Nitrate accumulation by wheat (Triticum aestivum) in relation to growth and tissue N concentrations

The accumulation of nitrate in relation to total N concentrations ([N]_i) in tissues of wheat (Triticum aestivum L., cv Sicco) grown in solution culture was investigated. Root, shoot and leaf tissues showed qualitatively similar relationships between internal nitrate concentrations and [N]_i, both expressed on a tissue water basis. At low [N]_i, no nitrate was detectable but once a particular [N]_i was exceeded, nitrate accumulated as a linear function of [N]_i. The threshold [N]_i values for nitrate accumulation were 110, 450, and 550 mM for roots, total shoot and leaf 4, respectively. The slope of the relationship between nitrate and [N]_i indicated that in all tissues nitrate accounted for 50–55% of the extra N accumulated above the threshold [N]_i. All growth requirements for N were satisfied before nitrate accumulated.