Effect of Previous Nitrate Deprivation on 15N-nitrate Absorption and Assimilation by Wheat Seedlings

Abstract

Nitrate uptake and assimilation were examined in intact 18 days old wheat ( Triticum aestivum, cv Capitole) seedlings either permanently grown on nitrate (high-N seedlings) or N-stressed by transfer to an 0 N-solution for the final 7 days (low-N seedlings). The N-stressed seedlings were characterized by a lower organic N content (2.5 mg instead of 4.9 mg per seedling) and an increased root dry weight. The seedlings received 15NO 3K for 7 h in the light. Nitrate uptake was 2.8 times higher in low-N than in high-N seedlings. The assimilation rate was 35 and 16 μmol NO 3 −· h−1· g −1 dry weight respectively. Partitioning of NO 3 − to reduction and assimilation was the very same in both kinds of seedlings. The results support the view that 50 % of the nitrate reduction in Triticum aestivum, cv Capitole could be achieved in the roots. The present observations are interpreted as evidence that factors closely associated with the seedling N-status may have a major role in regulating NO 3 − uptake and assimilation. In low-N seedlings, the high amount of carbohydrates in roots may add its stimulus to the specific inducing effect of nitrate whereas in high-N seedlings, excess of nitrate or amino-acids may set the pace by negative feedback control.