Exceptions to this idea occur when urea is the chief cause of nitrogen supply, in species in which ureides
play an significant physiological role (Martin and Ruby, 2004), when too much application of Zn, Cu, Mn, Fe, Ca, or Mg has been made over many years (Martin and Ruby, 2004), and possibly also in nitrogen-fixing crops grown on mineral-poor or highly nickel-fixing (high pH, high lime) soils.
Concentrations of ureides
(allantion and allantoic acid) in xylem sap were measured as the phenylhydrazine derivative of glyoxylate (Young and Conway.
Sap was collected at the pod-fill stage by Vacuum Extraction Method and stored in the freezer at -15degC, then concentrations of ureides
, nitrate and amino-N were determined to calculate the relative ureide
- N (%) and percent nitrogen derived from atmosphere (% Ndfa) by the following formula:
In soybean, ureides
(allantoin and allantoic acid) are the N transport molecules from the nodules to the leaves.
The substrates for mineralization are varied, and include such compounds as proteins, peptides, nucleic acids, aminopolysaccharides, urate, and ureides
Faizah AW, Suratmini P, Nurhayata DP, Bagnall DJ, Bergersen FJ (1991) Re-evaluation of the, role of ureides
in the xylem transport of nitrogen in Arachis-spp.
2] fixation in legumes are reported to be the amide asparagine or the ureides
allantoin and allantoic acid (Streeter, 1991).
Role of amides, amino acids, and ureides
in the nutrition of developing soybean seeds.
Subsequently, it was shown that ureides
are probably synthesized in root nodules (Fujihara and Yamaguchi, 1978).
In this procedure, the concentration of ureides
from petiole-tissue extracts is expressed as the RAU, which is the fraction of the N from ureides
relative to the sum of the N found in ureides
This sensitivity is not universal among grain legumes and appears to be a trait of those species that transport ureides
(allantoin and allantoic acid) from the nodules to the shoot (Sinclair and Serraj, 1995).
An increase in leaf ureides
(allantoin and allantoic acid), the major nitrogen compounds exported from soybean nodules, and a simultaneous decrease in nodule activity is a major feature of the drought-stress response.