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

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 [(14)C]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.