It is the most prevalent form of fertilisation with flowering plants, and it is accomplished through the passage of the pollen tube through the micropyle. In a small number of plants, the pollen tube enters through the chalazal region (chalazogamy), resulting in basigamous fertilisation; in a few plants, the pollen tube enters through the apex, resulting in acrogamous fertilisation; and in a few plants, the pollen tube enters through the apex, resulting in acrogamous fertilisation.
What does the term “fertilisation” mean?
The process by which plants reproduce sexually as a result of pollination and germination is known as fertilisation. Male gametes (pollen) combine with female gametes (ovum) in a physicochemical process after carpal pollination to produce a diploid zygote. The whole thing happens inside the zygote, which eventually turns into a seed. Pollinators deliver male gametes into female reproductive organs during the procedure (butterflies, birds, honey bees, bats, and flower beetles). As a result, a seed grows into an embryo. Flowers are angiosperms’ reproductive organs, and they reproduce uniquely from the rest of the plant.
Fertilisation in plants may be broken down into four basic steps.
- Pollen-coated male gametes are carried away by water, wind, or other agents like animals and insects, resulting in pollination. The pollen is subsequently guided to the stigma of the plant. This procedure is known as pollination.
- The pollen tube expands and penetrates the egg cell in a matter of minutes, which is known as germination. To reach the egg, the pollen grain travels via the tube.
The embryo sac, also known as the ovule, is penetrated by the pollen tube containing the
sperm.
- After successfully piercing the ovule, the sperms move down the tube to fertilise the egg. In most flower-bearing plants, the polar nuclei and eggs in the ovule are fertilised, resulting in double fertilisation.
- After fertilisation, the zygote cells split and grow into an embryo, also known as a developing plant. The embryo was encapsulated in a seed capsule and stayed dormant until it was able to mature into a plant due to favourable environmental conditions.
Fertilisation of Seed Plants
During the fertilisation process in gymnosperms or seed-bearing plants, seeds grow on both sides of leaves or scales, form cones, or predominate at the end of short stalks. The seed is stored within the ovary.
Fertilisation of Flowering Plants
Angiosperms, flower-bearing plants, have a second fertilisation mechanism in their core cell. Two sperm cells are released by each pollen grain. The first cell combines with the zygote during egg fertilisation, while the second fuses with the twin polar nuclei to produce endosperm.
Process of fertilisation
As previously established, fertilisation is the outcome of the fusion of female and male gametes. Fusion requires both female and male pollen grains to reach the stigma’s surface. This procedure is known as pollination. The pollen is transferred to the stigma, where it germinates before passing through the style and into the ovule. There are two types of cells in pollen or microspores: generative and pollen tube cells. This pollen tube cell produces a pollen tube through which generative cells can pass.
To germinate, pollen tubes need oxygen, water, and a variety of other chemical signals. The style’s tissue supports the pollen tube’s growth while pollen travels through it on its route to the ovule or embryo sac. During the entire process, if the generative cell has not yet ruptured into two cells, it breaks down into two sperm cells. The chemical synthesis of synergids in the embryo sac aids pollen penetration of the ovule through the micropyle.
When one sperm cell from the sperm cells germinates in the egg cell, a diploid zygote is generated. The surviving sperm cells’ polar nuclei unite to form a triploid cell that produces endosperm. The twin fertilisation episodes that occur in angiosperms or blooming plants are referred to as double fertilisation. After the fertilisation process is accomplished, no more sperm can enter. The fertilised embryo sac produces the seed, while the ovary tissues generate the fruit that envelops the seed.
Self-Fertilisation
Allogamy is the cross-fertilisation of gametes from two different species — male and female. Autogamy, or self-fertilisation, occurs when two gametes from a single person combine. Plants and flatworms, for example, are examples of hermaphrodites.
Types of Fertilisation
Based on how pollen tubes reach the ovule or embryo sac, there are three basic kinds of fertilisation.
Porogamy
The most common source of fertilisation is flowering plants, also known as angiosperms. Through a micropyle of this form, a pollen tube reaches the ovule. A common example is lilies.
Chalazogamy
The casuarina plant species undergoes this sort of fertilisation. The pollen tube enters the ovule through the chalaza rather than through the micropyle. This is a once-in-a-lifetime incident. Some examples include Casuarina, Betula, and Juglans.
Mesogamy
This method is used to fertilise cucurbit plants such as bitter gourd, ridge gourd, and a variety of other gourd plants, as well as pumpkin. A pollen tube penetrates the ovule in this form by going through integuments of the ovule’s centre section.
Double Fertilisation
Double fertilisation occurs when a single female gamete combines with two male gametes. The endosperm is formed when one sperm cell merges with the zygote and the other sperm cell fuses with the two nuclei. A double fertilisation treatment is performed on the entire angiosperm plant.
Conclusion
You get two things when double fertilise. The viability of angiosperm seeds is improved. The plant’s chances of surviving will be improved by polyembryony (the chance to form more than a single embryo from one seed or a single fertile ovum)The growing embryo is fed by the endosperm produced by multiple fertilisations. Pollen grains create two male gametes, which are put to good use. The numerous ways of fertilisation in plants, as well as the processes involved, are described here. To comprehend the distinctions between different types of fertilisation, you must first comprehend the concept of fertilisation.