Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/5/2005
Publication Date: 6/5/2005
Citation: Vance, C.P., Miller, S.S., Liu, J., Gantt, J.S., Samac, D.A. 2005. Carbon and nitrogen metabolism in legume nodules. 2005 Model Legume Congress, June 5-9, 2005, Pacific Grove, California. Paper No. S32, p. 43.
Technical Abstract: Nitrogen-fixing symbiotic root nodules of legumes are model factories for carbon (C) and nitrogen (N) metabolism. Although nodules generally comprise less than 3% of legume total biomass, they can catalyze the reduction of more than 100 kg N per hectare each year. Globally, some 60-90 Tg of N2 are fixed symbiotically each year, an amazing amount considering that only a few kgs of the microbial enzyme nitrogenase are involved in catalysis. Although root nodules comprise only a small proportion of plant weight, they consume 13-28% of legume total photosynthate. This striking use of C is because reduction of N2 to NH4+ requires a substantial energy input. Based upon the average of more than 30 studies, the legume plant expends some 6-7 grams of C per gram N reduced. The biological C cost of symbiotic N2 fixation is substantially higher than the theoretical C cost due to the intrinsic complexity of the symbiotic system including nodule growth and maintenance as well as plant N and C metabolism. It is, therefore, quite apparent that integration of N and C metabolism in root nodules plays a key role in legume plant N and C cycle as well as being critical for growth and development. Many genes involved in N and C metabolism show enhanced expression in nodules as compared to roots. These genes are involved in a multiplicity of processes occurring in infected and uninfected cells. They function in providing N and C for both plant and bacterial metabolism, nodule amino acid biosynthesis, adaptation to the low O2 environment of the nodule, and nodule osmotic adjustment. Modification of selected genes may be useful in enhancing N2 fixation and legume N metabolism.