Question

Development of dicot embryo- Describe in detail.

Answer 1

The oospore divides transversely forming two cells, a terminal cell and basal cell. The cell towards the micropylar end of the embryo sac is the suspensor cell (i.e., basal cell) and the other one makes to the embryo.cell (i.e., terminal cell). The terminal cell by subsequent divisions gives riseto the embryo while the basal cell contributes the formation of suspensor.The terminal cell divides by a vertical division forming a 4-celled 1-shaped embryo. In certain plants the basal cellalso forms the hypocotyl (i.e., the root end of the embryo) in addition of suspensor. The terminal cells of the four-celled pro-embryo divide verticallyat right angle to the first vertical wall forming four cells. Now each of the four cells divides transversely forming the octant stage (8-celled) of the embryo.The four cells next to the suspensor are termed the hypo-basal or posterior octants while the remaining four cells make the epibasal or anterior octants. The epibasal octants give rise to plumule and the cotyledons, whereas the hybobasal octants give rise to the hypocotyl with the exception of its tip. Now all the eight cells of the octant divide periclinally forming outer and inner cells.The outer cells divide further by anticlinal division forming a peripheral layer of epidermal cells, the dermatogen. The inner cells divide by longitudinal and transverse divisions forming periblem beneath the dermatogen and plerome in the centralregion. The cells of periblem give rise to the cortex while that of plerome form the stele.At the time of the development of the octant stage of embryo the two basal cells divide transversely forming a 6-10celled filament, the suspensor which attains its maximum development by the time embryo attains globular stage. The suspensor pushes the embryo cells down into the endosperm.The distal cell of the suspensor is much larger than the other cells and acts as a haustorium. The lowermost cell of the suspensor is known as hypophysis. By further divisions, the hypophysis gives rise to the embryonic root and root cap.With the continuous growth, the embryo becomes heart-shaped which is made up of two primordia of cotyledons. The mature embryo consists of a short axis and two cotyledons. Each cotyledon appears on either side of the hypocotyl. In most of dicotyledons, the general course of embryogenesis is followed as seen in Capsella bursa-pastoris.

Answer 2

Dicot embryo is enclosed in between two cotyledons.

Explanation:

Development of a dicot embryo consists of three steps.

(i) Embryo formation

(ii) Zygote division

(iii) Formation of globular and heart-shaped embryo occurs, which finally becomes horse shoe-shaped forms a mature embryo.

• Initially the "hypophysis" gives rise to the "embryonic root" and "root cap".
• Further development the seed turned into heart-shaped structure which is shaped of two primordial of cotyledons.
• The developed seed consists of a small axis and two cotyledons. Each cotyledon present on both "side of the hypocotyl".

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