Plant Secondary Metabolites Quiz

Plant Secondary Metabolites (PSM)

• PSM are complex organic compounds produced by plants in small quantities.
• Approximately 100,000 known structures exist, though only 5-15% of plant structures have been chemically studied.
• Crucial for plant survival and evolution, different from primary metabolites.

Comparison with Primary Metabolites

• PSM do not directly participate in plant growth or development.
• They fulfil diverse evolutionary roles including defense mechanisms, signaling, and adaptation.

Defensive Role of PSM

Mechanical Defense Strategies

• Thorns, trichomes, thick epidermis, and sticky/smooth surfaces deter herbivores.

Chemical Defense Compounds

• Major groups include alkaloids, phenols, terpenoids, iridoid glycosides, cardenolides, and cyanogenic glycosides.

Biosynthesis of PSM

Precursor Molecules

• Amino acids, activated isoprenes, shikimic acid are key precursor molecules.

Biosynthetic Pathways

• Primarily located in the cytoplasm, plastids, endoplasmic reticulum, and mitochondria.
• Multiple compounds can arise from a single enzyme, with reactions adapting evolutionarily. Genetic variations enable metabolic flexibility.

Diversity Mechanisms

• Single enzymes can synthesize multiple compounds.
• Organisms adapt their enzyme reactions and have genetic variation to enable metabolic flexibility.

Classification of PSM

Major Groups

• Terpenoids (>25,000 compounds)
• Phenylpropanoids (~2,000 compounds)
• Alkaloids (~12,000 compounds)

Temporal Changes

Ontogenetic Changes

• PSM concentration changes with plant maturation (genetically programmed).

Seasonal Changes

• Environmental factors (temperature, light, water, nutrients) influence seasonal PSM concentrations.

Small Group 1: Slimes (Mucilaginous Substances)

• Polysaccharides with high water retention capacity.
• Swell in water to form colloidal solutions or gels.
• Protect mucosa, act as emollients, and as laxatives/antidiarrheal agents.
• Examples: Marshmallow root, Mallow flower, Flaxseed.

Small Group 2: Glycosides

• Found in all plant organs.
• Compounds with a sugar (glycone) linked to a non-sugar moiety (aglycone).
• Mono-, di-, or oligoglycosides linked through O-, S-, or C-glycosidic bonds.
• Subtypes based on aglycone, include simple phenols, cyanogenic glycosides, steroidal glycosides, and anthraquinone glycosides.
• Glycosides have diverse therapeutic functions depending on their aglycone.

Large Group 1: Terpenoids (Isoprenoids)

• Synthesized from isoprene units via Mevalonate (cytoplasm) and Methylerythritol Phosphate (plastids) pathways.
• Subtypes based on isoprene units: Monoterpenes, Sesquiterpenes, Diterpenes, Triterpenes, Tetraterpenes.
• Possess >10 conjugated double bonds making them sensitive to oxidation.
• Serve as antioxidants, and defense mechanisms.
• Examples: Carotenoids (α-carotene, lycopene), Saponins (licorice root).

Large Group 2: Phenolics

• Aromatic metabolites with hydroxyl groups attached to aromatic rings.
• Biosynthetic Pathways include Shikimate-Chorismate (derived from amino acids) and Acetate-Malonate (building polyketide derivatives).
• Subtypes vary from simple phenols to phenols with 1-3 carbon atoms, to those with multiple aromatic rings (xanthones, stylbenes, flavonoids).
• Functions: Strengthen capillaries, reduce vein permeability, anti-inflammatory, and diuretic.
• Related groups include tannins (hydrolyzable and condensed) and lignans.

Large Group 3: Alkaloids

• Nitrogen-containing compounds biosynthesized from amino acids.
• Subtypes: True alkaloids, protoalkaloids, and pseudoalkaloids.
• Affect the nervous system (as stimulants, sedatives, or spasmolytics).
• Examples: Morphine, nicotine, caffeine.

Practical Applications

• PSM are crucial for plant survival.
• Highly diverse and complex in structure and function.
• Potential significant medicinal applications in treatment of chronic diseases and complementary medicine.

Test your knowledge on plant secondary metabolites (PSMs) and their functions! This quiz covers key concepts such as biosynthesis, diversity, and the role of PSMs in plant survival. Challenge yourself to identify major groups and precursor molecules related to PSMs.