Plant Metabolites Overview

Primary Metabolites

• Proteins, lipids, carbohydrates, and nucleic acids are called primary metabolites
• They are found in all plant cells
• They are essential for plant life

Secondary Plant Metabolites (Active Constituents)

• These metabolites act as protective agents, being waste products of metabolism.
• They aid plant survival and are physiologically active.
• They are categorized into various organic compounds.

Carbohydrates Related Compounds

• Composed of carbon, hydrogen, and oxygen as aldehydes, ketones, acids, or alcohols
• Examples include sucrose, lactose, starch, gums, mucilage, and pectin.
• Gums: Polysaccharides or salts of polysaccharides, formed in higher plants as protection after injury.
  • Gums yield arabinose, galactose, glucose, mannose, and various uronic acids following hydrolysis. The latter can form salts with Ca, Mg, and other cations.
  • Examples include gum acacia and gum tragacanth.
• Mucilage: Polysaccharide complexes found in various plants, similar to plant gums, insoluble in alcohol, and forming viscous non-adhesive colloid solutions in water but not jelly.
  • Types: Pectose type (red with ruthenium red), Callose type (red with corallin soda), and neutral (blue with methylene blue).
  • Associated health benefits include preventing constipation, regulating blood sugar, easing stomach troubles, and protecting the mucous membranes.

Pectin

• A purified carbohydrate obtained from dilute acid extracts of citrus fruit rinds or apple pomace.
• It forms a stiff gel when dissolved in water (20 parts water).
• Used as a protecting and suspending agent in anti-diarrheal preparations.

Glycosides

• Non-reducing organic compounds yielding one or more sugars following hydrolysis by dilute acids, alkalis, or enzymes.
• The non-sugar part is called aglycone (genin), and the sugar part is called glycone.
• Chemically, glycosides are sugar ethers formed by losing water and creating O- (oxygen), C- (carbon), S- (sulphur), or CN- (cyanophore) linkages.
• Generally soluble in water and hydro-alcoholic solvents due to the hydrophilic nature of sugar, but solubility decreases with increasing sugar content. Aglycones are soluble in organic solvents.
• Classification of Glycosides: Classified based on the aglycone's nature.
  • Simple phenolic glycosides: e.g., Arbutin (derived from Uva ursi leaves), used in treating uretritis and cystitis.
  • Flavonoid glycosides: Largest group of naturally occurring phenols, yellow compounds that dissolve in aqueous alkali and produce a canary-yellow color; e.g., Diosmin glycoside (Buchu) and Hesperidin glycoside (Citrus species).
  • Anthocyanin glycosides: Structurally related to flavonoids, give color to flower petals, and colors change with cell sap pH (e.g., from red-violet to blue; e.g. hibiscus).
  • Anthraquinones glycosides: Pharmacologically active constituents of laxatives and purgatives (e.g., Senna). Positive tests include Borntrager's and modified Borntrager's tests.
  • Alcoholic glycosides (Cardiac glycosides): Affect cardiac muscles directly and are potent.
    • Examples include Digitalis, which is vital for strengthening heart function.
  • Saponin glycosides: Cause foam and red blood cell hemolysis when introduced in the blood stream. They are also often sternutatory and irritating to mucous membranes (eyes and nose). Use as emulsifiers and cleaners.
  • Cyanophore glycosides: Yield HCN (hydrogen cyanide) during hydrolysis. Consequently, their use in medicine is restricted (e.g., detection by sodium picrate paper reactions).
  • Thioglycosides: Include Sinigrin (mustard irritant gas) and Sinalbin (non-volatile).

Tannins

• Large group of complex, non-crystalline substances.
• Form colloidal solutions in water, with strong astringent taste.
• Precipitate proteins and alkaloids.
• Used in medicine (gastrointestinal tract astringents and hemostatic agents), burn treatment, antidote for metal poisoning, leather tanning, and ink preparation.
• Types of tannins:
  • Hydrolysable tannins: Hydrolyzed by acids or enzymes, yield phenolic acids (e.g., gallic acid), reacting with FeCl3 (blue-black color). Examples include cloves and galls.
  • Condensed tannins: Not easily hydrolyzed, don't contain a sugar moiety, yield catechin on hydrolysis, react with FeCl3 (green color) and precipitate with Br2 in water. Tea and henna leaves are examples.

Alkaloids

• Basic nitrogenous compounds of biological origin, exhibiting physiological activity.
• Not all compounds containing nitrogen are alkaloids.
• Usually insoluble in water but soluble in organic solvents, while their salts are soluble in water, often with limited solubility in organic solvents.
• Detection: Using specific reagents, e.g., Mayer's reagent (potassium mercuric iodide) causes creamy white precipitates with alkaloids, except caffeine. Dragendorff's reagent gives orange color.

Volatile Oils (Essential Oils)

• Mixtures of hydrocarbons (mainly terpenes) and oxygenated compounds.
• Present in plant cells, secreted by canals, cavities, or glands.
• Volatile, evaporating at room temperature with steam.
• Non-saponifiable, don't form stains on filter paper, possess aroma/flavor
• Examples include Buchu leaves and lavender flowers.

Fixed Oils

• Triglyceryl esters of fatty acids.
• Found in the endosperm or embryo of seeds.
• Non-volatile, saponius, stain on filter paper.
• Often used in foods (e.g. linseed seed oil).
• Turn rancid when stored.

This quiz explores the essential roles of primary and secondary metabolites in plants. You will learn about the significance of carbohydrates and their related compounds, including gums and mucilage. Test your knowledge on how these metabolites contribute to plant life and survival.