REVIEW / SYNTHE ` SE Structural and permeability properties of the soybean seed coat Dinah Qutob, Fengshan Ma, Carol A. Peterson, Mark A. Bernards, and Mark Gijzen Abstract: The seed coat is a composite structure that serves as a conduit for nutrient acquisition for the developing em- bryo. Upon seed desiccation and maturation, the seed coat provides cover and protection for the embryo and may impose dormancy or trigger germination by controlling water uptake. For crop plants such as soybean, traits determined by the seed coat impact the overall quality of the seed and the utility of its derived products. There are remarkable examples of unusual genetic mechanisms that control seed coat pigmentation, lustre, and cracking that have been recently described in soybean. Studies on seed permeability to water have resulted in the formulation of new hypotheses to account for variation of this trait. This review summarizes the current advances in our understanding of the structural properties of the soybean seed coat with an emphasis on the control of permeability to water in mature seeds. Key words: cuticle, Glycine max, lustre, pigmentation, permeability, seed coat. Re ´sume ´: Le te ´gument de la graine constitue une structure composite servant de conduite pour l’obtention des nutriments chez l’embryon en de ´veloppement. Avec la dessiccation et la maturation de la graine, le te ´gument fournit couverture et protection a ` l’embryon et peut imposer la dormance ou de ´clencher la germination, en contro ˆlant l’absorption de l’eau. Chez les plantes agricoles comme le soja, les caracte `res de ´termine ´s par le te ´gument affectent l’ensemble des qualite ´s de la graine et l’utilite ´ de ses produits de ´rive ´s. Il existe des exemples remarquables de me ´canismes ge ´ne ´tiques peu communs qui contro ˆlent la pigmentation, le lustre et le craquellement des te ´guments, re ´cemment de ´crits chez le soja. Les e ´tudes sur la perme ´abilite ´ des graines ont conduit a ` la formulation de nouvelles hypothe `ses pour expliquer la variation de ce caracte `re. Cette revue re ´sume les progre `s re ´cents sur la compre ´hension des proprie ´te ´s structurales du te ´gument se ´minal du soja, en mettant l’accent sur le contro ˆle de la perme ´abilite ´a ` l’eau chez les graines matures. Mots-cle ´s : cuticule, Glycine max, lustre, pigmentation, perme ´abilite ´, te ´gument se ´minal. [Traduit par la Re ´daction] Introduction Soybean [Glycine max (L.) Merrill] is the world’s largest oilseed crop. It is a nitrogen-fixing legume that is commonly grown in rotation with cereals. Soybean is most widely used as a source of vegetable oil and protein-rich animal feed, but in addition to these products there are a multitude of spe- cialty food and industrial uses for the crop. There is an emerging trend in breeding programs to identify the factors that affect seed quality traits and to tailor cultivar develop- ment to particular end uses. The seed coat is receiving atten- tion in this regard because of its importance in seed development (Le et al. 2007) and its influence in determin- ing many traits that affect seed quality (Moı ¨se et al. 2005). The largest part of the seed coat develops from the inner and outer integuments of a fertilized ovule. Soybean has bi- tegumic ovules, as do other members of the Fabaceae (Boe- sewinkel and Bouman 1995; Miller et al. 1999; Carlson and Lersten 2004; Moı ¨se et al. 2005; Wang and Grusak 2005). In this family, the outer layers of the endosperm adhere to the inner integument as part of the seed coat. Among these endosperm layers, the outermost layer differentiates into the aleurone while most of the remainder of the endosperm de- generates and disintegrates during maturation (Miller et al. 1999; Ma et al. 2004b). An overview of soybean seed coat development and maturation is illustrated in Fig. 1, and a description of the main cell types and features is provided in Table 1. The functions of the seed coat change dramatically as the seed develops and matures. In the early phases of growth after fertilization, the seed coat contributes most of the seed mass. At this stage the seed coat provides a source and con- duit for nutrients that flow into the seed; the seed coat is a relatively soft, green tissue that is highly active metabol- ically. The rapid expansion of the seed, followed by its des- Received 22 October 2007. Published on the NRC Research Press Web site at botany.nrc.ca on 26 February 2008. D. Qutob and M. Gijzen. 1 Agriculture and Agri-Food Canada, 1391 Sandford Street, London, ON N5V 4T3, Canada. F. Ma and C.A. Peterson. Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada. M.A. Bernards. Department of Biology, University of Western Ontario, London, ON N6A 5B7, Canada. 1 Corresponding author (e-mail: gijzenm@agr.gc.ca). 219 Botany 86: 219–227 (2008) doi:10.1139/B08-002 # 2008 NRC Canada