Nitrate reductase activity in nitrogen and water-stressed plants of bread wheat

Effects of cessation of watering on Nitrate Reductase Activity (NRA) were studied in plants grown in bags in a greenhouse under two nitrogen regimes (application of urea or no application of nitrogen fertilizer). Nitrate Reductase Activity was reduced by water shortage only in plants well supplied with nitrogen. The effect was more marked on potential NRA (NRA+) than on actual NRA (NRA-, measured without addition of nitrate to the assay medium), and it was not associated to a reduced concentration of nitrates in the leaves. Low nitrogen level in the soil reduced strongly NRA and nitrate content of tissues. The level of nitrate present in the tissues (endogenous nitrate) seemed always to limit NRA activities, considering the lower values of actual NRA compared to potential NRA.