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Q.Give an account of the development of male gametophyte in angiosperms.

Odisha ChseOdisha CHSE +2 Science Board Exam 2023Subjective· 7mImportance★★★★★
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Microsporogenesis (meiosis in microspore mother cells) produces haploid microspores that develop into pollen grains; each pollen grain's single-celled stage divides mitotically into a vegetative cell and a generative cell, and the generative cell later divides to give two male gametes - completing the male gametophyte.

1. Microsporogenesis: Each anther has four microsporangia (pollen sacs), each containing diploid microspore mother cells (pollen mother cells, PMCs). Each PMC undergoes meiosis to produce a group of four haploid microspores, arranged as a microspore tetrad.

2. Release of microspores: As the anther matures and dehydrates, the microspores of a tetrad separate from one another and develop into individual pollen grains.

3. Pollen wall: The pollen grain develops a two-layered wall - a hard, resistant outer layer called the exine, made of sporopollenin (one of the most resistant organic materials known, capable of withstanding high temperatures, strong acids/alkalis, and enzymatic degradation, and bearing characteristic germ pores), and a thin inner wall called the intine, made of cellulose and pectin.

4. First mitotic division (formation of the 2-celled pollen grain): The haploid nucleus of a young pollen grain divides mitotically (an unequal division) to produce two unequal cells:

  • A large vegetative cell (tube cell), with abundant food reserves and an irregularly shaped nucleus - this cell later gives rise to the pollen tube.
  • A small generative cell, spindle-shaped/spherical with dense cytoplasm, which floats in the cytoplasm of the vegetative cell.

At this stage, the pollen grain is released from the anther as a 2-celled pollen grain in most angiosperms (about 60% of species).

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