membrane electron transport (redox) system. Na+ extrusion was induced in Dunaliella cells by elevation of intracellular Na+ with Na+-specific ionoph ores. Elevation of intracellular Na+ was found to enhance the reduction of an extracellular electron acceptor ferricyanide (FeCN). The quinone analogs NQNO and dicumarol inhibited FeCN reduction and led to accumulation of Na by inhibition of Na+ extrusion. These inhibitors also diminished the plasm a membrane potential in Dunaliella. Anaerobic conditions elevated, whereas FeCN partially decreased intracellular Na+ content. Cellular NAD(P)H level decreased upon enhancement of plasma membrane electron transport. These res ults are consistent with the operation of an electrogenic NAD(P)H-driven re dox system coupled to Na+ extrusion in Dunaliella plasma membrane. We propo se that redox-driven Na+ extrusion and recycling in Dunaliella evolved as m eans of adaptation to hypersaline environments. (C) 2001 Elsevier Science B .V. All rights reserved.