In vivo Characterization of Nitrate Reductase Activity in Cotton

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Abstract
The in vivo nitrate reductase activity in leaf tissue of cotton (Gossypium hirsutum L.) was characterized. Enzymatic activity was linear with time up to 60 min. The assay for nitrate reductase activity was optimized in leaf slices 400 μm wide incubated in an anaerobic system at 30°C, in a 0.02 M KNO3 medium at pH 7.0 with 1 % propanol. In vivo activity was highest in recently matured leaves at the top of the plant.Both light and nitrate enhanced in vivo enzymatic activity. The activity was highest after 9 hours in the light and then decreased steadily for several more hours even in the presence of light.The nitrate reductase activity was more strongly correlated to the levels of NO3‐N in the culture solution than to the NO3‐N level in the tissue. The utility of this technique in nitrate reductase assay in a tissue containing large amounts of phenolic compounds is discussed.