Nitrate reductase activity (Nra) and levels of nitrogenous compounds in leaves of crabwood (Carapa guianensis Aubl.) under three water regimes and suspension of the stresses

Abstract

The crabwood has high phenotypic plasticity due to its adaptability to different environments. The aim of this work was to evaluate the content of nitrate, free ammonium, nitrate reductase activity (Nra), and the levels of total soluble amino acids, proline, glycine betaine in young plants of crabwood (Carapa guianensis Aubl.) under to three water regimes and subsequent recovery process through the stresses suspension. The experiment was carried out on a greenhouse from Universidade Federal Rural da Amazônia, Capitão Poço city, PA State. A completely randomized design on factorial scheme 3×5 was used (three water conditions: irrigated control, water deficit and flooding; and five evaluation times: 0 day, 10 days, 20 days, 30 days and suspension of water stress after 72 hours from the 30th day) with five repetitions, totalizing 75 experimental units. The results showed that the water potential, nitrate concentration and the Nra decreased significantly in plants under water stress, as well as in plants under flooding, with average of -3.46 MPa, 0.6 NO3-/kg DM, 0.1294 μmoles of NO2-/g FM/h (water potential, nitrate and Nra, respectively). The ammonium (NH4+) levels increased in the plant under water stress. The increasing level was more significant in the plants under water deficit, averaging 4.0 of mmol of NH4+/kg of DM. The amino acids levels, proline and glycine betaine had a significant increase in plants with water stress, especially in the plants under water deficit. The plants subjected to flooding did not show any significant result. After the suspension of the water stress, only the contents of free ammonium and levels and total soluble amino acids recovered to their initial values. To others variables, the stress suspension period was not enough for plant's total recovering. The young plants of crabwood subjected to water stress promoted changes in nitrogen metabolic pathways. These changes showed a bigger tolerance of the plants of crabwood to flooding.