Structure of Pollen Grain — College Notes
1. Definition
A pollen grain is the male gametophyte of seed plants that produces male gametes
(sperm cells). It represents the microspore stage in the plant life cycle and is
responsible for carrying the male reproductive material to the female part during
fertilization.
2. Origin and Function
•Pollen grains are produced inside the anther’s microsporangia (pollen sacs).
•They develop from diploid microspore mother cells (microsporocytes) through
meiosis forming haploid microspores.
•Each microspore develops into a mature pollen grain containing the male
gametophyte.
•Main function: transfer of male gametes to the stigma for fertilization.
3. Structure of Pollen Grain
•Pollen grains are generally spherical or oval in shape, measuring about 25–250
µm in diameter.
•Each pollen grain is a single cell with a well-defined wall, cytoplasm, and nuclei.
•The pollen wall is highly resistant to decay and protects the male gametophyte
during transfer.
4. Layers and Components
•(a) Exine: The outer thick layer made of sporopollenin (a very tough,
decay-resistant substance). It shows various sculpturing patterns and has one or
more thin areas called germ pores through which the pollen tube emerges during
germination.
•(b) Intine: The inner thin, flexible layer composed of pectin and cellulose. It lies
just beneath the exine and forms the pollen tube during germination.
•(c) Cytoplasm: Contains reserve materials such as starch grains, proteins, and
lipids essential for germination.
•(d) Nucleus: In the mature pollen grain, there are usually two nuclei — a
generative nucleus (which divides to form two male gametes) and a vegetative
nucleus (which controls pollen tube growth).
•(e) Germ Pore: A thin area in the exine layer through which the pollen tube
emerges. Monocots often have one pore (monoporate), while dicots may have
three (triporate).
