EFFECTS OF NITRITE ON THE NUTRIENT-UPTAKE AND GROWTH OF WHEAT AND RICE SEEDLINGS

The effects of nitrite (NO2-) on the growth and uptake of potassium, p hosphate, sulphate and nitrate of wheat (Triticum aestivum L. cv. GK O thalom) and rice (Oryza sativa L. cv. Oryzella) seedlings were studied in hydroponic cultures at different pH values. The inhibitory effect of low concentrations (<1 mM) of NO2- on ion uptake and growth was sma ll or negligible between pH 6-7, but increasingly severe at lower (4-4 .5) pH. The toxic effect of NO2- differed considerably for the various nutrients and was also different for roots and shoots. The roots, esp ecially the root hairs, were particularly sensitive to nitrite treatme nts. The results of K+ efflux studies indicate that NO2- may initiate membrane damage at low pH. The presence of NO3- in the uptake and grow th solution diminished the inhibitory effect of NO2-. Experiments invo lving N-15-labelled NO2. proved that at least in a limited range of co ncentration, at non-acidic pH, the plants can utilize nitrite taken up by the roots. However, at low pH HNO2 is formed, usually considered a s a strong oxidant and toxic substance. Wheat and rice, in spite of ha ving very different environmental demands, showed similar reactions to nitrite treatment, but rice seems more sensitive to nitrite stress.