The process of formation of megaspore from Megaspore Mother Cell, (MMC), through meiosis is known as megasporogenesis. MMC is large nucleated with dense cytoplasm. It undergoes meiosis, which results in the production of 4 megaspores. Out of 4, 3 degenerates and one megaspore is functional which develops into female gametophyte. “Method of embryo sac formation from a single megaspore is known as Monosporic type of development”.
Developments of Female Gametophyte
Megaspore mother cell undergoes 3 successive mitotic division to form 8 nucleated embryo sac.
Development of Embryosac
First the functional megaspore nucleus divides mitotically to form 2 nuclei which move towards opppsite
pole forming 2- Nucleate embryo sac. The developing embryo sac enlarges in size due to formation of vacuole in the centre.
Each 2 nulei, divides and redivides, forming 4 neulei at micropylar end and 4 nuclei at chalazal end, here they undergo free nuclear division. At 8 celled stage cell wall formation.
Out of 4 nuclei at micropylar end, 3 differentiate to produce Egg apparatus = 1 Egg + 2 Synergid cells. 4 nuclei at chalazal, 3 remains at, polar region and form Antipodals.
One nucleus from micropylar end, one from chalazal end migrate towards the centre and fuse to form (2n) diploid secondary nucleus.
Thus a typical angiosperm embryosac at maturity though 8 nucleate, it is 7 celled.
