Plant Tissue Culture & Biotechnology: Techniques, Applications & Impact

TAKEAWAYS:

• Plant tissue culture grows entire plants from tiny cells/tissues under sterile conditions using nutrient media.
• Key steps: Surface sterilization → explant selection → culture media preparation → growth regulators (auxins/cytokinins).
• Applications: Mass propagation of orchids, disease-free plants, and GM crops (e.g., Bt cotton).
• Advantages: Faster, cheaper, and preserves rare species; disadvantages: High cost, contamination risks.
• Biotechnology tools: PCR, gene cloning, and CRISPR edit plant genes for traits like drought resistance.
• Ethics: GM crops raise debates on safety, biodiversity, and farmer rights.

1. What is Plant Tissue Culture?

Plant tissue culture is a lab technique where fragments of plants (cells, tissues, or organs) are grown on artificial nutrient media under sterile conditions. This method produces genetically identical plants (clones) quickly and efficiently.

Why Use Tissue Culture?

• Mass propagation: Grow thousands of plants from one parent (e.g., orchids, roses).
• Disease-free plants: Eliminates viruses/bacteria by growing from sterile explants.
• Conservation: Saves endangered species (e.g., Rhododendron).
• Genetic modification: Introduces new traits (e.g., pest resistance in potatoes).

Key Terms

A labelled flowchart showing:

1. Explant selection (e.g., meristem tip)
2. Surface sterilization (alcohol + bleach)
3. Culture on agar media (auxins + cytokinins)
4. Callus formation → shoot/root induction
5. Acclimatization (hardening in soil)

2. Steps in Plant Tissue Culture

Step 1: Surface Sterilization

• Why? Remove microbes (bacteria/fungi) that contaminate cultures.
• Methods:
  • Dip explant in 70% ethanol (30 sec) → bleach solution (10–15 min) → rinse in sterile water.
  • Meristem tips (young shoot tips) are often used—they’re naturally sterile.

Step 2: Explant Selection

Step 3: Culture Media

Media must provide nutrients, vitamins, and growth regulators. Common media:

• Murashige and Skoog (MS) medium: Standard for most plants.
• Components:
  • Macronutrients: N, P, K (for cell growth).
  • Micronutrients: Fe, Mn, Zn (enzymes cofactors).
  • Vitamins: Thiamine, nicotinic acid.
  • Carbohydrates: Sucrose (energy source).
  • Growth regulators:
    • Auxins (e.g., IAA, NAA) → root formation.
    • Cytokinins (e.g., kinetin) → shoot formation.
    • Ratio matters: High auxin:cytokinin → roots; low auxin:cytokinin → shoots.

A table showing MS medium ingredients with icons for each (e.g., 🌱 for nutrients, 🧪 for vitamins, 🔬 for growth regulators).

Step 4: Growth Phases

1. Callus induction: Explant forms undifferentiated cells (callus) on media with auxins + cytokinins.
2. Organogenesis: Callus differentiates into shoots/roots (adjust hormone ratios).
3. Shoot elongation: Transfer to media with low auxin + high cytokinin.
4. Rooting: Add auxin (e.g., IBA) to induce roots.
5. Acclimatization: Transfer plantlets to soil; gradually reduce humidity to harden.

3. Types of Plant Tissue Culture

A. Organ Culture

• Grow whole organs (e.g., anthers, embryos) on media.
• Example: Anther culture in haploid breeding (doubling chromosomes gives pure lines).

B. Cell Suspension Culture

• Callus cells grown in liquid media (shaken in flasks).
• Uses:
  • Produce secondary metabolites (e.g., shikonin from Lithospermum).
  • Bioreactors for large-scale production (e.g., vaccines in plants).

C. Protoplast Culture

• Plant cells stripped of walls (using enzymes) → fuse with other protoplasts.
• Uses:
  • Somatic hybridization (combine traits from different species).
  • Gene transfer (introduce foreign DNA).

A Mermaid flowchart showing:

[Protoplast A] --enzyme treatment--> [Wall-less cell]
[Protoplast B] --enzyme treatment--> [Wall-less cell]
[Wall-less cell A + B] --electrofusion--> [Hybrid protoplast] --> [Regenerated plant]

4. Applications of Plant Tissue Culture

5. Biotechnology in Plants

Plant biotechnology uses genetic engineering to modify plants for desired traits.

Key Techniques

1. Gene Cloning

   • Isolate a gene (e.g., Bt toxin for pest resistance) and insert it into a plasmid.
   • Use Agrobacterium tumefaciens (natural plant pathogen) as a vector.
   • Example: Bt cotton (resistant to bollworms).

2. PCR (Polymerase Chain Reaction)

   • Amplifies specific DNA sequences for analysis or cloning.
   • Steps:
     • Denature DNA (95°C) → Anneal primers (50–60°C) → Extend DNA (72°C).

3. CRISPR-Cas9

   • Gene editing tool: Cuts DNA at precise locations to modify traits.
   • Example: Drought-resistant golden rice (high vitamin A).

GM Crops: Pros and Cons

A Mermaid sequence diagram:

sequenceDiagram
    participant CRISPR as CRISPR-Cas9
    participant DNA as Target DNA
    CRISPR->>DNA: Guide RNA binds to target sequence
    DNA-->>CRISPR: DNA cut at specific site
    CRISPR->>DNA: Repair enzymes modify sequence
    note right of DNA: Edited gene expressed

6. Ethical and Environmental Issues

• Biodiversity loss: GM crops may outcompete native species.
• Farmer dependence: Patented seeds require repurchasing annually.
• Health risks: Allergies from new proteins (e.g., Brazil nut gene in soy).
• Labeling laws: Consumers should know if food is GM.

Exam Tip: How to Score Full Marks

1. Diagrams are key!

   • Draw labeled steps of tissue culture (explant → callus → plantlet).
   • Show MS medium composition (nutrients + hormones).
   • Sketch protoplast fusion or Agrobacterium-mediated transformation.

2. Compare techniques

   • Organ culture vs. cell suspension: Which is better for drug production? (Answer: suspension culture for bioreactors.)
   • GM crops vs. traditional breeding: Speed, precision, and risks.

3. Application-based questions

   • "How would you produce disease-free banana plants?" Answer:
     1. Sterilize meristem tip.
     2. Culture on MS media with auxins.
     3. Induce shoots → roots.
     4. Acclimatize in soil.

4. Ethics and risks

   • Always mention one advantage and one disadvantage of GM crops (e.g., "Bt cotton increases yield but may harm beneficial insects").

5. NEB-style short questions

   • "Define callus." → "Undifferentiated mass of cells formed from explants in tissue culture."
   • "Name two growth regulators." → Auxins (IAA) and cytokinins (kinetin).

Practice Questions (NEB Board Style)

Short Answer (3–5 marks)

1. Describe the role of auxins and cytokinins in plant tissue culture. Give one example of each.
2. Why is the meristem tip preferred for micropropagation? How is it sterilized?
3. What is protoplast fusion? State one application.

Long Answer (10–12 marks)

4. Explain the steps in plant tissue culture with a labeled diagram. How is this technique used to produce disease-free potato plants?
5. Compare traditional breeding and genetic engineering in plants. Give two examples of GM crops and their benefits.

Diagram-Based (5 marks)

6. Draw and label the composition of MS medium. Why is sucrose added to the medium?
7. Illustrate the process of Agrobacterium-mediated gene transfer in plants.

Summary Table: Key Techniques

Final Note: Plant tissue culture and biotechnology are revolutionizing agriculture—from saving endangered plants to feeding the world. Master the steps, media, and applications, and you’ll ace the NEB exam! 🌱🔬