The objective of the present work was to determine the effect of nitrogen toxicity on the metabolism of phenolic compounds and of oxidative stress in Phaseolus vulgaris L. cv. Strike. The nitrogen was applied to the nutrient solution as NH4NO3 at 5.4, 10.8, 16.2, 21.6 and 27 mM. The results indicate that the application of 27 mM N can be defined as toxic, as it drastically depressed growth of the green bean plants in our experiment. In addition, the abiotic stress from the application of this N dosage inhibited the enzymes polyphenol oxidase, peroxidase and cata-lase, and stimulated phenylalanine ammonia-lyase and superoxide dismutase activities. The result was foliar accumulation of phenolic compounds and hydrogen peroxide (H2O2). The accumulation of H2O2 also apparently caused a reduction in biomass production.

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The aim of the present work was to determine the effect of abiotic stress, such as nitrogen (N) deficiency, on phenol and oxidative metabolism. In addition, we analyzed whether the response of the two metabolic processes is a good bioindicator of N deficiency in French bean plants. The N was applied to the nutrient solution in the form of NH4NO3 at 1.35 mM (N1), 2.7 mM (N2) and 5.4 mM (N3), this latter dosage being considered optimal. The results indicated that application of 1.35 and 2.70 mM of N can be defined as suboptimal or deficient, as it depressed foliar biomass of the French bean plants in our experiment. In addition, abiotic stress from the application of these N dosages stimulated the enzymes PPO, POD and CAT, and inhibited PAL and SOD activities, resulting in the lowest foliar accumulation of phenolic compounds and H2O2.

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