The effect of nitrate feeding levels on the pathway of nitrogen incorporation into photosynthesizing leaf metabolism ofDatura stramonium L

Datura stramonium leaves fed K¹⁵NO₃ at 25 g N ml^–1 and 200 g N ml^–1 for 7 and 17 min show that at both time courses the main route of newly reduced nitrogen is to glutamate at the low N-feeding level, and to glutamine at the high N-feeding level. At the high N-feeding level the amido-N of glutamine shows higher¹⁵N enrichment than the amino-N, whereas at the low N-feeding level the opposite is true. Feeding of glutamine (¹⁵N amido labelled) at the 25 and 200 g N ml^–1 level produces¹⁵N enrichment of leaf amino acids, the prime routing being to glutamate. This indicates the operation of glutamate synthase at both feeding levels.It is possible that inDatura stramonium leaves both the glutamate dehydrogenase and glutamine synthetase/GOGAT pathways are simultaneously operative, the former route being favoured at low N-feeding levels, the latter at high N-feeding levels.