Structure of Pollen Grain and Micropore

Introduction to Pollen Grain

• Pollen grain is also called an immature male gametophyte.
• Questions can be asked in its name (like mature megasporangium, embryo sac).

Layers of Pollen Grain

Outer Layer (Exine)

• The outer layer is called exine.
• Importance:
  • This is very important as it is made up of 2 main compounds:
    • Cutin
    • Sporopollenin
  • Sporopollenin is a very strong and non-degradable material.
  • No natural or chemical material can degrade it.
• Question:
  • Often asked what the outer layer is made of.
  • In 2016, a question was asked which compound degrades sporopollenin? Answer: None.

Inner Layer (Intine)

• The inner layer is called intine.
• Characteristics:
  • It is thin, soft, and elastic.
  • It is made up of pectocellulose (a mixture of pectin and cellulose).

Germ Pores

• Germ pores are the places where exine is absent.
• Importance:
  • The pollen tube is formed from germ pores.

Characteristics of Pollen

Function of Pollenkitt

• Pollenkitt collects many pollen grains.
• It aids in pollination by insects.
• The surface of the pollen is sticky and protects from UV rays.

Different Characteristics of Pollen Grain

• Largest pollen grain is found in Mirabilis.
• Smallest pollen grain is found in Myosotis.
• Longest Pollen: Found in Zostera.
• Dumbbell Shape Pollen: Found in Vinca, Herbacea.

Process of Dehiscence

• The endothecium is hygroscopic.
• It absorbs water.
• When it releases water, it bursts, and the pollen grains are released.

Types of Dehiscence

1. Longitudinal Dehiscence
2. Valvular Dehiscence
3. The role of stomium is important.

Conclusion

• Understanding the structure of pollen grains gives us knowledge of its functioning and role.
• Complex structure and strong outer layer are its significant features.