title: Acquisition of physical dormancy and ontogeny of the micropyle--water-gap complex in developing seeds of Geranium carolinianum (Geraniaceae).
abstract: OBJECTIVE
  The 'hinged valve gap' has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum.
  
  
  METHODS
  Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy.
  
  
  RESULTS
  Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slow-drying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity.
  
  
  CONCLUSIONS
  Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a 'micropyle--water-gap complex'.
authors.affiliation: Department of Biology, University of Kentucky, Lexington, KY 40546, USA. nalinsuranjith@uky.edu
authors.forename: N S
authors.initials: NS
authors.lastname: Gama-Arachchige
authors.forename: J M
authors.initials: JM
authors.lastname: Baskin
authors.forename: R L
authors.initials: RL
authors.lastname: Geneve
authors.forename: C C
authors.initials: CC
authors.lastname: Baskin
mesh_terms: D001692:Biological Transport / Q000502:physiology*; D002463:Cell Membrane Permeability / Q000502:physiology; D003890:Desiccation; D031315:Geranium / Q000166:cytology / Q000196:embryology / Q000254:growth & development / Q000502:physiology*; D018525:Germination / Q000502:physiology*; D056771:Ovule / Q000502:physiology; D057445:Plant Dormancy / Q000502:physiology*; D012639:Seeds / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D013997:Time Factors; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water