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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #61983
Title: EVALUATION OF FEEDBACK AS THE MECHANISM OF NO3- INHIBITION OF N2ASE IN SOYBEAN

Author
item BACANAMWO, METHODE - UNIV OF ILLINOIS, URBANA
item Harper, James

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/29/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Despite extensive research, the mechanism of nitrogenase regulation in symbioses is not sufficiently understood to permit a targeted engineering of symbioses that achieves a high dinitrogen fixation rate under high levels of soil N. Involvement of carbohydrates has been particularly controversial. This study was conducted to evaluate the hypothesis that besides carbohydrate involvement, nitrate inhibition of nitrogenase may involve a feedback mechanism, i.e., the extent of nitrogenase inhibition by nitrate may be related to N levels in plant tissues. Plants were grown in growth chambers using a hydroponic system with limited combined N in the growth medium to promote nodulation. A wide range of C:N ratios in various plant tissues (9.6 to 39.8, 1.9 to 3.4, and 1.1 to 1.8, respectively, in shoots, roots, and nodules) was generated through a combination of light and CO2 levels, using two soybean genotypes differing in carbon and N acquisition rates. For both genotypes, a significant positive correlation (p<0.05) was observed between nitrogenase inhibition by nitrate (24 h after nitrate treatment) and N concentration in shoots prior to the initiation of nitrate treatment. Furthermore, nitrogenase inhibition by nitrate was significantly negatively correlated (p<0.05) to total nonstructural carbohydrates (TNC) and C:N ratio in shoot tissues for both genotypes. At the onset of nitrogenase inhibition by nitrate (24 h after nitrate treatment), TNC decreased in shoots but tended to increase in roots and nodules. N levels increased in shoots and roots but not in nodules following nitrate treatment. These results indicate that both C and N levels in shoot tissues are involved in regulation of nitrogenase activity.