WordNet

the gamete-bearing individual or phase in the life cycle of a plant having alternation of generations

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/11/13 22:26:30」(JST)

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Several gametophytes growing in a terrarium.

Pine gametophyte (outside) surrounding the embryo (inside)

A gametophyte is the haploid multicellular stage in the alternation of generations life cycle of plants and algae. It develops from a spore by mitotic cell division. Spores are the products of meiosis in sporophytes. Gametophytes produce haploid gametes by mitosis.

In some types of plants and algae (e.g. Ulva) gametes are isogamous--that is, the gametes are all of one size, shape and general morphology.^[1] In land plants, Anisogamy is universal. As in animals, female and male gametes are called, respectively, eggs and sperm. The fusion of male and female gametes produces a diploid zygote, which develops by repeated mitotic cell divisions into a multicellular sporophyte.

In bryophytes (mosses, liverworts, and hornworts), the gametophyte represents the longer lived, nutritionally independent and more visible stage of the life cycle. Sporophytes are typically attached to and dependent on gametophytes.^[2] Moss gametophytes originate from the germination of a spore. The initial phase of growth leads to a filament of cells (called the protonema). The mature gametophyte of mosses produces gametangia (gamete-producing structures). Eggs develop in archegonia and sperm in antheridia.^[3] In gametophyte dominant organisms, such as bryophytes, specialized structures or even whole individual plants that produce gametes are sometimes called gametophores (or gametangiophores).

Among vascular plants, an interesting pattern exists with regard to gametophytes. Homosporous vascular plants (plants that produce only one type of spore) have exosporic gametophytes—that is, the gametophyte develops outside of the spore wall. In addition, these exosporic gametophytes are normally bisexual (produce both sperm and eggs). In heterosporous vascular plants (plants that produce both microspores and megaspores), the gametophyte develops endosporically—within the spore wall. These gametophytes are unisex, producing either sperm or eggs but not both. All vascular plants are sporophyte dominant, and a trend toward smaller and shorter-lived gametophytes is evident as land plants evolved in a terrestrial environment.^{[citation needed]}

Extant lycophytes produce several different types of gametophytes. In the families Lycopodiaceae and Huperziaceae, gametophytes are subterranean and mycotrophic, deriving nutrients from symbiosis with fungi. Isoetes and Selaginella, which are heterosporous, megagametophytes develop inside the megaspores, which crack open to allow access to internal archegonia.^{[citation needed]}

In most ferns, gametophytes are photosynthetic free living organism called a prothallus. However in some groups, notably the clade that includes Ophioglossaceae and Psilotaceae, gametophytes are subterranean and subsist by forming mycotrophic relationships with fungi. In leptosporangiate ferns such as Dryopteris, the gametophyte is a free-living, autotrophic prothallus that maintains the sporophyte during its early multicellular development. By contrast, in seed plants (gymnosperms and angiosperms), gametophytes develop into multicellular organisms while still enclosed within the sporangium.^[4]

In heterosporous plants (water ferns, some lycophytes, gymnosperms and angiosperms) the egg producing gametophyte is known as a megagametophyte and the sperm producing gametophyte as a microgametophyte. In the seed plants, the microgametophyte is called pollen. Seed plant microgametophytes consists of two or three 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. In seed plants, the microgametophyte (pollen grain) travels to the vicinity of the egg cell (carried by a physical or animal vector), and produces two sperm by mitosis.

In gymnosperms the megagametophyte consists of several thousand cells and produces one to several archegonia, each with a single egg cell. The gametophyte becomes a food storage tissue in the seed.^[5]

In angiosperms, the megagametophyte is reduced to only a few nuclei and cells, and is sometimes called the embryo sac. A typical embryo sac contains seven cells and eight nuclei, one of which is the egg cell. Two nuclei fuse with a sperm nucleus to form endosperm, which becomes the food storage tissue in the seed.

