title: Unique stigmatic hairs and pollen-tube growth within the stigmatic cell wall in the early-divergent angiosperm family Hydatellaceae.
abstract: OBJECTIVE
  The ultrastructure of the pollen tubes and the unusual multicellular stigmatic hairs of Trithuria, the sole genus of Hydatellaceae, are described in the context of comparative studies of stigmatic and transmitting tissue in other early-divergent angiosperms.
  
  
  METHODS
  Scanning and transmission electron microscopy and immunocytochemistry are used to study the structure and composition of both mature and immature stigmatic hair cells and pollen-tube growth in Trithuria.
  
  
  RESULTS
  Trithuria possesses a dry-type stigma. Pollen tubes grow within the cell walls of the long multicellular stigmatic hairs. Immunocytochemistry results suggest that arabinogalactan proteins are involved in attracting the pollen tubes through the stigmatic cuticle. Most tubes grow along the hair axis towards its base, but some grow towards the hair apex, suggesting that pollen tubes are guided by both physical constraints such as microfibril orientation and the presence of binding factors such as unesterified pectins and adhesive proteins.
  
  
  CONCLUSIONS
  The presence of a dry-type stigma in Trithuria supports the hypothesis that this condition is ancestral in angiosperms. Each multicellular stigmatic hair of Hydatellaceae is morphologically homologous with a stigmatic papilla of other angiosperms, but functions as an independent stigma and style. This unusual combination of factors makes Hydatellaceae a useful model for comparative studies of pollen-tube growth in early angiosperms.
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK.
authors.forename: Christina J
authors.initials: CJ
authors.lastname: Prychid
authors.forename: Dmitry D
authors.initials: DD
authors.lastname: Sokoloff
authors.forename: Margarita V
authors.initials: MV
authors.lastname: Remizowa
authors.forename: Renee E
authors.initials: RE
authors.lastname: Tuckett
authors.forename: Shrirang R
authors.initials: SR
authors.lastname: Yadav
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Rudall
mesh_terms: D002473:Cell Wall / Q000378:metabolism* / Q000648:ultrastructure; D018525:Germination / Q000502:physiology; D007150:Immunohistochemistry; D008954:Models, Biological; D030702:Nymphaeaceae / Q000166:cytology* / Q000254:growth & development* / Q000648:ultrastructure; D053205:Pollen Tube / Q000166:cytology / Q000254:growth & development* / Q000648:ultrastructure; D012098:Reproduction / Q000502:physiology