AOBPreview originally published online on October 20, 2006
Annals of Botany 2006 98(6):1311-1319; doi:10.1093/aob/mcl222
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Embryo Development in the Lady's Slipper Orchid, Paphiopedilum delenatii, with Emphasis on the Ultrastructure of the Suspensor
1 Institute of Plant and Microbial Biology, Academia Sinica 115, Taipei, Taiwan, Republic of China
2 Department of Biological Sciences, University of Calgary Calgary, Alberta T2N 1N4, Canada
3 Department of Horticulture, National Taiwan University No. 1, Sec. 4, Roosevelt Rd, 106, Taipei, Taiwan, Republic of China
*For correspondence. E-mail bomchung{at}gate.sinica.edu.tw
Received: 22 June 2006 Returned for revision: 22 August 2006 Accepted: 31 August 2006 Published electronically: 20 October 2006
• Background and Aims Owing to large-scale collecting, the lady's slipper orchid, Paphiopedilum delenatii, is under threat of extinction. Asymbiotic germination provides a useful way to re-establish plants in the wild and for commercial propagation. A detailed study of embryo development would provide information on subsequent germination events and aid in the propagation of the species.
• Methods Developing capsules were collected for histochemical and ultrastructural studies by using both light and transmission electron microscopy.
• Key Results The suspensor of this species consists of three vacuolated cells. During the early globular stage of embryo development, structural differentiation occurs, revealing an abundance of smooth endoplasmic reticulum cisternae and wall ingrowths within the suspensor cells. These features are not present in cells of the embryo proper. Furthermore, the results of Nile red staining demonstrate that a cuticular layer is present only in the embryo proper, but absent from the suspensor. Cuticular material is also present in the inner walls of the seed coat, and persists through seed maturation.
• Conclusions The morphological features of the transfer cell and the absence of cuticular material in the suspensor cell wall corroborate the hypothesis that the suspensor is the major nutrient uptake site for the developing embryo in the lady's slipper orchid. The absence of an endosperm and presence of cuticular material in the inner walls of the seed coat enclosing the embryo proper further support the notion that nutrient uptake by the embryo is confined to the micropylar end of the seed through the suspensor.
Key words: Cuticular material, embryology, lady's slipper orchid, Paphiopedilum, suspensor