Female reproductive organs in flowering plants Megasporogenesis.

Female reproductive organs in flowering plant

• In flowering plants, the female reproductive structure is a pistil.

• It is also located on the receptacle inside the flower. A pistil is differentiated into three parts - Style, stigma  and ovary.

• Ovary is the basal and swollen part in which the embryo sac is enclosed inside the ovule.

Structure of ovule

• A typical ovule is described as megasporangium.

• Ovule has a stalk at the lower end called the funicle.

• By funicle, the ovule is attached to the ovary through the placenta.

• Ovule is covered by more than one envelope. These envelopes are termed as integuments. The cell of Integuments is called a nucellus.

• Integuments make complete covering over the ovule except a narrow opening. This opening is called micropyle.

• Hence the end where the micropyle is located is called the micropylar end. There is a chalazal end opposite to the micropylar end.

Megasporogenesis.

• At the time reproduction , one of cell of nucleus is differentiated and act as megaspore mother cells.

• This megaspore undergoes meiotic division and produces four megaspore.

• Out of four megaspore, three are degenerated and one remains functional and proceeds the process of megasporogenesis.

• The formation of an embryo sac from a single functional megaspore is called monosporic development.

• Megasprogenesis is quite different from the Microsporogenesis

• Now functional megaspore undergoes two sequential mitotic divisions.

• As a result,  first two nuclei, followed by four and finally eight nuclei are formed after two sequential mitotic divisions.

• When two nuclei are formed form the functional megaspore. This is called a two nuclei celled stage embryo sac and followed by four and Eight nuclei stages formed after the two sequential mitotic division.

• With the formation of eight nuclei, Now these nuclei are moved at different locations of developing embryo sac.

• Out of eight nuclei,Three are moved at the chalazal end and formed antipodal cells. 

• And three are grouped at the micropylar end and form egg apparatus.The egg apparatus is made up of two synergids and one egg cell.

• Remaining two nuclei are called polar nuclei. These nuclei are moved at the centre and enclosed in a large central cell.

• In this way, a complete embryo sac or female gametophyte is formed.

• A typical embryo sac has eight nucleus and seven cells. Thus the embryo sac is eight nucleate and seven celled.