Allantoin and Allantoic Acid in Tissues and Stem Exudate from Field-grown Soybean Plants

Samples of stem exudate and plant tissue collected from field-grown soybean (Glycine max [L.] Merr.) plants were analyzed for allantoin and allantoic acid. Nitrogen in nitrate plus amino acids exceeded ureide N concentration in stem exudate prior to flowering. During all of reproductive development (from about 40 days after planting until maturity), ureide N concentration was two to six times greater than amino acid plus nitrate N concentration. Allantoin and allantoic acid, not asparagine, are the principal forms of nitrogen transported from nodulated roots to shoots of the soybean plant. During pod and seed development ureide N comprised as high as 2.3, 37.7, and 15.8% of total N in leaf blades, stems + petioles, and fruits, respectively. The concentration of ureide in stems and fruits declined to nearly zero at maturity.Maximum ureide concentration of exudate collected from soybean nodules was 5.3 milligrams N per milliliter (94 micromoles allantoin per milliliter). This result supports evidence published by others that the site of allantoin synthesis is the nodule.