49. Describe the procedure of tissue culture in plants.

Tissue culture is a method used for plant propagation in addition to other traditional plant-breeding techniques. Scientists found that any part of a plant grown in nutrient media under sterile conditions can give rise to a whole new plant. This property of plant cells to give rise to a whole new plant is called totipotency. It requires a nutrient medium that contains sucrose, inorganic salts, vitamins, proteins and growth regulators such as auxins and cytokinins.

The first step is excising a small part of plant tissue, like the leaves, root or shoot of a plant then placing the cut-out part or explant in a suitable nutrient medium followed by allowing the explants to multiply and form a group of tissues called callus.
The callus is then allowed to multiply to form many plantlets which are then transferred to a different container for rapid multiplication.
Finally, the developed plantlets are transplanted to the soil for normal growth.
Therefore, tissue culture is performed using a small part of a plant to develop many plants and so is also called micropropagation. As all these plants are developed from the same part of the parent plant, they are genetically identical and called somaclones. Micropropagation, or tissue culture, is employed in the large-scale production of tomato, banana and apple.

This technique can also be used to propagate high-yielding disease-resistant varieties in a short span. Even if a plant is diseased, tissue culture can be used to get a healthy plant using the explant of the apical or axillary meristem. This is because the meristem is always free of disease and microbes. Culturing of meristems has been successfully carried out in plants such as banana, sugarcane and potato.

In addition to asexual propagation of plants, tissue culture is also used to mix two different species of plants that are otherwise sexually incompatible. Here, individual cells are isolated from each plant species and are placed in a culture medium. The cell wall gets digested in both cells which aids fusion of the two protoplasts of different species, resulting in a hybrid protoplast.

This process of developing a hybrid plant using somatic cells is called somatic hybridisation. It was employed while fusing the tomato and potato plants to obtain a hybrid plant. In this manner, tissue culture, somatic hybridisation and other plant-breeding techniques provide a huge potential for manipulation of plants to produce new varieties, boost food production and enhance crops.