Occurrence of Ureide Accumulation in Soybean Plants

Abstract

The effects of nitrogen fertilization and N₂ fixation on the accumulation of ureides, allantoin and allantoic acid, were investigated using soybeans (Glycine max L.) cultured by hydroponics during the vegetative growth. Application of nitrogen in the form of urea or ammonium and in some cases nitrate at 20 mM N increased the ureide concentration in plant tissues but not in xylem sap. The ureide concentration in the xylem sap was greater when the N₂-fixing activity of the nodules was higher, whereas the ureide concentration in the tissues was rather related to the nitrogen content of the tissues, although these relationships were not so strict. The leaf tissues supplied with glutamine, ammonium nitrate, urea, or glycine through their petioles were able to synthesize ureides. These results indicate that host plant tissues and nodules have the ability to produce ureides upon supply of N as combined. N or fixed-N and that the main source of ureides transported in xylem streams is that produced in the nodules. The ureide concentration in the xylem sap may be a better indicator of N₂-fixing activity than the ureide concentration in plant tissues.