The plasticity of plants and their totipotency nature, allows whole plants to be regenerated from any part of the plant, be it cell clumps, stem sections, leaves, and roots. Plasticity allows plants to be able to alter their metabolism in order to adapt and survive in a particular environment and totipotency allows the plant to maintain its genetic makeup or potential, thus the plant regenerated from any explants will have the same genetic make up as the parent plant. This is especially good in plant biotechnology when plants genetic makeup is manipulated as the cloned cells can be grown into whole plants whose genome will now carry the inserted genes and from that plant other plants of the same makeup can be regenerated.
As metabolites produced by plants are highly depended on the environmental conditions that the plant is exposed to, plants of the species in different environmental conditions, will be expressing different genes at different levels even, thus production of different secondary metabolites to survive in their environment. Thus to control this random expression of genes, science has come with a somewhat controlled way to produce plants that will do as is wished by the scientific researchers. This tool is tissue culture. Tissue culture is where plants are propagated from plant explants inside the laboratory in a controlled environment inside tissue culture vessels which can be made of glass or plastic. This is in vitro propagation of plants.
When growing plants in vitro, conditions under which they are grown can be manipulated. A good example is seed germination. Through different treatments of the seeds, such as scarification, sterilisation and other treatments, together with specific culture media content, seeds that would otherwise germinate after 3 months, can be germinated in a month. This serves as an example to show that tissue culture conditions can differ from species to species and thus different tissue conditions have to be established that is favorable to the particular species. However there are some things especially looking at the culture media content, that are standard.
Plant Tissue Culture Media
The basis components are a source of energy or fixed carbon and the sucrose is usually used. The second one is organic supplements to supply plants with vitamins and amino acids. Essential elements for plant growth also have to be included and these are supplied as a complex mixture of salts. Water is also added in preparation of the media, for solid culture a gelling agent such as agar has to be added. Apart from these basic necessities of plant growing media, other substances can be added to enhance growth and development of the plant. These are plant growth promoting substances.
In the 1950s, scientists were able to determine that cytokinin and auxin are important in tissue culture, although this of course does not exclude other plant hormones. Cytokinin promotes cell division and auxin does not only promote cell division but cell growth as well. Plants do produce these hormones naturally but when supplied this provides a readily available source and thus plants just takes up the hormones saving them energy to produce a lot of their own, thus enhanced growth. Equal concentration of auxin and cytokinin in media gives rise to explants producing an undifferentiated mass of cells referred as callus, higher concentrations of cytokinin to auxin directs growth to shoot formation and more auxin to cytokinin concentrations directs plant explants towards roots formation. Research has also recently shown that smoke can be added in tissue culture to enhance or promote seed germination.
Plants are sub-cultured onto new media after a while, can be a week, two weeks, a month or so, this is done mainly to remove plants from media that contains waste as plants directly excrete on the culture.Plants are cultured under sterile conditions. This is to eliminate bacterial and fungal infections thus more healthy plants. This comes in handy especially to plants which are susceptible to being infected by these pathogens in the natural environment. These microorganisms are always found on plant surfaces in nature, thus tissue culture eliminates them. Explants are sterilised in bleach or ethanol usually and explants are cultured under the laminar flow.
Some of the of Applications
.Multiply plants quickly getting mature plants in the absence or presence of seeds.
.Regenerating whole plants from transformed plant explants.
.Preserve germplasm such as seed culture, organ culture etc.
.Promote seed germination of seeds that otherwise germinates differences.
.Mutation selection and reduces or eliminates somaclonal variation.
.Establish callus cultures for continuous and increased production of compounds of interest.
.Rescue plants from attack by pathogens in the field as culturing conditions are sterile, thus reduce spread of pathogens.
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