Evidence that carbon dioxide enrichment alleviates ureide-induced decline of nodule nitrogenase activity uri icon


  • 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 nonstructural carbohydrate (TNC) levels were measured following addition of ureide to the nutrient solution of hydroponically grown soyabean. The plants were exposed to ambient (360 ┬Ámol mol-1) or elevated (700 ┬Ámol 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 day 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

publication date

  • 2003