ORBICULES IN RELATION TO THE POLLINATION MODES pp. 289-304
Authors: (B.G. Galati, M.M. Gotelli, S. Rosenfeldt, J.P. Torretta, G. Zarlavsky, Cátedra de Botánica, Facultad de Agronomía. Universidad de Buenos Aires, Argentina, and others)
Abstract: Orbicules or Ubisch bodies are corpuscles of sporopollenin that appear in the anther locule during pollen grain development. Their size ranges from 0.14 μm to 20 μm. They present different shapes with a smooth or ornamented surface. Orbicules often form aggregates and sometimes have a plaque-like appearance. Ultrastructurally, they may present a central core with different degree of transparency to electrons. Those that do not have a central core are observed completely solid. Orbicules are resistant to acetolisis, autofluorescent when irradiated with ultraviolet light and have the same reaction to colorants that the exine of pollen grains. Their presence is generally associated with a tapetal membrane in species with secretor type tapetum and with a peritapetal membrane in species with intermediate or plasmodial type tapetum. Although the shed of orbicules out of the anther along with the pollen grains is cited, they are usually attached to the inner surface of the locule when the anther opens. Investigations suggest that orbicules appear in approximately 80 families of Angiosperms and Gimnosperms. It is not certain whether orbicules are not developed in the rests of the families or are just not informed. Researches on ontogeny and ultrastructure of orbicules are rare. However, their tapetal origin and their simultaneous formation with the pollen grain wall are well established. The systematic value of orbicules is known and considered in a few families, such as Loganiaceae, Gentianaceae, Apocynaceae, Rubiaceae and Oxalidaceae. Evolutionary studies on these bodies or on its relationship with the different modes of pollination are lacking. Even though orbicules are so common among angiosperms, their function is unknown and only speculations are made. On this report a review on orbicules is made and an analysis of their presence, ontogeny and morphology is presented. Our aim is to supply information that will help understand orbicules function. Therefore, the orbicules morphology in relation with the pollination mode is studied.