Introduction to Plant tissue culture: an important application of Plant Biotechnology
Plant tissue culture may be defined as a process whereby small pieces of living tissues called explants are isolated from an organism (mother plant) and grown aseptically on a nutrient medium under controlled conditions. It can also be defined as a technique of growing plant cells, tissues, organs, seeds or other plant parts on a nutrient medium in a sterile environment. Tissues are group of cells which are identical in their shape, size and perform a same function. Two concepts viz., plasticity and totipotency are important for understanding plant cell culture and regeneration. Totipotency is the genetic potential of a plant cell to produce the entire plant and the ability of a plant cell to perform all the functions of development which are characteristic of zygote whereas plasticity is the ability of the plants to adapt to environmental conditions by altering their metabolism, growth and development to t suit their environment. When plant cell and tissues are cultured in vitro they generally exhibit a very high degree of plasticity which allows one type of tissue or organ to be initiated from another type. First time Haberlandt in 1902 gave the concept of totipotency.
To start the process of plant tissue culture the things such as sterilized glassware (i.e test tubes, jars, conical flasks, petri dish), nutrient medium, growth regulators, explants, chemicals for surface sterilization of explants (sodium hypochlorite, chlorax, commercial bleach and tween 20), culturing apparatus, growth chambers are required. When we look about each of above then we can explain these shortly as following. Different sterilization method such as wet, dry and filtration can be used for sterilization of glassware, nutrient medium and vitamins. The nutrient medium used for plant tissue culture is mostly MS medium which includes macronutrients, micronutrients, vitamins and chelators. Sucrose is used as source of carbon and agar is used as gelling agent to give semisolid nature to medium. Nutrient medium can be prepared manually (manual medium) in lab or it can be used as synthetic obtained from market (synthetic medium). Different growth hormones (auxins, cytokines and gibberellins) can be applied for successful tissue culturing. The plant tissue which is also called explants can be of one of shoot apical meristem (SAM), leaf, pith cells, stem node and internodes, seeds, anthers and inflorescence. Use of seed in tissue culture is not common practice but sometime seed is also used for callus induction and regeneration like in the case of rice, wheat, citrus and some species of Hypophae rhamnoidae. After complete sterilization of explants it is cultured on aseptic nutrient medium for next step and this is done in special environment inside laminar air flow cabinet which completely protect from microorganism contamination. Then finally these cultured explants were placed in growth chambers under controlled conditions where proper light duration 16/8 and temperature is provided to cultures for their normal growth.
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