Submitted to: Nitrogen Fixation International Congress
Publication Type: Abstract only
Publication Acceptance Date: 7/10/1997
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Plant carbon metabolism for N2 fixation in legume nodules has evolved a number of exquisite adaptations to function in an O2 limited environment. Foremost among these is the synthesis of copious amounts of malic acid, which is synthesized from the coordinated expression of three key enzymes: sucrose synthase (SS); phosphoenolpyruvate carboxylase (PEPC); and malate dehydrogenase (MDH). Although the cellular expression patterns for these proteins and mRNAs are not well defined, recent data suggest that uninfected cells play a significant role in carbon and energy metabolism. We have isolated and characterized alfalfa root nodule cDNAs encoding nodule enhanced forms of each of these enzymes. Moreover, cellular distribution patterns of mRNAs for these genes have been mapped in nodules through in situ hybridization. A promoter element capable of forming H DNA may be critical for regulating expression of PEPC in the infected cell zone. Lastly, of the five distinct MDH cDNAs isolated from nodules, one unique form has highly enhanced expression in effective nodules and has extremely high efficiency for malate formation. Funding source: USDA/NRI 94-37305-0575 and NSF/IBN 9206890.