The influence of ammonium on nitrate reduction in wheat seedlings

Summary Ammonium markedly inhibited nitrate absorption by nitrogenstarved wheat seedlings but did not decrease the proportion of absorbed nitrate that was reduced. Seedlings high in nitrate (absorbed prior to the experimental periods) reduced similar amounts of this nitrate regardless of whether or not ammonium was present and being absorbed during the period of measurement. Ammonium or products of ammonium assimilation did not interfere with the induction, stability, or activity of nitrate reductase. Consequently, the hypothesis that ammonium depresses nitrate uptake indirectly by inhibiting nitrate reduction is rejected, and it is suggested that the ammonium effect is directly on the nitrateuptake process.Paper No. 2800 of the Journal Series of the North Carolina State University Agricultural Experiment Station. These investigations were supported by the U.S. Atomic Energy Commission, Contract No. AT-(40-1)-2410.