Movement of Assimilated Nitrogen from the Root System of the Field Pea (Pisum arvense L.)

Changes in the composition of the amino fraction of bleeding sap collected from decapitated root systems of field pea were studied during the period of transition from cotyledon nutrition to the commencement of nitrogen fixation by root nodules. Output and composition of bleeding sap are described for uninoculated seedlings following application to the rooting medium of nitrate, ammonium, or urea. Assimilation by the root system of any external source of nitrogen results in progressive increase in the output of all bleeding-sap components, particularly the amide asparagine. The relative proportions of the various amino compounds and the balance of organic and inorganic nitrogen in the bleeding sap were found to vary with the source of nitrogen made available to the root system.