Nitrate reductase activity
Nitrate reductase activity (EC 1.6.6.1) was determined in vivo following the methods described by Hageman and Hucklesby (1971) and Jaworki (1971). Discs of 1 cm diameter in mature fresh leaves, or pieces of 1 cm in roots, were punched out. Samples (200 mg) were suspended in a glass vial containing 10 mL of 100 mM potassium phosphate buffer (pH 7.5), 1% (v/v) npropanol and 100 mM KNO3. The glass vial was subjected to vacuum infiltration three times in order to induce anaerobic conditions in the incubation medium. Plant samples were incubated in a water bath at 30 ◦C for 60 min in the dark and placed in a boiling water bath for 5 min to stop enzymatic reaction.