title: The uptake of NO3-, NO2-, and NH4+ by intact wheat (Triticum aestivum) seedlings.  I.  Induction and kinetics of transport systems.
abstract: The inducibility and kinetics of the NO3-, NO2-, and NH4+ transporters in roots of wheat seedlings (Triticum aestivum cv Yercora Rojo) were characterized using precise methods approaching constant analysis of the substrate solutions.  A microcomputer-controlled automated high performance liquid chromatography system was used to determine the depletion of each N species (initially at 1 millimolar) from complete nutrient solutions.  Uptake rate analyses were performed using computerized curve-fitting techniques.  More precise estimates were obtained for the time required for the extent of the induction of each transporter.  Up to 10 and 6 hours, respectively, were required to achieve apparent full induction of the NO3- and NO2- transporters.  Evidence for substrate inducibility of the NH4+ transporters requiring 5 hours is presented.  The transport of NO3- was mediated by a dual system (or dual phasic), whereas only single systems were found for transport of NO2- and NH4+.  The Km values for NO3-, NO2-, and NH4+ were, respectively, 0.027, 0.054, and 0.05 millimolar.  The Km for mechanism II of NO3- transport could not be defined in this study as it exhibited only apparent first order kinetics up to 1 millimolar.
authors.affiliation: Department of Agronomy and Range Science, University of California, Davis 95616, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Goyal
authors.forename: R C
authors.initials: RC
authors.lastname: Huffaker
mesh_terms: D001692:Biological Transport / Q000502:physiology; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003199:Computer Systems; D005308:Fertilizers; D009566:Nitrates / Q000378:metabolism / Q000493:pharmacokinetics*; D009573:Nitrites / Q000378:metabolism / Q000493:pharmacokinetics*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000493:pharmacokinetics*; D013997:Time Factors; D014908:Triticum / Q000187:drug effects / Q000378:metabolism*
chemical_list: D005308:Fertilizers; D009566:Nitrates; D009573:Nitrites; D000644:Quaternary Ammonium Compounds