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This article in AJ

  1. Vol. 70 No. 3, p. 393-396
    Received: Feb 12, 1977

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Influence of K on the Uptake, Translocation, and Reduction of Nitrate by Barley Seedlings1

  1. Dale G. Blevins,
  2. A. J. Hiatt,
  3. R. H. Lowe and
  4. J. E. Leggett2



The absorption, translocation, and metabolism of N is influenced by the source of N and by the availability and mobility of counter ions for transport. The purpose of this study was to determine the influence of K or Ca on nitrate uptake, translocation, and reduction in barley seedlings (Hordeum vulgare. cv. Compana). Six-day-old barley seedlings were grown for 2 to 36 hours in solutions of 1.0 meq/liter KNO3 or Ca(NO3)2, each containing 0.4 meq/liter of CaSO4. Experiments were conducted in a growth chamber at 27 C with a photosynthetic irradiance of 5.3 mW cm−2. Seedlings treated with Ca(NO3)2 (low K) had lower levels of nitrate uptake, nitrate reductase activity, and lower organic acid concentrations than seedlings treated with 1 mM KNO3. The solution pH and the expressed sap pH of roots and shoots of the low K seedlings increased during the experiment. The shoots of the low-K seedlings had much lower nitrate concentrations and lower levds of nitrate reductase activity than the roots, suggesting that K plays a major role in nitrate translocation. These results support the hypothesis that potassium malate is cycled from the tops to the roots where decarboxylation occurs, providing a source of HCO3- for exchange with NO3- during absorption.

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