Question

In a tissue culture media the resource of the phytohormone is

Answer 1

Major Types of Media:

The composition of the most commonly used tissue culture media is given in Table 43.1, and briefly described below.



White’s medium:

This is one of the earliest plant tissue culture media developed for root culture.

MS medium:

Murashige and Skoog (MS) originally formulated a medium to induce organogenesis, and regeneration of plants in cultured tissues. These days, MS medium is widely used for many types of culture systems.

B5 medium:

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Developed by Gamborg, B5 medium was originally designed for cell suspension and callus cultures. At present with certain modifications, this medium is used for protoplast culture.

N6 medium:

Chu formulated this medium and it is used for cereal anther culture, besides other tissue cultures.

Nitsch’s medium:

This medium was developed by Nitsch and Nitsch and frequently used for anther cultures. Among the media referred above, MS medium is most frequently used in plant tissue culture work due to its success with several plant species and culture systems.

Synthetic and natural media:

When a medium is composed of chemically defined components, it is referred to as a synthetic medium. On the other hand, if a medium contains chemically undefined compounds (e.g., vegetable extract, fruit juice, plant extract), it is regarded as a natural medium. Synthetic media have almost replaced the natural media for tissue culture.

Expression of concentrations in media:

The concentrations of inorganic and organic constituents in culture media are usually expressed as mass values (mg/l or ppm or mg I-1). However, as per the recommendations of the International Association of Plant Physiology, the concentrations of macronutrients should be expressed as mmol/l– and micronutrients as µmol/l–.

Constituents of Media:

Many elements are needed for plant nutrition and their physiological functions. Thus, these elements have to be supplied in the culture medium to support adequate growth of cultures in vitro. A selected list of the elements and their functions in plants is given in Table 43.2.



The culture media usually contain the following constituents:

1. Inorganic nutrients

2. Carbon and energy sources

3. Organic supplements

4. Growth regulators

5. Solidifying agents

6. pH of medium

Inorganic Nutrients:

The inorganic nutrients consist of macronutrients (concentration >0.5 mmol/l–) and micronutrients (concentration <0.5 mmol/l–). A wide range of mineral salts (elements) supply the macro- and micronutrients. The inorganic salts in water undergo dissociation and ionization. Consequently, one type of ion may be contributed by more than one salt. For instance, in MS medium, K+ ions are contributed by KNO3 and KH2PO4 while NO3– ions come from KNO3 and NH4NO3.

Macronutrient elements:

The six elements namely nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are the essential macronutrients for tissue culture. The ideal concentration of nitrogen and potassium is around 25 mmol I-1 while for calcium, phosphorus, sulfur and magnesium, it is in the range of 1-3 mmol I–. For the supply of nitrogen in the medium, nitrates and ammonium salts are together used.

Micronutrients:

Although their requirement is in minute quantities, micronutrients are essential for plant cells and tissues. These include iron, manganese, zinc, boron, copper and molybdenum. Among the microelements, iron requirement is very critical. Chelated forms of iron and copper are commonly used in culture media.