What is Triple Fusion? – Occurrence, Process, and Importance

What is Triple Fusion?

Triple fusion refers to the fusion of three nuclei that leads to the formation of the endosperm in angiosperms. The three nuclei involved are:

1. Two polar nuclei from the embryo sac
2. One sperm nucleus from the pollen grain

Triple Fusion in Plants

Triple fusion is an important process that occurs during double fertilization in flowering plants (angiosperms). It involves the fusion of two polar nuclei from the embryo sac with a sperm nucleus from the pollen grain.

These three nuclei fuse to form the primary endosperm nucleus, which develops into endosperm tissue that provides nourishment to the developing embryo.

Occurrence of Triple Fusion

Triple fusion occurs in all angiosperms during the process of double fertilization. However, it does not occur in gymnosperms like pine, fir, cedar etc. In gymnosperms, the endosperm develops from the megagametophyte itself, without any triple fusion.

In plants exhibiting triple fusion like rice, wheat, capsella bursa, the endosperm develops only after the fusion of polar nuclei and sperm nucleus. So triple fusion has a vital role in endosperm and embryo nutrition.

Nuclei Involved in Triple Fusion

The nuclei involved in triple fusion are:

• Two polar nuclei: These are diploid nuclei found within the central cell of the embryo sac. They are the result of the fusion of two haploid nuclei derived from the megaspore, the precursor cell of the embryo sac.
• One sperm nucleus: This is a haploid nucleus carried by one of the two sperm cells released from the pollen grain

After the pollen tube reaches the embryo sac, it releases two sperm nuclei. One sperm nucleus fuses with the egg cell, forming the zygote, the initial stage of the embryo. The other sperm nucleus travels towards the central cell.

The fusion of the three nuclei results in the formation of a triploid nucleus known as the primary endosperm nucleus. This nucleus gives rise to the endosperm, a nutrient-rich tissue that provides nourishment to the developing embryo.

Significance of Triple Fusion

Triple fusion leads to the formation of nutritive endosperm tissue. This provides nourishment to the developing embryo. So it plays a crucial role in the reproductive cycle of angiosperms.

The endosperm balances the ratio of paternal to maternal genome contributions. This is important for proper endosperm and embryo development.