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
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.
- 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|
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.
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.
Most abundant in young parts, activator of enzymes;
translocation of carbohydrates, cell division, permeability and hydration.
|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.|
|Fe||Ferric and ferrous compounds.||Constituent of fd, cytochromes; chlorophyll synthesis.||Chlorosis in young leaves.|
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.
Translocation of sugar; metabolism of carbohydrate and fat;
germination of pollen.
|Death of shoot tip, heart rot of sugar beet.|
Synthesis of tryptophan; activator of several enzymes;
role in protein synthesis, chlorophyll formation.
Interveinal chlorosis of older leaves;
stunted growth, malformation of leaves.
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.|