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Somaclonal Variation by Sadik Chaudhary
Learn in Brief
Somaclonal variation refers to genetic variations in plants derived
from tissue culture, resulting in differences among cloned plants. It
can be genetic or epigenetic, with epigenetic changes typically
disappearing after sexual reproduction.
History
The term "somaclonal variation" was first used by Larkin and Scowcroft
in 1981, though the phenomenon was initially observed in sugarcane in
1971 by Heinz and Meein.
Types of Somaclonal Variation
1. Based on Presence:
- Genetic Variation: Pre-existing in the explant due
to mutations or DNA changes.
- Epigenetic Variation: Develops during tissue
culture, not originally present.
2. Based on Tissue Culture Method:
- Calliclonal Variation: From callus culture.
- Protoclonal Variation: From protoplast culture.
- Gametic Variation: From gametic culture.
Causes of Somaclonal Variation
1. Physiological Causes: Factors like plant growth regulators,
temperature, pH, and culture conditions.
2. Genetic Causes: Changes in chromosome number, structure, gene
mutations, and DNA alterations.
3. Biochemical Causes: Lack of photosynthetic ability and
antibiotic resistance due to transgenic vectors.
Induction of Somaclonal Variation
1. Apply physical or chemical mutagens to callus tissue.
2. Conduct organogenesis to develop plants with induced variations.
3. Transfer regenerated plants to a greenhouse for hardening and
selfing.
4. Use somaclonal variants for further cycles.
Applications
1. Crop Improvement: Enhancing both qualitative and quantitative
traits.
2. Stress Tolerance: Developing plants resilient to environmental
stresses.
3. Nutritional Enhancement: Increasing the nutritional value of
crops.
4. Industrial and Medicinal Uses: Producing plants with higher
essential oils or medicinal properties.
5. Variety Development: Creating novel crop and ornamental plant
varieties.
6. Biotic Resistance: Developing disease- and insect-resistant
plants.
7. Genetic Research: Studying the genetic basis of specific
traits.
Achievements
1. Resistant maize lines to leaf blight.
2. Tomato lines resistant to bacterial wilt.
3. Sugarcane lines resistant to Fiji disease.
Advantages
1. Rapid source of variability for crop improvement.
2. Cheaper than other genetic manipulation methods.
3. Generates new genetic diversity quickly.
4. Enables selection of specific traits.
5. Can improve disease and pest resistance.
Disadvantages
1. Unpredictability: Random genetic changes can produce
undesirable traits.
2. Genetic Stability: Variants may not maintain stable changes
across generations.
3. Somatic Mutations: Non-heritable changes limit long-term trait
stability.
Factors Influencing Somaclonal Variation
1. Genotype of Donor Plant: Affects the type and frequency of
variation.
2. Explant Source: Different tissues exhibit different levels of
genetic stability.
3. Duration of Culture: Longer culture durations increase
variations.
4. Culture Conditions: Growth medium composition and presence of
growth regulators.
5. Stress and Hormonal Imbalances: Environmental and nutritional
stresses can trigger genetic changes.
Somaclonal variation is a type of variation like genetic variation. The
somaclonal variation takes place in plant tissue culture and this term is used
to show the difference between the outputs of plant tissue cultures.
Plant tissue culture has the major advantage of the production of uniform
plants. But sometimes, Genetic variation takes place in the produced plants.
The term used to explain this variation is 'Somaclonal Variation'.
Somaclonal variation
Somaclonal variation is a term used to describe the genetic variations
that occur in plants that have been derived from tissue culture or somatic
cells.
Or
The in vitro-induced genetic variation which occurs in some
clones
*Somaclones are those plants derived from plant tissue culture.
The Somaclonal Variation may be transient (Epigenetic) or genetic. But the
Epigenetic changes are expressed at the cell culture stage and then usually
disappear when plants are regenerated by sexual Process.
In the majority of cases, Somaclonal Variation is heterozygous in origin. It
occurs in both oligogenic and polygenic characters.
History of Somaclonal Variation
This term was first time used by
Larkin and Scowkraft in 1981.
However, this Variation was first time reported in
Sugarcane in 1971 by Heinz and Meein.
After this incident, this variation was noted in many crops.
Before 1971 plant tissue culture is extremely used for the production of
uniform plants especially in the Horticulture field.
Types of Somaclonal Variation:
There are two types of Somaclonal Variation.
A. Based on the Presence of Somaclonal Variation
1. Genetic Variation:
They are pre-existing variations in the somatic cell of the explant. It means
they are, already present in the cell before culturing, which may be due to
mutation and DNA changes.
2. Epigenetic Variation:
That variation developed during the tissue culture is known as Epigenetic
Variation. They are not already present in the cell.
B. Based on the Method of Tissue Culture
1. Calliclonal variation:
The variation which is observed among the Plants regenerated from callus
culture.
2. Protoclonal Variation:
Variations are observed among the plant regenerated from a protoplast.
3. Gametic Variation:
Variations are observed among the Plants which are regenerated from gametic
culture.
Reason Behind Somaclonal Variation:
The cause of somaclonal variation is divided into 3 parts.
1. Physiological Cause:
It involves physical factors like Plant growth regulators, Temperature, pH and
culture conditions which can cause somaclonal variation because their
requirements in the culture medium vary according to selected explants.
