Nitrate reductase activity in coffea cultivars

Abstract

Determination of nitrate reductase activity in vivo was standardized in coffee (Coffea arabica L.) leaves under controlled environmental conditions. Cultivars used in this study were: Nacional, Catuaí, Maragogipe, Mundo Novo and Angustifolia. Plants were growth in controlled chambers set at 28°C and 20°C, day and night temperatures, and 12-hour photoperiod. In all cultivar; lower nitrate reductase activity was determined in younger leaves and increased enzyme activity occurred in mature leaves. Highest activity was observed in leaves of the 2^nd, 3^rd and 4^th pairs counted from the top of the branch. Light induced increased enzyme activity which reached a maximum value approximately two hours after the beginning of the illumination period. Nitrate reductase activity usually decreased after six hours of continuous illumination. Addition of 0.05 M and 0.1 M of nitrate to the incubation medium caused a linear increase of enzyme activity during 15 to 90 or 120 minutes of reaction. Maximum enzyme activity was observed in the assays carried out in pH 8.0 and 33°C of temperature. The use of different buffers such as phosphate, hepes and tris, did not significantly affect enzyme activity, but borate buffer drastically inhibited the in vivo activity of nitrate reductase.