Variation in Nitrate Reductase, Nitrite, and Nitrite Reductase in Some Grasses and Cereals

Nitrite accumulation may result from unbalance between nitratereductase which produces nitrite and nitrite reductase whichremoves it. In the first experiment, using three light levelsand three nitrate levels, on Lolium, maize, and oats, both enzymesresponded to increased light, though not always significantly.The effect of nitrate was more variable. Nitrate reductase activityincreased to the intermediate or highest level of nitrate, butthere was no clear response in nitrite reductase activity orin nitrite concentration. In the second experiment, using fournitrate levels but only one, high, light intensity on Loliumand barley, the results were clearer. With increasing nitratesupply, nitrate reductase activity increased more than nitritereductase activity. This was particularly marked in Lolium,in which nitrite accumulated at the highest nitrate supply.Thus high nitrate supply unbalances the two enzymes in the directionleading to nitrite accumulation.