Question

Describe the development of the female gametophyte in angiosperms.

Answer 1

1. Origin: The female gametophyte develops from a single hypodermal cell in the nucellus of the ovule called the archesporial cell, which functions as or gives rise to the megaspore mother cell (MMC).
2. Megasporogenesis: The MMC undergoes meiosis, producing four haploid megaspores. Of these, three degenerate, and only one functional megaspore remains.
3. Megagametogenesis: The functional megaspore enlarges and undergoes mitotic divisions without cytokinesis, resulting in an eight-nucleate, coenocytic embryo sac.
4. Nuclear arrangement: The eight nuclei arrange in a specific pattern,three at the micropylar end (forming the egg apparatus: one egg cell and two synergids), three at the chalazal end (forming antipodal cells), and two nuclei migrate to the center to become polar nuclei.
5. Cell formation: Cellular walls form around the nuclei to produce a mature embryo sac with seven cells and eight nuclei,three antipodals, two synergids, one egg cell, and a central cell containing the two polar nuclei (which may later fuse).
6. Type: The monosporic 8-nucleate embryo sac, also known as the Polygonum type, is the most common type of female gametophyte. It can be found in about 81% of flowering plants.
7. Location and permanence: The female gametophyte remains embedded within the megasporangium (nucellus) throughout its development.