Plant Tissue Culture - Class 12 Biotechnology - Chapter 7 - Notes, NCERT Solutions & Extra Questions
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What is plant tissue culture?
Plant tissue culture (PTC) refers to the cultivation of undifferentiated plant cells, tissues, or organs on synthetic media under aseptic and controlled environmental conditions. Utilizing the totipotency of plant cells, which is their ability to regenerate into a whole plant or develop into specialized cells, PTC serves as a versatile tool in basic research and commercial applications. Key aspects include using suitable nutrient media, maintaining aseptic conditions, and controlling physical conditions like light and temperature to ensure successful cultivation and regeneration.
Describe the various components of plant tissue culture media.
Plant tissue culture media consists of inorganic components like macronutrients (C, Ca, H, K, Mg, N, O, P, S) and micronutrients (B, Co, Cu, Fe, Mn, Mo, Zn) for essential mineral supply. Organic supplements include amino acids (e.g., arginine, glycine) and vitamins (thiamine, nicotinic acid) for growth support. Sucrose often serves as the main carbon source. Plant growth hormones such as auxins and cytokinins regulate organogenesis. Gelling agents like agar help in media solidification, and antibiotics are added to prevent microbial contamination.
What are the general steps of plant tissue culture?
The general steps of plant tissue culture are:
Selection of Nutrient Media: Choosing and sterilizing the appropriate culture medium.
Explant Selection: Selecting the plant tissue or organ for culturing.
Surface Sterilization: Disinfecting the explant to prevent microbial contamination.
Inoculation: Placing the explant onto the nutrient media.
Culture Incubation: Growing the cultures under controlled environmental conditions to promote regeneration.
Regeneration: Inducing the formation of shoots and roots.
Transplantation: Transferring the regenerated plantlets to soil for acclimatization and further growth.
Describe various applications of plant tissue culture.
Plant tissue culture is utilized for micropropagation, producing large quantities of clones rapidly under controlled conditions. It supports the creation of artificial seeds, enhancing elite plant species propagation. Essential for generating virus-free plants, it ensures healthy clone production from virus-free meristems. It facilitates the production of somatic hybrids, overcoming species barriers by fusing different protoplasts. Additionally, it is instrumental in producing secondary metabolites like pharmaceuticals under consistent conditions, and haploids for breeding to achieve homozygous lines faster.
How are somatic hybrids developed?
Somatic hybrids are developed through somatic hybridization, which involves the fusion of protoplasts from different plant species. Protoplasts, which are plant cells with the cell wall enzymatically removed, are isolated and then induced to fuse under controlled laboratory conditions. Fusion can be facilitated chemically or electrically. The hybrid cells formed, called cybrids when combining different cytoplasmic genomes, are then cultured to regenerate plants that possess genetic material from both parent species. This method enables the transfer of traits between distantly related species, overcoming natural reproductive barriers.
What are somaclonal variations?
Somaclonal variations refer to genetic changes observed in plants regenerated from in vitro cultured tissues. These variations arise during tissue culture processes and can result from genetic changes in the tissue's DNA. Somaclonal variations are not present in the parent plant but appear in the progeny when somatic cells undergo genetic changes during culture. These variations can be beneficial, introducing new traits for crop improvement, but can also lead to undesirable alterations if the goal is to preserve specific plant characteristics. These changes include DNA mutations, chromosome rearrangements, or changes in gene expression.
Define explant and list five most commonly used explants for plant tissue culture.
An explant is any plant tissue, organ, or part used in plant tissue culture to regenerate a mass of dedifferentiated cells, tissues, organs, or a whole plant. The most commonly used explants in plant tissue culture are:
Root or shoot apical meristems
Leaves
Cotyledons
Hypocotyls
Immature embryos
These explants are chosen based on their ability to rapidly divide and differentiate under controlled conditions, facilitating efficient plant regeneration.
