Gametophyte stage is dominant in the mossâs life cycle Gametophytes are photosynthetic & have root-like rhizoids The diploid sporophyte has a complete set of chromosomes & produces spores by meiosis. Production of a new sporophyte directly from a gametophyte without syngamy (termed agamospory, a type of apomixis; see figure 1) has arisen independently in a diversity of fern families (Liu et al. Estimates of the proportion of fern species using this reproductive pathway range from 3% (Liu et al. 2012) to about 10% (Walker 1984).
Several gametophytes growing in a terrarium.
Pine gametophyte (outside) surrounding the embryo (inside)
A gametophyte (/É¡ÉËmiËtoÊfaɪt/) is one of the two alternating phases in the life cycle of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the sexual phase in the life cycle of plants and algae. It develops sex organs that produce gametes, haploid sex cells that participate in fertilization to form a diploidzygote which has a double set of chromosomes. Cell division of the zygote results in a new diploid multicellular organism, the second stage in the life cycle known as the sporophyte. The sporophyte can produce haploid spores by meiosis.
Algae[edit]
In some multicellulargreen algae (Ulva lactuca is one example), red algae and brown algae, sporophytes and gametophytes may be externally indistinguishable (isomorphic). In Ulva the gametes are isogamous, all of one size, shape and general morphology.[1]
Land plants[edit]
In land plants, anisogamy is universal. As in animals, female and male gametes are called, respectively, eggs and sperm. In extant land plants, either the sporophyte or the gametophyte may be reduced (heteromorphic).[2]
Bryophytes[edit]
In bryophytes (mosses, liverworts, and hornworts), the gametophyte is the most visible stage of the life cycle. The bryophyte gametophyte is longer lived, nutritionally independent, and the sporophytes are typically attached to the gametophytes and dependent on them.[3] When a moss spore germinates it grows to produce a filament of cells (called the protonema). The mature gametophyte of mosses develops into leafy shoots that produce sex organs (gametangia) that produce gametes. Eggs develop in archegonia and sperm in antheridia.[4]
In some bryophyte groups such as many liverworts of the order Marchantiales, the gametes are produced on specialized structures called gametophores (or gametangiophores).
Vascular plants[edit]
All vascular plants are sporophyte dominant, and a trend toward smaller and more sporophyte-dependent female gametophytes is evident as land plants evolved reproduction by seeds.[5]Vascular plants such as ferns that produce only one type of spore are said to be homosporous. They have exosporic gametophytesâthat is, the gametophyte is free-living and develops outside of the spore wall. Exosporic gametophytes can either be bisexual, capable of producing both sperm and eggs in the same thallus (monoicous), or specialized into separate male and female organisms (dioicous).
In heterosporous vascular plants (plants that produce both microspores and megaspores), the gametophyte develops endosporically (within the spore wall). These gametophytes are dioicous, producing either sperm or eggs but not both.
Ferns[edit]
In most ferns, for example, in the leptosporangiate fernDryopteris, the gametophyte is a photosynthetic free living autotrophic organism called a prothallus that produces gametes and maintains the sporophyte during its early multicellular development. Ring video doorbell 2 app. However, in some groups, notably the clade that includes Ophioglossaceae and Psilotaceae, the gametophytes are subterranean and subsist by forming mycotrophic relationships with fungi.
Lycophytes[edit]Fern Gametophyte Or Sporophyte Dominant
Extant lycophytes produce two different types of gametophytes. In the homosporous families Lycopodiaceae and Huperziaceae, spores germinate into bisexual free-living, subterranean and mycotrophic gametophytes that derive nutrients from symbiosis with fungi. In Isoetes and Selaginella, which are heterosporous, microspores and megaspores are dispersed from sporangia either passively or by active ejection.[6] Microspores produce microgametophytes which the produce sperm. Megaspores produce reduced megagametophytes inside the spore wall. At maturity, the megaspore cracks open at the trilete suture to allow the male gametes to access the egg cells in the archegonia inside. The gametophytes of Isoetes appear to be similar in this respect to those of the extinct Carboniferous arborescent lycophytes Lepidodendron and Lepidostrobus.[7]
Seed plants[edit]
The seed plants (gymnosperms and angiosperms) are endosporic and heterosporous. The gametophytes develop into multicellular organisms while still enclosed within the spore wall, and the megaspores are retained within the sporangium.[8]
Heteromorphy[edit]
In plants with heteromorphic gametophytes, there are two distinct kinds of gametophytes. Because the two gametophytes differ in form and function, they are termed heteromorphic, from hetero- 'different' and morph 'form'. The egg producing gametophyte is known as a megagametophyte, because it is typically larger, and the sperm producing gametophyte is known as a microgametophyte. Gametophytes which produce egg and sperm on separate plants are termed dioicous.
In heterosporous plants (water ferns, some lycophytes, as well as all gymnosperms and angiosperms), there are two distinct sporangia, each of which produces a single kind of spore and single kind of gametophyte. However, not all heteromorphic gametophytes come from heterosporous plants. That is, some plants have distinct egg-producing and sperm-producing gametophytes, but these gametophytes develop from the same kind of spore inside the same sporangium; Sphaerocarpos is an example of such a plant.
