Development OF endosperm and embryo part6

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Published on May 17, 2020 4:03:47 AM ● Video Link: https://www.youtube.com/watch?v=uOFc3eW5vaU

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Embryo (1994)

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DEVELOPMENT OF ENDOSPERM

The primary endosperm nucleus divides repeatedly. It forms polyploidy nutritive tissue called endosperm. There are two types of seeds for storage of food:

b) Endospertnic or albuminous seed: The endosperm supply food

to the 0.–weloping embryo. Such seeds are called endospermic seeds. in plants like corn, wheat, the endosperm tissue is present in the .ime of seed germination. So these are endospermic seeds.

c) Non–cntiospermic or ex–albuminous seeds: In some cases, the endosperm is completely utilized by developing embryo. Such seeds are known as non-endospermic seeds. In beans and peas the endosperm tissue is completely digested by the developing

embryo and stored in the cotyledons.

Formation of Endosperm

Endosperm is formed from the primary endosperm nucleus. Its formation starts before the formation of embryo. Primary endosperm nucleus is produced by fusion of monoploid polar nuclei (secondary nucleus) and a monoploid second male gamete. The endosperm is thus triploid (3n). However in some case, it may be pentaploid (Per aea). It may be even 9n (Pepromia).

Structure of Endosperm

The cells of the endosperm are isodiametric. They store large quantity of food materials. The storage food is present in the form of starch granules, granules of proteins, or oils. In certain plants, the endosperm cells develop very thick hard walls of hemicelluloses. The parietal layer of the endosperm of grass functions like a cambium. This layer produces on its inside layers of thin-walled cells. These cells are packed with starch. The cells of outermost layer stops dividing. It is filled with aleurone grains. This layer is called aleurone layer. The cells of this layer secrete diastase and other enzymes. These enzymes digest the food stored in endosperm for developing embryo.

Types of Endosperm

There are three types of endospenns on the basis of mode of development. These are nucelar type, cellular type and Helobial type. I. Nuclear Type: In this case, the primary endosperm nucleus divides by free nuclear divisions. Wall is not formed between them. A vacuole appears in the centre of the embryo sac. It increases in size and. Therefore, the nuclei are pushed to the periphery along the wall of the embryo sac. Later, walls develop between the nuclei. Thus cellular tissues are formed.

Cellular Type: In this case, the primary endosperm nucleus
divides and walls are formed between the daughter nuclei. These walls may be either transverse or longitudinal. It divides the embryo sac into two cells. Later, these cells divide by repeated divisions. It produces a tissue of irregularly arranged cells.

Helobial Type: This type of endosperm occurs in the order
Helobiales (Monocotyledons). In this case, first division of primary endosperm nucleus is followed by a transverse wall. This wall divides the embryo sac into a small chalazal chamber and a large micropylar chamber. Then the nuclei in each chamber divide by free nuclear divisions. But, there are few nuclear divisions in the calazal chamber. The endosperm in this chamber degenerate. Walls develop between nuclei in micropylar chamber. It produces cellular endosperm.

DEVELOPMENT OF EMBRYO

Development of Dicot Embryo

The development of Capsella bursa-pastoris (Shepherd’s purse) embryo is taken as model organism for the study of development of

embryo of dicots.

Following developmental changes take place in the embryo CopseIla bursa pasioris:

First division of Oospore: Its oospore increases in size. It divides transversely in two cells. The cell toward the microphyll end is called suspensor cell. The cells towards other side is called embryonal cell. Embryonal cell forms the major portion of embryo.
Formation of suspensor and radicle: The suspensor cell undergoes few transverse divisions. It produces short filament of cells called suspensor. The first cell of suspensor enlarges very -nuch. It becomes basal cell. It pushes the embryo down into the developing endosperm. Suspensor also acts as conductive tissues for the nutrients. The last cell of suspensor adjacent to embryonal cell is called hypophysis. Hypophysis divides further to form radicle.
BY Sourabh Sharma