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Megagametogenesis is the process of maturation of the female gametophyte, or megagametophyte, in plants. [1] During the process of megagametogenesis, the megaspore, which arises from megasporogenesis, develops into the embryonic sac, in which the female gamete is housed. [2] These megaspores then develop into the haploid female gametophytes. [2]
These plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gametophyte , which produces egg cells . These are fertilized by sperm produced by the male gametophyte developing from the microspore.
A megaspore mother cell, or megasporocyte, is a diploid cell in plants in which meiosis will occur, resulting in the production of four haploid megaspores. At least one of the spores develop into haploid female gametophytes, the megagametophytes. [1] The megaspore mother cell arises within the megasporangium tissue.
A megasporocyte inside a megasporangium or ovule undergoes meiosis, producing four megaspores. Only one is a functional megaspore whereas the others stay dysfunctional or degenerate. The megaspore undergoes several mitotic divisions to develop into a female gametophyte (for example the seven-cell/eight-nuclei embryo sac in flowering plants).
Nucellar embryony (notated Nu+) is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. Nucellar embryony is a type of apomixis , where eventually nucellar embryos from the nucellus tissue of the ovule are formed, independent of meiosis and sexual reproduction . [ 1 ]
A female pinecone produces the megaspores of this heterosporic plant. A male pinecone produces the microspores of this heterosporic plant. Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore, is male and the larger megaspore is
In seed plants, the microgametophyte is called pollen. Seed plant microgametophytes consists of several (typically two to five) cells when the pollen grains exit the sporangium. The megagametophyte develops within the megaspore of extant seedless vascular plants and within the megasporangium in a cone or flower in seed plants.
An endosperm is formed after the two sperm nuclei inside a pollen grain reach the interior of a female gametophyte or megagametophyte, also called the embryonic sac.One sperm nucleus fertilizes the egg cell, forming a zygote, while the other sperm nucleus usually fuses with the binucleate central cell, forming a primary endosperm cell (its nucleus is often called the triple fusion nucleus).