Introduction

Plant Tissue culture is the in vitro aseptic culture of cells, tissues, organs, or whole plant under controlled nutritional and environmental conditions often to produce the clones of plants.

• It refers to a collection of techniques used to maintain or grow plant cells, tissues, or organs under sterile conditions on a nutrient culture medium of the known composition. 
• The resultant clones are true-to-type of the selected genotype.

Principle of Plant Tissue Culture

• Plant tissue culture relies on the fact that many plant cells have the ability to regenerate a whole plant (totipotency).
• Single cells, plant cells without cell walls (protoplasts), pieces of leaves, stems or roots can often be used to generate a new plant on culture media given the required nutrients and plant hormones.
• The controlled conditions provide the culture an environment conducive for growth and multiplication.
• These conditions include the proper supply of nutrients, pH medium, adequate temperature, and proper gaseous and liquid environment.

Plant Tissue Culture Technique

1. Preparation of plant tissue for tissue culture is performed under aseptic conditions under HEPA filtered air provided by a laminar flow cabinet.
2. The tissue is grown in sterile containers, such as Petri dishes or flasks in a growth room with controlled temperature and light intensity.
3. Living plant materials from the environment are naturally contaminated on their surfaces (and sometimes interiors) with microorganisms, so their surfaces are sterilized in chemical solutions (usually alcohol and sodium or calcium hypochlorite) before suitable samples (known as explants) are taken.
4. The sterile explants are then usually placed on the surface of a sterile solid culture medium but are sometimes placed directly into a sterile liquid medium, particularly when cell suspension cultures are desired.
5. Solid and liquid media are generally composed of inorganic salts plus a few organic nutrients, vitamins, and plant hormones. Solid media are prepared from liquid media with the addition of a gelling agent, usually purified agar.
6. The composition of the medium, particularly the plant hormones and the nitrogen source (nitrate versus ammonium salts or amino acids) has profound effects on the morphology of the tissues that grow from the initial explant.
7. For example, an excess of auxin will often result in a proliferation of roots, while an excess of cytokinin may yield shoots.
8. A balance of both auxin and cytokinin will often produce an unorganized growth of cells or callus, but the morphology of the outgrowth will depend on the plant species as well as the medium composition.
9. As cultures grow, pieces are typically sliced off and subcultured onto new media to allow for growth or to alter the morphology of the culture. The skill and experience of the tissue culturist are important in judging which pieces to culture and which to discard.
10. As shoots emerge from culture, they may be sliced off and rooted with auxin to produce plantlets which, when mature, can be transferred to potting soil for further growth in the greenhouse as normal plants.

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Applications and Advantages of Plant Tissue Culture

• Plant tissue culture technology is being widely used for large scale plant multiplication.
• Apart from their use as a tool of research, plant tissue culture techniques have in recent years, become of major industrial importance in the area of plant propagation, disease elimination, plant improvement, and production of secondary metabolites.
• Small pieces of tissue (named explants) can be used to produce hundreds and thousands of plants in a continuous process. A single explant can be multiplied into several thousand plants in a relatively short time period and space under controlled conditions, irrespective of the season and weather on a year-round basis.
• Endangered, threatened, and rare species have successfully been grown and conserved by micropropagation because of the high coefficient of multiplication and small demands on the number of initial plants and space.
• In addition, plant tissue culture is considered to be the most efficient technology for crop improvement by the production of somaclonal and gametoclonal variants.
• The micropropagation technology has a vast potential to produce plants of superior quality, isolation of useful variants in well-adapted high yielding genotypes with better disease resistance and stress tolerance capacities