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

Datura stramonium leaves fed K15NO3 at 25 μg N ml-1 and 200 μg 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 higher 15N 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 μg N ml-1 level produces 15N 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 in Datura 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. (Auth.)