RIG/CAA: Unique Mechanisms of Pollen Tube Germination in Arabidopsis Thaliana

花粉粒将精子细胞传递和释放到花的可接受柱头表面。有人提出，柱头液体通过花粉壁上的一个孔进入干燥的花粉粒，从而引导花粉管通过该孔逃逸。令人惊讶的是，在拟南芥的花粉萌发过程中，无论气孔的位置如何，花粉管都会在与柱头表面接触的点处直接穿过籽粒壁。有证据表明，花粉壁是被弱化的表面下膨胀的果胶凝胶破裂的。基于这一发现，我们可以做出三个预测。首先，鉴于拟南芥花粉管向外的路径最短，据预测，柱头液体向内走的路径最短，直接穿过花粉壁，而不是使用孔道进入。将使用透射电子显微镜和原子力显微镜以及带有荧光量子点(半导体纳米颗粒)的渗透性分析来搜索多孔花粉壁。其次，由于拟南芥的花粉粒无法预测在授粉过程中哪一面会落在柱头上，因此据预测，在萌发之前，果胶均匀地分布在籽粒周围。这一预测将用抗体和染料来验证，以可视化花粉果胶的分布。第三，花粉萌发的经典模型仅基于对少数几种花粉的少数研究，因此，据预测，跨分类群的比较将揭示其他像拟南芥一样萌发的花粉。利用激光共聚焦扫描和原子力显微镜对不同物种的花粉萌发行为进行比较。这些研究具有潜在的农业价值，并将进一步了解生物体在各个领域面临的共同生物力学挑战：从孢子、孢囊、胚胎、种子或花粉壁中破壁而出。与研究型大学的合作将加强斯佩尔曼学院的研究和教学基础设施，并让来自代表性不足群体的学生接触尖端技术和实地工作。

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.