Proline metabolism in response to highest nitrogen dosages in green bean plants (Phaseolus vulgaris L. cv. Strike)
2001
Sanchez, E. | Lopez-Lefebre, L.R. | Garcia, P.C. | Rivero, R.M. | Ruiz, J.M. | Romero, L.
The objective of the present work was to determine what impact extremely high 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 vulgaris L. cv. Strike). In this effort, we identified the most favourable pathway of proline synthesis under our experimental conditions. The N was applied to the nutrient solution in the form of NH4NO3 at 5.4 mmol/L (N1, optimal level), 11.6 mmol/L (N2), 17.4 mmol/L (N3), and 23.2 mmol/L (N4). Our results indicate that the application of high N dosages in Phaseolus is characterized by the accumulation of NO3(-), NH4(+) and proline in root and foliar organs. However, although the enzymes in charge of proline biosynthesis, ornithine-delta-aminotransferase (OAT, EC 2.6.1.13) and delta1-pyrroline-5-carboxylate synthetase (P5CS, EC 2.7.2.11/1.2.2.41) vary in behaviour depending on the N status, in our experiment, this amino acid appears to be synthesized mainly by the enzyme ornithine-delta-aminotransferase. This suggests predominance of the ornithine pathway over the glutamine pathway. Finally, under our experimental conditions, proline can be defined as a good indicator of N excess of green bean plants.
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