title: Dynamic distribution and the role of abscisic acid during seed development of a lady's slipper orchid, Cypripedium formosanum.
abstract: OBJECTIVE
  Although abscisic acid (ABA) is commonly recognized as a primary cause of seed dormancy, there is a lack of information on the role of ABA during orchid seed development. In order to address this issue, the localization and quantification of ABA were determined in developing seeds of Cypripedium formosanum.
  
  
  METHODS
  The endogenous ABA profile of seeds was measured by enzyme-linked immunosorbent assay (ELISA). Temporal and spatial distributions of ABA in developing seeds were visualized by immunohistochemical staining with monoclonal ABA antibodies. Fluoridone was applied to test the causal relationship between ABA content and seed germinability.
  
  
  RESULTS
  ABA content was low at the proembryo stage, then increased rapidly from 120 to 150 days after pollination (DAP), accompanied by a progressive decrease in water content and seed germination. Immunofluorescence signals indicated an increase in fluorescence over time from the proembryo stage to seed maturation. From immunogold labelling, gold particles could be seen within the cytoplasm of embryo-proper cells during the early stages of seed development. As seeds approached maturity, increased localization of gold particles was observed in the periplasmic space, the plasmalemma between embryo-proper cells, the surface wall of the embryo proper, and the inner walls of inner seed-coat cells. At maturity, gold particles were found mainly in the apoplast, such as the surface wall of the embryo proper, and the shrivelled inner and outer seed coats. Injection of fluoridone into capsules resulted in enhanced germination of mature seeds.
  
  
  CONCLUSIONS
  The results indicate that ABA is the key inhibitor of germination in C. formosanum. The distinct accumulation pattern of ABA suggests that it is synthesized in the cytosol of embryo cells during the early stages of seed development, and then exported to the apoplastic region of the cells for subsequent regulatory processes as seeds approach maturity.
authors.affiliation: Biology Department, National Museum of Natural Science, No 1, Kuan-Chien Rd, 40453 Taichung, Taiwan, Department of Life Sciences, National Chung Hsing University, Taichung 40227, Taiwan, leeyungi@hotmail.com leeyungi@mail.nmns.edu.tw.
authors.forename: Yung-I
authors.initials: YI
authors.lastname: Lee
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, 115, Taipei, Taiwan.
authors.forename: Mei-Chu
authors.initials: MC
authors.lastname: Chung
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada and.
authors.forename: Edward C
authors.initials: EC
authors.lastname: Yeung
authors.affiliation: Department of Horticulture and Landscape Architecture, National Taiwan University, No 1, Sec. 4, Roosevelt Rd, 106, Taipei, Taiwan.
authors.forename: Nean
authors.initials: N
authors.lastname: Lee
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D029595:Orchidaceae / Q000254:growth & development* / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism*; D012639:Seeds / Q000254:growth & development / Q000378:metabolism
chemical_list: D010937:Plant Growth Regulators; D000040:Abscisic Acid
keywords: Abscisic acid; Cypripedium formosanum; Orchidaceae; developing seed; embryo; fluoridone; immunolocalization; lady’s slipper orchid; seed germination