Mineral Metabolism may be defined as a process in which mineral nutrient elements are incorporated into animal/plant metabolites. It’s a known fact that these mineral are got from the soil plants through their roots. Only during the first half of the nineteenth century, plant scientists began to understand the plant growth, development, and need of the chemical elements. These elements are absorbed from soil as inorganic ions. Inorganic ions in the soil are derived mostly from mineral constituents. Due to this reason, we term it as mineral nutrition.
Sixteen elements are known to be essential for higher form of life in terms of relative numbers with respect to molybdenum.
The level of essential elements known to be critical for the growth of multicellular plants.
All the elements present at concentration of 1000ppm or higher are termed macro nutrients (k, Ca, Mg, N, P, S, C, H, O).
Potassium, Calcium, and Magnesium are present in soil as cations (K+, Ca++, Mg++) whereas nitrogen, phosphorous and sulfur are normally present in soil as anions (NO3, H2PO4-, SO42-) except C, H, O all the other essential elements are mineral elements.
The micronutrients as the name suggests, are required in very small amounts but are equally essential for plant growth (Mo, Cu, Zn, Mn, Fe, B, Cl). In addition to these elements, other elements have been established as being essential for few species of higher plants e.g. Co, Si, Se are important for some higher plants.
Specific Functions of Essential Nutrients
Since each essential element performs one or more specific metabolic roles, a less than adequate supply of an essential element will be accompanied by distinctive metabolic disruptions, including change in activity of enzymes, in rate of metabolic reactions and concentration of metabolites. This also leads to characteristic changes in the physical appearance of plants, leaves, stem, fruits etc.
1. Sulfur: The higher plants take sulfur as sulfate ion by roots or may be absorbed as SO2 from atmosphere and it is assimilated by leaves. It is a component of cystine, cysteine, methionine and thus proteins, lipoic acid and coenzyme A, TPP, Glutathione, and biotin.
2. Phosphorous: Absorbed (HPO4- or H2PO4-) ion from the soil, the assimilation of phosphorus into ATP is through oxidative phosphorylation
Later this inorganic phosphate becomes a part of many molecules of the cell. For example, all the intermediates of glycolysis are phosphorylated. It is also an important component of nucleic acids (as phosphodiester linkage).
3. Magnesium: It serves as a structural component of cell and is involved as a cofactor in many enzymes systems. It is required by the photosynthetic cell containing chlorophyll. It is associated with phosphate transferring reaction.
Mg++ forms stable complexes with ATP, ADP, and AMP.
4. Calcium: Calcium has been associated with the cell wall structure as calcium pectate. It is also involved in IAA (Indole acetic acid) stimulated cell elongation and cell division.
Nodulation and successful symbiotic nitrogen fixation require relatively high concentration of calcium. Important in enzymic systems viz. Barley alpha-amylase, ATPase and phospholipase-D.
5. Potassium: Many enzymes require potassium for maximum activity viz. aldose (glycolysis), Pyruvate kinase, succinyl CoA synthetase, etc. Translocation of carbohydrates, stomatal opening, and osmotic regulation are affected by its deficiency.
6. Molybdenum: Molybdenum has been shown to be essential for fixation of nitrogen by azotobacter chroccum. It is a constituent of fungi, bacteria and higher plants and it is also a constituent of xanthine oxidase and aldehyde oxidase.
7. Copper: It is found in enzymes in which oxygen is used directly in the oxidation of substrate, e.g., tyrosinase, laccase, ascorbic acid oxidase.
It is also involved in oxidation of cytochrome oxidase.
8. Zinc: It is involved in many enzymes, viz, alcohol dehydrogenase, glucose 6-phosphate dehydrogenase, and triose phosphate dehydrogenase. It is highly involved with DNA and helps in regulation of its expression through zinc finger.
9. Manganese: It can replace magnesium in many of the reactions if found insufficient, eg. glucokinase, hexokinase etc. Many citric acid cycle enzymes require manganese for optimal activity.
Iron: It is a structural component of porphyrin ring and acts as the cofactor of many enzymatic reactions. In animals, it is associated with porphyrin ring of haemoglobin. It is also a component of electron transport chain, cytochrome b, b6, c, C2, and f. It is also a component of nonheme protein molecule, ferredoxin and in enzyme viz. cytochrome oxidase.