NITRATE REDUCTASE-ACTIVITY IN NITROGEN AND WATER-STRESSED PLANTS OF BREAD WHEAT

Effects of cessation of watering on Nitrate Reductase Activity (NRA) w ere 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 pl ants well supplied with nitrogen. The effect was more marked on potent ial NRA (NRA+) than on actual NRA (NRA-, measured without addition of nitrate to the assay medium), and it was not associated to a reduced c oncentration of nitrates in the leaves. Low nitrogen level in the soil reduced strongly NRA and nitrate content of tissues. The level of nit rate present in the tissues (endogenous nitrate) seemed always to limi t NRA activities, considering the lower values of actual NRA compared to potential NRA.