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Pollen Insights into Apomictic and Sexual Miconia (Miconieae, Melastomataceae)

The genus Miconia, Melastomataceae, has been highlighted for its high proportion of apomictic species, in which the occurrence of low pollen grain viability is commonly recorded. In this study, we compared aspects of pollen development and viability and ploidy level in a sexual species, Miconia pepericarpa, and an apomictic species, Miconia fallax, and investigated the possible causes of pollen grain sterility in apomictic species. Abnormal meiosis was observed only in apomictic M. fallax and leads to the formation of inviable pollen grains, often with little or no cytoplasmic content. Furthermore, the apomictic species is polyploid, and therefore, chromosomal imbalance would be expected. Symmetric mitotic division was found only in M. fallax, also resulting in inviable pollen grains, usually with cytoplasm content but without generative cell differentiation. At the end of development, the apomictic species also displays another difference when compared with the sexual species: the generative cell does not become fusiform but, rather, maintains a spherical shape. It is unknown whether the generative cell shape may interfere with its function.