Yield and biosynthesis of nitrogenous compounds in fruits of green bean (Phaseolus vulgaris L cv Strike) in response to increasing N fertilisation

The objective of the present work was to determine the effect of different dosages of N on the biosynthesis of organic N compounds in fruits and their influence on yield in green bean (Phaseolus vulgaris L cv Strike) plants. The nitrogen was applied to the nutrient solution as NH4NO3 at 1.5 (N1), 3 (N2), 6 (N3), 12 (N4), 18 (N5) and 24 mM (N6). Treatment N3 was considered optimal for efficient yield in green bean plants and also for the null presence of NO3−. Highest N dosages (18 and 24 mM) resulted in the accumulation of NO3− in pods and seeds. This accumulation encouraged nitrate reductase (NR) and nitrite reductase (NiR) activity in both tissues and treatments, and therefore NR activity might be considered as a good bioindicator of the presence of NO3− in edible fruits. The greater NH4+ assimilation by glutamine synthetase (GS) and glutamate synthase (GOGAT) occurred primarily in the pods of the N6 treatment, while the seeds acted as physiological sinks, these latter tissues presenting the highest concentrations of amino acids, proteins and organic N. The high accumulation of NO3− and NH4+ in both seeds and pods could be the direct cause of the reduction in fruit production, indicating that green bean plants are very sensitive to high N levels.  2004 Society of Chemical Industry