Growing a Whole Plant from a Piece
When traditional breeding could not keep pace with the demand for better crops, another technique came to the rescue: tissue culture. Scientists learnt in the 1950s that a whole plant could be regenerated from an explant — any part of a plant taken out and grown in a test tube, under sterile conditions, in a special nutrient medium.
The property that makes this possible is totipotency — the capacity of a single cell or explant to generate a whole plant. It is a striking idea: the full genetic instructions for the entire plant sit inside almost every one of its cells.
What the Nutrient Medium Must Supply
An explant cannot grow on nutrients alone from thin air; the medium has to provide everything the developing plant needs. It must contain a carbon source such as sucrose, along with inorganic salts, vitamins, amino acids, and growth regulators like auxins and cytokinins.
The growth regulators are especially important — they steer the explant towards forming roots, shoots and eventually a complete plantlet. Get the balance right, and a small piece of tissue becomes a whole plant.
Micropropagation and Somaclones
Because each explant can be coaxed into a full plant, tissue culture allows a very large number of plants to be produced in a very short time. This method of raising thousands of plants through tissue culture is called micropropagation.
A key feature is that every plant produced this way is genetically identical to the original plant it was grown from — such genetically identical plants are called somaclones. Many important food plants, including tomato, banana and apple, have been produced commercially by micropropagation.
Why This Matters for Agriculture
Micropropagation gives growers something conventional propagation cannot: speed, uniformity and scale. A single elite plant with desirable qualities can be multiplied into thousands of identical copies, all carrying the same good characteristics, and all raised in a short period under controlled, sterile conditions.
This is the foundation on which several later techniques build — from producing virus-free stock to combining traits from different plants — which the next section takes up.
Quick Recap
- Tissue culture regenerates a whole plant from an explant (any plant part) grown in vitro under sterile conditions on a nutrient medium.
- Totipotency = the capacity of a cell/explant to generate a whole plant.
- The medium must provide a carbon source (sucrose), inorganic salts, vitamins, amino acids and growth regulators (auxins, cytokinins).
- Micropropagation = producing thousands of plants through tissue culture; the plants are genetically identical somaclones.
- Commercial examples: tomato, banana, apple.
Solved Examples — Section 2
Q1. What is an explant?
Answer: Any part of a plant taken out and grown in a test tube under sterile conditions in a special nutrient medium.
Q2. Define totipotency.
Answer: The capacity of a single cell or explant to generate a whole plant.
Q3. Name the growth regulators that a tissue-culture medium must supply.
Answer: Auxins and cytokinins (along with a carbon source like sucrose, inorganic salts, vitamins and amino acids).
Q4. What is micropropagation?
Answer: The method of producing thousands of plants through tissue culture in a short duration.
Q5. Why are micropropagated plants called somaclones?
Answer: Because they are genetically identical to the original plant from which they were grown.
Q6. Give two food plants produced commercially by micropropagation.
Answer: Any two of tomato, banana and apple.