2. Genetic Cause:
It includes the following factors -
A. Change in chromosome numbers
B. Change in Chromosome Structure
C. Gene mutation
D. Alteration in DNA
E. Extra chromosomal gene mutation, etc.
* I will make a separate post on the above factors.
3. Biochemical Cause:
They include the following factors
A. Lack of photosynthetic ability - During the plant tissue culture
some developing plant lose their photosynthetic ability.
B. Anti-biotic resistance - Vectors which have Antibiotic resistance
genes are mostly used in transgenic plants and causes.
Induction of Somaclonal Variation:
For induction of Somaclonal Variation we generally take -
1. Callus tissue and apply physical or chemical mutagen (It may be any
physical or chemical factor that can be used to bring Somaclonal Variation).
2. After that organogenesis will take place.
3. Ultimately the callus became a plant after the organogenesis and has
particular Somaclonal variation due to the mutagen.
4 The regenerated plant transfer in a greenhouse for Hardening and
selfing.
5. Eventually, Somaclonal variants are developed. And we can make a cycle of
this process by taking explant from Somaclonal variants.
Applications of Somaclonal Variation:
1. Crop Improvement:
Somaclonal variation can be used as a tool for crop improvement. which is
useful for the improvement of both qualitative and quantitative traits as well
as the nuclear and cytoplasmic traits of crops.
2. Stress Tolerance:
Somaclonal variation can lead to the development of plants that are more
resilient to various environmental stresses, such as extreme temperatures,
salinity, or water availability.
3. Nutritional Enhancement:
Tissue culture and somaclonal variation can also be employed to increase the
nutritional value of crops.
4. Industrial and Medicinal Applications:
Somaclonal variation can be used to produce plants with desirable industrial
or medicinal properties. For instance, it has been used to generate variants
with higher essential oil content in aromatic plants or with enhanced
secondary metabolites for pharmaceutical purposes.
5. Variety Development:
It's helpful in the development of a novel variety of crops and ornamental
plants.
6. Biotic Resistance :
Insects or diseases Resistant plants can be developed through Somaclonal
variation.
7. Genetic Research:
Somaclonal variation provides a valuable tool for studying the genetic basis
of specific traits. By comparing the genetic and epigenetic changes in
somaclonal variants to the original plant.
Achievement of Somaclonal Variation
1. In maize, lines resistant to toxin have been selected and plants
regenerated from them were resistant to leaf blight caused by helmithosporium maydis.
2. A tomato line resistant to bacterial wilt caused by
pseudomonas solanacearum was isolated by screening plants
regenerated from unselected calli.
3. In Sugarcane, a line resistant to Fiji disease was isolated from the
variety Pindal is related to a new variety called "One" for commercial
cultivation.
Advantages
1. It's a rapid source of variability for crop improvement.
2. Somaclonal Variation is cheaper than other methods of genetic
manipulation.
3. Somaclonal variation generates new genetic diversity within a short period.
4. Somaclonal variation enables the selection of specific traits of interest.
Researchers can induce variation and then screen for plants exhibiting desired
characteristics, making it easier to target particular traits for improvement.
5. Somaclonal variation can lead to the development of plants with improved
resistance to diseases and pests.
Disadvantage
1. Unpredictability:
One of the significant drawbacks of somaclonal variation is the random and
unpredictable nature of genetic changes. While some variants may exhibit
desirable traits, others could have negative or undesirable characteristics,
making the process less controllable.
2. Genetic Stability:
Somaclonal variants may not always exhibit stable genetic changes across
successive generations. The genetic modifications that occur during tissue
culture can be subject to instability and may revert to the original state
over time.
3. Somatic Mutations:
Somaclonal variation is primarily driven by somatic mutations, which are
changes in the DNA of non-reproductive cells. As these mutations do not pass
through the germline, they are not heritable, limiting the long-term stability
of the desired traits.
Overall, somaclonal variation offers a valuable tool in plant breeding and
biotechnology, but its applications must be approached with caution and
careful evaluation of the generated variants to harness its advantages
effectively while mitigating its disadvantages.
Factor Influence Somaclonal Variation
1. Genotype of Donor plant:
The genetic makeup of the Donor plant can influence the type and frequency of
somaclonal variation.
2. Explant Source:
It's a very critical factor that influences the Somaclonal variation. Because
it observed that Somaclonal Variation is not exhibited in stem cutting.
Different tissues may have varying degrees of genetic stability, and the
choice of explant can influence the likelihood of generating specific genetic
changes.
3. Duration of Culture:
There is a direct effect of the duration of culture on Somaclonal variation.
It observed that the long duration of culture induces more Somaclonal
variations. So generally Somaclonal variation increase with the duration of
culture.
4. Culture condition:
The specific conditions of the tissue culture environment, including the
composition of the growth medium, the presence of growth regulators (such as
auxins and cytokinins), and the culture duration, can all influence the
occurrence of somaclonal variation.
5. Stress and Hormonal Imbalances:
During tissue culture, plants can experience stress due to changes in
environmental conditions, nutrient availability, or hormonal imbalances in the
growth medium. Stressful conditions can trigger genetic and epigenetic changes
in the cells, leading to somaclonal variation.
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Reference
Pundhan Singh. 2016. Objectives Plant biotechnology. Kalyani
publishes, New Delhi.
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