Gametophyte

A gametophyte, or gamete-bearing plant, is one of the two multicellular phases that occur in alternation of generations. The gametophyte is the haploid phase; that is, its cells contain only one set of chromosomes, in contrast to the sporophyte phase, where the cells contain two sets. The gametophyte develops from the germinating, haploid spore, which was produced by meiosis in the sporangium of the sporophyte phase. Gametophytes produce sperm and egg cells by mitosis , often in multicellular gametangia known as antheridia and archegonia, respectively. Fertilization, which occurs in the female gametophyte, establishes a new sporophyte generation. In some algae, like sea lettuce, the vegetative gametophyte is identical in form to the vegetative sporophyte, but in most organisms the gametophyte has a very different appearance from the sporophyte. In bryophytes the gametophyte is the highly visible, persistent phase of the plant, but in vascular plants the gametophyte is short-lived and often much reduced in size. Among land plants, gametophytes are of four different types. These include: (1) the green, leafy shoot systems of mosses, and leafy liverworts; (2) the green, thallus to prothallus forms of thalloid liverworts, hornworts, horsetails, most ferns, and some lycopods; (3) the colorless, subterranean, mycorrhizal axes of psilophytes and some lycopods; and (4) the small, endosporic forms of heterosporous lycopods, some ferns, and all seed plants. The smallest and least complex gametophytes are those of the flowering plants. The male gametophyte is the two- or three-celled pollen grain that is released from the anther, and the female gametophyte is the seven-celled embryo sac that is located in the base of the pistil of the flower.

see also Bryophytes; Reproduction, Alternation of Generations and; Reproduction, Fertilization and; Reproduction, Sexual; Sporophyte.

Barbara Crandall-Stotler

Bibliography

Graham, Linda. "The Origin of the Life Cycle of Land Plants." American Scientist 73 (1985):178-186.

gametophyte A haploid phase of the life cycle of plants, during which gametes are produced by mitosis. It arises from a haploid spore produced by meiosis from a diploid sporophyte. In lower plants (such as mosses), the gametophyte is the dominant and conspicuous generation. See also ALTERNATION OF GENERATIONS.

gametophyte The generation in the life cycle of a plant that bears the gamete-producing sex organs. The gametophyte is haploid. It is the dominant phase in the life cycle of mosses and liverworts, the sporophyte generation depending on it either partially or completely. In clubmosses, horsetails, and ferns it is the prothallus. In seed plants it is very much reduced. For example, in angiosperms the pollen grain is the male gametophyte and the embryo sac is the female gametophyte. See also alternation of generations.

ga·me·to·phyte / gəˈmētəˌfīt/ • n. Bot. (in the life cycle of plants with alternating generations) the gamete-producing and usually haploid phase, producing the zygote from which the sporophyte arises. It is the dominant form in bryophytes.DERIVATIVES: ga·me·to·phyt·ic / gəˌmētəˈfitik/ adj.

gametophyte A haploid phase of the life cycle of plants, during which gametes are produced by mitosis. It arises from a haploid spore produced by meiosis from a diploid sporophyte. In lower plants (such as mosses), the gametophyte is the dominant and conspicuous generation. See also alternation of generations.