Apomixis

(redirected from apomictic)
Also found in: Dictionary, Thesaurus, Medical.
Related to apomictic: apomixis

apomixis

[‚ap·ə′mik·səs]
(embryology)
Parthenogenetic development of sex cells without fertilization.

Apomixis

 

various forms of asexual reproduction by animals and plants. In a more common, narrow sense, apomixis is the formation of an embryo without fertilization. In apomixis the embryo develops not from a zygote, but directly from an unfertilized egg cell (parthenogenesis) or—in higher plants—from the cell of the gametophyte, from the embryonic sac (apogamy), and even from the somatic cells of a seed bud. Apomixis is known in the form of parthenogenesis in worms, insects, fish, and reptiles. However, it is more widespread among plants. Apomixis, or asexual seed reproduction (agamospermy), is especially frequent among angiosperms. There are several thousand apomictic species among 300 genera of angiosperms, belonging to 80 families. These include such common, widespread plants as grasses (60 genera), the composite family (28 genera), the rose family (15 genera), and the rue family (13 genera).

Apomixis can be autonomous—in which case both the embryo and endosperm form without fertilization—and mentoral (pseudogamic or stimulatory)—in which case the embryo is formed from an unfertilized egg cell, but its development is stimulated by the fertilization of the embryonic sac, which gives rise to the endosperm. Apomixis may be induced experimentally by some factors (induced apomixis). Apomixis sometimes manifests itself sporadically in certain organisms (facultative apomixis) or is the basic and even sole means of reproduction (obligatory apomixis).

As a rule, apomictic species occupy vast areas without showing any sign of becoming extinct (many species of hawkweed, dandelion, lady’s mantle, cinquefoil, meadow grass, European dewberry, and others). Apomixis is successfully utilized in the breeding of citrus fruits, figs, fodder grasses, and other plants. It can be used in producing hybrid corn seeds and other crops from apomictic haploids by means of doubling the number of their chromosomes. Especially important is the use of apomixis with fruit bushes and other woody bushes for which the development of homozygous strains by lengthy self-pollination in six to seven generations is practically impossible. Apomixis can be used to enhance crossbred vigor since it gives rise to a relatively constant progeny which conserves the particularities of the primary form. In the USA and Britain this is the basis of producing on an industrial scale uniform and hardy stock grown from apomictic seedlings of certain apple species. In California, seedlings from apomictic seed buds are used to replace degenerating and weakened clones of citrus trees, which are usually reproduced vegetatively.

REFERENCES

Khokhlov, S. S. Perspektivy evoliutsii vysshikh rastenii. Saratov, 1949.
Khokhlov, S. S. “Apomiksis: klassiflkatsiia i rasprostranenie u pokrytosemennykh rastenii.” In Uspekhi sovremennoi genetiki, vol. 1. Moscow, 1967.
Maheshwari, P. Embriologiia pokrytosemennykh. Moscow, 1954. (Translated from English.)
Poddubnaia-Arnol’di, V. A. Obshchaia embriologiia pokrytosemennykh rastenii. Moscow, 1964.
Petrov, D. F. Geneticheski reguliruemyi apomiksis. Novosibirsk, 1964.

S. S. KHOKHLOV

References in periodicals archive ?
As for the mechanism of MSI1, Quantitative RT-PCR analysis in ovaries of sexual and apomictic Hieracium have suggested that while an increase in HMSI1 is required for autonomous seed development, a decrease seems to precede sexual seed formation (Julio et al.
allocated at Campo Grande, Mato Grosso do Sul State, Brazil, comprising about 426 apomictic tetraploid accessions and 417 sexual tetraploid plants.
1981) and confirmation of its cross compatibility with apomictic tetraploid signalgrass and palisadegrass accessions (Ndikumana, 1985), applied brachiariagrass breeding programs quickly ensued, both at EMBRAPA and at CIAT (Miles and Valle, 1996; Miles et al.
This experiment was established in the low intertidal zone in late August 1988 prior to the peak reproductive period of both apomictic (September through November) and crustose (December through March) thalli of M.
After more than 5 years of research using both classical and molecular breeding methods, Kindiger and a team of research associates successfully developed apomictic corn plants that look, grow, and taste like corn.
Seeds from apomictic plants, however, yield successive generations with the same characteristics as the original hybrid parent.
In the only other field study known to us where life histories of mixed populations of sexuals and asexuals were extensively studied, Michaels and Bazzaz (1986) reported a higher seed production, but smaller seeds and lower survival, of apomictic Antennaria parlinii when compared to sexual conspecifics.
Uniquely human commitments to loyalty or compassion (even when they represent what we demand of ourselves as a prerequisite for self-respect) are viewed from this perspective as quaint and parochial, a poor substitute for apomictic, canonical moral formulae.
Apomyx plans to enter into strategic alliances with seed companies and to develop innovative apomictic seed products for worldwide distribution and sale.
Poliplodization is an important strategy used in forage breeding programs, because it may increase the expression of agronomic traits of interest, restore fertility of intra- and interspecific hybrids, and, in some cases, permit the exploration of genetic variability in apomictic species by duplicating sexual plants and equaling the ploidy to allow the accomplishment of crossings and obtaining fertile offspring (PEREIRA et al.
Allozyme diversity in the apomictic vine Bryonia alba: potential consequences of multiple introductions.
Goldenberg and Shepherd, (1998) confirm that apomictic species have a greater ability to colonize extreme environments, showing wider distribution than non-apomictic species.