What is the Difference Between Germinated and Ungerminated Pollen Grain

The main difference between germinated and ungerminated pollen grain is that the germinated pollen grain contains a developed pollen tube whereas the ungerminated pollen grain does not contain a pollen tube. Furthermore, germination of pollen grains occurs on the stigma of a flower while ungerminated pollen grain is the dispersal structure of the male gametophyte of seed plants.

Germinated and ungerminated pollen grains are two stages of the development of pollen grains. Generally, pollen grains are the fine granules which contain a reduced male gametophyte.

Key Areas Covered

1. What is the Germinated Pollen Grain
     – Definition, Structure, Role
2. What is the Ungerminated Pollen Grain
     – Definition, Structure, Role
3. What are the Similarities Between Germinated and Ungerminated Pollen Grain
     – Outline of Common Features
4. What is the Difference Between Germinated and Ungerminated Pollen Grain
     – Comparison of Key Differences

Key Terms

Germinated Pollen Grain, Male Microgametophyte, Pollen Tube, Ungerminated Pollen Grain, Water Absorption

What is the Germinated Pollen Grain

The germinated pollen grain is the pollen grain on the stigma with a developed pollen tube. Generally, ungerminated pollen grains disperse either through animals, wind, or water, falling on to the stigma of a flower of the same species. Here, stigma is the place on the pistil where pollen grains germinate. It is a sticky structure, which facilitates the deposition of pollen grains on it. Moreover, when deposited, pollen grains absorb water from the fluid on the stigma.

Figure 1: Germinated Pollen Grains with Pollen Tubes

Furthermore, this absorption of water from the stigma initiates the germination process of the pollen grain. As a result of this, the tube cell of the pollen grain starts to elongate, forming the pollen tube. The pollen tube grows towards the ovule of the pistol through the style. At this stage, the pollen grain is the mature male microgametophyte stage whose function is to discharge sperm nuclei to the ovule.

What is the Ungerminated Pollen Grain

The ungerminated pollen grain is the pollen grain containing the immature male microgametophyte. Generally, pollen grain contains the reduced male gametophyte, which is also known as the male microgametophyte. The pollen grains released from the pollen sacs are the ungerminated pollen grains whose function is to disperse the male gametophyte on to the stigma or the female gametophyte.

Figure 2: Ungerminated Pollen Grains of Apple

Moreover, the mass of cells inside the pollen sacs of angiosperms gives rise to the pollen grains. Four pollen sacs are arranged in the anther, which is the male reproductive structure of a flower. On the other hand, pollen grain develops inside the microsporangia of gymnosperms. The two types of cells in a pollen grain are the generative cells and the vegetative cells. Generative cells develop into the sperm cells while vegetative cells develop into the pollen tube upon germination. Also, terrestrial pollen grains consist of two walls: intine and extine. Intine is a thin, delicate wall of unaltered cellulose while extine is a tough, resistant outer cuticularized wall, mainly composed of sporopollenin. In addition, exine is a sculptured structure which contains warts or spines. Also, pollen grains of gymnosperms contain air bladders or vesicles known as sacci.

Similarities Between Germinated and Ungerminated Pollen Grain

• Germinated and ungerminated pollen grains are two developmental structures of the male gametophyte of seed plants.
• Both angiosperms and gymnosperms produce pollen grains.
• Also, their main function is to provide sperm cells required for the fertilization of the egg cells in the ovule.

Difference Between Germinated and Ungerminated Pollen Grain

Definition

Germinated pollen grain refers to the pollen grains with a tube cell elongated into a pollen tube while ungerminated pollen grain refers to the pollen grains which have not absorbed water.

Pollen Tube

The pollen tube is the main difference between germinated and ungerminated pollen grain. The germinated pollen grains contain a developed pollen tube while the ungerminated pollen grain does not contain a developed pollen tube.

Occurrence

Moreover, germination is a major difference between germinated and ungerminated pollen grain. The germination of pollen grains occurs on the stigma of the flower while ungerminated pollen grains can be on their dispersal process or they occur inside the pollen sac.

Absorption of Water

Absorption of water is another difference between germinated and ungerminated pollen grain. Germinated pollen grains have absorbed water from the stigma while ungerminated pollen grains have not absorbed water.

Stage of the Male Gametophyte

Furthermore, one other difference between germinated and ungerminated pollen grain is that the germinated pollen grain is the mature stage of the male microgametophyte while the ungerminated pollen grain is the immature male microgametophyte.

Role

Germinated pollen grain discharges sperm cells for fertilization at the ovule while the main function of the ungerminated pollen grain is to disperse from pollen sacs on to the stigma of a flower of the same species. Hence, this is another difference between germinated and ungerminated pollen grain.

Conclusion

The germinated pollen grain is the pollen grain on the stigma of a flower. It absorbs water and develops an elongated structure known as the pollen tube. The germinated pollen grain is responsible for releasing the sperm cells at the ovule for fertilization. In comparison, ungerminated pollen grains are the pollen grains which have left the pollen sacs and their function is to carry sperm cells to the female part of the flower. Therefore, it has no absorbed water or developed pollen tubes. The main difference between germinated and ungerminated pollen grain is the anatomical changes and the role.

References:

1. Wang, Huei-Jing, et al. “Pollen Germination and Tube Growth.” Advances in Botanical Research, 2010, pp. 1–52., doi:10.1016/s0065-2296(10)54001-1.

Image Courtesy:

1. “Germination of pollen (255 27) Total preparation (pollen tube visible)” By Doc. RNDr. Josef Reischig, CSc. – Author’s archive (CC BY-SA 3.0) via Commons Wikimedia  
2. “Жизнеспособность пыльцы 13” By Shuhrataxmedov – Own work (CC BY-SA 3.0) via Commons Wikimedia