Double Fertilization in Angiosperms

Double fertilization is a unique reproductive process that occurs in angiosperms, also known as flowering plants. It involves the fusion of two sperm cells with two different types of female gametophytic cells, resulting in the formation of both the zygote and endosperm. This process plays a crucial role in the successful sexual reproduction of angiosperms.

The Process of Double Fertilization:

1. Pollen Grain Development:
- Double fertilization begins with the development of a pollen grain in the anthers of the flower.
- Each pollen grain contains two sperm cells enclosed within a protective pollen tube.

2. Pollen Tube Formation:
- When a pollen grain reaches the stigma of a flower, it germinates and forms a pollen tube.
- The pollen tube grows down through the style and reaches the ovary, where the ovules are present.

3. Female Gametophyte Development:
- Within the ovule, the female gametophyte develops from a megaspore.
- The female gametophyte, also known as the embryo sac, contains seven cells and eight nuclei.

4. Pollination and Fertilization:
- The pollen tube enters the ovule through the micropyle, a small opening in the ovule's outer layer.
- One sperm cell travels down the pollen tube to reach the embryo sac.

5. Syngamy:
- The sperm cell fuses with the egg cell, resulting in the formation of a diploid zygote.
- This fertilization event is similar to the fertilization process in other plants.

6. Triple Fusion:
- The second sperm cell fuses with two polar nuclei within the embryo sac.
- This fusion event is known as triple fusion and results in the formation of a triploid (3n) endosperm nucleus.

7. Endosperm Development:
- The triploid endosperm nucleus divides repeatedly to form the endosperm.
- The endosperm serves as a nutrient-rich tissue that nourishes the developing embryo.

Significance of Double Fertilization:

- Double fertilization ensures the production of both a zygote and endosperm in angiosperms.
- The zygote develops into the embryo, while the endosperm provides nourishment to support embryo growth.
- This unique reproductive strategy contributes to the success of angiosperms by providing a nutrient-rich environment for embryonic development.
- The endosperm also plays a vital role in seed germination and early seedling growth.
- Double fertilization is one of the distinguishing features of angiosperms and has contributed to their evolutionary success and dominance in terrestrial ecosystems.