Plant Biology: Somatic Processes

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Questions and Answers

What are somatic embryos capable of forming?

Both shoots and roots (correct)

Neither shoots nor roots

Only roots

Only shoots

Which type of hybridization involves crosses between plants of the same variety?

Intravarietal hybridization (correct)

Interspecific hybridization

Intergeneric hybridization

Intervarietal hybridization

What is the initial step in the process of somatic hybridization?

Embryo rescue

Hybrid plant identification

Hybrid cells selection

Protoplast fusion (correct)

What term describes embryos formed through somatic embryogenesis?

Embryoids Signup and view all the answers

Which application is NOT a benefit of somatic hybridization?

Increased fruit size Signup and view all the answers

What occurs during the protoplast fusion step in somatic hybridization?

Combining genomes of two parents Signup and view all the answers

Which of the following is an example of an application of somatic hybridization?

Development of cold tolerance in tomatoes Signup and view all the answers

In somatic hybridization, what method is employed to create a hybrid cell?

Protoplast fusion Signup and view all the answers

Which type of explant is NOT typically used for somatic embryogenesis?

Seeds Signup and view all the answers

Which plant growth regulator is considered the best synthetic auxin for inducing somatic embryos?

2, 4-D Signup and view all the answers

What is primarily responsible for the formation of somatic embryos during the embryogenesis process?

Reduced form of nitrogen Signup and view all the answers

How does electrical stimulation promote embryogenesis in explants?

By exposing explants to a mild electric current Signup and view all the answers

Which characteristic is NOT true of somatic embryos in comparison to zygotic embryos?

Develop as a result of sexual recombination Signup and view all the answers

What defines the difference between direct and indirect somatic embryogenesis?

Indirect embryogenesis requires callus formation whereas direct does not Signup and view all the answers

What is the correct sequence of steps in the somatic embryogenesis process?

Initiation, Proliferation, Pre-maturation, Maturation, Plant development Signup and view all the answers

Which of the following statements about genotypes in somatic embryogenesis is true?

Genotypic variations can affect endogenous hormone levels Signup and view all the answers

What is the primary advantage of somatic embryogenesis in plant breeding?

It provides high propagation rates and germplasm conservation. Signup and view all the answers

Which of the following is NOT an application of somatic embryogenesis?

Creation of hybrid species Signup and view all the answers

How are somaclonal variations primarily produced?

Through genetic changes during tissue culture. Signup and view all the answers

Which type of clone is referred to as a 'calliclone'?

Clone derived from callus tissue. Signup and view all the answers

What is a major limitation of somatic embryogenesis?

It can only be applied to a few species. Signup and view all the answers

In which year was the term 'somaclonal variation' introduced?

1981 Signup and view all the answers

What is a key characteristic of somaclonal variations?

They can lead to new phenotypes in regenerated plants. Signup and view all the answers

Which type of clone is classified as a 'mericlone'?

Clone derived from a meristem. Signup and view all the answers

What is a common physiological cause of somaclonal variations?

Exposure to plant growth regulators Signup and view all the answers

Which type of chromosome change refers to having an extra or missing chromosome?

Aneuploidy Signup and view all the answers

Which of the following describes allopolyploidy?

Two or more chromosome sets from different species Signup and view all the answers

What is the primary focus of biochemical causes of somaclonal variations?

Alterations in carbon and nitrogen metabolism Signup and view all the answers

Which technique is commonly used for detecting somaclonal variants at the cellular level?

Cytological staining of meristematic tissues Signup and view all the answers

Which of the following is NOT considered a genetic cause of somaclonal variation?

Lack of photosynthetic ability Signup and view all the answers

What type of mutation involves changes in the DNA sequence that can affect protein production?

Gene mutation Signup and view all the answers

Which term describes the condition of having more than two chromosome sets derived from the same species?

Autopolyploidy Signup and view all the answers

Which of the following describes qualitative characters in plants?

Plant height Signup and view all the answers

What is the purpose of using pathogen or toxin selection agents during culture?

