Question

Describe the development of the angiosperm female gametophyte. Begin with the diploid megaspore mother cell (also called the megasporocyte). End with the embryo sac, and double fertilization. Include mitosis and meiosis in your description. Include where events are occurring within the flower.

Answer 1

The diploid megaspore mother cell is a cell that belongs to the sporophyte, as the name says, it contains 2 genome copies (diploid) and it is located in the femenine organs or the flower, the pistil. This megaspore will undergo meiosis, this process will produce 4 haploid megaspores, one of them tends to survive while the other 3 undergo cell death. This single megaspore.

The next steps are part of a process called megagametogenesis, and are dedicated to produce a gamethophyte that is formed by 7 cells. The megaspore undergoes 3 mitotic events but without any cytokinesis, this produces 8 nuclei in the cell, 2 of those nuclei migrate to the center of the cell, 3 migrate to one pole and the other 3 migrate to the other pole. Cytokinesis occurs in the poles and give membrane and cell wall to each one of the 6 nuclei in the poles. This forms 3 antipodal cells, one big central cell with 2 nuclei, 2 sinergic cells and 1 main egg cell. This whole structure is also called the emrbyo sac.

This concludes the formation of the megagametophyte, after this proces the structure remains latent until polen reaches the stigma and the 2 sperm cells in it enter the megagametophyte structure. One sperm cell fertilizes the egg to form and embryo and the other sperm cell fuses with the central cell to form a triploid cell that will form the endosperm in the seed