Classification Of Essential Elements

Mineral Nutrition In Plants of Class 11

The essential elements are further classified into two categories :

Macroelements (Major elements) : These elements are required by the plant in larger quantities. These are Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Potassium, Magnesium, Calcium.
Microelements (Minor elements or Trace elements) : These are required by the plant in low quantities (often less than 1 ppm.). Boron, Zinc, Manganese, Copper, Molybdenum, Chlorine, Iron.

The usual concentration of essential elements in higher plants according to D.W. Rains (1976) based on the data of Stout are as follows :

Element % of dry weight

Carbon - 45

Oxygen - 45

Hydrogen - 6

Nitrogen - 1.5

Potassium - 1.0

Calcium - 0.5

Magnesium - 0.2

Phosphorus - 0.2

Sulphur - 0.1

Chlorine - 0.01

Iron - 0.01

Manganese - 0.005

Boron - 0.002

Zinc - 0.002

Copper - 0.0001

Molybdenum -0.0001

Framework elements : Carbon, Hydrogen and Oxygen are considered as framework elements because they constitute the carbohydrates which forms cell walls.
Protoplasmic elements : Nitrogen, Phosphorus and Sulphur are considered as protoplasmic elements as they form part of protoplasm along with carbon, hydrogen and oxygen.
Catalytic elements : Some elements function as part of the enzyme i.e., without the presence of these elements some enzymes cannot function.
Balancing elements : Calcium, Magnesium and Potassium counteract the toxic effect of other minerals by causing ionic balance.
Influence on the osmotic pressure of the cells : Plant cells contain dissolved mineral elements in the cell sap which influences the osmotic pressure of the cell.

C, H and O known as frame work elements as these compose the bulk of plant body and enter into the composition of cell wall, protoplasm and so most of organic compounds.
Source − Atmosphere and water
Origin − Not of mineral origin but of gaseous origin.
Role – Synthesis of carbohydrates, fats and others.

Minerals	Source	Major Role	Deficiency symptom
N	Soil in the form of nitrate or ammonical salts; Atmospheric nitrogen by bacteria and cyanobacteria	Protein synthesis; constituent of proteins, nucleic acid, cytoplasm, chlorophyll, cytochromes etc,	Chlorosis; development of anthocyanin in stem, leaf veins, suppressed shoot growth, sparse foliage, early defoliations.
S	Soluble sulphate of the soil; atm. SO & shy;₂ and SO₃ in low conc,	Forms amino acids like cysteine and methionine; vitamins like thiamine; C oA, ferrodoxin, and volatile oils.	Chlorosis in young leaves; stunted growth, sparse foliage.
P	Soluble phosphate (HP₄ and H₃PO₄)	Constituent of lipoprotein membranes, nucleic acids, C oA, nucleoproteins, ATP, NADP, etc.	Stunted growth, premature leaf fall; necrotic areas develop on leaves.
Ca	Carbonate of lime	Constituent of middle lamella of cell wall; affects permeability of cell membrane; lipid metabolism activator of ATP-ase.	Death of growing regions of stem and leaves; chlorotic patches near margins of leaves unmature seed formation.
K	Inorganic salts	Most abundant in young parts, activator of enzymes; translocation of carbohydrates, cell division, permeability and hydration.	Interveinal chlorosis.
Mg	Carbonate, sulphate and silicate	Essential constituent of chlorophyll; acts as catalyst; activator for enzymes; stabilization of ribosomal particle.	Interveinal chlorosis, necrotic spots on leaves, defoliation.

MICRO NUTRIENTS

Element	Source	Role	Deficiency symptom
Fe	Ferric and ferrous compounds.	Constituent of fd, cytochromes; chlorophyll synthesis.	Chlorosis in young leaves.
Mn	Oxide forms	Activator of enzymes decarboxyleses, reductases; photolysis of water, formation of chloroplast.	Chlorosis and necrosis in old leaves.
Cu	Complex organic compounds	A part of Plastocyanin; as a catalyst in nitrogen fixation; constituent of acetic acid oxidase, Cytochrome oxidase, etc.	Necrosis at the tip of young leaves (die back) exanthema reclamation disease of oat.
B	Borate ions	Translocation of sugar; metabolism of carbohydrate and fat; germination of pollen.	Death of shoot tip, heart rot of sugar beet.
Zn	Magnetite	Synthesis of tryptophan; activator of several enzymes; role in protein synthesis, chlorophyll formation.	Interveinal chlorosis of older leaves; stunted growth, malformation of leaves.
Mo	Occurs in the soil in three forms: Dissolved, exchangeable and non exchangeable forms; available to the plants mostly as molybdate ions.	Essential constituent of the enzyme nitrogenase and thus very important in nitrogen metabolism.	Chlorosis in the old leaves: inhibit flowering.
Cl	Chloride ions	Activator of enzyme for photolysis of water,	Wilted leaves, stunted and thickened root, reduced fruiting, inhibition of photosynthesis.