Describe somatic embryogenesis and their application for the development of synthetic seeds.
Somatic embryogenesis is the process where embryos, called somatic embryos, develop from somatic cells, mimicking zygotic embryogenesis paths. These embryos are used to produce synthetic seeds by encapsulating them in protective matrices like calcium alginate, often with added nutrients and growth regulators resembling conventional seeds. Synthetic seeds enable long-term storage and rapid mass propagation of elite plant species and hybrids. This technology is vital for asexual propagation and maintaining genetic fidelity in species like carrot and grapes.
Describe briefly the role of pH in nutrient media.
The pH of nutrient media in plant tissue culture is critical as it influences the solubility of media salts and nutrient uptake by plant cells. Typically, the pH is adjusted to a range of about 5.8 to 6.0. Deviations can affect the solidification and consistency of the media; for instance, a higher pH can increase medium hardness, while a lower pH might impede proper solidification. Ensuring the correct pH is essential for optimal growth and development of cultured plant tissues.
Describe the method of somatic hybridization and its advantages.
Somatic hybridization involves the fusion of protoplasts from different species or varieties, facilitated by enzymes like cellulase. This method bypasses sexual reproduction barriers, enabling the combination of desirable traits from different genetic backgrounds. Hybrid plants, or cybrids, produced from these fused protoplasts, can exhibit enhanced qualities such as disease resistance or improved yield. Somatic hybrids allow for the blending of cytoplasmic genomes, enhancing traits like male sterility or photosynthetic efficiency, not typically achievable through conventional breeding.
What are somaclonal variations and discuss their role for improving crops.
Somaclonal variations are genetic modifications that occur in plants regenerated from tissue cultures. These variations, not present in the original plant, arise due to changes during the culture process. Though often seen as a challenge due to potential unwanted traits, somaclonal variations can be beneficial, offering novel genotypes with improved agricultural traits. For example, new cultivars of sugarcane and banana with disease resistance, or wheat with enhanced yield, have been developed by selecting advantageous somaclonal variations. This technique thus holds significance for crop improvement and breeding programs.
Which of the following tissues can be used as explant for regenerating complete plant through tissue culture?
(a) Shoot apical meristem
(b) Embryo
(c) Leaf segments
(d) All of the above
(d) All of the above
Each of the listed tissues—shoot apical meristem, embryo, and leaf segments—can be used as an explant for regenerating a complete plant through tissue culture, as highlighted in the chapter discussing the various explants that can lead to whole plant regeneration.
Which of the following explants are suitable for the production of virus free plants?
(a) Leaf segments
(b) Seeds
(c) Apical meristem
(d) Stem cuttings
The suitable explant for the production of virus-free plants is:
(c) Apical meristem
According to the chapter, apical meristems are generally free from virus particles and can be used to initiate cultures for the production of virus-free plants. This is crucial for maintaining the yield and quality of vegetatively propagated plants like sugarcane, banana, and potato.
The process of combining the nuclear genomes of one parent with the cytoplasmic genome of the other parent is called as:
(a) Cybridization
(b) Micropropagation
(c) Regeneration
(d) None of them
The process of combining the nuclear genomes of one parent with the cytoplasmic genome of the other parent is called:
(a) Cybridization
Which of the following components is not essential for Murashige and Skoog media?
(a) Inorganic nutrients
(b) Carbon source
(c) Antibiotics
(d) Organic Nutrients
The component that is not essential for Murashige and Skoog (MS) media as per the details provided in the book is:
(c) Antibiotics
Antibiotics are not a critical component of Murashige and Skoog media. They are optional and used to suppress bacterial growth if contamination is a concern, but they are not fundamentally necessary for the culture media's function to support plant tissue growth.
Decrease in the pH of the media may result in:
(a) Increase in hardiness of the solidified medium.
(b) May interfere with the solubility of media salts.
(c) Interfere with solidification of the medium and results in poor solidification.
(d) All of the above.
