Submitted to: Annals Of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2002
Publication Date: 11/21/2002
Citation: SERRAJ, R., SINCLAIR, T.R. EVIDENCE THAT CARBON DIOXIDE ENRICHMENT ALLEVIATES UREIDE-INDUCED DECLINE OF NODULE NITROGENASE ACTIVITY. ANNALS OF BOTANY. 2002. v. 91. p. 85-89. Interpretive Summary: Soybean is a critical crop because it is a major source of protein. Nitrogen, which is a major and essential component of protein, is obtained to a large extent by soybean through symbiotic fixation of atmospheric nitrogen. However, nitrogen fixation seems to be very tightly regulated in the soybean plant so that at times fixation rates are lower than required for high protein seed production. This research, which involved an ARS-USDA scientist, Gainesville, FL, was undertaken to develop additional information on the regulation of soybean nitrogen fixation by focusing on ureides that are the nitrogen products of nitrogen fixation. The experiment showed that nitrogen fixation was inhibited when ureides accumulated in the plant. However, under a treatment in which the breakdown of ureides in the leaves was accelerated, ureides did not accumulate and the nitrogen fixation was still decreased. These results indicate that a product of ureide breakdown may be the compound that directly regulates nitrogen fixation rates in soybean. Future research to identify the regulatory compound may allow manipulation of soybean to obtain the desired high rates of sustained nitrogen fixation.
Technical Abstract: The hypothesis that elevated [CO2] alleviates the inhibition of N2 fixation by ureides was tested by comparing the short-term responses of acetylene reduction assay (ARA), ureide accumulation and total nonstructural carbohydrate (TNC) levels to the application of ureide to the nutrient solution of hydroponically grown soybean. The plants were subjected to treatments of ambient [CO2] or 700 mmol CO2 mol-1. Application of 5 and 10 mM ureide to the nutrient solution inhibited N2 fixation activity under both ambient and elevated [CO2]. However, the percent inhibition with ureide treatment was significantly greater under ambient [CO2] as compared to elevated [CO2]. ARA under ambient [CO2] was less than under elevated [CO2] 1 d after ureide treatment. Under ambient [CO2], the application of ureide resulted in a significant accumulation of ureide in all plant tissues with the highest concentration increases in the leaves. However, application of exogenous ureide did not result in increased ureide concentration in any tissues of plants subjected to elevated [CO2]. The results of this study indicated that product(s) of ureide catabolism were critical in the regulation of N2 fixation rather than tissue ureide concentration itself.