UNIT 1: Plant Tissue Culture

Exam Focus: Define plant tissue culture based on the concept of totipotency. Know the essential components of culture media (especially plant growth regulators). Understand the steps and applications of **Micropropagation**.

Table of Contents

1. Plant Tissue Culture: Definition
2. General Techniques of Plant Tissue Culture
3. Culture Media
4. Micropropagation
5. Types of Culture
   • Embryo Culture
   • Callus Culture
   • Organ Cultures
   • Endosperm Culture
   • Meristem and Shoot Tip Culture

1. Plant Tissue Culture: Definition

Plant Tissue Culture (PTC) is the practice of growing or maintaining plant cells, tissues, or organs in a sterile (aseptic) environment on a nutrient culture medium under controlled temperature and light conditions.

It is based on the principle of **Totipotency**, the genetic potential of a plant cell to grow and develop into a complete, viable plant.

2. General Techniques of Plant Tissue Culture

The entire process of setting up a culture requires rigorous control over biological and physical factors:

1. **Explant Preparation:** Selection and isolation of a small piece of plant tissue (the **explant**) from the parent plant.
2. **Sterilization:** The explant and all tools, media, and containers must be sterilized to prevent microbial contamination.
3. **Media Preparation:** Preparation of the nutrient medium (often Murashige & Skoog or MS medium).
4. **Inoculation:** Transferring the sterile explant onto the sterile culture medium under aseptic conditions (usually in a Laminar Air Flow cabinet).
5. **Incubation:** Culturing the inoculated vessels under controlled conditions (temperature, light, humidity).

3. Culture Media

The medium supplies all the nutrients necessary for the explant to grow. A common medium is Murashige and Skoog (MS) medium.

• **Essential Components:**
  • **Macronutrients & Micronutrients:** Salts supplying essential elements (N, P, K, Ca, Mg, Fe, etc.).
  • **Carbon Source:** Sucrose is the most common energy source.
  • **Vitamins and Amino Acids:** Usually thiamine, nicotinic acid, and glycine.
  • **Gelling Agent:** Agar is used to solidify the liquid medium.
  • **Plant Growth Regulators (PGRs):** Hormones that dictate the developmental path:
    • **Auxins** (for root formation).
    • **Cytokinins** (for shoot formation and cell division).
    • The ratio of auxin to cytokinin determines the type of growth (e.g., high auxin/low cytokinin favors rooting; high cytokinin/low auxin favors shooting).

4. Micropropagation

A method of propagating plants in vitro using small explants, leading to the rapid clonal multiplication of selected plant genotypes.

• **Meristem and Shoot Tip Culture:** Used to culture the apical meristem or shoot tip. It is particularly important for producing **virus-free plants**, as the meristematic zone is usually free of systemic viruses.
• **Organogenesis:** The process of producing new organs (shoots or roots) directly from the explant or callus.
• **Embryogenesis (Somatic Embryogenesis):** The production of non-zygotic embryos (somatic embryos) from single plant cells, often in suspension culture.

5. Types of Culture

Embryo Culture

The aseptic isolation and growth of an **immature or mature embryo** in vitro. This is often used to rescue hybrid embryos that would normally abort (Embryo Rescue), especially in wide crosses.

Callus Culture

Callus is an unorganized, undifferentiated mass of proliferating cells produced when an explant is placed on a medium with an appropriate balance of auxins and cytokinins. Callus is the starting material for cell suspension cultures or regeneration via organogenesis.

Organ Cultures

The culture of specific, differentiated plant parts (e.g., root tips, shoot apices, floral parts) to study their development or maintain their characteristic structure.

Endosperm Culture

Culture of the endosperm tissue, which is typically triploid (3n). Used to produce triploid plants, which are often sterile and seedless (e.g., seedless watermelon).

Meristem and Shoot Tip Culture

Culture of the meristem (apical dome, 0.1 mm size) or the shoot tip (apical dome plus 1-3 leaf primordia). The primary use is for the **elimination of viruses** and rapid clonal propagation.