JXB Advance Access originally published online on November 29, 2005
Journal of Experimental Botany 2006 57(1):5-12; doi:10.1093/jxb/erj013
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REVIEW ARTICLE |
Update on ureide degradation in legumes
1Department of Biochemistry and Interdisciplinary Plant Group, 117 Schweitzer Hall, University of Missouri, Columbia, MO 65211, USA
2Department of Biochemistry, 117 Schweitzer Hall, University of Missouri, Columbia, MO 65211, USA
3Division of Plant Sciences and Interdisciplinary Plant Group, 1–31 Agriculture Building, University of Missouri, Columbia, MO 65211, USA
4Departamento de Biología Vegetal, Universidad de Córdoba, Rabanales Campus, Edificio Severo Ochoa, 1a Planta, E-14071 Córdoba, Spain
To whom correspondence should be addressed. E-mail: polaccoj{at}missouri.edu
Warm season N2-fixing legumes move fixed N from the nodules to the aerial portions of the plant primarily in the form of ureides, allantoin and allantoate, oxidation products of purines synthesized de novo in the nodule. Ureides are also products of purine turnover in senescing tissues, such as seedling cotyledons. A combination of biochemical and molecular approaches in both crop and model species has shed new light on the metabolic pathways involved in both the synthesis and degradation of allantoin. Improved understanding of ureide biochemistry includes two ‘additional’ enzymatic steps in the conversion of uric acid to allantoin in the nodule and the mechanism of allantoin and allantoate breakdown in leaf tissue. Ureide accumulation and metabolism in leaves have also been implicated in the feedback inhibition of N2-fixation under water limitation. Sensitivity to water deficit differs among soybean cultivars. Manganese supplementation has been shown to modify relative susceptibility or tolerance to this process in a cultivar-dependent manner. A discussion of the potential roles for ureides and manganese in the feedback inhibition of N2-fixation under water limitation is presented. The existing data are examined in relation to potential changes in both aerial carbon and nitrogen supply under water deficit.
Key words: Allantoate, allantoin, 5-hydroxyisourate, manganese, nitrogen fixation, urate, urea, ureide, water deficit
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