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

Abstract

A light-induced proton gradient (ApH) 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 Dwaiella saUna. The A light-induced proton uptake has been reported in Dunaliella (2). This proton uptake has been attributed to the activity of an Na+/H+ exchange mechanism which may be related to the maintenance of the Na+ concentration gradient between the cells and the surrounding medium (18). Neumann and Levine (20), on the other hand, suggested that the uptake of protons in the light is the result of CO2 uptake in photosynthesis. In the study reported here we confirm a light-induced proton uptake in intact Dunaliella cells. The response of the ApH to electron transport and ATPase inhibitors, to sulfhydryl reagent as well as to the Na+ concentration in the medium are reported. The data suggest that an (Na+/H+)-ATPase localized in the cell membrane may be involved in the uptake of protons in the light. MATERIALS AND METHODSDunaliella salina cells were grown as described previously (15,16). Cells were harvested by centrifugation at room temperature at 700g for 5 min and washed twice in growth medium in which the Tris buffer was replaced by 50 mm Hepes buffer (pH 7.5). Cell-free preparations were obtained by the addition of cold (2 C) distilled H20 to the cell suspension to yield final NaCl concentration of 0.2 M. This treatment resulted in a complete rupture of the cells. The cell-free suspension was then centrifuged (lO,000g, 10 min, 4 C) and resuspended in a medium containing 0.4 M sucrose and 5 mM MgCl2 in 50 mm Hepes buffer (pH 7.8).

Ionic regulation of the unicellular green algadunaliella tertiolecta

“…A Na/H exchange contributing to the mainte-nance of a low cell sodium has been suggested by Latorella and Vadas (1973) for Dunaliella teriolecta and by Kaplan and Schreiber (1981) for Dunaliella salina. This mechanism was found to occur when the cells were transferred to a medium of higher salinity.…”