Plant tissue culture is a technique used to maintain and grow plant cells, tissues or organs under controlled environmental conditions on an artificial nutrient culture medium of the known composition. The part which is cultured is called explant, i.e., any part of a plant taken out and grown in a test tube, under sterile conditions in special nutrient media. This capacity to generate a whole plant from any cell/explant is called totipotency. The steps used in tissue culture are:
(a) Explant culture- A cell, tissue or a piece of plant organ is extracted from the plant as an explant. It is sterilized and placed in a nutrient medium. The cells absorb nutrients and start multiplying.
(b) Callus formation and culture- An unorganized mass of cells produced by the growth of explant is called callus. The cells of callus are identical as they are produced by the process of mitosis.
(c) Organogenesis- The growth hormones like auxins and cytokinins in proper amounts are added to the callus to induce organ formation. Depending on the level of auxins and cytokinins, the root and shoot system begins to develop.
(d) Cell formation/ Suspension culture- The callus is transferred to a liquid medium and is agitated for the formation of cell or suspension culture. It is agitated at 100-250 rpm constantly. The callus and suspension culture result in cell biomass production which can be utilized for the regeneration of new plants.