01 Reproduction in Lower and Higher Plants - part 09 - Development of Embryo

01 Reproduction in Lower and Higher Plants - part 09 - Development of Embryo


Development of Embryo : 

  • The process of development of zygote into an embryo is called embryogenesis. 
  • The embryo is developed at the micropylar end of embryo sac. 
  • The growth of embryo triggers only  after certain amount of endosperm is formed. 
  • After fertilization the embryonic development begins. The zygote divides to form two- celled proembryo. 
  • The larger cell towards the micropyle is called basal or suspensor initial cell and smaller cell towards chalaza is called 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 suspensor helps in pushing the embryo in the endosperm. 
  • 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 where as 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 so as 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. 
  • 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 the seed and ovary into the fruit.



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