Based on the criteria of essentiality, some of the elements are considered to be very much essential for the growth and metabolism of the plant. These elements are further classified into two groups. They are micronutrients and macronutrients.
Essential elements participate in the metabolic processes of the plant cell like regulating the osmotic concentration of the cell sap, permeability of the cell membrane, buffering action, electron transport systems, and enzymatic activity. These elements form major part of the macromolecules and co-enzymes.
The various functions of the mineral elements are given here:
It is absorbed as nitrate, nitrite and ammonia. Nitrogen is taken by all parts of the plant including the meristematic tissues and metabolically active cells. Nitrogen is present in nucleic acids, proteins, hormones and vitamins.
It is absorbed in the form of phosphate ions. Phosphorus is part of the cell membranes, nucleic acids, proteins, nucleotides and is required in all the phosphorylation reactions.
It is absorbed as potassium ions and is utilized mostly in meristematic tissues, leaves, root tips, and buds. The anion-cation balance is maintained in the cells by the potassium. It is used in the protein synthesis, closure and opening of stomata, in the maintenance of cell turgidity and in the activation of enzymes.
It is absorbed in the form of calcium ions. It is utilized by the meristematic and differentiating tissues. Calcium is used in the cell wall synthesis in the form of calcium pectate in the middle lamella. It is also used in the formation of the mitotic spindle. Calcium is used in the normal functioning of the cell membranes. It helps in the activation of the enzymes and plays an important role in maintaining the metabolic activities.
This divalent cation is involved in the activation of the enzymes of respiration, photosynthesis and in the synthesis of DNA and RNA. Magnesium is part of the chlorophyll structure and it helps in the maintenance of the structure of the ribosome.
It is absorbed in the form of sulphate and is present in two amino acids called cysteine and methionine. Sulphur is also the major constituent of coenzymes, ferredoxin and vitamins.
It is the major constituent of proteins like cytochromes and ferridoxin that are associated in the transfer of electrons. It is used in the chlorophyll synthesis.
It is absorbed in the form of manganous ions. It activates the enzymes associated with respiration, photosynthesis and nitrogen metabolism. Manganese is involved in the water splitting to liberate oxygen at the time of photosynthesis.
It is absorbed as zinc ions. It stimulates various enzymes like carboxylases. This enzyme is required in the auxin synthesis.
It is absorbed as cupric ions. It is associated with the plant metabolism. Iron is involved in the enzymes of the redox reactions.
It is absorbed as borate ion. Boron is necessary for the uptake of calcium and its utilization, pollen germination, cell differentiation, cell elongation and carbohydrate translocation.
Plants absorb it in the form of molybdate ions. It is associated with the functioning of nitrogenase and nitrate reductase which participates in nitrogen metabolism.
It is absorbed in the form of chloride. It helps in the determination of solute concentration and anioncation balance in the cells.