Explain the Development of Male Gametophyte

Development of Male Gametophyte:

The process of development of male gametophyte from microspores or pollen grain is called micro-gametogenesis. Most of the development of male gametophytes is completed inside the microsporangium or pollen sac and a part of development occurs on the stigma after pollination.

Microspore or the pollen grain is the first cell of the male gametophyte. It contains only one haploid nucleus. The cell undergoes unequal division and forms a small generative cell and a large vegetative or tube cell. The pollen grains are generally discharged from the anther at this two-celled stage. In some plants, the generative cell divides further to give rise to two male gametes before their discharge. Further development occurs on the stigma after pollination.

The pollen grain absorbs water and nutrients from the stigmatic secretion through its germ pore. The tube cell enlarges and comes out the pollen grain through the germ pore to form a pollen tube. The pollen tube secretes some hydrolytic enzymes to create a passage through the style. The tube nucleus descends to the tip of the pollen tube. The generative cell divides into two nonmotile male gametes if it is not already divided. Each male gamete is lenticular to spherical in outline. The tube nucleus may degenerate completely. A pollen grain with a pollen tube carrying male gametes represents a mature male gametophyte. It is a 3-celled structure bearing one tube cell and two male gametes.

Characteristics of Development of Male Gametophyte:

1. A diploid microsporocyte present inside each microsporangium divides by meiosis to produce four haploid microspores.

2. Microspores undergo mitosis to produce a male gametophyte with only two cells, a generative cell, and a tube cell.

3. A pollen grain is composed of the generative cell and the tube cell surrounded by the spore wall.

4. Male Gametophyte maturation occurs within each pollen grain when its generative cell divides to form two sperm cells which usually occurs after pollen lands on a stigma, followed by the growth of the pollen tube.

5. A pollen tube which is a long cellular protuberance capable of rapid growth, delivers sperm to the female gametophyte.