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), Journal Name: Plant Physiol.; (United States) Vol. 85:1; ISSN PLPHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ALFALFA
ARGON
BACTERIA
CARBON 14 COMPOUNDS
CARBON DIOXIDE FIXATION
ELEMENTS
ENZYME ACTIVITY
ENZYMES
FLUIDS
GASES
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
LEGUMINOSAE
MICROORGANISMS
NITRO-GROUP DEHYDROGENASES
NITROGEN
NITROGENASE
NONMETALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDOREDUCTASES
OXYGEN
PLANTS
RARE GASES
RESPIRATION
RHIZOBIUM
ROOTS
TRACER TECHNIQUES