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Double Fertilisation In Angiosperms

Double Fertilisation In Angiosperms

Irshad AnwarUpdated on 02 Jul 2025, 07:09 PM IST

Double fertilisation is a feature of flowering plants that involves the fusion of two male gametes with two different cells of the female gametophyte. One male gamete fuses with the egg cell, forming a diploid zygote, which later develops into the embryo. The second male gamete fuses with the two polar nuclei to form a triploid primary endosperm nucleus, which gives rise to the endosperm. Double fertilisation is a special characteristic of Sexual Reproduction in Flowering Plants.

This Story also Contains

  1. What is Double Fertilisation?
  2. Double Fertilisation in Angiosperms
  3. Double Fertilisation Process
  4. Components of Double Fertilisation
  5. Significance of Double Fertilisation
  6. Variations and Exceptions in Double Fertilisation
  7. Double Fertilisation Applications
  8. Recommended Video On 'Double Fertilisation In Angiosperms'
Double Fertilisation In Angiosperms
Double Fertilisation In Angiosperms

The endosperm is a nutrient reserve that supports the developing embryo. The formation of the zygote and endosperm together ensures coordinated development. Double fertilisation improves the efficiency of reproduction and resource allocation. Double fertilisation is an important topic in the field of biology.

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.

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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.

Commonly Asked Questions

Q: What is the fate of each sperm cell during double fertilization?
A:
During double fertilization, one sperm cell fuses with the egg cell to form the zygote, which will develop into the embryo. The other sperm cell fuses with the two polar nuclei in the central cell to form the triploid endosperm nucleus, which will develop into the nutritive tissue for the embryo.
Q: How does the pollen tube deliver sperm cells to the ovule?
A:
The pollen tube grows through the style of the pistil, guided by chemical signals from the female tissues. It enters the ovule through the micropyle and releases the two sperm cells into the embryo sac, where fertilization occurs.
Q: What role does the pollen tube play in ensuring the success of double fertilization?
A:
The pollen tube plays a crucial role in the success of double fertilization by:
Q: How does pollination relate to double fertilization?
A:
Pollination is a prerequisite for double fertilization. It involves the transfer of pollen grains (containing sperm cells) from the anther to the stigma of a flower. After pollination, the pollen grain germinates and forms a pollen tube, which delivers the sperm cells to the ovule where double fertilization occurs.
Q: What is the significance of the micropyle in double fertilization?
A:
The micropyle is a small opening in the ovule through which the pollen tube enters to reach the embryo sac. It plays a crucial role in guiding the pollen tube to the correct location for sperm cell delivery, ensuring that double fertilization can occur efficiently and accurately.

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).

Component

Function

Structure of Pollen Grain

Houses male gametes and facilitates fertilisation

Pollen Tube

Transports sperm cells to the embryo sac

Egg Cell

Fusion with sperm cells forms the zygote

Synergids

Assist in guiding the pollen tube

Polar Nuclei

Fusion with sperm cells forms the endosperm

Central Cell

Contains polar nuclei for endosperm formation

Micropyle

The entry point for the pollen tube

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


Angiosperms (Double Fertilisation)

Gymnosperms (Single Fertilisation)

Fertilisation Process

Two sperm cells, the zygote and the endosperm

One sperm cell, only one zygote

Nutrient Source

Endosperm

Female gametophyte tissue

Evolutionary Advantage

Higher efficiency, resource allocation

Less efficient

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

Aspect

Monocots

Dicots

Number of Cotyledons

One

Two

Pollen Structure

Monosulcate

Tricolpate

Endosperm Formation

Persistent in many species

Often absorbed by the embryo

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.

Read more:

Recommended Video On 'Double Fertilisation In Angiosperms'


Frequently Asked Questions (FAQs)

Q: How does double fertilization relate to the concept of genetic imprinting?
A:
Double fertilization is closely related to genetic imprinting, particularly in the endosperm. The triploid nature of the endosperm, with two maternal and one paternal genome copies, allows for complex patterns of gene expression based on the parent of origin. This imprinting plays crucial roles in seed development and can influence seed size and viability.
Q: What are some of the evolutionary precursors to double fertilization in plants?
A:
Evolutionary precursors to double fertilization may have included:
Q: How does self-incompatibility in some plant species affect double fertilization?
A:
Self-incompatibility is a mechanism that prevents self-fertilization in some plant species. It can affect double fertilization by preventing pollen tube growth or sperm cell release in genetically similar individuals. This ensures genetic diversity but can also prevent double fertilization if compatible mates are not available.
Q: What is the fate of the central cell if double fertilization fails to occur?
A:
If double fertilization fails to occur, the central cell typically degenerates along with the other structures in the embryo sac. In some cases, it may develop into a nutritive tissue without fertilization (autonomous endosperm), but this is relatively rare and usually does not support full seed development.
Q: What is the significance of the fact that one pollen grain can fertilize only one ovule?
A:
The fact that one pollen grain can fertilize only one ovule ensures a 1:1 ratio between pollen grains and potential seeds. This promotes genetic diversity by allowing multiple pollen donors to contribute to seed formation within a single flower or plant. It also makes pollination a more precise and efficient process.
Q: What is the relationship between double fertilization and seed dormancy?
A:
While double fertilization doesn't directly cause seed dormancy, it sets the stage for it. The fertilization events trigger seed development, including the formation of the seed coat and the accumulation of storage compounds in the endosperm. These structures and compounds can contribute to seed dormancy mechanisms, which are important for seed survival and timely germination.
Q: How does the process of double fertilization differ in plants with different pollination mechanisms?
A:
The process of double fertilization itself doesn't differ significantly based on pollination mechanisms. However, the way pollen is delivered to the stigma can affect the timing and efficiency of the process. For example, wind-pollinated plants may produce more pollen to ensure successful pollination, while plants pollinated by specific insects may have more precise pollen delivery mechanisms.
Q: What role do plant hormones play in the process of double fertilization?
A:
Plant hormones play several roles in double fertilization:
Q: How does the nutritional status of the parent plant affect double fertilization?
A:
The nutritional status of the parent plant can affect double fertilization in several ways:
Q: What is the significance of the fact that the endosperm often has a different ploidy level than the embryo?
A:
The different ploidy level of the endosperm (triploid) compared to the embryo (diploid) is significant because:
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