Cellular Differentiation and Totipotency

Cellular Differentiation and Totipotency
Totipotency is the basis of plant cell and tissue culture techniques.

Term was coined by Morgan in the year 1901.

Definition
" Potential of a cell to grow and develop a multi-cellular or multi-organed higher organism is termed as totipotency."

Cellular Totipotency

 Plant body and cellularity is maintained by the zygote and this zygote contains all
the information referred the plant.

This information remains localized in the DNA, due to the mitosis

 zygote divide in to the cells are formed which carry genetic information.

 Many of the genes that remain inactive in differentiated tissues or organs are able to express undergo adequate culture conditions.

 To express totipotency differentiated cell first undergoes de-differentiated then redifferentiation.

 S.C. Steward exemplified totipotency by using in a model system.

*In tissue culture, cells obtained from stem, root or other plant part and are allowed to grow in cultural medium containing mineral nutrients, vitamins, hormones etc.

*To encourage cell division and growth. As a result, the cells in culture will produce an
unorganized mass of proliferative cells of a Callus Tissue.

* The cells that comprise the callus are totipotent thus a callus tissue may be in a broader sense totipotent.

 Theoretically, totipotency of all the cells are expressed at a time, it is expected that
equal number of shoots or embryoid will be represented from such cells

 but in experiment such results are not obtained.

Various reasons behind the limited expression of totipotency may be:

1. Variation in chromosome number of cells of callus tissue.

2. An association of cells may be sometime necessary to provide the appropriate
environment for certain individuals to express their totipotency.

3. The endogenous hormone level of a cell and exogenously supplied hormone
make a threshold level which actually induces the totipotent cell to expre
culture but the cells that comprise callus tissue absorb hormones and nutrients a
gradient, availability of hormones is not equal to all cells and thus all the cells
do not express totipotency.

Importance of Totipotency in Plants

1. Vegetative propagation can be done to produce plants of economic, medicinal
and agricultural importance.

2. Genetic modification of plants.

3. Production of homozygous diploid plants.

4. Desired characters can be obtained in the plants by plant breeders and  commercial plant growers.

5. Germplasm conservation.

Ways of Totipotency expression

1. Axillary bud proliferation.

2. Direct somatic embryogenesis.

3. Adventitious shoot bud formation.

4. Organogenesis in callus and suspension cultures.

5. Embryogenesis in callus and suspension cultures.

6. By androgenesis, gynogenesis.

7. Apical bud formation.