Question

Explain the development of male gametophyte in angiosperms (diagram is not expected).

Explain the development of male gametophyte in an angiosperm.

Answer 1

Before pollination in the pollen sac:

1. Pollen grain/microspore marks the beginning of the male gametophyte, thus it is the first cell of the male gametophyte.
2. It undergoes the first mitotic division to produce a bigger, naked vegetative cell and a small, thin-walled generative cell.
3. The vegetative cell is rich in food and having an irregularly shaped nucleus.
4. The generative cell floats in the cytoplasm of the vegetative cell.
5. The second mitotic division is concerned with generative cells only and gives rise to two non-motile male gametes.
6. The mitotic division of generative cells takes place either in the pollen grain or in the pollen tube.
7. The pollen grains are shed from the anther, at this two-celled stage in most of the angiosperms.

After pollination on the stigma:

1. After pollination, the two-celled pollen grain gets deposited on the stigma and absorbs the sugary stigmatic secretion.
2. Due to this, the volume of the cytoplasm increases, thus creating pressure on the intine.
3. The intine comes out in the form of a tube-like structure called a pollen tube through the germ pore.
4. The tube nucleus, cytoplasm, and generative cell, all migrate into the pollen tube.
5. The pollen tube grows through the style towards the ovule due to some chemical stimulus inside the ovary.
6. The generative cell of the pollen grain divides by mitosis and forms two haploid non-motile gametes.
7. The pollen tube consisting of two male gametes and a degenerating sterile vegetative nucleus represents the male gametophyte.