(b) May interfere with the solubility of media salts.
According to the chapter, decrease in pH mainly affects the solubility of the media salts. The pH change does not directly relate to solidification issues or general hardiness of the media which depend largely on other factors like gelling agents and media composition.
Somatic clonal variation can be present in which of the following plants?
(a) Plants regenerated through tissue culture
(b) Plant generated through seeds
(c) Plant generated through sexual reproduction which includes fertilisation of egg with pollen nuclei.
(d) None of the above.
Somatic clonal variation typically appears in plants regenerated from tissue culture. These are variations seen in plants regenerated from cultures of somatic tissues where genetic variations that occurred during the tissue culture process are carried over to the new plants.
Therefore, the correct answer is: (a) Plants regenerated through tissue culture
In vitro tissue culture can be used for the generation of:
(a) Virus free plants
(b) Somatic hybrid plants
(c) Synthetic seeds
(d) None of the above.
In vitro tissue culture can be used for the generation of: (a) Virus free plants(b) Somatic hybrid plants(c) Synthetic seeds
Based on the information provided in the chapter, the correct answer is that in vitro tissue culture can be used for the generation of virus-free plants, somatic hybrid plants, and synthetic seeds. Therefore, options (a), (b), and (c) are all correct.
Assertion: Somatic seeds are encapsulated by a layer called seed coat.
Reason: Seed coat is the protective layer which prevents water desiccation.
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
(d) Both assertion and reason are false.
Explanation: Somatic seeds, also known as synthetic seeds, are not encapsulated by a traditional seed coat but by an artificial encapsulation medium like calcium alginate. This encapsulation medium provides a protective layer but it is not called a seed and does not function solely to prevent water desiccation. The primary purpose of the encapsulation is to protect the somatic embryo and facilitate handling and sowing, not specifically for water desiccation prevention.
Assertion: Virus free plants can be produced by growing apical/axillary meristem of virus infected plants.
Reason: Apical/axillary meristems lack vascular bundle which is required by the virus to replicate.
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
(b) Both assertion and reason are true but the reason is not the correct explanation of the""") assertion.
Assertion: Virus-free plants can indeed be produced using apex/axillary meristems of virus-infected plants, because these meristematic regions are usually free from virus particles, allowing for the generation of healthy plants from diseased stock.
Reason: While it's true that apical/axillary meristems tend not to contain virus particles, it's not primarily because these areas lack vascular bundles. Instead, the typical reason is that these regions are characterized by high cellular activity and rapid division, which does not support the stable establishment and replication of viruses, rather than the absence of vascular tissue per se.
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Comprehensive Plant Tissue Culture Class 12 Notes
Introduction to Plant Tissue Culture
Plant tissue culture (PTC) is the practice of cultivating undifferentiated plant cells, tissues, or organs on synthetic media under aseptic and controlled environmental conditions. It is a significant tool for both basic research and commercial applications. The concept is based on the unique characteristic of plant cells known as totipotency, which is the ability of a vegetative cell to divide and differentiate into any specialised cell or regenerate into a whole plant.
Historical Perspective
In the 19th century, German scientists Theodor Schwann and Matthias Schleiden highlighted the idea that a cell is the basic unit of life, capable of division and growth. Around the 1890s, Gottlieb Haberlandt, another German botanist, pioneered the field of PTC with his idea of achieving continuous cell division in plant cells on nutrient media. His work laid down the principles of plant tissue culture and was foundational to the field.
Key Milestones
- 1902: Gottlieb Haberlandt proposed the concept of in vitro cell culture.
- 1926: Discovery of the first plant growth hormone, Indole Acetic Acid (IAA).
- 1957: Skoog and Miller described the chemical control hypothesis of root and shoot differentiation using auxin and kinetin.
