Explain the development of dicot embryo
Answers
Explanation:
Development of a dicot embryo (i) Embryo formation starts after a certain amount of endosperm is formed. (ii) Zygote divides by mitosis to form a proembryo. (iii) Formation of globular and heart-shaped embryo occurs, which finally becomes horse shoe-shaped forms a mature embryo. (iv) In dicot plants, embryo consists of two cotyledons and an embryonal axis between them.(v) The portion of embryonal axis above the level of attachment of cotyledons is epicotyl and it terminates in the plumule. (vi) The portion of embryonal axis below the level of attachment of cotyledon is the hypocotyl, it becomes radicle (root tip). The embryonic stages during the development of a mature embryo sac are:
(a) Fertilised embryo sac showing zygote and Primary Endosperm Nucleus (PEN).
(b) Stages in embryo development in a dicot.
DICOT EMBRYO -
- A dicotyledon embryo consists of two cotyledons and an embryonal axis.
- The embryonal axis is divided into epicotyl and hypocotyl that forms plumule and radicle respectively.
- The development of the embryo starts from the formation of two-celled pro-embryo containing basal cells towards the microphyle and terminal cells.
- Further, the basal cell proliferates to form a suspensor and the terminal cell forms a four celled structure. The pro-embryo transforms to a quadrant stage.
- The four cells in the quadrant stage divide transversely to form eight cells in two tiers. The structure formed is the Octet stage.
- Lower-tier forms tip and cotyledon while upper-tier forms hypocotyl.
- The suspensor swells to form haustorium and the last cell of the unit is hypophysis that later forms the root and the root cap.
- The eight cells further divide to form eight outer cells and eight inner cells.
- Outer cells form the dermatogen and the epiderm whereas the inner layer forms the plerome and periblem that forms the vascular strand and cortex and pith respectively.
- The hypocotyl and cotyledon enlarge to form the horseshoe-shaped mature embryo.
