The function of tonoplast ATPase in intact vacuoles of red beet is governed by direct and indirect ion effects |
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Authors: | C. Niemietz J. Willenbrink |
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Affiliation: | (1) Botanisches Institut, Lehrstuhl III, Universität zu Köln, Gyrhofstrasse 15, D-5000 Köln 41, Federal Republic of Germany |
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Abstract: | The pH gradient and the electric potential across the tonoplast in mechanically isolated beetroot vacuoles has been studied by following the uptake of [14C]methylamine and [14C]triphenyl-methylphosphoniumchloride. In response to Mg-ATP, the vacuolar interior is acidified by 0.8 units. This strong acidification is accompanied by a slight hyperpolarization of the membrane potential, which is probably caused by a proton diffusion potential. In preparations where only a small acidification (0.4 units) occurred, the membrane potential was depolarized by the addition of Mg-ATP. Different monovalent cations and anions were tested concerning their effect on the pH gradient and ATPase activity in proton-conducting tonoplasts. Chloride stimulation and NO3-inhibition were clearly present. The observed decline of the pH gradient upon the addition of Na+ salts is probably caused by an Na+/H+ antiport system.Abbreviations and symbol CCCP carbonylcyanide-m-chlorophenylhydrazone - Mes 2(N-morpholino)ethanesulfonic acid - TPMP+ triphenylmethylphosphoniumchloride - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol - membrane potentialDedicated to Professor A. Betz on the occasion of his 65th birthday |
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Keywords: | ATPase Beta (tonoplast) Membrane potential pH gradient Tonoplast Vacuole |
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