Why do you think that endosperm formation does not occur until fertilization takes place?
Endosperm formation does occur prior to fertilization in some angiosperms, a phenomenon called autonomous endosperm development. However, in most cases, endosperm formation is triggered by fertilization. Here are a few reasons why endosperm formation is often linked to fertilization:
Double Fertilization: In angiosperms, the process of fertilization involves two fertilizations. One sperm cell fuses with the egg cell to form the zygote, which develops into the embryo. The other sperm cell fuses with two polar nuclei in the central cell of the embryo sac, resulting in a triploid cell known as the endosperm mother cell or primary endosperm cell (PEC).
Activation of Endosperm Development: The fusion of the sperm cell with the polar nuclei triggers the activation of endosperm development. The PEC undergoes mitotic divisions to produce multiple free nuclei or a cellular endosperm, depending on the plant species.
Nutritive Function of Endosperm: Endosperm primarily serves as a nutrient-rich tissue that nourishes the developing embryo. It stores reserve materials such as starch, proteins, and lipids that are essential for embryo growth before and during seed germination. The endosperm also provides protection for the embryo within the seed.
Regulation by Plant Hormones: Fertilization leads to hormonal changes within the embryo sac and surrounding tissues. These hormonal signals, including auxin, cytokinin, and gibberellin, play a crucial role in regulating endosperm development. Fertilization-induced hormonal changes stimulate the division and differentiation of endosperm cells, ensuring the proper development of the endosperm.
Synchronization of Embryo and Endosperm Development: Linking endosperm formation to fertilization ensures the coordinated development of the embryo and endosperm. The growth and maturation of the embryo and endosperm are closely synchronized to meet the nutritional requirements of the developing embryo and prepare the seed for dispersal and germination.
By coupling endosperm formation with fertilization, angiosperms ensure the availability of nutrients for embryo development, synchronize the growth of both tissues, and protect the embryo within the seed.