Nitrate Uptake by Roots as Regulated by Nitrate Reduction Products of the Shoot

Authors

  • A. BEN ZIONI,

    1. Division of Life Sciences, Negev Institute for Arid Zone Research, Beer-Sheva, Israel
    Search for more papers by this author
    • Present address: Volcani Institute for Agricultural Research, Beit Dagan, Israel.

  • Y. VAADIA,

    1. Division of Life Sciences, Negev Institute for Arid Zone Research, Beer-Sheva, Israel
    Search for more papers by this author
    • Present address: Volcani Institute for Agricultural Research, Beit Dagan, Israel.

  • S. HERMAN LIPS

    1. Division of Life Sciences, Negev Institute for Arid Zone Research, Beer-Sheva, Israel
    Search for more papers by this author
    • Present address: Volcani Institute for Agricultural Research, Beit Dagan, Israel.


Abstract

A mechanism is proposed by which secondary products of nitrate reduction in the shoot control the uptake of nitrate by the roots. KNO3 enters the roots and is translocated to the shoot where nitrate is reduced and, at the same time, malate is produced. The reduction of nitrate is stoichiometric to the synthesis of malate (1). Part of the K-malate moves down to the root system in which malate is oxidized, yielding KHCO3 which exchanges for KNO3.

Nitrate reduction in the shoot promotes the synthesis of malate which, after its translocation to the root, allows the preferential uptake of nitrate. Thus, plants reducing large amounts of nitrate may take up the anion without a superfluous accumulation of the cation. Furthermore, the utilization of nitrate by the shoot regulates its uptake by the root.

Ancillary