title: Evidence that carbon dioxide enrichment alleviates ureide-induced decline of nodule nitrogenase activity.
abstract: The hypothesis that elevated [CO(2)] alleviates ureide inhibition of N(2)-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 micromol mol(-1)) or elevated (700 micromol mol(-1)) [CO(2)]. Addition of 5 and 10 mM ureide to the nutrient solution inhibited N(2)-fixation activity under both ambient and elevated [CO(2)] conditions. However, the percentage inhibition following ureide treatment was significantly greater under ambient [CO(2)] as compared with that under elevated [CO(2)]. Under ambient [CO(2)] conditions, ARA was less than that under elevated [CO(2)] 1 d after ureide treatment. Under ambient [CO(2)], 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 [CO(2)] did not result in increased ureide concentration in any tissues. TNC concentrations were consistently higher under elevated [CO(2)] compared with those under ambient [CO(2)]. For both [CO(2)] 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 N(2)-fixation.
authors.affiliation: USDA-ARS, c/o University of Florida, Agronomy Physiology and Genetics Laboratory, PO Box 110965, Gainesville, FL 32611-0965, USA.
authors.forename: Rachid
authors.initials: R
authors.lastname: Serraj
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Sinclair
mesh_terms: D000114:Acetylene / Q000378:metabolism; D020369:Bradyrhizobium / Q000502:physiology; D002245:Carbon Dioxide / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D013025:Glycine max / Q000201:enzymology / Q000378:metabolism*; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D002245:Carbon Dioxide; D014508:Urea; D009591:Nitrogenase; D000114:Acetylene