The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

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Abstract
Nitrate reductase activity (NRA, in vivo assay) and nitrate (NO-3) content of root and shoot and NO-3 and reduced nitrogen content of xylem sap were measured in five temperate cereals supplied with a range of NO-3 concentrations (0·1–20 mol m−3) and three temperate pasture grasses supplied with 0·5 or 5 0 mol m−3 NO-3 For one cereal (Hordeum vulgare L ), in vitro NRA was also determined The effect of external NO-3 concentration on the partitioning of NO-3 assimilation between root and shoot was assessed All measurements indicated that the root was the major site of NO3 assimilation in Avena satwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivum L and × Triticosecale Wittm supplied with 0·1 to 1·0 mol m−3 NO-3 and that for all cereals, shoot assimilation increased in importance as applied NO-3 concentration increased from 1.0 to 20 mol m−3 At 5.0–20 mol m−3 NO3, the data indicated that the shoot played an important if not major role in NO-3 assimilation in all cereals studied Measurements on Lolium multiflorum Lam and L perenne L indicated that the root was the main site of NO-3 assimilation at 0.5 mol m−3 NO-3 but shoot assimilation was predominant at 5.0 mol m−3 NO-3 Both NRA distribution data and xylem sap analysis indicated that shoot assimilation was predominant in Dactylis glomerata L supplied with 0.5 or 5.0 mol m−3 NO-3

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