CO/sub 2/ fixation in alfalfa and birdsfoot trefoil root nodules and partitioning of /sup 14/C to the plant
The objectives of this study were to determine if nonphotosynthetic CO/sub 2/ fixation by root nodules contributes carbon for the assimilation of fixed N/sub 2/ in alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.) and if assimilation products are partitioned to different plant organs. Effective alfalfa nodules excised from or attached to roots had apparent /sup 14/CO/sub 2/ fixation rates of 50 to 80 ..mu..g CO/sub 2/ kg/sup -1/s/sup -1/ (dry weight) at 0.0012 to 0.0038 mole fraction CO/sub 2/. Nodule CO/sub 2/ fixation rates increased six- to seven-fold as ambient CO/sub 2/ was raised from 0.0038 to 0.0663 mole fraction. Respiration rates of nodules (3 to 4 mg CO/sub 2/ kg/sup -1/s/sup -1/) were 10 to 100-fold higher than /sup 14/CO/sub 2/ fixation rates of nodules. Pulse chase experiments with /sup 14/CO/sub 2/ combined with nodule and xylem sap analysis demonstrated the initial products of root and nodule CO/sub 2/ fixation were organic acids. However, the export of fixed /sup 14/C from effective nodules was primarily in the form of amino acids. In contrast, nodule and/or root fixed /sup 14/C in ineffectively nodulated alfalfa and denodulated effective alfalfa and birdsfoot trefoil was transported primarily as organic acids. Aspartate, asparagine, alanine, glutamate, and glutamine were the most heavily labeled compounds in the amino acid fraction of both effective alfalfa and birdsfoot trefoil nodules exposed to /sup 14/CO/sub 2/. By contrast, asparate, asparagine, and glutamine were the predominantly labeled amino acids in xylem sap collected from nodulated effective roots exposed to /sup 14/CO/sub 2/. The occurrence of nodule CO/sub 2/ fixation in alfalfa and birdsfoot trefoil and the export of fixed carbon as asparagine and aspartate to roots and shoots is consistent with a role for CO/sub 2/ fixation by nodules in providing carbon skeletons for assimilation and transport of symbiotically fixed N/sub 2/.
- Research Organization:
- Monsanto Agricultural Products TIE, St. Louis, MO
- OSTI ID:
- 6905821
- Journal Information:
- Crop Sci.; (United States), Vol. 24:2
- Country of Publication:
- United States
- Language:
- English
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Nonphotosynthetic CO/sub 2/ fixation by alfalfa (Medicago sativa L. ) roots and nodules
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Related Subjects
CARBON DIOXIDE
ROOT ABSORPTION
LEGUMINOSAE
NITROGEN FIXATION
ALANINES
ASPARAGINE
CARBON 14 COMPOUNDS
GLUTAMINE
LABELLING
NITRIFICATION
ROOTS
TRACER TECHNIQUES
ABSORPTION
AMIDES
AMINO ACIDS
CARBON COMPOUNDS
CARBON OXIDES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL REACTIONS
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLANTS
UPTAKE
553001* - Agriculture & Food Technology- Tracer Techniques- (-1987)