AOBPreview originally published online on November 21, 2002
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Annals of Botany 91: 85-89, 2003
© 2003 Annals of Botany Company
Evidence that Carbon Dioxide Enrichment Alleviates Ureide-induced Decline of Nodule Nitrogenase Activity
1 USDA-ARS, c/o University of Florida, Agronomy Physiology and Genetics Laboratory, PO Box 110965, Gainesville, FL 32611-0965, USA
* For correspondence. Fax 001 352 392 6139, e-mail trsincl{at}mail.ifas.ufl.edu 
Present address: ICRISAT, Patancheru 502324, Andhra Pradesh, India.
Received: 15 July 2002; Returned for revision: 11 September 2002; Accepted: 17 October 2002 Published electronically: 21 November 2002
The hypothesis that elevated [CO2] alleviates ureide inhibition of N2-fixation was tested. Short-term responses of the acetylene reduction assay (ARA), ureide accumulation and total non-structural carbohydrate (TNC) levels were measured following addition of ureide to the nutrient solution of hydroponically grown soybean. The plants were exposed to ambient (360 µmol mol–1) or elevated (700 µmol mol–1) [CO2]. Addition of 5 and 10 mM ureide to the nutrient solution inhibited N2-fixation activity under both ambient and elevated [CO2] conditions. However, the percentage inhibition following ureide treatment was significantly greater under ambient [CO2] as compared with that under elevated [CO2]. Under ambient [CO2] conditions, ARA was less than that 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 to plants subjected to elevated [CO2] did not result in increased ureide concentration in any tissues. TNC concentrations were consistently higher under elevated [CO2] compared with those under ambient [CO2]. For both [CO2] treatments, the application of ureide induced a significant decrease of TNC concentrations in the leaves and nodules. For both leaves and nodules, a negative correlation was observed between TNC and ureide levels. Results indicate that product(s) of ureide catabolism rather than tissue ureide concentration itself are critical in the regulation of N2-fixation.
Key words: Carbon dioxide, Glycine max, nitrogen fixation, nodules, soybean, ureides.
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