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Effect of nitrogen source on ureides in soybean.
1Boyce Thompson Institute, Tower Road, Ithaca, New York 14853.
Plant Physiology
|February 1, 1984
Summary
Soybean nitrogen (N) transport in xylem as ureides correlates with N(2) fixation but is also influenced by nitrate availability. Phloem N composition remains consistent regardless of N source.
Area of Science:
- Plant Physiology
- Biochemistry
- Agronomy
Background:
- Soybeans (Glycine max) rely on symbiotic nitrogen fixation.
- Nitrogen transport in plants occurs via xylem and phloem.
- Ureides are key nitrogenous compounds transported in xylem.
Purpose of the Study:
- To investigate the relationship between nitrogen fixation and ureide content in soybean xylem.
- To determine the influence of nitrate availability on ureide levels.
- To compare nitrogen distribution from different sources (N(2), NH(4)(+), NO(3)(-)) in soybeans.
Main Methods:
- Field-grown soybeans were analyzed for xylem ureide content over a 9-week period.
- Acetylene reduction assay was used to estimate nitrogen fixation rates.
- Greenhouse experiments involved feeding labeled nitrogen isotopes ((15)N(2), (15)NH(4)(+), (15)NO(3)(-)) to assess N distribution.
Main Results:
- Xylem ureide-N percentage increased with higher N(2) fixation, ranging from 9.0% to 69.2%.
- A strong correlation (r=0.93) was observed between acetylene reduction and ureide-N during early pod fill.
- Nitrate availability significantly impacted ureide content; higher nitrate levels reduced ureide percentage in xylem sap.
Conclusions:
- While ureide content reflects N(2) fixation, it's also modulated by nitrate supply.
- Nitrogen derived from symbiotic fixation, ammonium, or nitrate is ultimately distributed similarly to plant parts and grain.
- Amino acids, not ureides, are the primary N form in the phloem, maintaining consistent composition.