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Studies on H⁺-Translocating ATPases in Plants of Varying Resistance to Salinity ¹

I. Salinity during Growth Modulates the Proton Pump in the Halophyte Atriplex nummularia

Department of Botany, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel

Membrane vesicles were isolated from the roots of the halophyte Atriplex nummularia Lindl. H⁺-translocating Mg²⁺-ATPase activity was manifested by the establishment of a positive membrane potential (measured as SCN^– accumulation); and also by the establishment of a transmembrane pH gradient (measured by quinacrine fluorescence quenching). H⁺-translocation was highly specific to ATP and was stable to oligomycin. Growing the plants in the presence of 400 millimolar NaCl doubled the proton-translocating activity per milligram of membrane protein and otherwise modulated it in the following ways. First, the flat pH profile observed in non-salt-grown plants was transformed to one showing a peak at about pH 6.2. Second, the lag effect observed at low ATP concentration in curves relating SCN^– accumulation to ATP concentration was abolished; the concave curvature shown in the double reciprocal plot was diminished. Third, sensitivity to K-2 (N-morpholino)ethanesulfonic acid stimulation was shown in salt-grown plants (about 40% stimulation) but was absent in non-salt-grown plants. Fourth, the KCl concentration bringing about 50% dissipation of ATP-dependent SCN^– accumulation was 20 millimolar for salt-grown plants and 50 millimolar for non-salt-grown plants. Vanadate sensitivity was shown in both cases. No clear NO₃^– inhibition was observed.

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