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Regulation of nitrate uptake into Chara corallina cells via NH+4 stimulation of NO3 efflux

Authors

  • C.E. DEANE-DRUMMOND

    Corresponding author
    1. Botany School, Cambridge University, Downing Street, Cambridge CB2 3EA. England
      Dr. C. E. Deane-Drummond, Botany Department, Durham University, Science Site, South Road, Durham DH1 3LE.
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Dr. C. E. Deane-Drummond, Botany Department, Durham University, Science Site, South Road, Durham DH1 3LE.

Abstract

Abstract. Net NO3 uptake by NO3 deficient Chara cells was used to calculate [NO3]c assuming that the cytoplasm occupies 10% total volume and that nitrate reduction and storage are negligible (i.e. maximum [NO3]c was calculated). A linear relationship was found between NO3 efflux and [NO3]c. There was an initial burst of NO3 efflux when NH+4 was added, followed by a slower efflux rate which matched influx rate such that net NO3 uptake was zero. Over 50% of NO3 that had been taken up in 2 h was lost within the first 5 min of NH+4 addition. The Nernst equation was used to predict the direction of the electrochemical driving force for NO3 entry. Under the experimental conditions used NO3 efflux is actively transported. The differential involvement of both NO3 influx and NO3 efflux in the regulation of NO3 uptake is discussed and a model is proposed to account for these results which envisages discrete NO3 influx and NO3 efflux carriers.

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