Tissue culture is the growth of new tissues, organs or whole plants from a few cells or a small piece of tissue in a sterile nutrient medium. When it is used to produce very large numbers of plant clones, it is called micropropagation.Steps in micropropagation1. A small piece of tissue, the explant, is cut from the plant to be cloned, usually from a meristem (for example a shoot tip or bud).
2. The explant is sterilised, for example with dilute bleach or ethanol, to kill bacteria and fungi. All work is done using aseptic technique.
3. The explant is placed on a sterile culture medium (agar) containing glucose, amino acids, minerals and plant hormones, including auxins and cytokinins.
4. The cells divide by mitosis to form a mass of undifferentiated cells called a callus.
5. The callus is divided into many small pieces, each of which is transferred to a new medium with a different balance of hormones. A high cytokinin to auxin ratio stimulates shoot growth, and a higher auxin ratio stimulates root growth.
6. The plantlets are moved to a greenhouse and gradually acclimatised to lower humidity before being planted out.
Worked example: if one callus is split into 20 pieces, and each new callus is split into 20 again at the next subculture, one explant gives 20 × 20 = 400 plantlets after two rounds.Using meristem tissue is useful because meristems are often free of viruses, so micropropagation can produce disease-free plants. It is used for orchids, bananas and many other crops.
2. The explant is sterilised, for example with dilute bleach or ethanol, to kill bacteria and fungi. All work is done using aseptic technique.
3. The explant is placed on a sterile culture medium (agar) containing glucose, amino acids, minerals and plant hormones, including auxins and cytokinins.
4. The cells divide by mitosis to form a mass of undifferentiated cells called a callus.
5. The callus is divided into many small pieces, each of which is transferred to a new medium with a different balance of hormones. A high cytokinin to auxin ratio stimulates shoot growth, and a higher auxin ratio stimulates root growth.
6. The plantlets are moved to a greenhouse and gradually acclimatised to lower humidity before being planted out.
Worked example: if one callus is split into 20 pieces, and each new callus is split into 20 again at the next subculture, one explant gives 20 × 20 = 400 plantlets after two rounds.Using meristem tissue is useful because meristems are often free of viruses, so micropropagation can produce disease-free plants. It is used for orchids, bananas and many other crops.