A comparative study has been carried out of the growth of two lines of Datura innoxia (Mill.) Previous studies in this laboratory (8) suggested that Datura innoxia suspension cultures could be a model system from which higher plant cell mutants could be derived. The recent isolation of an auxotrophic cell line requiring pantothenate for growth (19) has lent support to this contention.Here, details are given of the isolation and partial characterization of a chlorate-resistant variant isolated from D. innoxia cell cultures. MATERIALS AND METHODS CELL CULTURE

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.

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