The Influence of Nitrate and Chloride Uptake on Expressed Sap pH, Organic Acid Synthesis, and Potassium Accumulation in Higher Plants 1

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The influence of NO3− uptake and reduction on ionic balance in barley seedlings (Hordeum vulgare, cv. Compana) was studied. KNO3 and KCl treatment solutions were used for comparison of cation and anion uptake. The rate of Cl− uptake was more rapid than the rate of NO3− uptake during the first 2 to 4 hours of treatment. There was an acceleration in rate of NO3− uptake after 4 hours resulting in a sustained rate of NO3− uptake which exceeded the rate of Cl− uptake. The initial (2 to 4 hours) rate of K+ uptake appeared to be independent of the rate of anion uptake. After 4 hours the rate of K+ uptake was greater with the KNO3 treatment than with the KCl treatment, and the solution pH, cell sap pH, and organic acid levels with KNO3 increased, relative to those with the KCl treatment. When absorption experiments were conducted in darkness, K+ uptake from KNO3 did not exceed K+ uptake from KCl. We suggest that the greater uptake and accumulation of K+ in NO3−-treated plants resulted from (a) a more rapid, sustained uptake and transport of NO3− providing a mobile counteranion for K+ transport, and (b) the synthesis of organic acids in response to NO3− reduction increasing the capacity for K+ accumulation by providing a source of nondiffusible organic anions.

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