Plants are cloned using micropropagation, a sophisticated technique that produces many genetically identical plants from a small piece of parent plant tissue under sterile laboratory conditions.
Understanding Micropropagation
Micropropagation, also known as tissue culture, is a powerful method used for rapidly multiplying plants, especially those that are difficult to propagate through conventional methods like seeds or cuttings. It allows for the production of disease-free plants and preservation of desirable traits.
The core principle is totipotency – the ability of a single plant cell to regenerate into a whole plant. By providing the right nutrients, hormones, and environment, this potential is harnessed.
The Step-by-Step Process of Micropropagation
The process involves several key stages, conducted with strict sterile techniques to prevent contamination by microorganisms.
1. Initiation Stage
This stage involves selecting the parent plant and obtaining the starting material.
- Selecting the Parent Plant: A healthy, vigorous parent plant with desirable characteristics is chosen.
- Obtaining Explants: Cells are scraped from the parent plant (these cells are known as explants). Explants are small pieces of tissue, such as shoot tips, nodal segments, root tips, or even single cells, taken from the chosen plant.
2. Sterilisation Stage
Sterility is crucial to prevent microbial contamination, which can quickly destroy the cultures.
- Surface Sterilisation: The surface of the explants are sterilised using a disinfectant followed by a rinse with sterile water. Common disinfectants include dilute bleach (sodium hypochlorite) or ethanol. This step removes bacteria, fungi, and other contaminants from the surface of the explant without damaging the plant cells inside.
3. Multiplication Stage
Sterile explants are placed in a growth medium under controlled conditions to induce growth and multiplication.
- Transfer to Nutrient Medium: Sterilised explants are transferred to a sterile petri dish containing sterile nutrient agar. This agar-based medium contains all the essential nutrients, vitamins, and plant hormones (like auxins and cytokinins) required for cell division and growth. The specific hormone balance determines whether the explant develops into callus (undifferentiated mass of cells), shoots, or roots.
- Culture Conditions: The petri dishes or culture vessels are placed in a growth chamber with controlled temperature, light intensity, and humidity. Hormones in the medium stimulate rapid cell division and differentiation, leading to the formation of multiple shoots or embryos from a single explant.
4. Rooting Stage
Once sufficient shoots have been produced, they are transferred to a different medium to induce root formation.
- Transfer for Rooting: Individual shoots are separated and transferred to a rooting medium, which typically contains a higher concentration of auxins compared to the multiplication medium. This encourages the development of a strong root system.
5. Acclimatisation (Hardening) Stage
Plants grown in sterile, high-humidity lab conditions are very fragile and need to be gradually adjusted to external environmental conditions.
- Transfer to Soil: Once roots have developed, the plantlets are carefully removed from the culture vessel and transferred to a non-sterile substrate, such as potting mix or compost, initially under protected conditions (e.g., in a greenhouse or under plastic covers to maintain high humidity).
- Gradual Acclimatisation: The young plants are gradually exposed to lower humidity, more variable temperatures, and different light levels over several weeks. This "hardening" process allows the plants to develop a cuticle, strengthen their tissues, and become self-sufficient before being planted in the field or garden.
Through these stages, a small piece of tissue from a parent plant can be multiplied into hundreds or even thousands of genetically identical clones.
