Describe in sequence the events that lead to the development of a 3-celled pollen grain from microspore mother cell in angiosperms.

Pollen grain (male gametophyte) 

(i) The pollen grains represent the first cell of 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 mature pollen grain contains two cells namely, 

(c) Vegetative cell 

(d) Generative cell 

Vegetative cell  : 

It is bigger ceil 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.

1.  The pollen grains are shed at the 2-celled stage in Flowering Plants.

2.  ln other plants, the generative cell divides mitotically to give rise to the two male Sometimes before pollen grains are shed in 3-celled stage. 

3.  Once they are shed, pollen grains have to land on the stigma before they lose viability.

● Each cell of the sporogenous tissue in a microsporangium acts as a potential pollen mother cell (PMC) or microspore mother cell. 

● PMC undergoes meiotic divisions to form cluster of four cells called microspore tetrad. 

● On maturity, the anther dehydrates and the microspores separate from each other to form pollen grains. 

● The newly differentiated pollen grain has a central nucleus and dense cytoplasm. 

● The protoplast mitotically divides into two unequal cells—bigger vegetative cell which is rich in food reserve and smaller spindle-shaped generative cell with dense cytoplasm and a nucleus. This is called 2-celled stage. 

● In majority angiosperms, pollens are released in this 2-celled stage, whereas in other species, the generative cell divides into 2 male gametes and thus pollen is said to be in 3-celled stage.