Characterization of an Anion Transporter in the Plasma Membrane of Barley Roots |
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Authors: | Yamashita, Kousei Yamamoto, Yoko Matsumoto, Hideaki |
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Affiliation: | Research Institute for Bioresources, Okayama University Kurashiki, Okayama, 710 Japan |
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Abstract: | To examine the relationship between H+-ATPase and the transportof anions, we investigated the effects of various inhibitorson the activity of the H+-ATPase, the transport of protons,and the transport of Cl- ions using plasma membrane vesiclesprepared from barley roots. Some inhibitors, namely, 4,4-diisothiocyano-2,2-stilbenedisulfonate (DIDS) and Zn2+ ions markedly inhibited H+- ATPaseactivity. Other compounds, such as phenylglyoxal (PGO) and niflumicacid (NIF), inhibited H+-ATPase activity by 20-30%, while anthracene-9-carboxylate(A-9-C) and tetraethylammonium chloride (TEA-Cl) had littleeffect on this activity. The ATP-dependent acidification ofthe interior of vesicles was strongly dependent on the presenceof permeant anions, such as chloride (Cl-) and nitrate (NO3-),and it was completely inhibited by 0.2 mM NIF. Other compounds,namely, A-9-C of 0.1 mM and TEA-Cl of 10 mM, did not affectH+-transport activity. The inhibition of H+-transport activityby NIF was observed even when the activity was assayed in thepresence of KCl, KNO3, or bis-tris-propane (BTP)-Cl. Using 36cl,we quantified Cl--transport activity by measuring the uptakeof Cl- ions into the plasma membrane vesicles. The uptake dependedon the potential difference across the membrane that was generatedby H+-ATPase; it was enhanced by an inside-positive potentialgradient. At 0.1 mM, NIF completely blocked the voltage-dependentCl--transport activity. From these properties of the Cl- transporterand the inhibition of H+-transport activity by NIF, we suggestthat H+-transport activity across the plasma membrane mightbe modulated by the transport of anions via a NIF-sensitiveanion-permeable transporter that acts to collapse the inside-positivepotential generated by H+-ATPase. (Received September 7, 1995; Accepted July 23, 1996) |
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