NITRATE UPTAKE KINETICS AND METABOLIC PARAMETERS IN TWO RICE VARIETIES GROWN IN HIGH AND LOW NITRATE

A study was conducted on the effect of nitrate (NO3) levels on nitrate uptake kinetics and nitrogen (N) metabolism in two rice varieties, Piaui (landrace) and IAC-47 (improved). At 27 days after germination (DAG) N supply was suspended for 72 h, and then restored as 0.2 or 2 mM nitrate. The nitrate uptake kinetics was determined by the depletion method. Plants were harvested at 0, 6, and 24 h. Plants of the Piaui variety under 0.2 mM nitrate showed higher Vmax and lower KM, indicating higher efficiency of nitrate uptake at low supply. In the sheaths of both varieties, there was a greater accumulation of nitrate and lower activities of nitrate reductase and glutamine synthetase. The V-H+-ATPase activity increased between 0 and 6 h accompanying the nitrate influx, suggesting that the activity of this proton pump is necessary for the antiport activity (H+/2NO-3) involved in the accumulation of nitrate into vacuoles.