Light-Induced Proton Gradient Formation in Intact Cells of Dunaliella salina

A light-induced proton gradient (DeltapH) increase as exhibited by an increase of 9-aminoacridine fluorescence quenching is demonstrated between the external medium and the interior of the halophytic green alga Dunaliella salina. The formation and maintenance of the DeltapH is sensitive to electron transport inhibitors and to uncouplers. It is inhibited by p-chloromercuribenzenesulfonic acid (50% inhibition at 3 micromolar), which does not affect photosynthetic O(2) evolution. It is concluded that the observed DeltapH is located across the plasmalemma or the chloroplast envelope. The formation and maintenance of the light-induced proton gradient requires the presence of Na(+). Substitution of NaCl by KCl or glycerol results in inhibition of the DeltapH formation. The proton gradient is also sensitive to ATPase and energy transfer inhibitors. It is suggested that a Na(+)/H(+) pump mechanism may be involved in the formation of the proton gradient in intact Dunaliella cells.