The Regulation of Sperm Cells Delivery to the Embryo Sac

Pollination, or the first contact between male and female gametophytes, is one of the most important steps in plant reproduction. After pollination, the pollen grains, male gametophytes, are hydrated and then germinate pollen tubes. The pollen tube initially penetrates and grows through the intercellular spaces of the stigma and then grows through the transmitting tract to the placenta connected to an ovule. The pollen tube grows along the surface of the ovule’s funiculus, through the micropyle, and into the female gametophyte. After the pollen tube enters the female gametophyte, it ruptures and releases two sperm cells with its contents. The two sperm cells then move toward and fuse with the egg cell and central cell to produce embryo and endosperm, respectively. Multiple sperm cells typically strive to “win the race” and fertilize an egg cell during animal fertilization; however, in flowering plants, each ovule harboring an egg cell generally encounters only one of many pollen tubes conveying plant sperm cells. This chapter mainly addresses reproductive strategies of plants following pollination from the pollen tube extension and the guidance of two sperm cells to the female gametophyte for fertilization in the ovule.