Passive Nitrate Transport by Root Plasma Membrane Vesicles Exhibits an Acidic Optimal pH like the H⁺-ATPase

• Published in: Plant physiology (Bethesda) 2000-01, Vol.122 (1), p.265-273
• Main Authors: Pierre Pouliquin, Boyer, Jean-Christophe, Jean-Pierre Grouzis, Gibrat, Rémy
• Format: Article
• Language: English
• Subjects: Absorption. Translocation of ions and substances. Permeability; Agronomy. Soil science and plant productions; Anions; Biochemistry and Macromolecular Structure; Biological and medical sciences; Biological Transport; Cell Membrane - metabolism; Cell membranes; Cell physiology; Coated Vesicles - metabolism; Corn; Economic plant physiology; Electric potential; Fundamental and applied biological sciences. Psychology; Genetics; Guard cells; Hydrogen-Ion Concentration; Life Sciences; Liposomes; Nitrates; Nitrates - metabolism; Nutrition. Photosynthesis. Respiration. Metabolism; Plant physiology and development; Plant roots; Plant Roots - metabolism; Plants; Plants genetics; Plasma membrane and permeation; Zea mays - metabolism
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.122.1.265

The net initial passive flux ($J_{\text{Ni}}$) in reconstituted plasma membrane (PM) vesicles from maize (Zea mays) root cells was measured as recently described (P. Pouliquin, J.-P. Grouzis, R. Gibrat [1999] Biophys J 76: 360-373). $J_{\text{Ni}}$ in control liposomes responded to membrane potential or to NO3 - as expected from the Goldman-Hodgkin-Katz diffusion theory. $J_{\text{Ni}}$ in reconstituted PM vesicles exhibited an additional component ($J_{\text{Nif}}$), which was saturable (Km for NO3 - approximately 3 mM, with $J_{\text{Nifmax}}$ corresponding to 60 × 10-9 mol m-2 s-1 at the native PM level) and selective (NO3 - = $\text{ClO}_{3}{}^{-}$ > Br- > Cl- = $\text{NO}_{2}{}^{-}$; relative fluxes at 5 mM: 1:0.34:0.19). $J_{\text{Nif}}$ was totally inhibited by La3+ and the arginine reagent phenylglyoxal. $J_{\text{Nif}}$ was voltage dependent, with an optimum voltage at 105 mV at pH 6.5. The activation energy of $J_{\text{Nif}}$ was high (129 kJ mol-1), close to that of the H+-ATPase (155 kJ mol-1), and $\text{J}_{\text{Nif}}$ displayed the same acidic optimal pH (pH 6.5) as that of the H+ pump. This is the first example, to our knowledge, of a secondary transport at the plant PM with such a feature. Several properties of the NO3 - uniport seem poorly compatible with that reported for plant anion channels and to be attributable instead to a classical carrier. The physiological relevance of these findings is suggested.