Abstract
Abstract The effect of ammonium nitrate fertilization on ureide synthesis, xylem transport and assimilation was examined in four week old nodulated soybean plants. In nodules the activity of 5‐phosphoribosylpyrophosphate amidotransferase, a key enzyme of ureide biosynthesis, declined 75%, while enzymes of purine oxidation (xanthine dehydrogenase and uricase) showed no response to nitrogen treatment. Xylem sap concentrations of allantoin and allantoate, as compared to untreated controls, were reduced by about 85% and 65%, respectively. Despite the substantial decline in ureide synthesis and transport, allantoate concentration in leaves of ammonium nitrate treated plants increased by about three‐fold. No ureide accumulation was observed in leaf tissue following a suppression of ureide formation in nodules by allopurinol, an inhibitor of xanthine dehydrogenase. In the pathway of ureide assimilation in leaves, application of inorganic nitrogen had no effect on activity of allantoinase, but caused a 50% drop i...
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