Somaclonal variation is the variation seen in plants that have been produced by
plant tissue culture
Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues, or organs under sterile conditions on a nutrient culture medium of known composition. It is widely used to produce clones of a plant in a method know ...
.
Chromosomal
A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most importa ...
rearrangements are an important source of this variation. The term somaclonal variation is a phenomenon of broad taxonomic occurrence, reported for species of different ploidy levels, and for outcrossing and inbreeding, vegetatively and seed propagated, and cultivated and non-cultivated plants. Characters affected include both qualitative and quantitative traits.
Somaclonal variation is not restricted to, but is particularly common in, plants regenerated from
callus
A callus (: calluses) is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, b ...
. The variations can be
genotypic or
phenotypic
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...
, which in the latter case can be either genetic or
epigenetic
In biology, epigenetics is the study of changes in gene expression that happen without changes to the DNA sequence. The Greek prefix ''epi-'' (ἐπι- "over, outside of, around") in ''epigenetics'' implies features that are "on top of" or "in ...
in origin. Typical genetic alterations are: changes in chromosome numbers (
polyploidy
Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...
and
aneuploidy
Aneuploidy is the presence of an abnormal number of chromosomes in a cell (biology), cell, for example a human somatic (biology), somatic cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more plo ...
), chromosome structure (
translocations,
deletions,
insertion
Insertion may refer to:
*Insertion (anatomy), the point of a tendon or ligament onto the skeleton or other part of the body
*Insertion (genetics), the addition of DNA into a genetic sequence
*Insertion, several meanings in medicine, see ICD-10-PCS
...
s and
duplication
Duplication, duplicate, and duplicator may refer to:
Biology and genetics
* Gene duplication, a process which can result in free mutation
* Chromosomal duplication, which can cause Bloom and Rett syndrome
* Polyploidy, a phenomenon also known ...
s) and DNA sequence (base mutations). A typical epigenetics-related event would be
gene methylation.
If no visual,
morphogenic changes are apparent, other plant screening procedures must be applied. There are both benefits and disadvantages to somaclonal variation. The phenomenon of high variability in individuals from plant cell cultures or adventitious shoots has been named somaclonal variation.
Advantages
The major likely benefit of somaclonal variation is plant/crop improvement. Somaclonal variation leads to the creation of additional genetic variability. Characteristics for which somaclonal mutants can be enriched during ''in vitro'' culture includes resistance to disease
pathotoxins, herbicides, high salt concentration, mineral toxicity and tolerance to environmental or chemical stress, as well as for increased production of secondary metabolites.
Suitable for breeding of new species.
Disadvantages
A serious disadvantage of somaclonal variation occurs in operations which require clonal uniformity, as in the horticulture and forestry industries where tissue culture is employed for rapid propagation of elite genotypes.
* Sometimes leads to undesirable results
* Selected variants are random and genetically unstable
* Require extensive and extended field trials
* Not suitable for complex agronomic traits like yield, quality etc.
* May develop variants with
pleiotropic
Pleiotropy () is a condition in which a single gene or genetic variant influences multiple phenotypic traits. A gene that has such multiple effects is referred to as a ''pleiotropic gene''. Mutations in pleiotropic genes can impact several trait ...
effects.
Reducing somaclonal variation
Different steps can be used to reduce somaclonal variation. It is well known that increasing numbers of subculture increases the likelihood of somaclonal variation, so the number of subcultures in micropropagation protocols should be kept to a minimum. Regular reinitiation of clones from new
explants might reduce variability over time. Another way of reducing somaclonal variation is to avoid
2,4-D
2,4-Dichlorophenoxyacetic acid is an organic compound with the chemical formula . It is usually referred to by its ISO common name 2,4-D. It is a systemic herbicide that kills most broadleaf weeds by causing uncontrolled growth, but most gra ...
in the culture medium, as this hormone is known to introduce variation.
See also
*
Somatic embryogenesis
Somatic embryogenesis is an artificial process in which a plant or embryo is derived from a single somatic cell. Somatic embryos are formed from plant cells that are not normally involved in the development of embryos, i.e. ordinary plant tissue. N ...
References
Plant reproduction
{{botany-stub