Journal of Experimental Botany, Vol. 51, No. 349, pp. 1459-1465,
August 2000
© 2000 Oxford University Press
Ureide degradation pathways in intact soybean leaves1
USDA-ARS, Agronomy Department, Agronomy Physiology Laboratory, IFAS Building 350, University of Florida, PO Box 110965, Gainesville, FL 32611–0965, USA
Ureides dramatically accumulate in shoots of N2-fixing soybean (Glycine max L. Merr.) under water deficit and this accumulation is higher in cultivars that have N2 fixation that is sensitive to water deficit. One possible explanation is that ureide accumulation is associated with a feedback inhibition of nitrogenase activity. A critical factor involved in ureide accumulation is likely to be the rate of ureide degradation in the leaves. There exists, however, a controversy concerning the pathway of allantoic acid degradation in soybean. Allantoate amidinohydrolase was reported to be the pathway of degradation in studies using the cultivar Maple Arrow and allantoate amidohydrolase was the pathway that existed in the cultivar Williams. This investigation was undertaken to resolve the existence of these two pathways. An in situ technique was developed to examine the response of ureide degradation in leaf tissue to various treatments. In addition, the response of ureide accumulation and N2 fixation activity was measured for intact plants in response to treatments that differentially influenced the two degradation pathways. The results from these studies confirmed that Maple Arrow and Williams degraded allantoic acid by different pathways as originally reported. The existence of two degradation pathways within the soybean germplasm opens the possibility of modifying ureide degradation to minimize the influence of soil water deficits on N2 fixation activity.
Key words: Ureide degradation, allantoate amidohydrolase, boric acid, water deficit.
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