Polysporangiate anthers in Microlicia D.Don (Melastomataceae Juss.)

Abstract

Polysporangiate anthers are found in a small number of Microlicia species, a genus of Melastomataceae with a large number of endemic species in Brazil. This study describes for the first time the processes of formation and degeneration of the septa found in these particular anthers of Microlicia, providing relevant information about the structure and the functional role of septate anthers in the genus, which is an uncommon condition in angiosperms. The formation of septa begins when some initial cells enlarge and differentiate into sporogenous tissue, while other, more peripheral cells, are not affected by this increase and form the parenchymatous septum. The septa are present up until microgametogenesis, degenerating after the formation of the pollen grains. The mechanism of pollen release in stages, as suggested previously by some authors, could not be demonstrated for the studied species since the septa degenerated at flower anthesis. Thus, we propose that the transverse septa present during the formation of the sporogenous tissue and microspores are associated with providing better nutritional conditions for pollen development.