Nonphotosynthetic CO/sub 2/ fixation by alfalfa (Medicago sativa L. ) roots and nodules
The dependence of alfalfa (Medicago sativa L.) root and nodule nonphotosynthetic CO/sub 2/ fixation on the supply of currently produced photosynthate and nodule nitrogenase activity was examined a various times after phloem-girdling and exposure of nodules to Ar:O/sub 2/. Phloem-girdling was effected 20 hours and exposure to Ar:O/sub 2/ was effected 2 to 3 hours before initiation of experiments. Nodule and root CO/sub 2/ fixation rates of phloem-girdled plants were reduced to 38 and 50%, respectively, of those of control plants. Exposure to Ar:O/sub 2/ decreased nodule CO/sub 2/ fixation rates to 45%, respiration rates to 55%, and nitrogenase activities to 51% of those of the controls. The products of nodule CO/sub 2/ fixation were exported through the xylem to the shoot mainly as amino acids within 30 to 60 minutes after exposure to /sup 14/CO/sub 2/. In contrast to nodules, roots exported very little radioactivity, and most of the /sup 14/C was exported as organic acids. The nonphotosynthetic CO/sub 2/ fixation rate of roots and nodules averaged 26% of the gross respiration rate, i.e. the sum of net respiration and nonphotosynthetic CO/sub 2/ assimilation. Nodules fixed CO/sub 2/ at a rate 5.6 times that of roots, but since nodules comprised a small portion of root system mass, roots accounted for 76% of the nodulated roots system CO/sub 2/ fixation. The results indicate that nodule CO/sub 2/ fixation in alfalfa is associated with N assimilation.
- Research Organization:
- Univ. of Minnesota, St. Paul (USA)
- OSTI ID:
- 6995239
- Journal Information:
- Plant Physiol.; (United States), Vol. 85:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALFALFA
CARBON DIOXIDE FIXATION
ROOTS
ARGON
CARBON 14 COMPOUNDS
ENZYME ACTIVITY
NITROGEN
NITROGENASE
ORGANIC ACIDS
OXYGEN
RESPIRATION
TRACER TECHNIQUES
BACTERIA
ELEMENTS
ENZYMES
FLUIDS
GASES
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
LEGUMINOSAE
MICROORGANISMS
NITRO-GROUP DEHYDROGENASES
NONMETALS
ORGANIC COMPOUNDS
OXIDOREDUCTASES
PLANTS
RARE GASES
RHIZOBIUM
551001* - Physiological Systems- Tracer Techniques