Question

What is meant by monosporic development of female gametophyte?

Answer 1

Hint: The female gametophyte is also called the megagametophyte or the embryo sac. Whereas the male gametophyte is also called the microgametophyte or the pollen grain.

Complete Answer:
The female gametophyte’s formation from one single functional megaspore is known as Monosporic development.
- The functional megaspore’s nucleus divides mitotically and forms two nuclei - which move to the opposite poles. Thus, forming a two-nucleate embryo sac.
- Two more mitotic nuclear divisions occur, and form the four-nucleate and eight-nucleate stages of the embryo sac.
- These are free nuclear type mitotic divisions, in which karyokinesis is not immediately followed by cytokinesis.
- After the eight-nucleate stage, the walls are laid down, thus organising the typical female gametophyte. Six out of the eight nuclei are surrounded by cell walls and are organized into cells; the remaining two nuclei, called the polar nuclei are situated below the egg apparatus.
- A typical angiosperm embryo sac at maturity is eight nucleate and seven cells. The mature embryo sac contains 3 synergid cells at the micropylar end, 3 antipodal cells at the chalazal end, an egg cell at the center, and a 2 polar nuclei, which fuse together to form the secondary nucleus.

Additional information:
- In most of the flowering plants, a single megaspore mother cell is present at the micropylar end of the ovule’s nuclear region. It undergoes meiosis to form four haploid megaspores.
- Later, out of these four megaspores, only one functional megaspore develops into the female gametophyte, while the remaining three degenerate.

Note: The female gametophytes form the female gametes and produce the physical and molecular basis for beginning of the seed development and fertilisation.