THE PARTITIONING OF NITRATE ASSIMILATION BETWEEN ROOT AND SHOOT OF A RANGE OF TEMPERATE CEREALS AND PASTURE GRASSES

Nitrate reductase activity (NRA, in vwo assay) and nitrate (NO3) content of root and shoot and NO3and reduced nitrogen content of xylem sap were measured m five temperate cereals supplied with a range of NO3concentrations (0-1-20 mol m-3) and three temperate pasture grasses supplied with 0-5 or 5 0 mol m-3 NO3For one cereal (Hordeum vulgare L), in vitro NRA was also determined The effect of external NO3concentration on the partitioning of NO3assimilation between root and shoot was assessed All measurements indicated that the root was the major site of NO3assimilation in Avena satwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestwum L and x Tnticosecale Wittm supplied with 0-1 to 1-0 mol m-3 NO3and that for all cereals, shoot assimilation increased in importance as applied NO3concentration increased from 10 to 20 mol m-3At 50-20 mol m-3NO3−the data indicated that the shoot played an important if not major role in NO3assimilation in all cereals studied Measurements on Lohum multiflorum Lam and L perenne L indicated that the root was the main site of NO, assimilation at 05 mol m-3 NO3but shoot assimilation was predominant at 50 mol m-3NO3Both NRA distribution data and xylem sap analysis indicated that shoot assimilation was predominant m Dactylis glomerata L supplied with 05 or 50 mol m-3 NO3. © 1992 Annals of Botany Company.