title: Phosphate uptake across the tonoplast of intact vacuoles isolated from suspension-cultured cells of Catharanthus roseus (L.) G. Don.
abstract: Transport of inorganic orthophosphate (Pi) across the tonoplast membrane was studied using intact vacuoles isolated from suspension-cultured cells of Catharanthus roseus. Orthophosphate uptake was strongly stimulated in the presence of Mg-ATP and Mg-pyrophosphate and inhibited by bafilomycin and concanamycin which are potent inhibitors of the vacuolar H+-ATPase. These results indicated that the build-up of an electrochemical gradient by the H - pumps was essential for the uptake of Pi. Potassium thiocyanate, which dissipates the membrane potential across the tonoplast, strongly inhibited the Mg-ATP-stimulated uptake of Pi, while only a weak inhibition was observed in the presence of NH4Cl, which dissipates the pH gradient. These results indicate that, as observed for other anions like malate or chloride, the electrical component is the driving force of Pi uptake, whereas the deltapH plays only a minor role. Possible competitive inhibitors of Pi, MoO4(2-) , VO4(3-) and CrO4(2-) were tested. Among them, CrO4(2-) strongly inhibited Pi uptake into the vacuoles. Various inhibitors of anion transport were also tested. Only 4,4-diisothiocyanostilbene-2,2'-disulfonic acid strongly inhibited Pi uptake into the vacuoles. The function of the vacuolar Pi transporters for cytoplasmic Pi homeostasis is discussed.
authors.affiliation: Institut de Botanique, Lab. de Physiologie Végétale, Université de Neuchâtel, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Massonneau
authors.forename: E
authors.initials: E
authors.lastname: Martinoia
authors.forename: K J
authors.initials: KJ
authors.lastname: Dietz
authors.forename: T
authors.initials: T
authors.lastname: Mimura
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000643:Ammonium Chloride / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D009544:Niflumic Acid / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism*; D059828:Plant Cells; D010944:Plants / Q000378:metabolism*; D011339:Probenecid / Q000494:pharmacology; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D010710:Phosphates; D000643:Ammonium Chloride; D009544:Niflumic Acid; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D011339:Probenecid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid