Classification Of Essential Elements

Mineral Nutrition In Plants of Class 11

Classification Of Essential Elements |Mineral Nutrition In Plants

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

GENERAL FUNCTIONS OF MINERAL ELEMENTS

  • 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.

MACRO NUTRIENTS

  • 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.

 

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