Cell and Tissue Culture Techniques
Virtually any part of a plant, such as leaves, apical meristems, embryos, and cotyledons, can be used as starting material (explants) for tissue culture. The regenerated plants can be achieved primarily by two morphogenetic pathways – organogenesis and somatic embryogenesis.
Organogenesis involves inducing the formation of vegetative organs from cells or tissues in plant tissue culture. It is guided significantly by the relative concentration of growth hormones, especially auxins and cytokinins.
Somatic Embryogenesis refers to the formation of embryos from somatic cells, following pathways similar to zygotic embryos.
Steps of Plant Tissue Culture
- Selection of Suitable Nutrient Media and its sterilisation.
- Selection of Explants, such as root or shoot apical meristems, leaves, cotyledons, etc.
- Surface Sterilisation of explants using disinfectants like sodium hypochlorite.
- Inoculation of explants onto the nutrient media.
- Growth of Cultures under controlled conditions, leading to callus formation.
- Regeneration of Shoots by transferring small calli to suitable media.
- Rooting of Shoots by transferring them to rooting media.
- Transfer of Plantlets to sterilised soil for hardening before field transfer.
Nutrient Media
The success of in vitro plant cultures largely depends on the composition of the culture medium, which typically contains:
- Inorganic Components: Macronutrients and micronutrients.
- Organic Supplements: Usually amino acids and vitamins.
- Carbon Source: Sucrose is most commonly used.
- Plant Growth Hormones: Auxins and cytokinins are critical.
- Gelling Agents: Agar is the most common.
- Antibiotics: To prevent microbial contamination.
Types of Culture
- Organ Culture: Cultivating plant organs such as roots or embryos.
- Callus Culture: Unorganised mass of cells used for genetic transformation studies.
- Cell Suspension Culture: Isolated single cells cultured in a liquid medium.
- Protoplast Culture: Culturing plant cells without cell walls.
Applications of Plant Tissue Culture
Micropropagation
Micropropagation is a tissue culture technique for multiplying plants without sexual reproduction, resulting in genetically identical clones. It has been successfully employed in agriculture, horticulture, and forestry for plants like potatoes, bananas, and chrysanthemums.
Artificial Seed Production
Artificial seeds, or synthetic seeds, are produced by encapsulating somatic embryos in a protective coating. This method is useful for the rapid propagation of elite plant species and hybrids, and it has been successfully used in plants such as carrots and grapes.
Haploid and Triploid Production
Haploid plants possess only one set of chromosomes and can be used to produce homozygous diploid plants by doubling the chromosome number with colchicine. These double haploids are valuable in cross-breeding.
Somatic Hybrids and Cybrids
Somatic hybridisation involves the fusion of protoplasts from different species to create hybrids, thus overcoming species barriers. Cybrids combine the nuclear genome of one parent with the cytoplasmic genome of another, enabling the combination of desirable traits.
Production of Virus-Free Plants
Virus-free plants can be achieved by culturing apical or axillary meristems, typically free from virus particles, which is crucial for vegetatively propagated crops like sugarcane and potatoes.
Somaclonal Variations (Genetic Variability)
Somaclonal variations refer to genetic variations introduced during the culturing process. These variations can be both advantageous and disadvantageous, depending on the objective of the culture.
Production of Secondary Metabolites
Plant tissue cultures can be used to produce valuable secondary metabolites such as alkaloids, flavonoids, and steroids, which are crucial for pharmaceuticals, flavours, and fragrances. Tissue cultures offer a controlled environment, allowing consistent production irrespective of external factors.
Summary
Plant tissue culture is a powerful tool in modern biology, offering numerous applications from basic research to large-scale commercial production. It harnesses the totipotency of plant cells, allows for the rapid and disease-free multiplication of plants, enables the production of valuable secondary metabolites, and facilitates genetic transformation and hybridisation. The meticulous composition of nutrient media and the controlled environment ensure the success and reliability of this technique. These comprehensive notes serve as a key resource for Class 12 students to grasp the essentials of plant tissue culture.
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