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Membranes and Bioenergetics

Osmotically Induced Proton Extrusion from Carrot Cells in Suspension Culture ¹

Department of Botany, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel, Dipartimento di Biologia, Universita Degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy, Station de Physiologie Végétale, Institut National de la Recherche Agronomique, Centre de Recherches de Bordeaux, 33140 Pont-de-la-Maye, France

Addition of 200 mM of a polyol to anthocyanin containing carrot (Daucus carota L.) cells in suspension culture decreased turgor pressure to zero and induced hyperpolarization of the membrane potential and acidification of the medium due to H⁺ extrusion. These changes were shown to be slightly affected by vanadate. In parallel, a decrease in intracellular ATP and total adenylate concentrations were observed. However, when the osmoticum was NaCl acidification of the medium occurred in the absence of considerable changes in intracellular ATP concentration. These results are interpreted as indicating that a drop of turgor, by addition of a polyol, triggers a proton extrusion activity which is only slightly inhibited by vanadate but apparently ATP utilizing. The observed decrease in ATP level occurs without a change in respiration rate and is accompanied by a drop in total adenylate pool. However when NaCl is the osmoticum it is assumed that _µH+ is enhanced through a Na⁺/H⁺ antiporter. The difference between the two types of osmotica as related to their ability to penetrate through the cellular membrane is discussed.

¹ This research was supported by a grant from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel.

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