The Effect of Different Inorganic Nitrogen Sources and Plant Age on the Composition of Bleeding Sap of Phaseolus vulgaris

The composition of the bleeding sap N of Phaseolus vulgaris varied with the inorganic nitrogen source fed to the plant but was not changed by a fourfold difference in external nitrate concentration. Highest sap N concentration and fastest growth were observed in ammonium nitrate grown plants. With nitrate grown plants 60 % of the total sap N was inorganic nitrate-N and 40 % organic-N whereas with ammonium nitrate grown plants nitrate contributed 30 % to the total N and organic-N 70 %. Virtually all of the N in the sap of ammonium grown plants was organic-N. Allantoic acid was the major individual reduced N compound in the bleeding sap of plants fed with nitrate, ammonium or ammonium nitrate. During the development of the plant from seedling to mature plant with ripened pods, the concentration of N in the bleeding sap of nitrate grown plants decreased sharply initially and then gradually during pod formation; it increased again when the pods had ripened. Nitrate reductase activity of leaf extracts was correlated with nitrate content of bleeding sap and was not much affected by increases in reduced N compounds in the sap