Megasporogenesis is the process of forming megaspores, occurring in the female reproductive part of plants known as the gynoecium. A primary archesporial cell becomes the megaspore mother cell, which undergoes meiosis to produce four haploid megaspores, of which one remains functional and develops into an embryo sac. The embryo sac eventually contains eight nuclei, including a diploid secondary nucleus and structures forming the egg apparatus and antipodal cells.

1. Megasporogenesis
Dambar Singh Khatri

2. • Formation of megaspores is termed as Megasporogenesis.
• The female reproductive part of plant is called gynoecium. The unit of gynoecium is called pistil. Pistil bears
stigma, style and ovary. Ovary bears ovule in the cavity of ovary called placenta.
• Initially, ovule bears homogenous mass of cells called nucellus.
• The nucellus is surrounded by two layer of integuments and attached with placenta by a short stalk called
funiculus.
• At early stage, one cell grows in size having dense cytoplasm which is known as primary archesporial cell.
Later it divides mitotically into two cell, the megaspore mother cell and parietal cell
• The megaspore mother cell increase in size and divides twice by meiotically to form four haploid megaspore.

4. • Out of four megaspores, three degenerates while one remains functional.
• The functional megaspore grows rapidly by absorbing nutrition from
nucellus, and forms embryo sac. The embryo sac consists one nucleus.
• The nucleus of embryo sac further divides by mitosis into two cell. These
nucleus move towards opposite poles. The pole of the embryo sac close to
chalaza is called chalaza end and the one closer to micropyle is called
micropylar end.

5. Structure of ovule

6. • Each daughter nuclei divides again, and results in four nuclei. Each nuclei
divides again forming eight nuclei.
• One nuclei from each end come to the center and fuse to form diploid
secondary nucleus.
• Three nuclei in the chalazal end called antipodal cells. Similarly the nuclei at
the micropylar end form egg apparatus, consisting of two haploid synergids
on either side of a large, central haploid egg cell.