A Study on the Octad Pollen Development in Disepalum plagioneurum (Annonaceae)

Octad pollen can be an important taxonomic character. Knowledge about the development of octad pollen, though, is very limited, and few reports have some contradictions. Disepalum is known for having octad pollen, but until now there is no report on its octad pollen development. In present study, the octad pollen development of D. plagioneurum (Diels) D.M. Johnson was observed. The results show the anthers of D. plagioneurum are septate, having 10-15 sporangial chambers, each containing one sporogenous cell, which then develops into a pair of connected pollen mother cells partitioned by a cell plate. The paired pollen mother cells undergo meiosis synchronously, generating two tetragonal tetrads that remain connected to each other but partitioned by a cell plate, thus forming a single octad in each sporangial chamber Each tetrad of the octad is coated by pollen mother cell wall, which is digested quickly, but incompletely. The incomplete digestion makes each microspore rotate 180 degrees, which pulls the distal side towards the center of the tetrad to reestablish as the proximal side, while the former proximal side becomes the distal side. At maturity, the pollen octad is about 200 mu m long and 100 mu m wide. The tapetum and septa among the anther locules are almost wholly digested, leaving only tapetal residue or a space among the octads. Our study confirms the rotation of microspores in octad pollen development and finds the main process of octad pollen development has no significant difference between D. plagioneurum and Cymbopetalum baillonii. (C) 2019 Friends Science Publishers