Tissue culture
Tissue culture is a major technique in biotechnology regarding to the production of plants on a large scale with specific desirable traits among whole population with no variation. This technique involves culturing of a small piece of plant in aseptic in vitro conditions on a special culture media, comprising over nutrients and plant hormones (auxin and cytokinin) into a full mature plant. Tissue culture mainly exploits the idea of totipotency of plants. Term 'totipotency' refers to the 'ability of any plant part to develop into a new plant'. Different plants have different level of totipotency. This ability of plant tissues has enabled scientists to conserve the plants of interest and also maximize the number of newly developed plants in a small area.

Popularity of plant tissue culture technique has been increasing day by day due to its widespread uses, low cost and greater number of plants propagation in minimum time period.

In plant tissue culture a small piece of plant is taken and is termed as Explants. These explants are sterilized with some disinfecting agent (e.g. Mercuric chloride, Sodium or Calcium hypochlorite). These explants are kept in culture broth or on solid culture media. Most often liquid medium is only used when cell suspension culture is required. Otherwise, the liquid medium is solidified by gelling agent and explants are kept on the surface of the nutrient culture. The chemical composition and ratio of plant hormones play critical role in the growth of explants as the excess of auxins promote the growth of roots and excess of cytokinins initiate the shoots development but, the balance of both gives rise to undifferentiated callus development. The explants give rise to the clumps of undifferentiated cells named as 'Callus'. This callus is easily cut into disks and sub cultured on other mediums e.g. shoots may be cut into pieces and cultured on auxin medium for initiation of rooting. When plantlets are enough mature, they are transferred to the pots.

• Callus culture: Callus culture consists of the clump of undifferentiated cells, formed after the growth on nutrient medium. Callus consists of the cells of defined and known genetic make up which may be employed for further research and propagation of defined plants, through the process of regeneration. Callus culture has successfully been used in Nicotiana tabacum, Salix carpraea and Daucus carota.
• Organ culture: organ culture, as the term depicts, is related to the formation of specific organs of required characters through tissue culture. Most often, the explants used for organ culture are derived from the same organ. Ovary of Lycopersicum esculentum, seedlings of tomato, wheat and leaves of a fern Osmunda cinnamomea have printed the success stories on the screen of organ culture.
• Cell suspension culture: Cell suspension culture refers to the formation of cell culture without sticking to the surface of medium as well as the cells like itself. This technique is mostly applied to the microorganisms but, it can also be used for those cells which do not adhere with the other cells of their own kind and can be studied independently. Sticking of cells can also be prevented by making the surface hydrophobic. This technique is exploited when a scientist wants to study the effects of individual cells or from agricultural point of view; for obtaining a large number of plants of same genetic make up from single cells. Cell suspension culture has successfully been applied to carrots and Nicotiana tabacum.
• Cytodifferentiation: Cytodifferntiation refers to the ability of a cell, due to some chemical or metabolic effects; develop into a specific functional cell. Cell tissue culture enables scientists to evaluate the affects of various chemicals and plant hormones on their process of differentiation.
• Anther and pollen culture: As the name denotes, anther and pollen culture is related to the culturing of plant on nutrient media through anther containing pollens. This method is utilized to grow haploid culture and scientists have successfully grown the haploid callus of Ginkgo biloba, Nicotiana tabacum and Datura innoxia.

These are some basic types of plant tissue culture which have dramatically uplifted the scope and nature of biological research and development by increasing the chances of mating of distant types of organisms successfully and serving the human kind in a novel way.

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