Sexual Reproduction in Flowering Plants

Endosperm Development

The endosperms are very vital parts of the fertilized embryo. An endosperm forms the surrounding tissue of the growing embryo. They are the primary storage tissue and their main function is to provide starch and other nutrients to the growing embryo.

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Types of Seed

Depending on the utilization of the endosperm, there are two types of seeds :

  • Albuminous seed: The endosperms provide nutrition to the developing embryo but remain even during the germination of the seed in this type.
  • Exalbuminous seed: This type of seed utilizes the endosperms completely. Thus, these seeds are non-endospermic in nature.

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Development of Endosperm

There are three types of Endosperms:

  • Nuclear
  • Cellular
  • Helobial

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But before understanding these types, we need to understand what gives rise to the endosperm. A phenomenon called as ‘double fertilization‘. Each pollen grain consists of two male gametes. Once they reach the ovary, one of the male gametes fuses with the female gamete and forms the zygote.

The other male gamete fuses with the central cell which is diploid resulting in the formation of a triploid endosperm. Thus, the endosperm can be polyploid as well in certain cases. But, in gymnosperms, the endosperm is haploid.

Nuclear Endosperms

In this type, the cell divisions are free-nuclear divisions where each cell division is not followed by formation of a cell wall. They may or may not form a cell wall towards later stages. With the cell divisions, the nuclei are pushed towards the periphery of the sac giving rise to a large vacuole in the centre.

This type of endosperm is the most common type and is found in maize, wheat, areca nut and coconut. The endosperm of the coconut gives rise to a large central vacuole that gets eventually filled up with the nutritious coconut water.

Cellular Endosperms

This type is the opposite of the nuclear endosperm. In this type, Cell wall formation follows each cell division. Thus, the endosperm divides into many segments. There might not be coherency in the divisions and they can happen along different planes.

Cellular divisions of the endosperm consequently lead to the formation of the coconut meat. Plants like petunia and Dhatura have this kind of endosperm.

Helobial Endosperms

This is an intermediate form between the other two types. In this type, Cell wall formation follows the first cell division. But the subsequent divisions do not lead to cell wall formation. The first cell division occurs along the transverse plane giving rise to clear micropylar and chalazal ends.

The subsequent division after the first often occurs in the micropylar end. Once the number of division in the micropylar end begin to increase, the chalazal end starts to degenerate or disintegrate.

Solved Example for You

Question: Which of the following options are true about Nuclear Endosperms?

  1. Cell wall formation        
  2. Cell wall formation consequently follows only the first cell division
  3. Embryo uses the Endosperms
  4. No cell wall formation consequently follows the nuclear divisions

Solution: Option D. No cell wall formation is seen following the nuclear divisions.

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