Difference Between Double Fertilization and Triple Fusion

Main Difference – Double Fertilization vs Triple Fusion

Double fertilization and triple fusion are two processes involved in the sexual reproduction of angiosperms. Flowers are the reproductive structures found in angiosperms. They contain both male reproductive structures called stamens and female reproductive structures called pistils. Pollen grains are produced by the anthers of the stamens. They are deposited on the stigma of pistils during the process called pollination. After the pollination, pollen grains are germinated, producing a pollen tube, which carries two sperm cells into the embryo sac of the pistils. Once sperm cells reach the ovary, fertilization occurs. The main difference between double fertilization and triple fusion is that double fertilization is the fusion of the embryo sac with two sperm cells whereas triple fusion is the fusion of sperm nucleus with the two polar nuclei in the central cell of the embryo sac.

This article looks at,

1. What is Double Fertilization
      – Definition, Characteristics, Process
2. What is Triple Fusion
      – Definition, Characteristics, Process
3. What is the difference between Double Fertilization and Triple Fusion

What is Double Fertilization

Double fertilization is the fusion of the embryo sac with two male gametes. It occurs in angiosperms. Pollination is the deposition of pollen grains from anthers on the stigma of a flower, facilitating the fertilization, which is one of the major events of sexual reproduction of plants. Pollen contains two cells, a tube cell, which produces the pollen tube, and a generative cell, which produces two sperm cells. After the pollination, pollen grains are germinated on the stigma, producing the pollen tube, which goes down the style until it reaches the micropyle in the ovule. Once it meets the micropyle, pollen tube bursts, releasing the two sperm cells which are carried through the pollen tube. One of the haploid sperm cells is fertilized with the haploid egg cell in the embryo sac, while the other haploid sperm cell fertilizes the central cell, which is also found in the embryo sac of the female gametophyte. Fertilization of the two gametes is called syngamy. The fertilization of a sperm cell with the central cell is called triple fusion. Since the embryo sac is fertilized twice, the fertilization of gametes in angiosperms is called double fertilization.

After fertilization, the ovule is developed into the seed. The fusion of egg cell with the sperm cell produces the diploid zygote, which is developed into the embryo. First, the zygote is divide into two cells called terminal cell and basal cell by mitosis. The basal cell divides to produce the suspensor, which provides nutrients from mother plant to the growing embryo. The division of the terminal cell produces the pre-embryo. Further development of the embryo is arrested until the germination of the seed.

Figure 1: Double fertilization

What is Triple Fusion

Triple fusion is the fertilization of the two polar nuclei in the embryo sac. It occurs during the double fertilization of angiosperms. While one sperm cell fertilizes the egg cell in the embryo sac, the other sperm cell fertilizes the two polar nuclei found in the central cell. Since the fusion of three haploid nuclei forms a triploid nucleus, the process is called triple fusion. The triploid nucleus serves as the primary endosperm nucleus. It gives rise to the endosperm of the seed, which stores nutrients of the seed.

During triple fusion, three types of endosperm development are observed: nuclear endosperm development, cellular endosperm development, and helobial endosperm development. Liquid endosperm is developed from the nuclear endosperm development as in coconut water. Coconut meat is an example for the cellular endosperm development and monocots have helobial endosperm development.

Figure 2: Cells in the embryo sac

Difference Between Double Fertilization and Triple Fusion

Definition

Double Fertilization: The fertilization process of angiosperms is called the double fertilization.

Triple Fusion: Triple fusion is the fertilization of two polar nuclei in the embryo sac with a single sperm cell.

Correspondence

Double Fertilization: Double fertilization is the fusion of embryo sac with two sperm cells.

Triple Fusion: Triple fusion is one of the two fertilizations of double fertilization.

Result

Double Fertilization: Double fertilization forms a diploid zygote, which is developed into the embryo along with the endosperm.

Triple Fusion: Triple fusion forms the endosperm.

Ploidy

Double Fertilization: Double fertilization produces a diploid zygote as well as the triploid endosperm.

Triple Fusion: Triple fusion produces the triploid endosperm.

Conclusion

Double fertilization and triple fusion are the two processes that occur during the sexual reproduction of angiosperms. Following the pollination of a flower, germination of pollen grain occurs on the stigma. A single pollen contains two sperm cells; one is fertilized with the egg cell and the other is fertilized with the two polar nuclei in the central cell of the embryo sac. This dual fertilization is called double fertilization. The fusion of gametes is called syngamy, producing the diploid zygote. The zygote is developed into the embryo in the seed. The fertilization of the two polar nuclei in the central cell produces a triploid nucleus, which is ultimately developed into the endosperm, which contains nutrients required for the germination of the seed. The formation of the triploid nucleus by fusing three haploid nuclei is called the triple fusion. Double fertilization and triple fusion both are two events occurring during the fertilization of angiosperms. But, the main difference between double fertilization and triple fusion is in the mechanisms of the each process.

Reference:
1.”Double Fertilization in Plants – Boundless Open Textbook.” Boundless. Boundless, 26 May 2016. Web. 27 Apr. 2017.
2.”Double Fertilization.” Double Fertilization | BIOL 011. N.p., n.d. Web. 27 Apr. 2017.
3.”What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.” Saral Study. N.p., n.d. Web. 27 Apr. 2017.
4.Singh, Kalpana. Short essay on Embryo and Endosperm development. N.p., n.d. Web. 27 Apr. 2017.
Image Courtesy:
1. “Double Fertilization” By The original uploader was Triploid at English Wikipedia – Transferred from en.wikipedia to Commons. (CC BY 3.0) via Commons Wikimedia
2. “Embryosac” By Tameeria at English Wikipedia – Created by Tameeria using Powerpoint (Public Domain) via Commnons Wikimedia