Plant tissue culture is a technique done on an artificial nutrient culture medium of known composition to grow plants, seeds and various parts of the plants (organs, embryos, tissues, single cells and protoplasts). It is done under sterile conditions. When many clones of a plant are produced in this way it is termed as micro propagation.
As the plant cells are mature and differentiated the cells have the ability of totipotency which means it has the ability to change to meristematic state to differentiate into a whole plant. In order to get the desired results mostly rDNA technology is utilized. Tissue culture has played a major role in understanding plant metabolic reactions, growth pattern, differentiation and morphogenesis.
This technique has many advantages over the traditional ones, they produce copies with desirable traits without using seeds in a quick manner. Regeneration from plant cells are also possible with required gene modification, disease resistant plants can be produced. It is possible to regenerate genetically modified cells after protoplast fusion.
The seeds can be produced in sufficient quantity. Higher number of plants can be stored for longer time in much smaller place. Tissue culture of plants like banana, teak, fig, biodiesel trees are very common in order to obtain mass production of superior grade planting material. The meristem tissue which grows very rapidly and does not have pathogens is taken and is grown in an artificial nutrient medium. Later, under controlled environment they are multiplied many times in specific medium. From here, the plantlets are taken from the laboratory to a controlled green house for acclimatization. This takes around eight to twelve weeks for the plants to harden. The hardened plantlets have a well-developed root system and leaves and they are ready to be taken to the field.
If the growth of any cultured tissue is slow in that case optimization of the culture medium is necessary or/and culturing of the responsive tissues part. Necrosis is another problem which may spoil the cultured tissues. It has been observed that this can be overcome by culturing highly responsive tissues.
However, there may be some disadvantages as it is more expensive than the traditional ways, a monoculture produced after micro propagation may be prone to diseases resulting in the infection of the complete progeny. Sometimes the fungal infection cannot be overcome.
Hairy root cultures are produced by using the explant (plant tissue) which is inoculated along with the cells of the pathogenic bacterium, Agrobacterium rhizogenes. These are organ culture systems and are used for the production of various secondary metabolites. For the production of secondary metabolites a lot of interest is for the production of antibiotics as they are utilized in the cure of many diseases.
With tissue culture it is possible to obtain pathogen-free plants and production of many biologically important and high valued compounds and pharmaceuticals. All these applications have attracted many molecular biologists, plant breeders and industrialists to do research and development in this field. The tissue obtained from a plant to be cultured is termed as an explant. Important colours, flavour compounds for specific notes could be produced. Plant tissue cultures have a number of advantages as the yields are mostly much higher, the plants/ compounds could be produced in the assigned location with uniform yields. Also, under the controlled conditions, there is no effect of environment and pests. Many cell cultures also show high growth rates in relation to those for conventional systems.
When the cells are cultivated in a bioreactor it helps in obtaining a controlled supply of the metabolites with assured quality and yield. This is very useful for the industries. In order to enhance the reactions various elicitors (biotic or abiotic chemicals) are supplemented into the medium. They can be heavy metals, pesticides or detergents. They may also be any physical factors like cold shock, UV radiation or high pressure which may induce the enzyme action triggering the accumulation of secondary metabolites.
Tissue culture technique is very useful for conservation of rare or endangered plant species, screening the cells alone rather than the whole plants to check for herbicide resistance. Through plant tissue culture technique it is possible to cross different species by protoplast fusion and then regeneration of the novel hybrid, to study the molecular basis for physiological, biochemical, and reproductive mechanisms in plants and also in the selection of stress tolerant plants. Cross-pollination of distant species and then tissue culturing the embryo obtained after the pollination (Embryo Rescue) has become possible which otherwise does not survive. Production of polyploidy which is desirable in certain cases is possible with the application of antimitotic agents.
As plant tissue culture is a very labour-intensive process, it is better to determine the needs, market, commercial viability before taking up the work.
– Dr Renu Agrawal
(Ex. Chief Scientist, CFTRI, Mysore)