INORGANIC MEDIUM COMPONENTS
Plant tissues and organs are grown in vitro on artificial media, which supply the nutrients necessary for growth. The success of plant tissue culture as a means of plant propagation is greatly influenced by the nature of the culture medium used. For healthy and vigorous growth, intact plants need to take up from the soil:
• relatively large amounts of some inorganic
elements (the so-called major plant nutrients): ions of nitrogen (N), potassium (K), calcium (Ca),
phosphorus (P), magnesium (Mg) and sulphur (S);
and,
• small quantities of other elements (minor plant nutrients or trace elements): iron (Fe), nickel (Ni), chlorine (Cl), manganese (Mn), zinc (Zn), boron (B), copper (Cu), and molybdenum (Mo).
According to Epstein (1971), an element can be considered to be essential for plant growth if:
1. a plant fails to complete its life cycle without it;
2. its action is specific and cannot be replaced completely by any other element;
3. its effect on the organism is direct, not indirect on the environment;
4. it is a constituent of a molecule that is known to be essential.
The elements listed above are - together with carbon (C), oxygen (O) and hydrogen (H) - the 17
essential elements. Certain others, such as cobalt (Co), aluminium (Al), sodium (Na) and iodine (I), are essential or beneficial for some species but their widespread essentiality has still to be established.
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