Q. What is plant tissue culture?

This is a term used to describe the range of procedures used to maintain and grow plant tissues and organs (stems, roots, embryos) in aseptic (sterile) cultures. Plant tissue culture is widely used for the in vitro vegetative propagation of plants in a process known as micropropagation. Click on image to enlarge.

Q. How is micropropagation carried out?

A small piece of plant tissue (explant) is taken from the donor plant and cultured on a nutrient medium in sterile containers. By altering the composition of the medium and the environmental conditions (temperature, light regime, etc.) the development of this piece of tissue can be directed along different patterns and finally the whole plant can be regenerated. The offspring all come from a single plant and thus have identical genetic make-ups to each other and to the mother plant. They are thus called clones.

Q. What are the advantages of micropropagation over the conventional method of growing plants?

It is a fast method of propagation, producing thousands of plantlets in a matter of months.
Healthy plant material is ensured since soil and disease-causing organisms are excluded during the propagation cycle.
The method is programmable to meet specific targets of time and quantity because it is independent of seasonal changes and the weather.
Micropropagation saves an enormous amount of care usually required by cuttings and seedlings (watering, weeding, spraying etc.)
Excess material produced can often be stored over long periods
Species and cultivars can be stored in small spaces.

Q. What are the constituents of tissue culture nutrient media?

Water
Inorganic salts
Plant growth regulators
Vitamins
Amino acids
Carbon sources
Solidifying agents (in case of a solid medium)

Q. How can we ensure that the plants produced from tissue culture are free from viruses?

This can be achieved by developing a biophysical, immunological and molecular-technique based virus-diagnosis programme, and molecular-based quality control programme for the plant species of interest. Immunodiagnosis is the most useful technique using polyclonal and monoclonal antibodies raised against viruses. Polyclonal antibodies are now available in the country for groups of viruses such as potyviruses, tospoviruses, tobamoviruses, potexviruses, luteoviruses, badnaviruses, closteroviruses, etc. These polyclonal antibodies have been very useful in the identification of specific viruses and their strains, and for plant virus diagnosis.

Q. How do plant growth regulators affect plant morphogenesis in culture?

Two plant growth regulators affect plant differentiation:

Auxins: Stimulate root development
Cytokinins: Stimulates shoot development

Generally, the ratio of these two hormones can determine plant development:
Auxin> cytokinin = Root development
Cytokinin> auxin = Shoot development
Auxin = Cytokinin = Callus development

Q. What is organogenesis?

Organogenesis: The process of initiation and development of a structure that shows natural organ form and/or function.

Q. What is embryogenesis?

Embryogenesis: The process of initiation and development of embryos or embryo-like structures from somatic cells (somatic embryogenesis).

Q. What are the various stages of micropropagation?

Stage 0 – Selection and preparation of the mother plant
– Sterilization of the plant tissue takes place

Stage I - Initiation of culture
– Explant placed into growth media

Stage II - Multiplication
– Explant transferred to shoot media; shoots can be constantly divided

Stage III - Rooting
– Explant transferred to root media

Stage IV - Transfer to soil
– Explant returned to soil; hardened off

Q. What is the embryo rescue technique?
It is an in vitro technique in which the embryo (resulting from a wide hybridization where fertilization occurred, but embryo development did not occur) is cultured.
Its merits are:
Rescues F1 hybrid from a wide cross
Overcomes seed dormancy, usually with addition of hormone to media (GA)
Overcomes immaturity in the seed
– To speed generations in a breeding programme
– To rescue a cross or self (valuable genotype) from a dead or dying plant