The response of proline metabolism to nitrogen deficiency in pods and seeds of French bean (Phaseolus vulgaris L cv Strike) plants

The objective of the present work was to determine the impact of nitrogen deficiency on proline metabolism in order to use this amino acid as a bioindicator of the N status of the pods and seeds of French bean (Phaseolus vulgaris L cv Strike) plants. We also identify the pathway of proline synthesis which is favoured under our experimental conditions. N was applied to the nutrient solution in the form of NH4NO3 at 1.45 mM (N1), 2.90 mM (N2) and 5.80 mM (N3, optimal level). Our results indicate that N deficiency is characterised by a decline in proline accumulation in both the pod and the seed, fundamentally because proline degradation is encouraged by stimulation of the enzyme proline dehydrogenase under these conditions. However, although the enzymes in charge of proline biosynthesis (ornithine-δ-aminotransferase and Δ1-pyrroline-5-carboxylate synthetase) vary in behaviour depending on the N status, this amino acid appeared to be synthesised mainly by the enzyme ornithine-δ-aminotransferase, suggesting predominance of the ornithine pathway over the glutamine pathway. Finally, under our experimental conditions, proline can be regarded as a good indicator of N deficiency, particularly in the seeds of French bean plants. © 2001 Society of Chemical Industry