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Journal of Experimental Botany, Vol 50, 1365-1372, Copyright © 1999 by Oxford University Press

ARTICLES

The characterization of inhibition of net nitrate uptake by salt in salt-tolerant barley (Hordeum vulgare L. cv. California Mariout)

A PeukeWD Jeschke
Julius-von-Sachs-Institut fur Biowissenschaften, Lehrstuhl fur Botanik I der Universitat, Julius-von-Sachs-Platz 2, D-97082 Wurzburg, Germany; Corresponding author at: Institut fur Forstbotanik und Baumphysiologie, Professor fur Baumphysiologie, Am Flughafen 17, D-79085 Freiburg, Germany

Barley seedlings (Hordeum vulgare L. cv. California Mariout) grown hydroponically for 14-19 d without addition of NaCl were used for describing the effects of salt application on net nitrate uptake and for the calculation of kinetic parameters. The addition of NaCl, KCl, CaCl2, and Na2SO4 to the uptake solution in the experiments led to similar inhibition of nitrate uptake, only at low and very high salt concentrations were ion-specific effects found. The same decrease in nitrate uptake can also be achieved by sorbitol or betaine at corresponding osmolalities. Thus it was concluded that the inhibition of uptake was caused mainly by the osmotic effects of salts. Differences in the mechanisms of inhibition were detected between the two systems of nitrate uptake (high affinity system: HATS, and low affinity system: LATS). The HATS was inhibited non-competitively by NaCl, an apparent Ki of 60 mol m-3 was calculated using a Dixon-plot. Fitting an equation assuming a non-competitively inhibited HATS by computer program to the raw data resulted in an apparent Ki of about 37 mol m-3. In contrast, the LATS was affected in a complex way: up to 60 mol m-3 NaCl the affinity was increased, which led to a stimulation of nitrate uptake at low nitrate concentrations (<2 mol m-3). An inhibition of the LATS became obvious at concentrations above 3 mol m-3 nitrate (for all applied salt concentrations) or with 100 mol m-3 NaCl (throughout the whole nitrate range). Related plots of the data pointed to a competitive effect.Key words: Hordeum vulgare L., net nitrate uptake, high affinity transport system (HATS), low affinity transport system (LATS), salt, inhibition, apparent kinetic parameters.
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