title: Pollen-wall formation in Arum alpinum.
abstract: OBJECTIVE
  Arum alpinum has a quite uncommon pollen wall. A sporopolleninous ektexine is missing. The outermost pollen wall layer is formed by the endexine which is covered by polysaccharidic ornamentation elements. An ontogenetical investigation was accomplished to clarify pollen-wall development, with special reference to callose and pollen-wall development.
  
  
  METHODS
  Plants of Arum alpinum grown in their natural habitat were collected once a week within the vegetative period and processed for semi- and ultra-thin sectioning.
  
  
  RESULTS
  At any stage of pollen-wall formation callose is missing. Microspores are released from the tetrad by invagination of the amoeboid tapetum. The polysaccharidic wall ornamentations are formed by the tapetum.
  
  
  CONCLUSIONS
  There appears to be no truth in the dogma that callose is essential for microspore separation and release from the tetrad. The lack of callose does not influence fertility but could be the reason for the uncommon pollen wall, where a sporopolleninous ektexine is missing.
authors.affiliation: Department of Palynology and Structural Botany, Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria.
authors.forename: Elisabeth M
authors.initials: EM
authors.lastname: Anger
authors.forename: Martina
authors.initials: M
authors.lastname: Weber
mesh_terms: D031058:Arum / Q000033:anatomy & histology / Q000254:growth & development / Q000648:ultrastructure*; D002462:Cell Membrane / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000648:ultrastructure; D035264:Flowers / Q000166:cytology / Q000254:growth & development / Q000648:ultrastructure; D005936:Glucans / Q000502:physiology; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D011058:Pollen / Q000254:growth & development / Q000648:ultrastructure*; D011134:Polysaccharides / Q000502:physiology
chemical_list: D005936:Glucans; D011134:Polysaccharides; C048306:callose