In Vivo Determination of Parameters of Nitrate Utilization in Wheat (Triticum aestivum L.) Seedlings Grown with Low Concentration of Nitrate in the Nutrient Solution

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Abstract
Six genotypes of winter wheat (T. aestivum L.) differing in grain protein concentration were grown on a nutrient solution containing low concentrations of NO3- (2 mm). Total NO3- uptake varied between genotypes but was not related to grain protein content. An in vivo nitrate reductase assay was used to determine the affinity of the enzyme for NO3-, and large phenotypic variations were observed. In vivo estimations of the concentration and size of the metabolic pool were variable. However, the 3 genotypes with the higher ratios of metabolic pool size to leaf total NO3- concentration were the high protein varieties. It is proposed that a high affinity of nitrate reductase for nitrate might be a biochemical marker for the capacity of the plant to continue assimilating NO3- for a longer period during the last stage of growth. The potential use of such physiological criteria as markers is discussed, in particular with respect to breeding programs for the development of plants with efficient N utilization.