POST FERTILIZATION CHANGES: Development of endosperm:

Endosperm is the nutritive tissue for the nourishment of developing embryo.

In Angiosperms, the product of second fertilization or triple fusion is Primary Endosperm Nucleus (PEN). It develops into endosperm.

The endosperm is post fertilization product and is commonly a triploid tissue.

In some cases, endosperm is totally consumed during embryo development so that the mature seeds do not possess endosperm and such seeds are called non endospermic or ex-albuminous seeds, e.g. pea, bean, gram, ground nut, etc.

In other Angiosperms, the endosperm persists in the mature seeds and it continues to support the growth of embryo during seed germination. Such seeds are called endospermic or albuminous seeds, e.g. castor, sunflower, coconut, and cereals like maize, wheat, etc.

 

Types of Endosperms

Depending upon the mode of development, three types of endosperm are recognized. These are as follows:

1. Nuclear Endosperm

2. Cellular Endosperm

3. Helobial Endosperm

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Nuclear Endosperm:

In this type, the primary endosperm nucleus undergoes free nuclear divisions or karyokinesis (i.e. nuclear-divisions are not followed by cytokinesis).

This result in formation of large number of tiploid nuclei freely suspended in common cytoplasm of central cell.

Later on wall formation occurs around these nuclei in a centripetal manner to form cellular mass.

It is the most common type of endosperm.

 

Cellular Endosperm:

In this type, the primary endosperm nucleus undergoes nuclear divisions which are followed by cytokinesis.

Therefore, endosperm development occurs in cellular form right from the beginning. It is less common and seen mostly in dicots.

 

Helobial Endosperm:

In this type, first division of primary endosperm nucleus is followed by wall formation.

As a result, the central cell is divided into a large micropylar and a small chalazal chamber.

In both, further development of endosperm occurs as nuclear type.

Thus it is an intermediate type which is common in Helobiae series of monocots, hence the name.