Abstract
Abstract The activity of nitrate reductase (NR) and glutamine synthetase (GS) was followed during 4 weeks in various tissues of tomato plants (Lycopersicon esculentum Mill. cv. Vedettos) grown in growth chambers under two photosynthetic photon flux (PPF; 125 and 250 μmol·s−1·m−2, high-pressure sodium lamps) conditions for 18 hr and with four N fertilization regimes (5, 10, 15, and 20 meq·liter−1). In roots, NR increased with increased PPF but not with increasing N. Leaf NR activity was stimulated by increased PPF. Leaf NR increased over time in all treatments, but the highest values were obtained at lower N concentrations. Glutamine synthetase was stimulated by both light and N increases; its activity also increased throughout the 4 weeks of treatment. Nitrate reductase activity was highly correlated with the fruit fresh weight : leaf fresh weight ratio. On a mature tomato plant, NR activity was found mainly in leaves opposite developing fruits (sixth and seventh leaves), while GS activity was concentrated in the upper portion of the plant (second and third leaves).
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