Glutamine synthetase activity in Solanaceous cell suspensions accumulatingalkaloids or not. C-13 NMR and enzymatic assay

The metabolism of labelled pyruvate followed by C-13 NMR and the measure of glutamine synthetase (GS) showed, according to previous results, a high ac tivity of this enzyme in suspension cells of Nicotiana plumbaginifolia. Thi s activity could derive glutamate from the alkaloid synthesizing pathways. However, a recent work showed that the rate of the GS gene transcription wa s inversely proportional to the Gln/Glu ratio. The measures of Gln and Glu concentrations in Nicotiana plumbaginifolia cells revealed that high GS act ivity correlates with the weak value of Gln/Glu ratio. Therefore, the hypot hesis of GS dysfunctioning for the non-biosynthesis of alkaloids in N. plum baginifolia suspension cells can be discarded. This conclusion is strengthe ned by the results obtained when using a CS inhibitor. (C) 1999 Academie de s sciences/Editions scientifiques et medicales Elsevier SAS.