Physiologia Plantarum 135: 19–28. 2009 Copyright ª Physiologia Plantarum 2008, ISSN 0031-9317 Ureide metabolism during seedling development in French bean (Phaseolus vulgaris) Francisco Antonio Quiles, Marı´a Jose ´ Raso, Manuel Pineda and Pedro Piedras* Departamento de Bota ´nica, Ecologı´a y Fisiologı´a Vegetal, Grupo de Fisiologı´a Molecular y Biotecnologı´a de Plantas, Campus Rabanales, Edif. Severo Ochoa, 1 a Planta, Universidad de Co ´ rdoba, 14071-Co ´ rdoba, Spain Correspondence *Corresponding author, e-mail: bb2pimop@uco.es Received 18 July 2008; revised 28 August 2008 doi: 10.1111/j.1399-3054.2008.01173.x French bean (Phaseolus vulgaris) is a legume that transports most of the atmospheric nitrogen fixed in its nodules to the aerial parts of the plant as ureides. Changes in ureide content and in enzymatic activities involved in their metabolism were identified in the cotyledons and embryonic axes during germination and early seedling development. Accumulation of ureides (ca. 1300 nmol per pair of cotyledons) was observed in the cotyledons of dry seeds. Throughout germination, the total amount of ureides slightly decreased to about 1200 nmol, but increased both in cotyledons and in embryonic axes after radicle emergence. In the axes, the ureides were almost equally distributed in roots, hypocotyls and epicotyls. The pattern of ureide distribution was not affected by the presence of nitrate or sucrose in the media up to 6 days after imbibition. Ureides are synthesized from purines because allopurinol (a xan- thine dehydrogenase inhibitor) blocks the increase of ureides. Allantoin and allantoate-degrading activities were detected in French bean dried seeds, whereas no ureidoglycolate-degrading activity was detected. During germi- nation, the levels of the three activities remain unchanged in cotyledons. After radicle emergence, the levels of activities in cotyledons changed. Allantoin- degrading activity increased, allantoate-degrading activity decreased and ureidoglycolate-degrading activity remained undetectable in cotyledons. In developing embryonic axes, the three activities were detected throughout germination and early seedling development. The embryonic axes are able to synthesize ureides, because those compounds accumulated in axes without cotyledons. Introduction Seed germination and postgerminative growth are crucial to the life cycle of higher plants. During these stages, seedlings are heterotrophic in the sense that they completely depend on seed reserves. At the end of this period the seedling must achieve photoautotrophism before its nutrient reserves become exhausted. This process can be divided into three phases: imbibition, increased metabolic activity, and initiation of growth. Morphologically, growth initiation corresponds to radicle emergence; subsequent growth is generally termed as seedling growth. By definition, germination sensu stricto begins with water uptake by the quiescent dry seed and terminates with radicle protrusion (Bewley 1997). Many seed proteins are mobilized and metabolized during germination and seedling growth (Shutov et al. 2003). Protein mobilization starts much earlier in the embryonic axis than in the cotyledons, where mobiliza- tion only begins after axes protein reserves are depleted (Tiedemann et al. 2000). As a consequence, there is Abbreviations – AP, allopurinol; DAI, days after imbibition; FW, fresh weight; PPD, phenylphosphorodiamidate. Physiol. Plant. 135, 2009 19 Physiologia Plantarum An International Journal for Plant Biology