How does double fertilization occur in flowering plants?

Double fertilization is a unique reproductive process characteristic of angiosperms (flowering plants). It involves two distinct fusion events following the transfer of pollen to the stigma and the subsequent growth of a pollen tube into the ovule.1234

Once the pollen tube reaches the embryo sac, it discharges two sperm cells. The process proceeds as follows:34

• Zygote Formation: One sperm cell fuses with the egg cell to form a diploid zygote, which eventually develops into the embryo.324
• Endosperm Initiation: The second sperm cell fuses with the two polar nuclei (or the fusion nucleus) located in the central cell of the embryo sac. This second fusion typically results in a triploid (3n) primary endosperm nucleus.32

This endosperm serves as a vital nutritive tissue that supports the developing embryo and, in many cases, the seedling after germination. While the ploidy level of the endosperm can vary, the formation of this tissue through double fertilization is a defining feature of flowering plants.524