Pollination and Fertilisation

6.3

Pollination and Fertilisation

Introduction to Pollination

Pollination is a process where a mature pollen is transferred from an another to a stigma.
Pollination can be occured by pollination agents such as insects,wind and animals.
Two types of pollination:

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The Formation of Pollen Tube and Male Gametes

The wall of anther from mature pollen will dry, shrink dan split. Pollen grains in the pollen sac are released.
The released pollen grains are transferred to the stigma of the same flower or different flowers by pollinating agent.
The pollen grains that have been transferred to the stigma will germinate and form a pollen tube. The pollen tube grows down towards the ovule through the style.
The generative nucleus will move along the pollen tube towards the ovule. At the same time, the generative nucleus will divide by mitosis to form two male gametes (n).
The end of the pollen tube will secrete an enzyme to digest the tissues of the style.
When it reaches the embryo sac, the pollen tube will penetrate the ovule through the micropyle. The tube nucleus will degenerate and both male gametes enter the embryo sac.

Double Fertilisation in the Formation of Diploid Zygote and Triploid Nucleus

Double fertilisation involves two male gametes, in which the first male gamete fertilises the egg cell to form a diploid zygote whereas the second male gamete fuses with polar nuclei to form a triploid endosperm tissue.
The generative nucleus undergoes mitosis in the pollen tube to produce two male gametes which are haploids.
Both male gametes will enter the embryo sac for fertilisation.
When it reaches the embryo sac, the pollen tube will penetrate the ovule through the micropyle. The tube nucleus will degenerate and both male gametes enter the embryo sac.
One of the male gametes fertilises the egg cell and produces a diploid zygote. The second male gamete fuses with the two polar nuclei to form a triploid endosperm nucleus.

Importance of Double Fertilisation for the Survival of Flowering Plants

The fusion of one of the male gametes with the egg cell produces a zygote.
- (Genetic information is passed down from one generation to the next.
- Restores haploid condition in gametes with the formation of the diploid zygote.
The fusion of another male gamete with two polar nuclei produces endosperm tissue.
- This tissue is used for the development of an embryo for the survival of plant species.
- In eudicots such as legumes, mangoes and mustard, the endosperm is fully utilised by the embryo to develop before the seed matures.
- In most monocots such as coconut, wheat, barley and corn, only a part of the endosperm is utilised for the development of an embryo. Some of them are stored in the cotyledon to be utilised during the germination of the seed. The endosperm tissue enables the embryo to survive in the seed for a long time if conditions are not favourable for germination to occur.