Distinct from the motile flagellated sperm of animals and early land plants, the non-motile sperm cells of flowering plants are carried in the pollen grain to the female pistil. After pollination, a pair of sperm cells are delivered into the embryo sac by pollen tube growth and rupture. Unlike other walled plant cells with an equilibrium between internal turgor pressure and mechanical constraints of the cell walls, sperm cells wrapped inside the cytoplasm of a pollen vegetative cell have only thin and discontinuous cell walls. The sperm cells are uniquely ellipsoid in shape, although it is unclear how they maintain this shape within the pollen tubes and after release. In this study, we found that genetic disruption of three endomembrane-associated cation/H⁺ exchangers specifically causes sperm cells to become spheroidal in hydrated pollens of Arabidopsis. Moreover, the released mutant sperm cells are vulnerable and rupture before double fertilization, leading to failed seed set, which can be partially rescued by depletion of the sperm-expressed vacuolar water channel. These results suggest a critical role of cell-autonomous osmoregulation in adjusting the sperm cell shape for successful double fertilization in flowering plants.

与动物和早期陆生植物的运动有鞭毛的精子不同，开花植物的非运动精子细胞在花粉粒中携带到雌性雌蕊中。授粉后，一对精子细胞通过花粉管的生长和破裂被送入胚囊。与其他在内部膨胀压力和细胞壁机械约束之间平衡的有壁植物细胞不同，包裹在花粉营养细胞的细胞质内的精细胞只有薄而不连续的细胞壁。精子细胞具有独特的椭圆形形状，尽管尚不清楚它们如何在花粉管内和释放后保持这种形状。在这项研究中，我们发现三种内膜相关阳离子/H ^{+的遗传破坏}交换剂特异性地使精子细胞在拟南芥的水合花粉中变成球形。此外，释放的突变精子细胞在双受精前易受伤害并破裂，导致种子设置失败，这可以通过精子表达的液泡水通道的耗尽来部分挽救。这些结果表明细胞自主渗透调节在调节精子细胞形状以在开花植物中成功双受精方面发挥着关键作用。