Changes in biomass, enzymatic activity and protein concentration in roots and leaves of green bean plants (Phaseolus vulgaris L. cv. Strike) under high NH4NO3 application rates

The objective of the present work was to determine the effect of NH4NO3 toxicity on nitrogen metabolism in Phaseolus vulgaris L. cv. Strike. The NH4NO3 was applied to the nutrient solution at 6 (N1), 12 (N2), 18 (N3), and 24 mM (N4). The availability of NO3− and NH4+ in the roots and leaves of green bean proved to be influenced by the different NH4NO3 treatments, being the NO3− and NH4+ translocated towards the aerial part of the plant and subsequently assimilated in the leaves. The most important enzymatic activities within nitrogen metabolism, such as nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase were affected negatively by the highest NH4NO3 rate (N4). Finally, in our experiment, possibly the high accumulation of NO3−, and principally of NH4+, in both organs due to the application of high NH4NO3 rates could be the direct causes of the reduced biomass production in plants and of the reduction of N assimilation process in roots and leaves, indicating that green bean plants are highly sensitive to high N levels. © 2003 Elsevier B.V. All rights reserved.