Pollen grains are male gametophyte - spherical in shape.
Microspore or pollen grain is haploid, uninucleate, minute spores produced in large numbers as a result of meiosis in microspre mother cells inside the microsporangia. The pollen grains represent the male gametophytes. Pollen grains are generally spherical measuring about 25-50 micrometers in diameter. It has two layered wall exine and intine.
Exine - It is outer layer and composed of sporopollenin which is one of the most resistant organic material. It can withstand high temperatures and strong acids and alkali. At one or more places, the exine is very thin or absent. These regions are called germ pores.
Intine - It is inner layer and composed of pectin and cellulose.
- apertures on exine where sporopollenin is absent
- forms pollen tube.
A plasma membrane surrounds cytoplasm of pollen grain.
The cytoplasm of pollen grain is surrounded by a plasma membrane. Mature pollen grain has two cells, the vegetative cell and generative cell. The vegetative cell is bigger, has abundant food reserve and a large irregularly shaped nucleus. The generative cell is small and floats in the cytoplasm of the vegetative cell. It is spindle shaped with dense cytoplasm and a nucleus.
Other Points :-
Pollen grains of many species cause many allergies and bronchial afflictions in some people.
Pollen grains are rich in nutrients. So pollen tablets are used as food supplements.
— A mature pollen consist of 2 cells with nucleus (Vegetative and Generative)
Abundant food reserve
Large irregular nucleus
Responsible for the development of pollen grain
Involves in syngamy (fuse with an egg)
Dense cytoplasm and nucleus.
Effect of Pollen on Human:
Pollen grains cause allergy and bronchial afflictions
Leading to chronic respiratory disorders like asthma, bronchitis Eg :- Parthenium (carrot grass)
Rich in nutrient.
Pollen tablets and syrup
- food supplements
- claims to increase performance of athletes and race horse.
Period of viability
Once shed the pollen grains have to land on the stigma before they lose viability if they have to bring about fertilization.
Period of viability depends on temperature and humidity. Example:- cereals takes 20 minutes and members of rosaceae, leguminoseae, solanaceae take months.
Pollen grains stored by CRYOPRESERVATION.
Used in crop breeding programmes.