Proline metabolism in response to highest nitrogen dosages in green bean plants (Phaseolus vulgaris L. cv. Strike)

The objective of the present. work was to determine what impact extremely h igh nitrogen dosages would have on proline metabolism in order to use this amino acid as a bioindicator of N status of green bean plants (Phaseolus vu lgaris L, cv. Strike). In this effort, we identified the most favourable pa thway of proline synthesis under our experimental conditions. The N was app lied to the nutrient solution in the form of NH4NO3 at 5.4 mmol/L (N1, opti mal level), 11.6 mmol/L (N2), 17.4 mmol/L (N3), and 23.2 mmol/L (N4). Our r esults indicate that the application of high N dosages in Phaseolus is char acterized by the accumulation of NO3-, NH4+ and proline in root and follar organs. However, although the enzymes in charge of proline biosynthesis, or nithine-delta -aminotransferase (OAT, EC 2.6.1.13) and Delta (1)-pyrroline- 5-carboxylate synthetase (P5CS, EC 2.7.2.11/1.2.2.41) vary in behaviour dep ending on the N status, in our experiment, this amino acid appears to be sy nthesized mainly by the enzyme ornithine-delta -aminotransferase. This sugg ests predominance of the ornithine pathway over the glutamine pathway. Fina lly, under our experimental conditions, proline can be defined as a good in dicator of N excess of green bean plants.