To identify disease resistance variants Signup and view all the answers

Which advantage of somaclonal variations helps in creating new varieties for species with limited genetic diversity?

They occur frequently and do not need genomic knowledge. Signup and view all the answers

How can one reduce the occurrence of somaclonal variations?

By avoiding long-term cultures Signup and view all the answers

What is a common limitation of somaclonal variations?

They may result in reduced fertility. Signup and view all the answers

Which type of stress tolerance can be selected for in tobacco plants?

High salt tolerance Signup and view all the answers

What is an effect of adding herbicides to cell culture systems?

It allows for the generation of herbicide-resistant plants. Signup and view all the answers

Which type of characters would yield of flowers, seeds, and wax content fall under?

Quantitative characters Signup and view all the answers

Study Notes

Somatic Cell

Any biological cell that forms the body of a multicellular organism, excluding gametes and germ cells.
Basically, any cell of a plant or animal that isn't involved in sexual reproduction.

Somatic Embryo

Bipolar structures with both apical and basal meristematic regions, forming shoots and roots respectively.

Somatic Embryogenesis

Process where somatic cells or tissues develop into embryos, ultimately regenerating plants.
Embryos resulting from this process are called embryoids.

Hybridization

Combining characters of two species through artificial pollination.
Different types:
- Intravarietal: Crosses between plants of the same variety.
- Intervarietal: Crosses between different varieties of the same species.
- Interspecific: Crosses between different species of the same genus.
- Intergeneric: Crosses between plants from different genera.

Somatic Hybridization

Combining the genomes of two desired parent plants, regardless of taxonomic relation.
A hybrid cell is produced through protoplast fusion in vitro.
The fused protoplast develops into a hybrid plant.
Novel approach for genetic modification at a cellular level.
Can be used for genetic manipulations and crop improvement.
Offers an advantage over sexual hybridization.
Steps: Protoplast fusion, hybrid cell selection, and hybrid plant identification.

Applications of Somatic Hybridization

Disease-resistant plants: e.g. tobacco plants resistant to tobacco mosaic virus.
Environment tolerance: e.g. developing cold tolerance in tomatoes.
Somatic hybrids for specific traits: e.g. producing tobacco with high nicotine content.

Factors Affecting Somatic Embryogenesis

Explants: Immature zygotic embryos, inflorescence, cell suspension cultures, petioles, protoplasts, leaves, stems, roots.
Plant Growth Regulators: Auxins (2,4-D is a common synthetic auxin used for inducing somatic embryos), Cytokinins (Zeatin promotes embryogenesis when applied to embryogenic cells 3-4 days after transfer from the proliferation medium).
Nitrogen Source: Reduced form of nitrogen is essential for embryo formation.
Electrical Stimulation: Exposing explants to mild electric current (0.02 V DC for 20h) can enhance embryogenesis.
Genotype: Genotypic variations can influence hormone levels.

Steps in Somatic Embryogenesis

Initiation of embryogenic culture.
Proliferation of embryogenic culture.
Pre-maturation of somatic embryos.
Maturation of somatic embryos.
Plant development.

Types of Somatic Embryogenesis

Direct Somatic Embryogenesis: Embryos form directly from the explant tissue, producing an identical clone without callus formation. Specialized cells within the explant are already committed to embryo development and only need to be triggered.
Indirect Somatic Embryogenesis: Explants produce an undifferentiated mass of cells (callus) which can differentiate into embryos. Callus formation and the redetermination of embryogenic development require specific growth regulators and culture conditions.

Somatic Embryos vs Zygotic Embryos

Somatic embryos mirror zygotic embryos in structure and growth potential - both can develop into complete plants.
Somatic embryos develop from somatic cells, unlike zygotic embryos, which originate from the fusion of male and female gametes (zygotes).
Somatic embryos facilitate clonal propagation as they are genetically identical to the parent plant.
Zygotic embryos develop through sexual processes, leading to genetic variation.