In some multicellular green algae, red algae, or brown algae (Ulva lactuca is one example) sporophytes and gametophytes may be externally indistinguishable (isomorphic) or either the sporophyte or the gametophyte may be reduced (heteromorphic).^{[citation needed]}

References

^ Sadava, David; Hillis, David; Heller, H. Craig; Berenbaum, May (2012). Life: The Science of Biology, Volume 1 (10th ed.). Macmillan. ISBN 978-1464141225.
^ Budke, J.M., Goffinet, B. and Jones, C.S. (2013):Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica. Annals of Botany doi:10.1093/aob/mct033
^ Ralf Reski (1998): Development, genetics and molecular biology of mosses. In: Botanica Acta 111, pp 1-15.
^ C.Michael Hogan (2010): Fern. Encyclopedia of Earth. National council for Science and the Environment. Washington, DC
^ "Vascular Plants :: Description". Digimuse.nmns.edu.tw. Retrieved 2014-07-13.

English Journal

Sphingolipid metabolism is strikingly different between pollen and leaf in Arabidopsis as revealed by compositional and gene expression profiling.

Luttgeharm KD1, Kimberlin AN2, Cahoon RE3, Cerny RL4, Napier JA5, Markham JE6, Cahoon EB7.
Phytochemistry.Phytochemistry.2015 Jul;115:121-9. doi: 10.1016/j.phytochem.2015.02.019. Epub 2015 Mar 17.
Although sphingolipids are essential for male gametophytic development in Arabidopsis thaliana, sphingolipid composition and biosynthetic gene expression have not been previously examined in pollen. In this report, electrospray ionization (ESI)-MS/MS was applied to characterization of sphingolipid c
PMID 25794895

No evidence for Fabaceae Gametophytic self-incompatibility being determined by Rosaceae, Solanaceae, and Plantaginaceae S-RNase lineage genes.

Aguiar B1,2, Vieira J3,4, Cunha AE5,6, Vieira CP7,8.
BMC plant biology.BMC Plant Biol.2015 Jun 2;15(1):129. doi: 10.1186/s12870-015-0497-2.
BACKGROUND: Fabaceae species are important in agronomy and livestock nourishment. They have a long breeding history, and most cultivars have lost self-incompatibility (SI), a genetic barrier to self-fertilization. Nevertheless, to improve legume crop breeding, crosses with wild SI relatives of the c
PMID 26032621

Diversification and distinctive structural features of S-RNase alleles in the genus Solanum.

Brisolara-Corrêa L1, Thompson CE, Fernandes CL, de Freitas LB.
Molecular genetics and genomics : MGG.Mol Genet Genomics.2015 Jun;290(3):987-1002. doi: 10.1007/s00438-014-0969-3. Epub 2014 Dec 12.
The multigenic and multiallelic S-locus in plants is responsible for the gametophytic self-incompatibility system, which is important to prevent the detrimental effects of self-fertilization and inbreeding depression. Several studies have discussed the importance of punctual mutations, recombination
PMID 25501309

Japanese Journal

Evolutionary Analysis of Genes for S-RNase-based Self-incompatibility Reveals S Locus Duplications in the Ancestral Rosaceae

Morimoto Takuya,Akagi Takashi,Tao Ryutaro
The Horticulture Journal advpub(0), 2015
… The Solanaceae, the Rosaceae, and the Plantaginaceae have the S-RNase-based gametophytic SI (GSI) system, which uses S-RNase and F-box proteins as the pistil S and pollen S determinants, respectively. …
NAID 130005064826

DNA Markers and the Molecular Mechanism of Self-(in)compatibility in Japanese Pear (Pyrus pyrifolia Nakai)

Okada Kazuma
The Horticulture Journal advpub(0), 2015
… This species exhibits gametophytic self-incompatibility (GSI), which is controlled by a single S-locus with multiple S-haplotypes. …
NAID 130005064823