How does the pollen grain develop?

How Pollen Grains are Formed

Where are pollen grains formed?

In flowering plants, pollen grains are formed with the anther. If you look at the diagram to the right, you will see that the anther is a part of the stamen. Essentially, the anther is where the pollen grains are produced! 

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The Formation of a Pollen Grain

STEP 1: CHAMBER DEVELOPMENT

As the anther begins to develop, four patches of tissue grow and become four chambers or “pollen sacs.” These chambers are where the pollen grains will eventually develop. 

Visualization(Photo Credit: Kylie Bucalo)

The image to the right is of a young Lily anther. Within the image you will see two large chambers or “pollen sacs” on the left and a large chamber that is fusing to become one during step 2. At this point, however, there are a total of four “pollen sacs.”

Within each of the chambers you will see white dots. These dots represent cells or “pollen-grains-in-training.” At this stage, the cells are known as microsporocytes

STEP 2: CELL DIVISION

During this stage, the pollen sacs and the cells within them undergo some major changes. Through cell division, the microsporocytes change to form clusters or groups of four called quartets within each of the four different chambers. 

Visualization(Photo Credit: Kylie Bucalo)

As the anther matures, the “pollen sac” walls between adjacent pairs breakdown, creating two chambers instead of four. You can see this process happening on the right side of the picture above to the left. 

The microspores within the chambers(white dots) within the chambers are almost ready to become pollen grains but first they must undergo 3 more changes which occur almost simultaneously! 

STEP 3: THREE FINAL CHANGES

The 3 final steps are as follows:

1. Members of the quartet(groups of 4 microsporocytes/cells) separate from one another.

2. Each microspore then undergoes nucleus division. The two nucleus that are developed are the generative nucleus and the vegetative nucleus which are involved in how the pollen grain achieves fertilization. 

3. A two layered wall develops around each microspore

When these events are completed, the microspores have become pollen grains! See the picture to the right for a close up of the final product!

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DEFINITIONS

TERM DEFINITION
Anther The circular part of the stamen found atop the filament known for pollen production
Generative Nucleus The nucleus that falls behind the vegetative nucleus and will eventually aid in sperm production
Microspore  A tiny plant spore that will eventually become a pollen grain
Microsporocytes A cell that goes through meiosis in order to become a full-blown microspore
Vegetative Nucleus The nucleus that stays at the tip of the pollen and helps the tube grow