Magnesium :
- Absorbed in the form of Mg2+.
- Activates enzymes of respiration, photosynthesis.
- Involved in the synthesis of DNA and RNA.
- Constituent of the ring structure of chlorophyll.
- Maintain ribosome structure.
Sulphur :
- Absorbed in the form of sulphate SO42-.
- Present in two amino acids cystine and methionine
- Main constituent of several coenzyme, vitamins and ferredoxin.
Iron :
- Obtained in the form of ferric ions (Fe3+).
- Required in larger amount in comparison to other elements.
- Constituent of proteins involved in the transfer of electron like ferredoxin and cytochromes.
- Activates catalase enzyme.
- Essential for formation of chlorophyll.
Manganese :
- Absorbed in the form of manganous ions (Mn2+).
- Activates many enzymes of photosynthesis, respiration and nitrogen metabolism.
- Photolysis of water and evolution of oxygen during light reaction.
Zinc :
- Obtained in the form of Zn2+.
- Activates enzymes like carboxylase.
- Required in synthesis of auxin.
Cupper :
- Absorbed in the form of cupric ions (Cu2+).
- Essential for overall metabolism.
- Associated with enzyme involved in redox reactions.
Boron :
- Absorbed in the form of BO33- or B4O72-.
- Required in uptake and utilization of Ca2+.
- Pollen germination.
- Cell elongation.
- Cell differentiation.
- Carbohydrate translocation.
Molybdenum :
- Obtained in the form of molybdate ions (MoO22-).
- Component of enzyme like nitrogenase and nitrate reductase.
- Required in nitrogen metabolism.
Chlorine :
- Absorbed in the form of chloride anion (Cl-).
- Along with Na+ and K+ it determines the solute concentration.
- Maintain anion cation balance of the cell.
- Essential for photolysis of water during light reaction of photosynthesis.
Deficiency symptoms of essential elements :
- Critical concentration: the concentration of the essential element below which plant growth is retarded.
- The element is said to be deficient when present below the critical concentration.
- For the elements that are actively mobilized within the plant that show the deficiency symptoms in the older tissues. (nitrogen, potassium and magnesium)
- The deficiency symptoms tend to appear first in the young tissues whenever the elements are relatively immobile and are not transported out of the mature organs.(sulphur and calcium)
- Deficiency symptom includes chlorosis, necrosis, and stunted growth, premature fall of leaves and buds, and inhibition of cell division.
- Chlorosis: is the loss of chlorophyll.
- Necrosis: death of cells and tissues.
Toxicity of Micronutrients :
- Micronutrient required in low amount.
- Moderate decrease causes the deficiency symptoms.
- Moderate increase causes toxicity.
- Any mineral ion concentration in tissues that reduces the dry weight of the tissues by 10 percent is considered toxic.
