Double Fertilisation In Angiosperms

What is Double Fertilisation?

Double fertilisation is a unique process of reproduction found in flowering plants whereby a pollen grain fertilises two different cells within the same ovule. One of the sperm contents fuses with the egg to form a diploid zygote, and another combines with the two polar nuclei to form a triploid endosperm that nourishes the developing embryo.

It is the indispensable process of seed development and one that uniquely characterises angiosperms, setting them apart from other plant groups. This formation of the zygote and the endosperm, taking place simultaneously in flowering plants, ensures efficient resource utilisation and also explains their evolution in plants.

Also Read:

• Entomophily

• Difference Between Self-Pollination and Cross-Pollination

• Difference Between Pollination And Fertilisation

Double Fertilisation in Angiosperms

Double fertilisation in angiosperms is an important process to ensure the proper synchronisation of embryo development with endosperm development. The endosperm nutritionally supports the embryo with the necessary nutrition to improve seed health, which eventually supports successful germination. This efficient method of resource allocation is associated with flowering plants' reproductive success and diversification.

Double Fertilisation Process

In the process of double fertilisation, there is a chronological series of steps that a plant undergoes, starting from pollination to the formation of the zygote and the endosperm. Each step is basic to the successful reproduction of angiosperms.

Pollination and Pollen Tube Formation

• Pollination: The process of transferring pollen grains from the anther to the stigma.

• Events in the Germination of Pollen Grains: A pollen grain germinates on the stigma, forming a pollen tube.

• Growth of Pollen Tube: A pollen tube grows through the style towards the ovule.

Entry of Pollen Tube into the Ovule

The pollen tube enters the ovule through the micropyle, which is a small opening in the integuments of the ovule.

Mechanism of Sperm Cell Delivery

• The pollen tube releases two sperm cells into the embryo sac.

• One sperm cell fertilises the egg cell, thereby forming a diploid zygote.

• The other sperm cell fuses with the two polar nuclei to form the triploid endosperm.

Role of Synergids and Egg Cell

• Synergids: Help direct the pollen tube to the egg cell.

• Egg Cell: This is fertilised by one of the sperm cells to develop into the zygote.

Development of Zygote and Endosperm

• The fertilised egg cell becomes the zygote, which then develops into the embryo.

• The triploid cell formed from the fusion of the sperm cell and polar nuclei develops into an endosperm that nourishes the embryo.

Components of Double Fertilisation

Double fertilisation involves two main components: syngamy (fusion of one male gamete with the egg cell) and triple fusion (fusion of the second male gamete with the two polar nuclei to form the endosperm).

Significance of Double Fertilisation

The process of double fertilisation has several advantages and helps much in the development of the seed and evolutionary success.

Advantages of Seed Development

• Provides the development of the embryo and endosperm

• Better seed viability and the success of germination

• Nutrient-rich endosperm for the developing embryo

• Resource efficiency is attained by developing endosperm only when the egg is fertilised.

Evolutionary Significance

• Contributes to the diversity and adaptability of flowering plants.

• Improves reproductive efficiency and success.

Comparison with Single Fertilisation in Gymnosperms

Variations and Exceptions in Double Fertilisation

While double fertilisation is typical in angiosperms, it is absent in gymnosperms and some parasitic flowering plants. In rare cases, variations may occur due to structural anomalies or reproductive adaptations. The details are given below:

Double Fertilisation in Monocots vs. Dicots

Double Fertilisation Applications

Double fertilisation has important applications in agriculture and biotechnology that affect crop improvement and future research directions.

Agricultural practices

• Development of hybrid seeds having desirable features.

• Improved yields and quality of crops.

• Improves disease and pest resistance.

Applications of Biotechnology

• Genetic engineering of improved varieties of plants.

• The activities and functions of different genes are researched and studied.

Scope for Further Research and Genetic Engineering

• Genetic control mechanism under study.

• Probability of developing nutritionally more valuable crops.

• Study on different types of apomixis for clonal seed production.

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