Short Term Studies of Nitrate Uptake into Barley Plants Using Ion-Specific Electrodes and 36ClO3−

Publisher Website
Google Scholar
Abstract
The influence of NH4+, in the external medium, on fluxes of NO3- and K+ were investigated using barley (H. 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 .mu.M NO3- were sensitive to external NH4+ when uptake was measured in 100 .mu.M NO3-. By contrast, NO3- uptake (from 100 .mu.M NO3-) by plants previously grown at this concentration was not reduced by NH4+ treatment. Plants pretreated for 2 days with 5mM NO3- showed net efflux of NO3- when roots were transferred to 100 .mu.M NO3-. This efflux was stimulated in the presence of NH4+. NH4+ also stimulated NO3- efflux from plants pretreated with relatively low nitrate concentrations. Short-term effects on net uptake of NO3- probably occur via effects upon efflux. By contrast to the situation for NO3-, net K+ uptake and influx of 86Rb+-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 min of NH4+ addition. The latter ion exerts a direct effect upon K+ influx.