AOBPreview originally published online on February 9, 2005
Annals of Botany 2005 95(5):737-747; doi:10.1093/aob/mci080
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Published by Oxford University Press 2005
Structure and Development of Medicago truncatula Pod Wall and Seed Coat
1 Department of Biology, University of Arkansas-Little Rock, Little Rock, AR, USA and 2 USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX, USA
* For correspondence. E-mail hxwang{at}ualr.edu
Received: 1 September 2004 Returned for revision: 1 November 2004 Accepted: 3 December 2004 Published electronically: 9 February 2005
• Background and Aims Medicago truncatula has gained much attention as a genomic model species for legume biology, but little is known about the morphology of its pods and seeds. Structural and developmental characteristics of M. truncatula pod walls and seed coats are presented.
• Methods Plants of M. truncatula ecotype A17 were grown under controlled conditions in a greenhouse. Flowers were date-tagged at anthesis, so that pods of known age could be collected. Harvested pods were fixed and sectioned for light microscopy. Structural attributes of pod walls and seed coats were characterized at four time points throughout early to mid-stages of pod development (3, 6, 13 and 20 d post-pollination).
• Key Results Basic features of the pod wall are an exocarp comprised of a single epidermal layer, a mesocarp with seven to 14 layers of parenchyma cells, and an endocarp composed of an inner epidermal cell layer and three to five layers of sclerenchyma cells adjacent to it. Vascular bundles are abundant in the pod wall and include one lateral carpellary bundle, one median carpellary bundle and nine to 12 vascular bundles, all embedded within the mesocarp parenchyma. Seed coat features include an epidermal layer of macrosclereids, a sub-epidermal layer of osteosclereids, and two to five rows of internal parenchyma cells. The hilar region contains the tracheid bar and the chalazal vascular bundle, the latter of which expands to form only two short branches.
• Conclusions This characterization provides a needed understanding of pod structure and development in this model legume, and should facilitate various molecular investigations into legume fruit and seed biology.
Key words: Development, structure, morphology, microscopy, pod, pod wall, seed, seed coat, Fabaceae, Medicago truncatula, legumes
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