Pollen Grain Structure and Properties

Study Notes

Pollen grains are spherical, measuring 25-50 micrometers in diameter.
The pollen grain wall has two layers: exine and intine.
The exine is the hard outer layer, composed of sporopollenin, a highly resistant organic material.
Sporopollenin can withstand high temperatures, strong acids, and alkali, and is resistant to enzymatic degradation.
The exine has prominent apertures called germ pores, where sporopollenin is absent.
The hard exine helps protect the pollen grain from environmental factors and ensures its preservation as fossils.
The exine exhibits a wide range of patterns and designs.

The intine is the thin, continuous inner layer of the pollen grain wall, composed of cellulose and pectin.
The cytoplasm of the pollen grain is surrounded by a plasma membrane.
The pollen grain contains two cells: the vegetative cell and the generative cell.

The vegetative cell is larger, with abundant food reserves and a large, irregularly shaped nucleus.
The generative cell is smaller, spindle-shaped, with dense cytoplasm and a nucleus, and floats in the cytoplasm of the vegetative cell.

In over 60% of angiosperms, pollen grains are shed at the 2-celled stage.
In the remaining species, the generative cell divides mitotically to form two male gametes before pollen grains are shed (3-celled stage).

Pollen grains of many species can cause severe allergies and bronchial afflictions in some people, leading to chronic respiratory disorders such as asthma and bronchitis.
Parthenium or carrot grass, a contaminant introduced with imported wheat, has become widespread in India and causes pollen allergy.