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 a major part of the
macromolecules and co-enzymes.
The various functions of the mineral elements are given
here:
Nitrogen
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.
Phosphorus
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.
Potassium
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.
Calcium
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.
Magnesium
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.
Sulphur
It is absorbed in the form of sulfate and is present in
two amino acids called cysteine and methionine. Sulfur is also the major
constituent of coenzymes, ferredoxin, and vitamins.
Ferrous
It is the major constituent of proteins like cytochromes
and ferredoxin that are associated with the transfer of electrons. It is used
in the chlorophyll synthesis.
Manganese
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.
Zinc
It is absorbed as zinc ions. It stimulates various
enzymes like carboxylases. This enzyme is required in the auxin synthesis.
Copper
It is absorbed as cupric ions. It is associated with the
plant metabolism. Iron is involved in the enzymes of the redox reactions.
Boron
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.
Molybdenum
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.
Chlorine
It is absorbed in the form of chloride. It helps in the
determination of solute concentration and anion-cation balance in the cells.
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