Glutamine as a major acceptor of reduced nitrogen in leaves.

The feeding of K(15)NO3 via the xylem stream to photosynthesising leaves of Datura stramonium L. shows a massive routing of (15)N to glutamine, increasing with rise in the N-feeding level (between 0 and 400 μg N ml(-1)). At each feeding level the glutamine and glutamate pools have very similar (15)N enrichment despite disparity in pool size. Amino-compound pool-size and (15)N enrichment do not increase above the 300 μg ml(-1) feeding level which corresponds to the normal level of nitrate-N in the xylem stream of the experimental plants. Thus, the rôle of glutamine as an N storage compound and ammonia "detoxifier" in many plants extends to the incorporation of photosynthetically reduced N newly produced in Datura leaves; the level of N incorporation into glutamine is apparently dependent on the level of nitrate feeding and the degree of induction of nitrate-reducing enzymes.