関: prothallia

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/09/04 07:16:12」(JST)

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Liverwort Prothallus

A prothallium, or prothallus (from Latin pro = forwards and Greek θαλλος (thallos) = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young gametophyte of a liverwort or peat moss as well.

The prothallium develops from a germinating spore. It is a short-lived and inconspicuous heart-shaped structure typically 2-5 millimeters wide, with a number of rhizoids (root-like hairs) growing underneath, and the sex organs: archegonium (female) and antheridium (male). Appearance varies quite a lot between species. Some are green and conduct photosynthesis while others are colorless and nourish themselves underground as saprotrophs.

Alternation of generations[edit source | edit]

Prothallus of the tree fern Dicksonia antarctica (note new moss plants for scale)

Spore-bearing plants, like all plants, go through a life-cycle of alternation of generations. The fully grown sporophyte, what the layman refers to as the fern, produces genetically unique spores in the sori by meiosis. The haploid spores fall from the sporophyte and germinate by mitosis, given the right conditions, into the gametophyte stage, the prothallus. The prothallus develops independently for several weeks; it grows sex organs that produce ova (archegonia) and flagellated sperm(antheridia). The sperm are able to swim to the ova for fertilization to form a diploid zygote which divides by mitosis to form a multicellular sporophyte. In the early stages of growth, the sporophyte grows out of the prothallus, depending on it for water supply and nutrition, but develops into a new independent fern, which will produce new spores that will grow into new prothallia etc., thus completing the life cycle of the organism.

Advantages of alternation of generations[edit source | edit]

There are two important evolutionary advantages to the alternation of generations plant life-cycle. Firstly, by forming a haploid gametophyte, there is only one allele for any genetic trait. Thus, all alleles will be expressed because no allele may be masked by a dominant counterpart (there is no counterpart). The benefit of this is that any mutation that causes a lethal, or harmful, trait expression cannot be masked and will cause the gametophyte to die; thus, the trait cannot be passed on to future generations, preserving the strength of the gene pool. Also, crossing-over during meiosis in the formation of spores, and sexual reproduction in the gametophytes, produces genetic diversity, which also inhibits harmful recessive genes from "surfacing" and being expressed.

External links[edit source | edit]

Liverwort Sporophyte
Fern Life-Cycle

English Journal

Lygodium japonicum fern accumulates copper in the cell wall pectin.

Konno H, Nakato T, Nakashima S, Katoh K.SourceResearch Institute for Bioresources, Okayama University, Kurashiki, Okayama 710-0046, Japan. hakonno@rib.okayama-u.ac.jp
Journal of experimental botany.J Exp Bot.2005 Jul;56(417):1923-31. Epub 2005 May 31.
The present work reports the results of a study on the growth kinetics and characterization of matrix polysaccharides in the cell walls of Lygodium japonicum prothallium grown in the presence of copper (Cu). When the prothallium was cultured in the media containing 0.2 mM or 0.4 mM CuSO(4), it showe
PMID 15928016

[Effect of various sugars on the growth of the prothallium of ferns].

HUREL-PY G.
Comptes rendus hebdomadaires des séances de l'Académie des sciences.C R Hebd Seances Acad Sci.1955 Mar 7;240(10):1119-21.
PMID 14364890

[Notes on the prothallium colonies of Gymnogramme calomelanos with central necroticed mass].

SOSSOUNTZOV I.
Comptes rendus des séances de la Société de biologie et de ses filiales.C R Seances Soc Biol Fil.1952 Mar;146(5-6):380-3.
PMID 12988423

Japanese Journal

無配生殖型ベニシダ(Dryopteris erythrosora)胞子培養の適正培地の検討

松浦和枝,林蘇娟
島根大学生物資源科学部研究報告 18, 17-21, 2013-09-30
… Furthermore, it was confirmed that the nutrient medium of 3％ sucrose obstructed the prothallium formation, but promoted the increase of the undifferentiated cells. …
NAID 120005587512

無配生殖型ベニシダ(Dryopteris erythrosora)胞子培養の適正培地の検討

松浦和枝,林蘇娟
島根大学生物資源科学部研究報告 18, 17-21, 2013-09-30
NAID 110009616662

モエジマシダの胞子発芽時における砒素耐性および前葉体の砒素吸収能力

榊原正幸,渡邉彩,井上雅裕 [他],佐野栄
愛媛大学理学部紀要 11, 7-11, 2005-03-25
Arsenic hyperaccumulation and tolerance in gametophytes and spores ofPteris vittata L. (brake fern) have been investigated. Gametophytes are able to grow normally in medium containing 50 to 200 or 300 …
NAID 110004715621