The effect of ammonium ions on uptake of glutamine and other amino compounds by cultured cells of rapeseed

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Abstract
Nitrogen starvation for 24 h, particularly NH 4 + deprivation, of cultured repeseed (Brassica napus L.) cells caused them to develop the potential for a rapid increase in the rate of uptake of several amino compounds. Time-course studies, primarily using [14C]glutamine, showed that the increase in uptake rate continued for about 10 h after the 24-h N-starvation period. Addition of 2 mM NH 4 + to N-starved cells caused the increase in glutamin-uptake rate to cease, and the rate began to fall after 3–6 h to the level observed in cells grown continuously in the presence of NH 4 + . Neither pH changes in the medium caused by the presence of NH 4 + nor the competitive inhibition by NH 4 + of glutamine transport into the cells were responsible for the changes in the glutamine uptake rate. Similar results were obtained in time-course studies with [14]leucine.