Altered influx/efflux relations of nitrate in roots due to nutrient stress. I. Effect of phosphorus and zinc deprivation

Abstract

Short‐term experiments were carried out with squash and barley seedlings to analyse the nitrate (NO₃ ^‐) influx/efflux relations as a response by the carrier‐mediated transport to phosphorus (P) and zinc (Zn) stress in the nutrient solution by using ¹³N‐labelling and continuous monitoring. Nitrate influx was markedly decreased after transient P deficiency followed by a 2 h P restoration but also when P deficiency was maintained. Similarly, Zn stress induced a strong reduction of the NO₃ ^‐ influx. In both P‐ and Zn‐stressed plants NO₃‐ efflux was only modestly affected at the level of the high affinity uptake but contributed to a certain degree to the depression of the NO₃ ^‐ net uptake. The NO₃ ^‐ influx recovered soon after the short‐term stress was relieved. The results are discussed in the light of NO₃ ^‐ uptake and its relation to membrane integrity.