gametophyte

 

(gəmē'təfīt') , phase of plant life cycles in which the gametes, i.e., egg and sperm, are produced. The gametophyte is haploid, that is, each cell contains a single complete set of chromosomes, and arises from the germination of a haploid spore. In many lower plants, the gametophyte phase is the dominant plant form; for example, the familiar mosses are the gametophyte form of the plants. The alternate phase of the plant life cycle is the sporophyte, the diploid plant form, with each cell containing two complete sets of chromosomes. For example, in mosses the sporophyte is a capsule atop a slender stalk that grows out of the top of the gametophyte. The sporophyte develops from the union of two gametes, such as an egg fertilized by a sperm; in turn, the sporophyte forms spores that develop into gametophytes. The alternation between haploid gametophyte and diploid sporophyte phases, known as alternation of generations, occurs in all multicellular plants. As plants advanced in evolutionary development, the sporophyte became the increasingly dominant plant form and the gametophyte form has been correspondingly reduced. In contrast to mosses, for example, in the advanced angiosperms the male and female gametophytes are reduced to three-celled and seven-celled structures, respectively, found within the reproductive organs of the familiar flowering plant (the sporophyte). See also fertilization; reproduction.

In plants that undergo alternation of generations, a gametophyte is the structure, or phase of life, that contains only half of the total complement of chromosomes:

• The sporophyte produces spores, in a process called meiosis. These spores develop into a gametophyte. These spores and the resulting gametophyte have only half of the total complement of chromosomes.
• The gametophyte produces male or female gametes (or both), in a process called mitosis. The fusion of male and female gametes produces a zygote which develops into the sporophyte.

In mosses (bryophytes) the gametophyte is the commonly known phase of the plant. An early developmental stage in the gametophyte of both mosses and ferns (immediately following the meiospore) is called the Protonema.

In most other plants the gametophyte is very small (as in ferns) or even reduced as in flowering plants (angiosperms), where the female form (ovule) is known as a megagametophyte and the male form (pollen) is called a microgametophyte.

See also

• Sporophyte
• Alternation of generations
• Archegonium
• Antheridium

Botany
Subdisciplines of botany	Ethnobotany · Paleobotany · Plant anatomy · Plant ecology · Plant morphology · Plant physiology
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Plant life cycles	Gametophyte · Plant sexuality · Pollen · Pollination · Seed · Spore · Sporophyte
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