title: Characterization of citrate transport through the plasma membrane in a carrot mutant cell line with enhanced citrate excretion.
abstract: The superior ability of citrate excretion in a carrot (Daucus carota L.) mutant cell line, namely IPG (insoluble phosphate grower) [Takita et al. (1999a) Plant Cell Physiol. 40: 489] cells has been characterized in terms of citrate transport at the plasma membrane. IPG cells released about a 20-fold increase in citrate in comparison with malate, while the concentration of malate was only 35% lower than that of citrate in the cell sap. Citrate excretion was sensitive to anion channel blockers, such as niflumic acid and anthracene-9-carboxylic acid. These results indicate that IPG cells release citrate through the plasma membrane using citrate specific anion channels. The rate of citrate release from IPG cells was not affected by the concentration of aluminum (0 and 50 micro M), soluble P(i) (0 or 2 mM) and the pH (4.5-5.6) of the medium, suggesting that anion channels would not be regulated by such external conditions. Citrate excretion correlated with the H(+) efflux, possibly from the action of H(+)-ATPase on the plasma membrane. The activity of plasma membrane H(+)-ATPase was about three times higher in IPG cells than in wild-type cells, and might be involved in the high citrate excretion ability.
authors.affiliation: Laboratory of Plant Cell Technology, Department of Biotechnology, Faculty of Agriculture, Gifu University, 1-1, Yanagido, Gifu, 501-1193 Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ohno
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Koyama
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Hara
mesh_terms: D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D019343:Citric Acid / Q000378:metabolism*; D018552:Daucus carota / Q000235:genetics / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000037:antagonists & inhibitors; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D009154:Mutation; D010710:Phosphates / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D017494:Proton Pumps / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D002412:Cations; D007473:Ion Channels; D010710:Phosphates; D017494:Proton Pumps; C020723:citrate-binding transport protein; D019343:Citric Acid; D014638:Vanadates; D006180:Proton-Translocating ATPases; D011188:Potassium