Ureide and amino acids in xylem sap of soybean (Glycine max L.) are affected by both nodulation and nitrogen supply from soil

To estimate the effect of nitrogen fixation on the nitrogen metabolism of soybean, changes in the concentrations of nitrogenous compounds in the xylem sap from nodulated plants of soybean (Glycine max. L. cv. T202) were compared with those from the non-nodulated isoline (T201) grown in fields. Although changes in the concentrations of 16 out of 19 amino acids in the xylem sap from non-nodulated plants were correlated with those of ureides, none of them in the xylem sap from nodulated plants showed any significant correlation with ureides. On the other hand, for some of the amino acids from the nodulated plants, the changes in the concentrations showed significant correlations with each other, in the same way as those of the non-nodulated plants. These results suggested that nitrogen fixation affects differently on the concentrations of the various nitrogenous compounds in the xylem sap and that it is possible to discriminate between ureides derived from N-2 fixation and those derived from other sources.