Tissue culture refers to a method in which fragments of plant tissue are introduced into a new, artificial environment, where they continue to function or grow. While fragments of a tissue are often used, it is important to note that entire organs are also used for tissue culture purposes. Here, such growth media as broth and agar are used to facilitate the process.
Seed culture is the type of tissue culture that is primarily used for plants such as orchids. For this method, explants ,tissue from the plant, are obtained from an in-vitro derived plant and introduced in to an artificial environment, where they get to proliferate. In the event that a plant material is used directly for this process, then it has to be sterilized to prevent tissue damage and ensure optimum regeneration.
Embryo culture is the type of tissue culture that involves the isolation of an embryo from a given plant for in vitro growth.
Embryo culture may involve the use of a mature or immature embryo. The mature embryos for culture are essentially obtained from ripe seeds, immature embryo (embryo rescue) involves the use of immature embryos from unripe/hybrid seeds that failed to germinate.
For embryo culture, the ovule, seed or fruit from which the embryo is to be obtained is sterilized, and therefore the embryo does not have to be sterilized again. Salt sucrose may be used to provide the embryo with nutrients. The culture is enriched with organic or inorganic compounds, inorganic salts as well as growth regulators.
Callus is referred to unspecialized, unorganized and a dividing mass of cells. A callus is produced when explants (cells) are cultured in an appropriate medium – A good example of this is the tumor tissue that grows out of the wounds of differentiated tissues/organs.
Callus culture involves the growth of a callus (composed of differentiated and non- differentiated cells), which is then followed by a procedure that induces organ differentiation.
Organ culture is a type of tissue culture that involves isolating an organ for in vitro growth. Here, any organ of plant can be used as an explant for the culture process (Shoot, root, leaf, and flower).
With organ culture, or as is with their various tissue components, the method is used for preserve their structure or functions, which allows the organ to still resemble and retain the characteristics they would have in vivo. Here, new growth (differentiated structures) continues given that the organ retains its physiological features. As such, an organ helps provide information on patterns of growth, differentiation as well as development.
There are number of methods that can be used for organ culture. These include:
- Plasma clot method – Here, the method involves the use of a clot that is composed of plasma and chick embryo extract (or any other extract) in a watch glass. This method is particularly used for the purposes of studying morphogenesis in embryonic organ rudiments and more recently for studying the actions of various hormones, vitamins and carcinogens of adult mammalian tissues.
- Raft method – For this method, the explant is placed on a raft of lens paper/rayon acetate and floated on a serum in a watch glass.
- Agar gel method – The medium used for this method is composed of a salt solution, serum as well as the embryo extract or a mixture of various amino acids and vitamin with 1 percent agar. The explant has to be subcultured every 5 to 7 days. The method is largely used for the study of developmental aspects of normal organs and tumors.
- Grid method – Grid method, as the name suggests involves the use of perforated stainless steel sheet, on which the tissue of interest is placed before being placed in a culture chamber containing fluid medium.
Protoplast is the cell without cell wall. A protoplast is the term used to refer to cell (fungi, bacteria, plant cells etc) in which the cell wall has been removed, which is why they are also referred to as naked cells.
Protoplasts may be cultured in the following ways:
- Hanging-drop cultures
- Micro culture chambers
- Soft agar matrix
Once a protoplast has regenerated a cell wall, then it goes through the process of cell division to form a callus, which may then be subcultured for continued growth.