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ARS Home » Research » Publications at this Location » Publication #107946
Title: ASPARAGINE AND UREIDE ACCUMULATION IN NODULES AND SHOOTS AS FEEDBACK INHIBITORS OF N2 FIXATION IN SOYBEAN.

Author
item VADEZ, V. - UNIVERSITY OF FLORIDA
item Sinclair, Thomas
item SERRAJ, R. - MARRAKECH, MOROCCO

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: A major advantage in growing legumes, including soybeans, is that these plants support the biological fixation of atmospheric nitrogen for use by the plants and hence do not require the application of manufactured nitrogen fertilizer. The process of biological nitrogen fixation, however, has been shown to be highly sensitive to a number of environmental factors. This study was undertaken in cooperation with a USDA-ARS scientist at Gainesville, FL to understand the biochemical regulation of nitrogen fixation so that options for decreasing its sensitivity to the environment can be developed. This research showed that increased levels of both the amino acid asparagine and ureides in the plant result in decreased nitrogen fixation rates. It appears that mechanisms that minimize the feedback inhibition on nitrogen fixation by either or both of these compounds would result in plants that are tolerant of their environment and can accumulate greater amounts of fixed nitrogen.

Technical Abstract: Asparagine (Asn) and ureide accumulation in shoots and nodules were investigated as potential signal compounds in inhibiting N2 fixation in soybean. The levels of these two compounds were measures in response to treatments inhibiting nodule activity (acetylene reduction assay, ARA) including applications of Asn, ureide, or polyethylene glycol to the plant nutrient solution, boric acid on leaves, and imposition of a water deficit. ARA inhibition and the concentration of Asn and ureide were correlated to the level of ureide treatment. Applying Asn also induced an increase in nodule Asn and ureide concentration. Spraying boric acid on leaves also inhibited ARA in parallel to an increase in shoot ureide and nodule Asn concentration while nodule ureide remained unchanged. By contrast, polyethylene glycol (PEG) inhibited ARA in parallel to an increase in nodule Asn and ureide concentration while shoot ureide was unchanged. All treatments except PEG largely increased shoot ureide. The decline in ARA upon water deficit was simultaneous to an increase in nodule Asn and ureide. It appears both ureide and Asn are signal compounds inhibiting nitrogen fixation in soybean.