Pollen grains deliver and release sperm cells to the receptive stigma surface of the flower. It has been proposed that stigma fluid enters a desiccated pollen grain through an aperture in the pollen wall, thereby directing the pollen tube to escape through that same aperture. Surprisingly, during pollen germination in Arabidopsis thaliana, pollen tubes instead break directly through the grain wall at its contact point with the stigma surface, regardless of aperture position. Evidence suggests that the pollen wall is ruptured by a swelling pectin gel beneath a weakened surface. Three predictions can be made based on this finding. First, given that the Arabidopsis pollen tube takes the shortest route outward, it is predicted that stigma liquid takes the shortest route inward, passing directly across the pollen wall, rather than using apertures for access. A search for porous pollen wall will be undertaken using transmission electron and atomic force microscopy and a permeability assay with fluorescent quantum dots (semi-conducting nanoparticles). Second, given that Arabidopsis pollen grains cannot anticipate which side will land against the stigma during pollination, it is predicted that before germination, pectin is evenly distributed around the grain perimeter. This prediction will be tested using antibodies and dyes to visualize pollen pectin distributions. Third, the classic model of pollen germination was based on only a few studies of a few pollens and as such, it is predicted that comparisons across taxa will reveal other pollens that germinate like Arabidopsis. Pollen germination behaviors in a variety of species will be compared using confocal laser scanning and atomic force microscopes. These studies have potential agricultural value, and will further understanding of a common biomechanical challenge faced by organisms across kingdoms: that of breaking out from spore, cyst, embryonic, seed or pollen walls. Collaborations with research universities will strengthen research and teaching infrastructure at Spelman College and expose students from under-represented groups to cutting-edge technology and field work.
