The concept of totipotency

The concept of totipotencyWhat is totipotency?It is the potential/ability of plant cell to regenerate into completely functional plant

In 1902 the idea was conceived by Gottileb Haberlandt

TerminologyTo express totipotency the differentiated cell first undergoes dedifferentiation and then redifferentiation

The phenomenon of a mature cell reverting to a meristematic state and forming undifferentiated callus tissue is termed dedifferentiation

The ability of a dedifferentiated cell to form a whole plant or plant organs is termed redifferentiation

Thus, cell differentiation is the basic event of development in higher organisms and conveniently referred to as cytodifferentiation

Morphogenesis refers to the development of organs (shoots, roots,or owers) and overall plant shape and structure

Plant morphogenesis in vitro can be achieved via two pathways, somatic embryogenesis or organogenesis

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

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

Cells within the explant are induced to divide, forming zones of localized cell division, which subsequently leads to the organization of meristematic centers referred to as meristemoidsWhat is needed?

Tissue culture has several critical requirements:

Appropriate tissue (some tissues culture better than others)

A suitable growth medium containing energy sources and inorganic salts to supply cell growth needs. This can be liquid or semisolid

Aseptic (sterile) conditions, as microorganisms grow much more quickly than plant and animal tissue and can over run a cultureGrowth regulators - in plants, both auxins & cytokinins

Frequent sub-culturing to ensure adequate nutrition and to avoid the build up of waste metabolites

An essential mineral is dened as an element that is critical or essential for a plant to complete its life cycle

To be classied as essential the mineral must fulll the following criteria:

(1) an obligatory requirement for normal growth and reproduction

(2) it is not possible to replace the mineral with another mineral or substance

(3) have a direct or indirect role in plant metabolism Essential mineral nutrients are classied into two groups macro- or micronutrients, depending on the relative amount of each element required for growth

Macronutrients such as nitrogen, phosphorus, and sulfur are important components of macromolecules such as proteins and nucleic acids, as well as constituents of many small molecules

Micronutrients are required in much smaller quantities than macronutrients and function in various roles such as enzyme cofactors or components of electron transport proteins In plant tissue culture, the basis of all nutrient media is a mixture of mineral salts combining the essential macro- and micronutrients

Vitamins are compounds required by animals in very small amounts as necessary ancillary food factors

Many of the same substances are also needed by plant cells as essential intermediates or metabolic catalysts, but intact plants, unlike animals, are able to produce their own requirements

Thiamine (Vit. B1)Nicotinic acid (niacin) Pyridoxine (Vit. B6) and Myo-inositol

Myo-inositol is the only one of the nine theoretical stereoisomers of inositol which has significant biological importance

Thiamine (Vit. B1) in the form of thiamine pyrophosphate, is an essential cofactor in carbohydrate metabolism and is directly involved in the biosynthesis of some amino acids