Understanding Plant Tissue Culture
Plant Tissue Culture can be understood as the technique of growing various plant parts like cells, tissues, seeds or organs in a sterile environment provided by a medium of nutrients. A typical culture media used in this regard is composed of complex mixture of essential elements; organic supplements like vitamins; carbon source like sugar sucrose; gelling agents; plant growth regulators and antibiotics.
It is possible to grow plant cells in isolation from plants in tissue culture mediums. The cells thus grown in this method possess the characteristic features of callus cells, as distinguished from other plant cell types. Plant cells grown through tissue culture resemble the cells that usually appear on cut surface areas when a plant is injured. These are the type of cells that cover and seal the wounded region.
Under plant tissue culture, segments of plant tissue will divide and develop into transparent masses of cells if maintained under special conditions. Some of the essential conditions involved in the process of plant tissue culture include the following. The process must be initiated from appropriate tissue of the given plant variety. The growth media should contain optimum levels of growth regulators like auxin and cytokinins in addition to organic and inorganic compounds that help in sustaining the cells. The medium should also be maintained under aseptic conditions during the growth phase to guard against competition from microorganisms. As the growth process matures, the plant cells develop on a solid surface as friable lumps pale brown in colour. They may also be found as individual or small clusters of cells suspended in a liquid medium. The plant tissues grown like this can be maintained for indefinite period if they are regularly sub-cultured into fresh growth medium.
Generally, plant cells developed under the tissue culture process do not possess all the features of most plant cells. These cells have a small vacuole like structure and do not have chloroplasts and photosynthetic pathways. Also, the typical physical and chemical features that identically distinguish a type of plant cell from another are not found. Broadly speaking cells developed through tissue culture resemble those plant cells seen in meristematic regions that would further develop into different types of cells as they mature. Cells cultured under this process can easily be stimulated to re-differentiate themselves into whole plants by making appropriate alterations to the growth media.
To initiate a plant tissue culture process, cells can be gathered from any part of a given plant. Generally, the physiological state of a plant is never known to influence the way the cells would respond to tissue culture. However, there are a few things to be noted while selecting a plant for collection of cells. The source plant or what is called as the explants must be very healthy and free of diseases. Younger plant tissues have their own advantages with regard to tissue culture in the sense that they contain a higher degree of actively dividing cells which can vigorously respond to the program when compared to the cells of a plant that is about to enter its dormancy period. Cultural requirements for the process of plant tissue culture differ from species to species. The most appropriate conditions for a given species must always be evolved out of experimentation.
History of Plant Tissue Culture
The idea of plant tissue culture was first suggested in 1838 by Schleiden and Schwann in their cell theory. The first ever experimental approach was tried by Haberlandt in 1902 but in vain. However, his contribution insisted that it was possible to culture single plant cells. In 1930, White did a commendable work in tissue culture while plant growth regulators were discovered in the same year in addition to the importance of vitamins for shoot and root culturing. Carrel too succeeded in the process using animal cells. Gautheret reported some encouraging results with plant cells in the year 1934. Indole-Acetic Acid (IAA) was discovered in 1937.
Only in the year 1939, Gautheret, NobÃ©court and White independently solved the issue. During its initial phase, the progress in this field was rather very slow since it could attract only a few people. In the year 1954, the most important segments of this topic were opened. In 1958, Miller and Skoog from the University of Wisconsin â€“ Madison discovered Kinetin which plays a very active role in organogenesis. In the same year, Steward could successfully grow somatic embryo from carrot cells. In 1960, Morel independently cultured orchids and dahlias and relieved them from a deadly viral disease. An important boost for research in these lines came up when Murashige and Skoog developed a recipe for MS Medium in 1962.
In the years that followed, some vital applications in the arena developed including tissue culture, improving the growth substances in the media, cell culture, enhancing the process of organ formation and propagation through vegetative method, trials to get secondary products and application to a number of pathological problems.
In the year 1966 Guha and Maheshwari evolved androgenesis. Parallel to this, Murashige cloned plants in vitro and significantly promoted the technique of developing commercial plant tissue culture processes in laboratories. Most importantly, he raised haploid plants from pollen grains in 1966 and used protoplast fusion to hybridize two different species of tobacco into one plant in the year 1972. Plant tissue culture received a major momentum in 1980s while concrete techniques were evolved to introduce foreign DNA into plant cells, which marked the beginning of genetic engineering. In 1982, the International Congress in Plant Tissue Culture was held at Lake Yamanaka, Japan bearing testimony for the concrete development achieved in this field.