EMBRYO OF A DICOT SEED

A seed is a little embryonic plant with a seed coat around it. During sexual reproduction, male and female gametes unite to produce a zygote. After a time of rest, the zygote splits again and eventually develops into an embryo. There is no difference between monocot and dicot in the early stages of embryo development, although their development differs in later stages. Embryogeny is the process of developing a mature embryo from a zygote.

EMBRYO OF DICOT SEED

The plant embryo, also known as the seed embryo, is the component of a seed or bud that includes the plant’s roots, stem, and leaves in their earliest stages. The embryo develops after a fertilized adult plant flowers and is normally contained within a seed or bud. 

Seed: A seed is an embryonic plant that is surrounded by a protective layer. Seeds with two embryonic leaves and cotyledons are known as dicot seeds (Dicotyledons). 

A seed has three parts:

• Seed Coat
• Endosperm
• Embryo

Seed Coat:

The internal parts of the seed are protected by a seed coat. There are two layers to the seed coat. The testa refers to the thick outer layer. The thin inner layer is known as Tegmen. A thick seed coat protects the seed from the light and water. It keeps parasites out and prevents the seeds from losing water. In poor environmental circumstances, the stiff seed coatings impede germination. The micropyle is an aperture in the integument of the ovule that may be seen on various seed coverings. The hilum, which is similar to the naval in humans and is where the umbilical cord is connected, is also visible.

Endosperm:

The nutrients are stored in the endosperm. It provides starch, carbohydrates, and proteins to the seed to aid in the germination of the embryo. Underneath the seed coat is where you’ll find it. The seeds may be maintained alive until they germinate by eating nutrients. Mealy, continuous, or ruminate endosperm are all possibilities. The chromosomal complement of an endosperm is triploid. Endosperm makes up a large amount of the seed in maize and other grains. The endosperm is used in the embryo development of seeds like beans, although it is not present in the seed. The liquid endosperm of the coconut is called coconut.

Embryo:

A seed’s embryo is its most crucial component. Because it was produced from a fertilized egg, it is diploid. The embryo has all of the cells it needs to develop into a mature embryo.

Seed Growth

In angiosperms, seed development begins with double fertilization, which includes the nuclei of the egg and sperm coming together to create a zygote. The second phase in this process is the fusion of the polar nuclei with a second sperm cell nucleus, which results in the production of primary endosperm. Although the major endosperm divides fast to form endosperm tissue, the zygote is basically inactive after fertilization. This tissue provides nutrients to the newborn plant until the roots have formed after germination. The seed coat is made up of the integuments, or outer layers of ovule cells, which are made up of tissue from the mother plant: the inner integument creates the tegmen, and the outside integument makes the testa. The seed coat is also known as the testa when it consists of only one layer, albeit not all testa are homologous from one species to the next.

Food Storage in the Seed

The endosperm of endospermic dicots stores food reserves. Similar to monocots, the two cotyledons operate as absorptive organs during germination, absorbing the enzymatically produced food stores. The triploid endosperm develops properly in non-endospermic dicots after multiple fertilisation, but the endosperm food stores are swiftly remobilized and moved into the developing cotyledon for storage.

Seed Germination

When dicot seeds germinate, the epicotyl takes the shape of a hook, with the plumule pointing downwards; this plumule hook remains as long as germination takes place in the dark. As a result, the plumule is shielded from injury as the epicotyl pushes through the thick and abrasive soil. The hypocotyl hook straightens up when exposed to light, the juvenile foliage leaves face the sun and expand, and the epicotyl continues to extend. The radicle is also developing and forming the major root at this time. Lateral roots branch off to both sides as it develops downward to produce the tap root, resulting in the characteristic dicot tap root structure.

EMBRYO OF DICOT SEED DIAGRAM

Embryo: A seed’s embryo is its most crucial component. Because it was produced from a fertilized egg, it is diploid. The embryo has all of the cells it needs to develop into a mature embryo.

The components of an embryo are as follows:

• Epicotyl

• Hypocotyl
• Radicle
• Cotyledons

Epicotyl is a tiny shoot that provides the foundation for the complete plant shoot system.

During germination, the major root develops first. Hypocotyl is another name for it. It secures the plant’s position in the soil.

Radicle is a small embryonic root.

Cotyledons: It provides nutrition to many areas of the embryo. During the development of the seedling, it emerges from the earth as a small or fleshy leaf. It stores carbs and protein as well as other nutrients. The earliest leaves to emerge above ground are the embryonic leaves. A fertilized egg grows into an embryo.

What is meant by Embryo in the seed…?

Embryogeny in Dicots: In a normal dicot, the zygote elongates and then separates into two unequal cells by a transverse wall. Suspensor cells are the largest basal cells. The phrase “terminal cell” or “embryo cell” refers to the cell that is closest to the antipodal end. A filamentous suspensor with 6-10 cells is formed when the suspensor cell splits transversely a few times. The suspensor aids in the embryo’s insertion into the endosperm. The first cell of the suspensor, which is closest to the micropylar end, swells and serves as a haustorium. Similar to transfer cells, the haustorium possesses wall ingrowths. Hypophysis is the final cell of the suspensor that is close to the embryo. The radicle and root cap are produced subsequently by hypophysis.

The embryo cell divides twice vertically (quadrant stage) and once transversely to generate eight cells grouped in two tiers, epi-basal (terminal) and hypo-basal (hypo-basal) (near the suspensor). The two cotyledons and the plumule are formed by epi-basal cells. Except for the tip, the hypocotyl is produced by hypo-basal cells. The eight embryonic cells, or octants, divide peri-clonally to form a protoderm or dermatogen outer layer. Procambium (= Pleroma) and ground meristem (= periblem) are formed from the inner cells. The protoderm gives birth to the epidermis, the procambium to the steel or vascular thread, and the ground meristem to the cortex and pith.

The embryo is undifferentiated and spherical at first. Proembryo refers to an early embryo having radial symmetry. With the development of the radicle, plumule, and cotyledons, it transforms into an embryo. Two cotyledons divide from the sides by a thin plumule in the center. The embryo takes on the form of a heart at this point.

CONCLUSION

Seeds are merely containers, and not all plants reproduce by using them, despite the fact that we frequently think of them as the beginning of new plant life. The foundations of new plant life, like those of animals, have less to do with the container, whether it’s an egg or a womb, and more to do with what’s within that container: the embryo. Whether contained in a seed or a bud, the embryo in plants contains the early form of the organs the plant requires to survive.