Mineral Elements, Macro
Based on the amount needed, mineral elements are usually classified into two groups: macroelements and microelements. Macroelements consist of elements in large supply, while microelements are usually only needed in trace amount.
Calcium (Ca): Calcium functions as a cofactor with many enzymes and is particularly important in cell well synthesis. Calcium deficiency may result in shoot tip necrosis. Calcium used in plant tissue culture is mostly in the forms of calcium chloride and calcium nitrate in a concentration of 1-3 mM.
Magnesium (Mg): Magnesium is critical for enzyme functioning, and an integral component of chlorophyl molecule. Magnesium is also a cation in plant to balance negative ions. The most used form of magnesium in plant tissue culture is magnesium sulfate in a concentration of 1-3 mM.
Nitrogen (N): Nitrogen is essential to plant life. It is a constituent of many important molecules, including amino acids, proteins, nucleic acids, certain hormones and chlorophyll. The nitrate ion (NO3- oxidized) and the ammonium ion (NH4+ reduced) are the two nitrogen forms that are mostly used in plant tissue culture. Nitrate is usually added at 25-40 mM and ammonium at 2-20 mM with a total amount of inorganic nitrogen at 25-60 mM. Many plants appear to grow best if given both forms. Nitrogen may also be given in organic forms as amino acids, hydrolysates and organic acids. Organic forms of nitrogen cannot totally replace inorganic forms.
Phosphorus (P): Phosphorus is an integral part of nucleic acids and other structural compounds in plants. Phosphorus is supplied in culture media as phosphate (PO4-) in a form of sodium or potassium hydrogen phosphate at 1-3 mM.
Potassium (K): Potassium is major positive ion in plants to balance negative ions. The amount of potassium needed in a plant tissue culture medium varies depending on the plant species. Usually it is supplied at 20-30 mM in correlation with that of nitrate.
Sulfur (S): Sulfur is important in protein structure where disulphide bonds between neighboring cystein and methionine residues contribute to the tertiary structure. Sulfur is also a constituent of the vitamins thiamine and biotin and of coenzyme A, an important component in respiration and fatty acid metabolism. In the form of iron-sulfur proteins it is important in electron transfer reactions of photosynthesis. Sulfur is supplied as the SO4- ion usually with magnesium as the cation at 1-3 mM.
Iron (Fe): Iron is required for chlorophyll synthesis as well as in many oxidation/ reduction reactions. Iron usually present in media at 1 ìM. Since iron forms insoluble compounds in alkaline pH, being unavailable to plant in culture, medium pH is critical for iron supply. Fe-EDTA is often used in culture media and enable iron to be available to cultures over a wider pH range than other agents.