Megagametogenesis
Encyclopedia
Megagametogenesis is the development of a megaspore
into an embryo sac, which is the gametophyte
- though a highly reduced one - stage in the life cycle of vascular plants.
of a plant. The details of the process vary by species, but the process described here is common. This process starts with a single diploid megasporocyte in the nucleus. This megasporocyte undergoes meiotic cell division to form four cells that are haploid. Three cells die and one that is most distant from the micropyle develops into the megaspore. This megaspore becomes larger and the nucleus of it undergoes mitosis
three times until there are eight nuclei. These eight nuclei are then arranged into two groups of four. These groups both send a nucleus to the center of the cell which then becomes the polar nuclei. The three cells left at the end of the cell near the micropylar become the egg apparatus with an egg cell in the center and two synergids. A cell wall forms around the other set of nuclei and forms the antipodals. The cells in the center develop into the central cell. This entire structure with its eight nuclei is called the embryo sac.
2-hilam
3-integuments
4-micropyle
5-chalaza
6-nucellus
7-embryosac
Megaspore
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These types of plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gametophyte, which is fertilized by sperm produced...
into an embryo sac, which is the gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
- though a highly reduced one - stage in the life cycle of vascular plants.
Eudicots
In eudicot plants, the entire process happens inside the ovuleOvule
Ovule means "small egg". In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: The integument forming its outer layer, the nucellus , and the megaspore-derived female gametophyte in its center...
of a plant. The details of the process vary by species, but the process described here is common. This process starts with a single diploid megasporocyte in the nucleus. This megasporocyte undergoes meiotic cell division to form four cells that are haploid. Three cells die and one that is most distant from the micropyle develops into the megaspore. This megaspore becomes larger and the nucleus of it undergoes mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
three times until there are eight nuclei. These eight nuclei are then arranged into two groups of four. These groups both send a nucleus to the center of the cell which then becomes the polar nuclei. The three cells left at the end of the cell near the micropylar become the egg apparatus with an egg cell in the center and two synergids. A cell wall forms around the other set of nuclei and forms the antipodals. The cells in the center develop into the central cell. This entire structure with its eight nuclei is called the embryo sac.
See also
- egaspore- it is the female part of the flower in which seeds are formed. it consists of 7 parts-1-funicle
2-hilam
3-integuments
4-micropyle
5-chalaza
6-nucellus
7-embryosac
- icrospore- it is the male part of the flower in which pollen grains are stored.
- GametophyteGametophyteA gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....