(i) When the anther develops, each cells of sporogenous tissue undergo melutic divisions to form microspore tetrads.
(ii) Each one is a microspore mother cell (MMC).
(iii) The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis.
(iv) The microspores get arranged in a cluster of four cells and hence are microspore tetrad. (y) As the anthers mature and dehydrate, the microspores dissociate from each ether and develop into pollen grains.
(v) From each microsporangium, thousands of pollen grains are formed and released with the dehiscence of anther.
Pollen grain (male gametuphyte)
(i) The pollen grains represent the male gametophytes.
(ii) A pollen grain has a two-layered wall namely,
(a) Exine
(b) Intine
Exine:
It is the hard outer layer which is made up of sporopollenin.
Intine:
(i) It is the inner, thin and continuous layer which is made up of cellulose and pectin.
(ii) A matured pollen grain contains two cells namely,
(a) Vegetative cell
(b) Generative cell
Vegetative cell:
It is bigger cell having abundant food reserve and a large irregularly shaped nucleus.
Generative cell:
(i) It is small cell that floats in the cytoplasm of the vegetative cell.
(ii) It is spindle shaped with dense cytoplasm and a nucleus.
- This pollen grains are shed at the 2-celled stage in flowering plants.
- In other plants, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed in 3-celled stage.
- Once they are shed, pollen grains have to land on the stigma before they lose viability.
