![]() The pollen tube invades one of the synergids whereupon it ruptures, ejecting sperm and rendering them available for fertilization 3, 11. It is a thickened cell wall region crisscrossed by an abundance of cell membrane protrusions from the synergids 9, 10, the pair of cells flanking the egg ( Fig. The filiform apparatus is located at the entrance of the female gametophyte. Guided by female cues 7, 8, the pollen tube enters the ovule via the micropyle. Pollen tube growth in the pistil is highly regulated and fertilization is achieved only after a series of interactive events between the penetrating pollen tube and specific pistil tissues 4, 5, 6 and cells 7, 8. The egg cell and a pair of synergid cells are located at one end of the female gametophyte, close to the ovular aperture called micropyle. They are borne inside the pollen tube, the male gametophyte, and rely on its polarized growth inside the female organ, pistil, for transportation and delivery to the female gametophyte located inside an ovule for fertilization ( Fig. Unlike fertilization in animal where flagellated sperm swim to fuse with the oocyte, sperm cells in flowering plants are immotile. Our results provide evidence for a RHO GTPase-based signalling mechanism to mediate sperm release for fertilization in plants. Pollen tube growth assays in vitro and in the pistil demonstrate that hydroxyl free radicals are likely the most reactive oxygen molecules, and they induce pollen tube rupture in a Ca 2+-dependent process involving Ca 2+ channel activation. We show that FER controls the production of high levels of reactive oxygen species at the entrance to the female gametophyte to induce pollen tube rupture and sperm release. Here we utilize the Arabidopsis FERONIA (FER) receptor kinase mutants, whose female gametophytes fail to induce pollen tube rupture, to decipher the molecular mechanism of this critical male–female interactive step. The female gametophyte induces rupture of the penetrating pollen tube, resulting in sperm release and rendering them available for fertilization. In flowering plants, sperm are transported inside pollen tubes to the female gametophyte for fertilization. ![]()
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June 2023
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