Pollen Grain Structure and Properties

Pollen Grain Structure

• 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.

Intine and Cytoplasm

• 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.

Cells of the Pollen Grain

• 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.

Pollen Grain Maturation

• 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).

Allergenic Effects of Pollen Grains

• 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.