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ARS Home » Research » Publications at this Location » Publication #105784
Title: IN SITU UREIDE DEGRADATION IN SOYBEAN LEAVES.

Author
item VADEZ, V. - UNIVERSITY OF FLORIDA
item Sinclair, Thomas

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: An important advantage of soybean in cropping systems is its ability to symbiotically fix atmospheric nitrogen. Unfortunately, nitrogen fixation is very sensitive to the development of water deficits in the soil such that under most commercial conditions there is a loss in yield. Research done by ARS-USDA scientists at Gainesville, FL led to the development of a new technique to readily measure traits in the plant that might ameliorate the sensitivity to water deficit. Basically, products of nitrogen fixation in soybean, i.e. ureides, accumulate in leaves upon water deficit, and those varieties that do not accumulate these products are likely to be tolerant of water deficits. This new technique based on individual leaves allows the rate of degradation of these products in the leaves to be readily measured to assist in the development of improved soybean varieties.

Technical Abstract: Ureides dramatically accumulate in shoots of nitrogen fixing soybean (Glycine max Merr.) under water deficit and this accumulation is higher in cultivars that are sensitive to water deficit. One possible explanation is that ureide accumulation is associated with a feedback inhibition of nitrogenase activity. Shoot ureide accumulation may be explained by differences in the ureide degradation capacity of tolerant and susceptible cultivars, or by an impaired ureide degradation under water deficit. Therefore, a method was developed to measure the rate of ureide degradation in leaves that allows screening of genotypes with high ureide degradation rate, or to test the effects of environmental factors that influence the response of plants to water deficit. The method developed here consisted in harvesting the second or third fully expanded leaf of soybean and feeding the leaves a 5 to 7.5 mM allantoic acid solution in test tubes under an artificial light for a 13-h period. After feeding, 1.6-cm diameter leaf discs were incubated and harvested at regular intervals within a 5-8-h period. Remnant ureide in the leaf discs was measured as a measure of the ureide degradation activity.