Short Term Studies of Nitrate Uptake into Barley Plants Using Ion-Specific Electrodes and ClO(3): II. Regulation of NO(3) Efflux by NH(4) |
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Authors: | Deane-Drummond C E Glass A D |
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Affiliation: | Botany Department, University of British Columbia, Vancouver, British Columbia, Canada V6T 2B1. |
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Abstract: | The influence of NH4+, in the external medium, on fluxes of NO3− and K+ were investigated using barley (Hordeum vulgare cv Betzes) plants. NH4+ was without effect on NO3− (36ClO3−) influx whereas inhibition of net uptake appeared to be a function of previous NO3− provision. Plants grown at 10 micromolar NO3− were sensitive to external NH4+ when uptake was measured in 100 micromolar NO3−. By contrast, NO3− uptake (from 100 micromolar NO3−) by plants previously grown at this concentration was not reduced by NH4+ treatment. Plants pretreated for 2 days with 5 millimolar NO3− showed net efflux of NO3− when roots were transferred to 100 micromolar NO3−. This efflux was stimulated in the presence of NH4+. NH4+ also stimulated NO3− efflux from plants pretreated with relatively low nitrate concentrations. It is proposed that short term effects on net uptake of NO3− occur via effects upon efflux. By contrast to the situation for NO3−, net K+ uptake and influx of 36Rb+-labeled K+ was inhibited by NH4+ regardless of the nutrient history of the plants. Inhibition of net K+ uptake reached its maximum value within 2 minutes of NH4+ addition. It is concluded that the latter ion exerts a direct effect upon K+ influx. |
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