title: Microspore development in Annona (Annonaceae): differences between monad and tetrad pollen.
abstract: •
  
  
  OBJECTIVE
  Permanent tetrads are the most common form of pollen aggregation in flowering plants. The production of pollen in monads is plesiomorphic in angiosperms, but the aggregation into tetrads has arisen independently different times during the evolution of flowering plants. The causes behind the recurrent evolution of pollen aggregation from monads remain elusive. Permanent tetrad pollen is quite common in the Annonaceae, the largest family in the early-divergent order Magnoliales. In some genera, such as Annona, both tetrad- and monad-producing species can be found.•
  
  
  METHODS
  In this comparative study of pollen development, we use immunolocalization, cytological characterization, and enzymatic assays of four species in the genus Annona and one species in its closely related genus Asimina that release pollen in tetrads and two species in the genus Annona that release pollen in monads.•
  
  
  RESULTS
  The main difference between species with tetrad and monad pollen is a delayed digestion of callose and cellulose at the pollen aperture sites that resulted in nonlayering of the exine in these areas, followed by a rotation and binding of the young microspores at the aperture sites.•
  
  
  CONCLUSIONS
  Small changes in development resulted in clear morphological changes on pollen dispersal time and open a window on the possible selective advantage of the production of aggregated pollen.
authors.affiliation: Department of Pomology, Estación Experimental 'Aula Dei', CSIC, Apdo. 13034 50080 Zaragoza, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Lora
authors.affiliation: Department of Pomology, Estación Experimental 'Aula Dei', CSIC, Apdo. 13034 50080 Zaragoza, Spain.
authors.forename: Maria
authors.initials: M
authors.lastname: Herrero
authors.affiliation: Department of Subtropical Fruits, Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora" (IHSM-UMA-CSIC) 29750 Algarrobo-Costa, Málaga, Spain.
authors.forename: Jose I
authors.initials: JI
authors.lastname: Hormaza
mesh_terms: D031041:Annona / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D005075:Biological Evolution; D002473:Cell Wall; D005936:Glucans / Q000378:metabolism; D011058:Pollen / Q000254:growth & development* / Q000378:metabolism; D012098:Reproduction
chemical_list: D005936:Glucans; C048306:callose
keywords: Annona; Annonaceae; aperture; callose; monad; pollen development; tetrad