title: Nitrate transport across the tonoplast of Cucumis sativus L. root cells.
abstract: Nitrate transport across the tonoplast has been studied using vacuole membranes isolated from cucumber roots grown in nitrate. The addition of NO3- ions into the tonoplast with ATP-generated transmembrane proton gradient caused the dissipation of delta pH, indicating the NO3(-)-induced proton efflux from vesicles. NO3(-)-dependent H+ efflux was almost insensitive to the transmembrane electrical potential difference, suggesting the presence of an electroneutral NO3-/H+ antiporter in the tonoplast. Apart from saturation kinetics, with respect to nitrate ions, NO3(-)-linked H+ efflux from the tonoplast of cucumber roots showed other characteristics expected of substrate-specific transporters. Experiments employing protein modifying reagents (NEM, pCMBS, PGO and SITS) indicated that a crucial role in the activity of tonoplast nitrate/proton antiporter is played by lysine residues (strong inhibition of NO3-/H+ antiport by SITS). None of the ion-channel inhibitors (NIF, ZnSO4 and TEA-Cl) used in the experiments had a direct effect on the nitrate transport into tonoplast membranes. On the other hand, every protein reagent, as well as NIF and ZnSO4, significantly affected the ATP-dependent proton transport in vesicles. Only TEA-Cl, the potassium channel blocker, had no effect on the vacuolar proton pumping activity.
authors.affiliation: Plant Physiology Department, Institute of Botany, Wrocław University, Kanonia 6/8, 50-328 Wrocław, Poland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kabała
authors.forename: Grazyna
authors.initials: G
authors.lastname: Kłobus
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Janicka-Russak
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001386:Azides / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D018553:Cucumis sativus / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D018942:Macrolides; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D018517:Plant Roots / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D017680:Potassium Compounds / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001386:Azides; D018942:Macrolides; D009566:Nitrates; D017680:Potassium Compounds; C057620:bafilomycin A; D014638:Vanadates; D006180:Proton-Translocating ATPases; C023844:potassium nitrate