Plant Metabolites : Introduction


          Medicinal Botany is a branch of botany or bio-sciences, which deals with ‘study of herbal medicines obtained from various plant parts, e.g., root, stem or bark, flowers, fruits and seeds'. These medicinal properties are due to number of special chemical compounds present in plants and such compounds or constituents are known as ‘Plant Metabolites’, ‘Phytochemicals’ or ‘Bio-molecules’.

          Plant Metabolites are of two types, i.e. Primary Metabolites and Secondary Metabolites.


          This phytochemicals or Primary metabolites or basic nutrients which are required for growth and reproduction of plant.
          Primary metabolites are synthesized plants using various elements such as Carbon (C), Nitrogen (N), Phosphorous (P), Potassium (K), Iron (Fe), Magnesium (Mg), Calcium (Ca), etc. Primary metabolites are produced in large quantity and stored in various cells and tissues of plants.

There are three types of primary metabolites and are as follows:

1. Carbohydrates: 
These compound are made up of C, H, (O) group and are required for structural purpose and energy production. Plant consist of three basic type of carbohydrates i.e. monosaccharides, oligosaccharides, and polysaccharides. Out of these sucrose and starch are most comm0n sugars of plants.

2. Proteins:
Proteins are chain of amino acids linked by polypeptide bond. Proteins are mainly required for structural purpose however proteins are also functioning as enzyme and regulatory factors.

3. Lipids:
Lipids are generally composed of fatty acids and alcohol, they exist in solid (fats) or liquid (oils) state. Lipids are mainly required for formation of cell membrane apart from this they also works as an energy molecules.


         Secondary metabolites are special type of compounds which are produced during various biochemical pathways. They do not contribute as nutrients. They are usually produced in smaller quantity as compared to primary metabolites.
          Usually secondary metabolites produced in certain type of cells or tissues and stored specific part of plant. They mainly act as a defensive mechanism, Many of the secondary metabolites protect plant from various infections and diseases some of them can attract different insects or birds for pollination.

There are 4 types of secondary metabolites and are as follows:

1. Alkaloids:
Alkaloids are nitrogen containing alkali like substance present in certain types of plants. They are ‘basic’ in nature (pH > 7.0), usually they are crystalline and stored in various parts of plants e.g. ‘Dhatura’ consist of ‘tropane alkaloid’, while morphine alkaloid is present in fruits and seeds of afu (papaver) plant.
Alkaloid is a major category of secondary metabolites and produced by not only higher plants but also algae and fungi.

2. Glycosides:
Glycosides are the chemical constituents which are made up of sugar and non-sugar compounds. This is also major category of secondary metabolites. Glycosides are mainly crystalline or amorphous in nature.
Some of the glycosides are sweet in taste e.g. liquorice (Glycyrrhiza gabra) (ज्येष्ठमध ) is sweeter than normal table sugar and used for expectorant activity (cough relief activity). Most of the glycosides are used as cardiac tonic, antioxidant and kidney tonic.

3. Tannin:
Tannins are polyphenolic compounds usually brown in colour. Most of the plant tannins are stored in bark and leaves of plants, e.g. tannins present in tea leaves.
Tannins are astringent in taste and they are highly useful against various infections, they are used tannery industry for leather production.

4. Essential oils: 
These oils are made up of aromatic compound such as turpins, aldehyde, ketones, and derivatives of organic compounds.
They get evaporated at room temperature and gives out particular scent or smell.
The oils are stored in special cavities or glands of various plant parts, e.g. Tulsi plant (Ossimum sanctum) store Tulsi oil in glandular hair present on entire plant.


1.    Defensive compounds against various pathogens and grazing animals.
2.    Some of the compounds attract animals and insects species for pollination purpose and seed dispersal.
3.    Secondary metabolites acts as agent for plant competition.
4.    Mankind is using secondary metabolites in manufacturing of medicines, insecticides, flavors, scent, rubber making (latex- rubber plant), spices and other industrial materials like gum and resins.

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