Practical Applications of Somatic Embryogenesis

Clonal Propagation: Reproducing identical plants.
Raising Somaclonal Variants: Producing genetically diverse plants from tissue culture.
Synthesis of Artificial Seeds: Producing seeds outside of the traditional sexual reproduction process.
Source of Regenerable Protoplast System: Enables genetic manipulation by fusing protoplasts (cells without cell walls) to create hybrids.
Genetic Transformation: Introducing new genes into plants to create transgenic varieties.
Synthesis of Metabolites: Producing valuable plant compounds of medicinal or industrial interest.

Advantages of Somatic Embryogenesis

Observable and controllable culture conditions.
Not limited by material availability.
High propagation rate.
Germplasm conservation.
Labour saving.
Disease and virus elimination.
Model system for plant breeding, mass propagation, and rapid genetic improvement.

Limitations of Somatic Embryogenesis

Limited to certain species.
Somatic embryos may have difficulty germinating due to physiological and biochemical immaturity.
Long-term cultures can lead to cell instability, making commercial exploitation and mass propagation challenging.

Somaclonal Variations

Genetic variations in plants originating from tissue culture.
Can be detected as genetic or phenotypic traits.
Plants derived from these cells are called somaclones.
The term "somaclonal variation" was introduced by Larkin and Scowcroft in 1981.
Phenomenon of new phenotypes emerging from in-vitro culture.

Basic Features of Somaclonal Variations

Variations in Karyotype: Changes in chromosome sets, including euploidy, monoploidy, polyploidy, and aneuploidy.
Generally heritable mutations that persist in plant populations even after field cultivation.

Mechanism of Somaclonal Variations

Genetic: Heritable changes caused by pre-existing variations in somatic cells, mutations, or DNA alterations. Occurs with high frequency.
Epigenetic: Non-heritable changes arising during tissue culture. Caused by temporary phenotypic alterations, occurring at low frequency.

Causes of Somaclonal Variations

Physiological Cause: Exposure to plant growth regulators and culture conditions.
Genetic Cause: Changes in chromosome number (euploidy, monoploidy, polyploidy, aneuploidy), or structure (deletion, inversion, duplication, translocation).
Biochemical Cause: Altering photosynthetic ability through changes in carbon or nitrogen metabolism, resulting in antibiotic resistance.

Detection And Isolation of Somaclonal Variants

Variant detection by cytological Studies: Staining meristematic tissues with acetocarmine helps determine chromosome count and morphology.
Analysis of Morphological Characters: Analyzing qualitative (plant height, maturity date, flowering date, leaf size) and quantitative traits (yield of flower, seeds, wax content in plant parts) can identify variations.
Variant detection by gel electrophoresis: Electrophoretic patterns can reveal changes in enzyme, protein, and chemical product concentrations (pigments, alkaloids, amino acids).
Detection of disease resistance variants: Using pathogens or toxins responsible for disease resistance as selection agents during culture can identify resistant variants.
Detection of herbicide resistance variant: Introducing herbicide to the cell culture system can identify herbicide-resistant plantlets.
Detection of environmental stress tolerant variant: Identifying cell lines tolerant to salt, water-logging, drought, temperature stress, or mineral toxicities.

Advantages of Somaclonal Variations

Easier, faster, and cheaper than traditional breeding methods, especially for perennial species.
High frequency of variations compared to conventional mutagenesis.
Useful for species with limited genetic diversity.
Introduces new traits like disease, herbicide, and environmental stress resistance.
Creates varieties with enhanced production of valuable metabolites.

Limitations of Somaclonal Variations

Some variations can be unstable and non-heritable.
Variations can negatively impact fertility, growth, and regeneration ability.
Repeated selection is needed to confirm the stability of a cell/plant line obtained from somaclones.

Reducing Somaclonal Variations

Avoid prolonged cultures.
Utilize axillary shoot induction systems when possible.
Propagate chimeras through other clonal systems.

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Description

Explore the fascinating world of somatic cells, somatic embryogenesis, and hybridization in plants. This quiz covers the key concepts and processes involved in plant regeneration and artificial pollination methods. Test your understanding of the different types of hybridization and their significance in plant biology.