Octad pollen formation in Cymbopetalum (Annonaceae): the binding mechanism

Publication Type:Journal Article
Year of Publication:2007
Authors:C. H. Tsou, Fu Y. L.
Journal:Plant Systematics and EvolutionPlant Systematics and Evolution
Volume:263
Pagination:13-23
Date Published:Jan
ISBN Number:0378-2697
Accession Number:ISI:000243660600003
Keywords:angiosperms, Annona, Annonaceae, ASIMINA-TRILOBA ANNONACEAE, CALLOSE DISSOLUTION, callosic envelope, compound pollen, Cymbopetalum, DEVELOPMENTAL, EVENTS, EVOLUTION, GENERA, microspore rotation, octad pollen, SPORODERM DEVELOPMENT, TAPETUM, TETRADS
Abstract:

Our recent study of tetrad pollen formation in Annona (Annonaceae) revealed that after meiosis the callose-cellulose envelope forms a special conjugation with individual microspores and the forthcoming callose digestion is incomplete. The undigested part forms a central binder holding the four microspores of the tetrad together. This process causes the microspores to rotate 180 degrees. In this paper we describe pollen formation in another annonaceous genus, Cymbopetalum, in which the pollen is shed in octads, through use of light microscopy, epifluorescence microscopy, and TEM. In Cymbopetalum, two meiocytes, connected by abundant cytomictic channels, are produced in each sporangium. Octad pollen formation in Cymbopetalum is shown to be comparable to the synchronized formation of two connected Annona tetrads, which then integrate into a single octad. Unique features of Annona polyad formation, e.g. special binding between the callose-cellulose envelopes and microspores, incomplete callose digestion, and microspore rotation, also occur in Cymbopetalum. In addition, formation of the Cymbopetalum octad involves development of a cushion-like structure that binds the distal pronexine of all eight microspores, and there is the production of intine protrusions. The evolutionary origin of the callose-cellulose binding mechanism within the family is discussed.

Short Title:Pl. Syst Evol.
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith