Related Experiment Video
Updated: Aug 8, 2026

Generation of Composite Plants in Medicago truncatula used for Nodulation Assays
Published on: March 27, 2011
Asparagine Biosynthesis in Alfalfa (Medicago sativa L.) Root Nodules
1The Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55108.
Abstract:
Rapid direct conversion of exogenously supplied [(14)C]aspartate to [(14)C] asparagine and to tricarboxylic cycle acids was observed in alfalfa (Medicago sativa L.) nodules. Aspartate aminotransferase activity readily converted carbon from exogenously applied [(14)C]aspartate into the tricarboxylic acid cycle with subsequent conversion to the organic acids malate, succinate, and fumarate. Aminooxyacetate, an inhibitor of aminotransferase activity, reduced the flow of carbon from [(14)C]aspartate into tricarboxylic cycle acids and decreased (14)CO(2) evolution by 99%. Concurrently, maximum conversion of aspartate to asparagine was observed in aminooxyacetate treated nodules (30 nanomoles asparagine per gram fresh weight per hour. Metabolism of [(14)C]aspartate and distribution of nodulefixed (14)CO(2) suggest that two pools of aspartate occur in alfalfa nodules: (a) one involved in asparagine biosynthesis, and (b) another supplying a malate/aspartate shuttle. Conversion of [(14)C]aspartate to [(14)C]asparagine was not inhibited by methionine sulfoximine, a glutamine synthetase inhibitor, or azaserine, a glutmate synthetase, inhibitor. The data did not indicate that asparagine biosynthesis in alfalfa nodules has an absolute requirement for glutamine. Radioactivity in the xylem sap, derived from nodule (14)CO(2) fixation, was markedly decreased by treating nodulated roots with aminooxyacetate, methionine sulfoximine, and azaserine. Inhibitors decreased the [(14)C]aspartate and [(14)]asparagine content of xylem sap by greater than 80% and reduced the total amino nitrogen content of xylem sap (including nonradiolabeled amino acids) by 50 to 80%. Asparagine biosynthesis in alfalfa nodules and transport in xylem sap are dependent upon continued aminotransferase activity and an uninterrupted assimilation of ammonia via the glutamine synthetase/glutamate synthase pathway. Continued assimilation of ammonia apparently appears crucial to continued root nodule CO(2) fixation in alfalfa.
More Related Videos
09:27Functional Complementation Analysis (FCA): A Laboratory Exercise Designed and Implemented to Supplement the Teaching of Biochemical Pathways
Published on: June 24, 2016
10:58Plant Promoter Analysis: Identification and Characterization of Root Nodule Specific Promoter in the Common Bean
Published on: December 23, 2017
Related Concept Videos
Amino Acid Biosynthetic Pathways
Inorganic Nitrogen Assimilation
Biosynthesis of Nucleic Acids
Peptidoglycan Synthesis
Overview of Nitrogen Metabolism
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this nitrogen...