REPRODUCTION in ANGIOSPERMS - POLLEN GRAIN

POLLEN GRAIN (MALE GAMETOPHYTE)

• Haploid (one set of chromosomes)

Structure-

1. Outer wall - EXINE

• Made up of sporopollenin.
• Sporopollenin- one of the most resistant organic material on earth. So it is Nonbiodegradable.
• It can withstand- high temperature, acid, alkali and also resistant to enzymes.
• Because of this sporopollenin, pollen grains form fossils.

Germ pore- 

• An opening/ aperture in Exine.
• Here sporopollenin is absent.
• Function- when the pollen grain germinates, pollen tube comes out from this germ pore.

2. Inner wall - INTINE

• Thin layer.
• Continuous layer.
• Made up of cellulose and pectin.

2 cells- 

1. Vegetative cell-

• Large
• Dense cytoplasm- abundant food reserve
• Function- provides nutrition to generative cell.

2. Generative cell-

• Small
• Spindle shaped
• Floats in the cytoplasm of vegetative cell
• Function- It later gives rise to male gamete.

Note-

• In 80% of angiosperms- pollen grains are released in 2 celled stage
• But, in rest of the angiosperms- generative cell divides by mitosis and give rise 2 male gametes. And thus released in 3 celled stage.

Facts about pollen grains-

1.Pollen grains are like dust. They can cause allergies and respiratory problems and bronchial diseases eg. Asthma, chronic obstructive pulmonary disease, bronchitis etc.

Eg. Parthenium grass- this produces huge amount of pollen dust.

2. Pollen grains are rich in nutrients. So they are used as food supplements as tablets and syrups.

They are known to increase the performance of athletes and horses.

Viability

• We do not know how much time it will take a pollen grain to reach to the stigma of a appropriate flower.
• This time period, from its release till the pollen grain remain alive is called viability.
• Viability of different plants are variable.
• Example- 1. Rice, wheat pollen grains viability= approx. 30 minutes.  
• 2. Some members of family, rosaceae, solanaceae, leguminoceae, pollen grain viability= for months

Pollen banks-

• Just like seed banks.
• Pollen grains are stored at very low temperature, -196℃ (in liquid nitrogen) 
• At this temperature in pollen banks, pollen can be stored for years.
• And after this period of storage they can be used to pollinate the flower.