In this phenomenon, one female gamete fuses with two male gametes to form a new gamete. The formation of a zygote occurs when one of the male gametes fertilises an egg, and the construction of an endosperm occurs when the other male gamete joins with two polar nuclei to form an endosperm.
Double fertilisation stimulates the growth of the plant, culminating in the development of ovules into fruits and the development of ovarian development into the seed. It is only after the haploid male gametes and female gametes unite that the plant is restored to its diploid state.
Double Fertilisation in Angiosperms
Angiosperms are flower-bearing plants, and they are the most diversified category of terrestrial plants in terms of their structure and function. Angiosperm flowers are the reproductive organs of the plant, with male and female reproductive organs located on opposite sides of the flower. Every cell in the body contains gametes – sperm and egg cells, for example.
Pollination aids in the transportation of pollen grains to the stigma via the style. The two sperm cells enter the ovule-synergid cell, which is responsible for fertilisation. This is followed by the process of fertilisation.
Fertilisation results in two structures in angiosperms, namely, the zygote and the endosperm, which is why they are referred to as “double fertilisation.”
Single-cell fertilisation is a complicated process that involves the union of one of the two sperm cells with an egg cell and the union of the other with two polar nuclei, which results in the formation of two diploid (2n) zygotes and a triploid (3n) primary endosperm nucleus (PEN), respectively.
Because endosperm is formed by the fusion of three haploid nuclei, the process is referred to as triple fusion. It is eventually possible for a primary endosperm nucleus to develop into a primary endosperm cell (PEC) and subsequently into an endosperm.
Development of Embryo in Angiosperms
As soon as fertilisation is complete, embryonic development begins, and no additional sperms may be introduced into the ovaries. The fertilised ovule develops into a seed, and the ovarian tissues produce a fleshy fruit that encircles and protects the seed during development.
When the zygote is fertilised, it divides into two cells: an upper terminal cell and a lower basal cell. The basal cell matures into a suspensor cell, which aids in the transfer of nutrients to the developing embryo during development. The terminal cell evolves into a pro-embryo during the development process.
Phases of Development of Embryo in Angiosperms
The following are the stages of an embryo’s development that occur at various times throughout its life:
- The terminal cell dissociates during the earliest period of development, resulting in the formation of a globe-shaped pro-embryo. As an added bonus, the basal cell divides and becomes a suspensor.
- Because of the presence of cotyledons, the growing embryo takes on a heart-shaped form as it develops.
- During development, the developing embryo becomes crowded and begins to adjust into various shapes.
- The embryo takes up the entirety of the seed’s surface area.
Pollination
Pollination is essential before the possibility of double fertilisation may be realised. Pollination is the process by which a pollen grain produced by a flower’s stamen lands on the carpel of another flower, which is known as fertilisation. A pollen grain must precisely settle on the sticky platform, or stigma, of a carpel in order for it to be considered successful. An individual pollen grain is a protective structure that contains sperm. Once it has landed on the stigma, it begins to develop a pollen tube. This structure will develop from the style of a carpel to the ovary of the flower. In the ovary, there will be two times the amount of fertilisation.
Significance of Double Fertilisation
The following are some of the implications of double fertilisation:
- As a result of the twofold fertilisation process, two products are produced.
- There is a possibility of polyembryony, and the plant will have a better chance of surviving.
- Double fertilisation results in the formation of an endosperm, which is responsible for providing sustenance to the developing embryo.
- It improves the viability of angiosperm seeds by increasing their germination rate.
- It makes use of both the male gametes produced by the pollen grains.
CONCLUSION
Double fertilisation is currently believed to be widespread among flowering plants, according to current research. The pollen grain (male gametophyte) germinates on the pistil, which is a flowering plant. During the growth process, a tube is formed in which two male gametes are transported toward an embryo sac (female gametophyte), which contains in particular two female gametes, the egg, and the central cells, as well as two synergis. As soon as the pollen tube reaches the embryo sac, it causes the two male gametes to be released into a degenerated synergid, which is then released into the environment. One fuses with the egg cell to make a zygote, which grows further into the embryo, while the other fuses with the central cell to generate a polyploid (usually triploid) cell, which develops further into the endosperm, which is produced by the fusion of the two cells. As a result, two fertilizations take place at the same time.