Studies of nitrate influx into barley roots by the use of 36ClO3− as a tracer for nitrate. 1. Interactions with chloride and other ions

Abstract

The effect of various anions on the short-term influx on NO3− into barley roots was examined by the use of 36ClO3− as a tracer for nitrate. NO3− (36ClO3−) influx was found to be extremely sensitive to inhibition by external Cl− (Ki = 0.035 mM). By contrast 36Cl− influx was not significantly affected by external NO3−. Other anions, SO42− and H2PO4−, had no effect on NO3− (36ClO3−) influx, while HPO42−exerted a slight inhibitory effect. In the range from pH 4 to pH 8 no significant effect of OH− concentration on NO3− (36CIO3−) influx was detected. When barley roots were pretreated for periods up to 4 h with 10 mM NO3−, there was a significant reduction in NO3− (36ClO3−) and 36Cl− influx. KCl at the same concentration (10 mM) caused similar reductions of NO3− (36ClO3−) and Cl− influx. When plants were pretreated with lower NO3− or Cl− concentrations (0.05–5.0 mM) for 2 days, Cl− influx was found to be more sensitive than NO3− (36ClO3−) influx to nitrate or chloride pretreatment.