4.2 TISSUE CULTURE :
Tissue culture is another technology, which helps
- to keep pace with increasing food demand
- to provide sufficiently fast and efficient systems for crop improvement.
Cellular totipotency :
The ability of a single plant cell to divide and differentiate into a mature plant if placed in the appropriate environment is called cellular totipotency.
Plant tissue culture is invaluable when traditional plant breeding cannot generate plants with desired traits.
"The culturing or growing isolated protoplasts or cells or tissue or organ on nutrient medium under controlled aseptic conditions to produce complete plant or plant parts is called tissue culture technique.
Haberlandt in 1902 was the first to demonstrate the totipotency and introduced plant tissue culture.
It is essential for us to know some important terms used commonly in tissue culture technology.
Terminology used:
Explant:
It is a tissue or part excised from the plant for tissue culture. Parenchyma tissue from root, stem, tubers or the shoot meristem is generally used as explants.
Callus:
It is produced due to growth of the explant and can be defined as 'an unorganized mass of loosely arranged parenchyma cells'.
Morphogenesis or Organogenesis:
The process of development of different organs such as root, stem, leaves etc. from the callus is called organogenesis.
Clones:
The genetically identical organisms produced from the original parent organism are described as clones of each other.
Requirements of tissue culture technique:
The basic and essential requirements for tissue culture experiments are -
- Plant material from which the explant is taken.
- Specialized nutrient or culture medium according to requirement.
- Aseptic laboratory conditions.
- Facility to control different factors such as temperature, light, humidity, etc.
- Different growth factors such as auxins, cytokinins, etc
Nutrient or Culture medium used:
The culture medium used for the experiment may be liquid or semi solid according to the need.
The medium is generally supplied with various ratios and concentrations of organic and inorganic nutrients, certain vitamins, sucrose, and plant growth hormones such as auxin and cytokinin.
For solid or semisolid medium agar-agar (actually a polysaccharide), a solidifying agent obtained from red algae is used.
The pH of the medium is adjusted between 5 - 5.8.
Haberlandt had used a medium with Knop's salt solution and sucrose.
Now use of MS medium (Murashige and Skoog) is more common.
Sterilization:
In tissue culture technique, different apparatus, medium used and the explant also is to be properly sterilized to avoid the contamination due to which the experiment may fail.
The methods used for sterilization may be
- dry or wet sterilization
- Alcohol sterilization etc.
The explants used can be sterilized by using
- 1% sodium hypochloride or
- 70% ethyl alcohol or
- 10% hydrogen peroxide.
