Post Fertilization in Plant: Development of Embryo (Embryogeny)

Post Fertilization in plant: Development of Embryo 

1) Embryogenesis-  

• Embryogenesis is the process through which a zygote, formed after fertilization, develops into an embryo. This process begins at the micropylar end of the embryo sac, where the zygote divides and forms different structures.  

• As the embryo develops, the suspensor helps push it into the nutrient-rich endosperm. The embryo eventually takes on a recognizable shape with structures like the radicle, cotyledons, and plumule, which will grow into parts of the new plant. 

2) Development of Dicot Embryo as in Capsella: 

• The embryo is developed at the micropylar end of embryo sac. The growth of embryo triggers only after a certain amount of endosperm is formed.  

• After fertilization embryonic development begins. The zygote divides to form two- celled proembryo. Basal or suspensor initial cell and terminal or embryonal initial cell.  

• The suspensor cell divides transversely in one plane to produce filamentous suspensor of 6-10 cells.   

• The first cell of the suspensor towards the micropylar end becomes swollen and function as a haustorium. The lowermost cell of suspensor is known as hypophysis. 

• The embryonal initial undergoes three successive mitotic divisions to form octant.  

• The planes of divisions are at right angles to each other. The lower tier of four cells of octant give rise to hypocotyl and radicle whereas four cells of upper tier form the plumule and the one or two cotyledons.  

• The hypophysis by further division gives rise to the part of radicle and root cap. Subsequently, the cells in the upper tier of octant divide in several planes to become heart shaped which then forms two lateral cotyledons and a terminal plumule.  

• Further enlargement of hypocotyl and cotyledons result in a curvature of embryo and it appears horse-shoe shaped. 

 Development of Dicot Embryo as in Capsella 

3) Development of Monocot (grass) Embryo: 

• The embryo development is similar in both dicots and monocots up to the octant stage. The difference appears later.  

• In monocot embryo, single cotyledon occupies terminal position and plumule is lateral. The single shield shaped cotyledon is called as scutellum.  

• The protective sheath of plumule is called coleoptile and that of radicle is coleorhiza. Finally, ovule is transformed into seed and ovary into fruit. 

 Development of Monocot (grass) Embryo