Monocot and dicot embryo development

 

Monocot and dicot embryo development

• After the development of an endosperm in a flowering plant, The development of the embryo takes place at micropyle end and developed from the zygote.

• Most of the zygote divide only when endosperm is formed. This is an adaptation to ensure the nutrition to developing embryo.

• The development of an embryo from zygote is called embryogenesis.

• On the basis of cotyledons, embryos are of two types- Monocotyledons and Dicotyledons embryos.

• The monocotyledon has one cotyledon at its apex whereas The dicotyledon embryo has two cotyledons.

• Both types of embryo have an embryonal axis, it is common in both embryos.

• The early stage of embryo development in monocotyledons and dicotyledons are the same up to the globular stage of embryo. After the globular stage,differences can be marked.

Structure and development of  Dicotyledons embryo

• After a period of rest, zygotes divide by transverse division at first and form apical and basal cells.

• The basal cell is always located close to the micropyle.

• The basal cell and apical are divided by a transverse and longitudinal wall respectively and the structure of the embryo is called proembryo.

• After the division of basal cell and apical cell , embryo assumes shape like 'T'.

• The terminal cell of T shaped embryo near apical cell divides again by longitudinal division and T shaped embryo is changed into quadrant stage.

• Each cell of the quadrant stage divides by the transverse wall and gives rise to the octant stage.

• Now basal cells undergo several divisions and give rise to an elongated suspensor with 8-10 cells.

• The cell of suspensor located near proembryo acts as a hypophysis.

• The cell of the spherical region of proembryo undergoes  repeated division and two cotyledons are differentiated. This stage of embryo looks like a cordate body.

• Now The mature embryo has two cotyledons and an embryonal axis.

• The portion above the level of cotyledons form plumule or epicotyl whereas below the level of cotyledons form radicle or hypocotyl.

• When seed germinates, the plumule form shoot system and radical form root system.

• The reserve food material that is stored in cotyledons is used for the development of seedling. For ex- Mango, apple, radish rose.

Structure and development of  Monocotyledons embryo

• All stages in dicotyledons and monocotyledons embryos are similar up to the octant stage.

• When a monocotyledon's embryo matures, it has the structures different from dicotyledons. The monocotyledon embryo has one cotyledon with an embryonal axis.

• The cotyledons are situated at one side of the embryonal axis called Scutellum.

• The radical and root cap are situated at the lower end of the embryonal axis in a sheath. This sheath is called coleorhiza.

• The Shoot apex and leaf primordia is closed in a hollow structure called coleoptile at the upper end of the embryonal axis. For ex- Grass , Banana , bamboo, palm etc.