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. In seed plants, the microgametophyte (pollen) 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.[9]
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 the endosperm, which becomes the food storage tissue in the seed.
See also[edit]References[edit]Gametophyte Generation
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Gametophyte&oldid=916663577'
A gametophyte represents the sexual phase of the plant life. This cycle is named alternation of generations and organisms alternate between a sexual phase, or gametophyte generation and an asexual phase, or sporophyte generation. The term gametophyte may refer to the gametophyte phase of the plant life cycle or to the particular plant body or organ that produces gametes.
It is in the haploid gametophyte structure that gametes are formed. These male and female sex cells, also known as eggs and sperm, unite during fertilization to form a diploid zygote. The zygote develops into a diploid sporophyte, which represents the asexual phase of the cycle. Sporophytes produce the haploid spores from which haploid gametophytes develop. Depending on the type of plant, most of its life cycle may be spent in either the gametophyte generation or sporophyte generation. Other organisms, such as some algae and fungi, may spend most of their life cycles in the gametophyte phase.
Gametophyte Development
Gametophytes develop from the germination of spores. Spores are reproductive cells that can give rise to new organisms asexually (without fertilization). They are haploid cells that are produced by meiosis in sporophytes. Upon germination, the haploid spores undergo mitosis to form a multicellular gametophyte structure. The mature haploid gametophyte then produces gametes by mitosis.
This process differs from what is seen in animal organisms. In animal cells, haploid cells (gametes) are only produced by meiosis and only diploid cells undergo mitosis. In plants, the gametophyte phase ends with the formation of a diploid zygote by sexual reproduction. The zygote represents the sporophyte phase, which consists of the plant generation with diploid cells. The cycle begins anew when the diploid sporophyte cells undergo meiosis to produce haploid spores.
Gametophyte Generation in Non-vascular Plants
The gametophyte phase is the primary phase in non-vascular plants, such as mosses and liverworts. Most plants are heteromorphic, meaning that they produce two different types of gametophytes. One gametophyte produces eggs, while the other produces sperm. Mosses and liverworts are also heterosporous, meaning that they produce two different types of spores. These spores develop into two distinct types of gametophytes; one type produces sperm and the other produces eggs. The male gametophyte develops reproductive organs called antheridia (produce sperm) and the female gametophyte develops archegonia (produce eggs).
Non-vascular plants must live in moist habitats and rely on water to bring the male and female gametes together. Upon fertilization, the resulting zygote matures and develops into a sporophyte, which remains attached to the gametophyte. The sporophyte structure is dependent upon the gametophyte of nourishment because only the gametophyte is capable of photosynthesis. The gametophyte generation in these organisms consists of the green, leafy or moss-like vegetation located at the base of the plant. The sporophyte generation is represented by the elongated stalks with spore-containing structures at the tip.
Gametophyte Generation in Vascular Plants
In plants with vascular tissue systems, the sporophyte phase is the primary phase of the life cycle. Unlike in non-vascular plants, the gametophyte and sporophyte phases in non-seed producing vascular plants are independent. Both the gametophyte and the sporophyte generations are capable of photosynthesis. Ferns are examples of these types of plants. Many ferns and other vascular plants are homosporous Rayman jungle run apk download. , meaning that they produce one type of spore. The diploid sporophyte produces haploid spores (by meiosis) in specialized sacs called sporangia.
Sporangia are found on the underside of the fern leaves and release spores into the environment. When a haploid spore germinates, it divides by mitosis forming a haploid gametophyte plant called a prothallium. The prothallium produces both male and female reproductive organs, which form sperm and eggs respectively. Water is needed for fertilization to take place as sperm swim toward the female reproductive organs (archegonia) and unite with the eggs. After fertilization, the diploid zygote develops into a mature sporophyte plant that arises from the gametophyte. In ferns, the sporophyte phase consists of the leafy fronds, sporangia, roots, and vascular tissue. The gametophyte phase consists of the small, heart-shaped plants or prothallia.
Gametophyte Generation in Seed Producing PlantsFern Gametophyte Development
In seed producing plants, such as angiosperms and gymnosperms, the microscopic gametophyte generation is totally dependent upon the sporophyte generation. In flowering plants, the sporophyte generation produces both male and female spores. Male microspores (sperm) form in microsporangia (pollen sacs) in the flower stamen. Female megaspores (eggs) form in megasporangium in the flower ovary. Many angiosperms have flowers that contain both microsporangium and megasporangium.
The fertilization process occurs when pollen is transfered by wind, insects, or other plant pollinators to the female portion of the flower (carpel). The pollen grain germinates forming a pollen tube that extends downward to penetrate the ovary and allow a sperm cell to fertilize the egg. The fertilized egg develops into a seed, which is the beginning of a new sporophyte generation. The female gametophyte generation consists of the megaspores with embryo sac. The male gametophyte generation consists of microspores and pollen. The sporophyte generation consists of the plant body and seeds.
Fern SporophyteGametophyte Key Takeaways
SourcesMoss Sporophyte
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