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After entering one of the synergids, the pollen tube releases two male gametes into the cytoplasm of the synergid. One of the male gametes moves towards the egg cell and fuses with its nucleus, completing syngamy and forming a diploid zygote. Simultaneously, the other male gamete moves towards the two polar nuclei in the central cell and fuses with them, resulting in the formation of a triploid primary endosperm nucleus (PEN). This fusion involving three haploid nuclei is referred to as triple fusion. Endosperm development occurs before embryo development. This sequence is observed because the primary endosperm cell undergoes repeated divisions, giving rise to a triploid endosperm tissue. The cells of this tissue accumulate reserve food materials. In the most common type of endosperm development, the primary endosperm nucleus undergoes successive nuclear divisions, resulting in the formation of free nuclei. This stage of endosperm development is known as free-nuclear endosperm.

Endosperm is a food laden tissue and develops from :

Primary endosperm nucleus

The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN). The central cell, after undergoing triple fusion, becomes the primary endosperm cell (PEC) and develops into the endosperm.

After triple fusion, the fusion of one male gamete with the two polar nuclei results in the formation of the triploid PEN. The PEN represents the primary nucleus of the endosperm. The central cell, which contained the two polar nuclei prior to fertilization, now becomes the PEC.

The primary endosperm cell (PEC) undergoes subsequent divisions to form the endosperm. These divisions can occur either through free-nuclear divisions or cellular divisions, depending on the plant species. In free-nuclear endosperm development, the PEC undergoes multiple rounds of nuclear divisions without cytokinesis, resulting in the formation of a multinucleate syncytium or coenocyte. This means that the endosperm consists of multiple nuclei enclosed within a single cytoplasmic compartment.

In cellular endosperm development, the PEC undergoes cellular divisions, forming distinct cells within the endosperm tissue. These cells may contain one or multiple nuclei, depending on the species. Throughout endosperm development, the endosperm cells accumulate reserve food materials such as starch, proteins, oils, and other nutrients. The endosperm serves as a nutrient source for the developing embryo, providing essential resources for its growth and development.

In summary, the central cell, after triple fusion with the male gamete, becomes the primary endosperm cell (PEC). The PEC then undergoes subsequent divisions to form the endosperm, a tissue rich in nutrients that supports the growth and development of the embryo.