Double fertilization
This process involves the fusion of a female gametophyte or megagametophyte, also called the embryonic sac, with two male gametes (sperm).
It begins when a pollen grain adheres to the stigmatic surface of the carpel, the female reproductive structure of angiosperm flowers.
The tip of the pollen tube then enters the ovary by penetrating through the micropyle opening in the ovule, and releases two sperm into the embryonic sac (megagametophyte).
The haploid sperm and haploid egg fuse to form a diploid zygote, the process being called syngamy, while the other sperm and the diploid central cell fuse to form a triploid primary endosperm cell (triple fusion).
[3] Double fertilization was discovered more than a century ago by Sergei Nawaschin in Kyiv,[4] and Léon Guignard in France.
[5] Lilium martagon and Fritillaria tenella were used in the first observations of double fertilization, which were made using the classical light microscope.
[6] A far more rudimentary form of double fertilization occurs in the sexual reproduction of an order of gymnosperms commonly known as Gnetales.
[10] The additional fertilization product in Ephedra does not nourish the primary embryo, as the female gametophyte is responsible for nutrient provision.
[9] The more primitive process of double fertilization in gymnosperms results in two diploid nuclei enclosed in the same egg cell.
[11] Comparative molecular research on the genome of G. gnemon has revealed that gnetophytes are more closely related to conifers than they are to angiosperms.
[15] In vitro double fertilization is often used to study the molecular interactions as well as other aspects of gamete fusion in flowering plants.
One of the major obstacles in developing an in vitro double fertilization between male and female gametes is the confinement of the sperm in the pollen tube and the egg in the embryonic sac.
[17] The female gametophyte, the megagametophyte, that participates in double fertilization in angiosperms which is haploid is called the embryonic sac.
