Double Fertilization in Angiosperms

In Angiosperms, double fertilisation is a complicated process. Flowering plants are known as angiosperms. They are the most diverse collection of plants on the planet. They produce seeds in the form of fruits. They are the most common plants on the planet’s surface and the primary food source for birds, animals, and people.

The fusing of the egg and sperm, as well as the simultaneous fusion of a second sperm and two polar nuclei, results in the creation of the endosperm (food-storage tissue) of the seed in flowering plant reproduction. This is known as double fertilisation because the true fertilisation (the fusion of a sperm with an egg) is accompanied by a fusion process that resembles fertilisation (the fusing of a sperm with the polar nuclei). This sort of double fertilisation is only seen in flowering plants (angiosperms), and it is responsible for the creation of both the embryo and the seed’s potential food supply.

THE PROCESS OF DOUBLE FERTILIZATION

Pollination

Pollination is required before double fertilisation can occur. When a pollen grain produced by a flower’s stamen settles on the carpel of another bloom, it is known as pollination. The pollen grain must specifically fall on the sticky platform, or stigma, of a carpel.

A pollen grain is a sperm-containing protective structure. It grows a pollen tube after it settles on the stigma. This structure will develop from a carpel’s style to its ovary. Double fertilisation will take place in the ovary.

Double Fertilization

At least one ovule is seen in each ovary. Cells divide within an ovule to create an egg and two additional cells known as polar nuclei. These three cells are haploid, meaning they only have one pair of chromosomes, and are labelled with the symbol n. Angiosperm cells are generally diploid, meaning they have two sets of chromosomes. One pair of chromosomes originates from the male parent, while the other set comes from the female parent in diploid cells.

A pollen grain’s sperm cells, like its eggs and polar nuclei, are haploid. When the pollen tube reaches the micropyle, or ovule opening, two haploid sperm cells are released into the ovule. A diploid zygote is formed when one sperm cell fuses with the egg. The other sperm cell will fuse with the two polar nuclei to form a triploid structure that will quickly develop into an endosperm. This is referred to as double fertilisation.

Development of Embryo

Other sperms cannot enter the ovary since fertilisation has already occurred. The fertilised ovule begins to develop into a seed, while the ovary begins to develop into a fruit.

The development phase has started as a result of fertilisation. The embryo begins to grow, and the zygote begins to divide. The zygote divides into two cells: a basal cell (also known as the bottom cell) and a terminal cell (also called the upper cell).

A suspensor arises from the basal cell. This suspensor helps the embryo move food and nutrients from the parent plant. Pro-embryo develops from the terminal cell. In certain situations, the embryo’s form is similar to that of the heart.

After fertilisation, cell division begins, with the zygote splitting into upper-end and lower-basal cells. The basal cell develops into a suspensor, which helps carry food to the growing embryo. The pro-embryo develops from the higher terminal cell. Due to the presence of two main cotyledons, this is the case. The embryo develops until it has consumed all of the seed’s area. The embryo’s growth is thus interrupted, but it continues once the seed begins to expand.

Advantages 

1 .It creates a food source for the seed – During double fertilisation, an embryo grows within the seed, which will eventually lead to growth. Certain plants can use this method as an extra food source if the growth circumstances are less than ideal when the new plant first emerges.

2. It gives the plant more protection – double fertilisation almost ensures the longevity of a flowering species. Because there are two male gametes, there is a significantly higher possibility that they will engage with a female gametophyte.

3.  After being fertilised by a sperm cell, the endosperm created by the fusing of the two polar nuclei and sperm begins to expand and store nutrients. With this technique, the plant does not have to devote energy-intensive resources to an egg that will not be fertilised, making it less fit.

4. .It conserves energy –Because of the method of multiple fertilisations, the flowering plant is able to conserve energy as the embryo begins to shape. The seed contains all of the necessary nutrients, allowing the plant to thrive for as long as possible.

5. It allows for faster seed growth – Because two male gametes are engaged in the reproductive process, the seed develops at a faster rate than in other kinds of reproduction. The endosperm nucleus splits fast to provide nutrient-rich tissue, allowing the embryo to grow rapidly.

Conclusion

Double fertilisation is a characteristic feature of reproductive development in the angiosperms, or flowering plants, which are the most evolutionarily successful and wonderfully diversified group of plants on the planet. Angiosperm seeds are contained within a fruit, unlike gymnosperm seeds, which are generated as exposed units on the surface of sporophylls or similar structures. Although the study of angiosperm reproductive biology has a long history, ongoing genetic and molecular research on the subject is a recent development.