Mitosis is the type of cell division that produces new cells for growth and to replace old cells that are worn out, damaged or dead. An application of mitosis is in cloning and tissue culture.

Tissue culture is the growth of tissues or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth media, such as broth or agar. Tissue culture commonly refers to the culture of animal cells and tissues, while the more specific term plant tissue culture is used for plants.

Plant tissue culture is a practice used to propagate plants under sterile conditions, often to produce clones of a plant.

Nature has been cloning organisms for billions of years. For example, when a strawberry plant sends out a runner (a form of modified stem), a new plant grows where the runner takes root. That new plant is a clone. Similar cloning occurs in grass, potatoes and onions. ORIGIN OF PLANT TISSUE CULTURE

Scientists have been able to clone plants by taking pieces of specialized roots, breaking them up into root cells and growing the root cells in a nutrient-rich culture. In culture, the specialized cells form calluses(undifferentiated mass of tissue). The calluses can then be stimulated with the appropriate plant hormones to grow into new plants that are identical to the original plant.

A piece of tissue called explant is taken from the parent plant and cut into small pieces. The pieces of tissues are sterilised with dilute sodium hypochlorite solution to prevent the growth of pathogens (bacteria and fungus). Each sterile tissue piece is placed onto a growth medium (gel containing nutrients and growth regulators). The tissue cells divide by mitosis to produce a mass of loosely arranged and undifferentiated cells called callus. Callus is stimulated with shoot-stimulating hormones to form multiple shoots. The shoots are separated and each is placed in nutrient medium with root- stimulating hormones to encourage rooting. Once the roots grow, the plantlets (little plants) are planted in sterile compost to grow.

DIAGRAM AND CHARTS OF PLANT TISSUE CULTURE

Micropropagation using meristem and shoot culture to produce large numbers of identical individuals. Screening programmes of cells, rather than plants for advantageous characters. Large-scale growth of plant cells in liquid culture as a source of secondary products. Crossing distantly related species by protoplast fusion and regeneration of the novel hybrid. Production of dihaploid plants from haploid cultures to achieve homozygous lines more rapidly in breeding programmes. As a tissue for transformation, followed by either short-term testing of genetic constructs or regeneration of transgenic plants. Removal of viruses by propagation from meristematic tissues.

The production of exact copies of plants that produce particularly good flowers, fruits or have other desirable traits. To quickly produce mature plants. The production of multiples of plants in the absence of seeds or necessary pollinators to produce seeds. The regeneration of whole plants from plant cells that have been genetically modified. The production of plants in sterile containers that allows them to be moved with greatly reduced chances of transmitting diseases, pests, and pathogens. The production of plants from seeds that otherwise have very low chances of germinating and growing such as orchids and nepenthes. To clean particular plant of viral and other infections and to quickly multiply these plants as 'cleaned stock' for horticulture and agriculture.

Decreases genetic variation and limits biodiversity. It is very expensive and time consuming. An infected plant sample can produce infected progeny. Not all plants can be successfully tissue cultured, often because the proper medium for growth is not known or the plants produce secondary metabolic chemicals that stunt or kill the explant. Sometimes plants or cultivars do not come true to type after being tissue cultured. Infection may continue through generations if precautions are not taken.