Skip to main content
padlock icon - secure page this page is secure

Free Content Loading of nitrate into the xylem: apoplastic nitrate controls the voltage dependence of X-QUAC, the main anion conductance in xylem-parenchyma cells of barley roots

Download Article:

You have access to the full text article on a website external to Ingenta Connect.

Please click here to view this article on Wiley Online Library.

You may be required to register and activate access on Wiley Online Library before you can obtain the full text. If you have any queries please visit Wiley Online Library


We report here that NO3 in the xylem exerts positive feedback on its loading into the xylem through a change in the voltage dependence of the Quickly Activating Anion Conductance, X-QUAC. Properties of this conductance were investigated on xylem-parenchyma protoplasts prepared from roots of Hordeum vulgare by applying the patch-clamp technique. Chord conductances were minimal around − 40 mV and increased with plasma membrane depolarisation as well as with hyperpolarisation. Two gates with opposite voltage dependences were postulated. When 30 mmCl in the bath was replaced by NO3, a shift in the midpoint potential of the depolarisation-activated gate by about − 60 mV from 43 to − 16 mV occurred (Km = 3.4 mm). No such effect was seen when chloride was replaced by malate. Addition of 10 mmNO3 to the pipette solution and reduction of [Cl] from 124 to 4 mm(to simulate cytoplasmic concentrations) did not interfere with the voltage dependence of X-QUAC activation, nor was it affected by changes in external [K+]. If only the NO3 effect on gating was considered, an increase of the NO3 concentration in the xylem sap to 5 mmwould result in an enhancement of NO3 efflux by about 30%. Although the driving force for NO3 efflux would be reduced simultaneously, NO3 efflux into the xylem through X-QUAC would be maintained with high NO3 concentrations in the xylem sap; a situation which occurs for instance during the night.
No References
No Citations
No Supplementary Data
No Article Media
No Metrics

Keywords: Hordeum vulgare; anion channel; channel gating; patch clamp; salt transport; xylem loading

Document Type: Original Article

Affiliations: 1: Universität Potsdam, Institut für Biochemie und Biologie, Lehrstuhl für Molekularbiologie, Karl-Liebknecht-Str. 25, Haus 20, 14476 Golm, Germany. 2: Biozentrum, Am Hubland, 97074 Würzburg, Germany. 3: Albrecht-von-Haller-Institut für Pflanzenwissenschaften der Universität Göttingen, Untere Karspüle 2, 37073 Göttingen, Germany.

Publication date: April 1, 2002

  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more