Abstract

Pollen grains of flowering plants display a fascinating diversity, and this diversity is determined by the developmental mechanisms implicated in the establishment of pollen morphology. Pollen grains are surrounded by a resistant wall interrupted in regions called apertures, which play a key role in reproduction since the pollen tube usually germinates through these regions. Aperture shape, number and position are determined during microsporogenesis (male meiosis). We investigate in detail the unfolding of microsporogenesis in 17 species (belonging to 12 families) producing ulcerate, tetraporate, monosulcate, disulcate, tricolporate, decacolpate, colpate and syncolpate pollen grains. In all species, we observed additional callose deposits at the position of the future apertures. Additional callose deposits are not associated with particular features of microsporogenesis such as the type of cytokinesis, cell wall formation or tetrad shape. The presence of additional callose deposits located at the future apertural regions concerns pollen grains with various aperture shapes (sulcus, pore, colporus or fused sulci) produced by species belonging to all major groups of angiosperms (monocots, eudicots and early diverging angiosperms), suggesting that callose deposits might be a common feature of microsporogenesis, occurring in most angiosperms.