Important points
- The study of pollen is called palynology.
- Typical shape – spherical
- Size – 25–50 μm (in diameter)
- The pollen grain represents the male gametophyte, i.e. it carries the male gametes to the female reproductive parts in gymnosperms and angiosperms.
Structure of pollen
Pollen wall
Pollen has a prominent two-layered wall, i.e. exine and intine.
Exine
- Outermost protective layer of the pollen.
- Hard and thick layer.
- Discontinuous layer, as the exine has prominent apertures called germ pores.
- The exine exhibits a fascinating array of patterns and designs.
- Made up of sporopollenin (the most resistant organic material known).
Sporopollenin can withstand high temperatures and strong acids and alkalis, and no known enzyme can degrade it. This is why pollen grains are well preserved as fossils. Germ pores are the places where sporopollenin is absent.
Intine
- Thin and elastic layer.
- Continuous layer.
- Made up of cellulose and pectin.
Cells
A mature pollen grain consists of two cells, i.e. the vegetative cell and the generative cell.
Vegetative cell
- Large in size.
- Nucleus is large and irregularly shaped.
- Contains abundant food reserves.
- Function – helps in the development of the pollen tube.
Generative cell
- Small in size.
- Floats in the cytoplasm of the vegetative cell.
- Spindle-shaped.
- Contains dense cytoplasm.
- Function – divides by mitosis to form two non-motile male gametes.
In over 60% of angiosperms, pollen grains are shed at the 2-celled stage. In the rest, the generative cell divides before shedding, so the pollen is shed at the 3-celled stage.
Advantages of pollen
To plants
- Carries male gametes to the female sex organ for fertilisation.
- Enabled the higher plants (gymnosperms and angiosperms) to grow in a wide range of terrestrial habitats, as pollen eliminated the dependence on water for fertilisation.
To humans
- Pollen grains are rich in nutrients and are used as food supplements.
- Pollen consumption is claimed to increase the performance of athletes and race horses.
- Pollen can be preserved using liquid nitrogen for future use (cryopreservation).
Disadvantages of pollen
- Pollen grains are small in size, so they can be inhaled during breathing.
- The pollen of many species causes severe allergies and bronchial afflictions in some people.
Parthenium (carrot grass), which came into India as a contaminant with imported wheat, is NCERT’s example of a plant whose pollen causes allergy. Pollen is stored in pollen banks at −196 °C in liquid nitrogen.