Endosperm - Diagram, Types, Development, Double Fertilisation

Endosperm: Endosperm is a vital tissue found in flowering plant seeds that surrounds and nourishes the embryo. It is a transient but essential component, accounting for the majority of the grain. Endosperm, which is high in carbohydrates, proteins, and lipids, supplies the developing embryo with essential nutrition in the form of starch, oils, and protein. It also acts as a protective barrier, regulating embryo growth throughout seed development and germination. Endosperm is essential for human nutrition because it provides roughly two-thirds of all human calories. The article below provides students in Class 12 with detailed information about endosperm.

Sexual Reproduction in Flowering Plants

What is Endosperm Class 12?

Endosperm Diagram

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Types of Endosperm

1. Nuclear Endosperm: This type is prevalent among plants. In nuclear endosperm, the Primary Endosperm Nucleus (PEN) undergoes multiple mitotic divisions without cytokinesis. This results in numerous free nuclei within the cell, arranged peripherally around a large central vacuole. The chalazal and micropylar ends contain more nuclei compared to the sides. Cell wall formation commences from the periphery towards the centre, culminating in multicellular endosperm.

2. Cellular Endosperm: This type is less common. Cellular endosperm development involves PEN division (karyokinesis) followed by cytokinesis, resulting in transverse division and the formation of two cells. These cells give rise to the chalazal and micropylar chambers, followed by further divisions leading to cellular endosperm formation.

3. Helobial endosperm: This type is predominant in monocotyledons. It begins with a division akin to cellular endosperm, resulting in a large micropylar cell and a small chalazal cell. Subsequent divisions in the micropylar cells resemble nuclear endosperm. Helobial endosperm thus represents an intermediate type, combining characteristics of both nuclear and cellular endosperms.

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Double Fertilisation

1. Pollination: A pollen grain lands on the stigma, the receptive part of the carpel (the female reproductive organ) in a flower.
2. Pollen tube formation: The pollen grain germinates, forming a pollen tube that grows down through the style (the structure connecting the stigma to the ovary) towards the ovule.
3. Double fertilisation: The pollen tube enters the ovule through a small opening known as the micropyle. Inside the ovule, the pollen tube releases two sperm cells.

• One sperm cell fertilizes the egg cell, forming a zygote with a full set of chromosomes. This zygote develops into the embryo of the seed.
• The other sperm cell combines with the two polar nuclei (central cell) in the ovule, producing a triploid primary endosperm nucleus (PEN). This PEN develops into the endosperm, which provides nutrients for the developing embryo.

Importance of Double fertilisation includes:

• Being an important stage in the sexual reproduction of flowering plants.
• Ensure the growth of both the embryo (which gives rise to the new plant) and the endosperm (which feeds the developing embryo). developing embryo).
• The triploid nature of the endosperm may enhance its ability to store nutrients.

Development of Endosperm

1. Double Fertilisation: Endosperm development begins with the process of double fertilisation, which is a unique feature of flowering plants. In this process, one sperm nucleus fertilises the egg cell to form the embryo, while the other sperm nucleus fertilises the central cell, leading to the formation of the endosperm.
2. Syncytial Stage: After fertilisation, the endosperm goes through a phase of rapid nuclear divisions without cytokinesis, resulting in a multinucleate structure called a syncytium. This stage is crucial for the rapid accumulation of nutrients in the endosperm.
3. Cellularisation: Subsequently, the syncytial endosperm undergoes cellularisation, during which cell walls form around individual nuclei, leading to the formation of distinct cells within the endosperm. This cellularisation process is essential for the proper development and function of the endosperm.
4. Nutrient Accumulation: Throughout its development, the endosperm accumulates various nutrients, including starch, proteins, and lipids. These nutrients serve as a source of energy and building blocks for the developing embryo and seedling.
5. Regulation by Genes and Hormones: The development of the endosperm is tightly regulated by a complex interplay of genetic and hormonal factors. Genes encoding storage proteins and other compounds are expressed at specific stages to facilitate nutrient accumulation. Hormones such as auxins, cytokinins, and gibberellins also play critical roles in coordinating endosperm development.
6. Variation among Species: The structure and composition of the endosperm can vary among plant species. For example, some plants have endosperm that is rich in starch, while others have endosperm that is rich in proteins or oils. These variations can influence the nutritional content and other characteristics of the seed.
7. Significance for Agriculture: Understanding the development of the endosperm is important for agriculture, as it can influence crop yield and quality. Manipulating endosperm development through breeding or genetic engineering can lead to the development of crops with improved nutritional content, yield, and resilience to environmental stresses.

Female Gametophyte

Endosperm Functions

• Endospermic Seeds: In some dicots like castor, mature seeds store food in the endosperm.
• Exalbuminous Seeds: In beans, peas, and gram seeds, the endosperm is completely absorbed during development, and food is stored in two cotyledons.

Vegetative Propagation

Endosperm Examples

1. Castor Seeds: Endospermic seeds store food for seedling growth.
2. Beans, Peas, Gram Seeds: Exalbuminous seeds absorb endosperm during development.
3. Grains (Wheat, Maize, Barley, Corn): Endosperm is the main food source for seedlings.
4. Coconut: Coconut seeds contain liquid endosperm.
5. Wheat Seeds (White Flour): White flour is made from the endosperm of wheat seeds.
6. Orchids: Orchid seeds do not have endosperm.