Groups and Function of Secondary Metabolites

8/3/2019 Groups and Function of Secondary Metabolites

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Groups And FunctionOf SecondaryMetabolites


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IntroductionPlants have number of mechanism to

protect itself from herbivorous and

pathogens.Secondary metabolites are one of the

mechanism.


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Secondary MetabolitesSecondary metabolites are organic

compound that have no significant role

in plants growth and development.It protect plants from herbivorous and

pathogens.

These are the species specific.


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Groups of secondaryMetabolitesThere are generally three major

classes of secondary metabolites-

1.Terpenes

2.Phenolics

3.Nitrogen containing compound


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Terpens / TerpenoidsTerpenes are largest class of

secondary metabolites.

Terpenes are Insoluble in water.

Terpenes are occasionally referred asisoprenoids.


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Terpens are biosynthesized by-

1. Mevalonic acid

2. 3 PGA / Pyruvate pathway


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Classification of terpenesOn the basis of five carbon units theycontain terpens are classified as

Monoterpenes (10 C, two C5 unit)Sesquiterpenes (15 C, three C5 units)

Diterpenes (20 C, four C5 units)

Triterpenes (30 C, six C5 unitsTetraterpenes (40 C, eight C5 units)

Polyterpenes ({C5}n)


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Function of terpenesMonoterpenes:

It act as insecticide agent, accumulate

in resin duct(in needle, twig, trunk) andmake it toxic.

Essential oil having mixture of

monoterpenes and sesquiterpenesgive odor to the foliage.


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Essential oil act as insect repellent. Ex.Menthol of peppermint oil, limonene of

lemon oil.It was observed that in some plant it is

produced after the insect have begun

feeding. This attract the predatory,parasitic insect that eat them.


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Sesquiterpenes:

These are antiherbivore in nature.

Gossypol(sesquiterpenes of cotton)provide resistance to insects.

Diterpenes:

are toxic and feeding deterrent toherbivore.


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Plant resin contain significant amountof Diterpenes that outflow on piercing

the plant trunk by insect or predatorand chemically deter them to eatfurther.

Phorbol(in euphobiaceae) cause skinirritation and internal toxin to mammal.


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Phenolic CompoundPhenolics are characterised by the

presence of the 6 membered benzene

ring along with the alcohol (-OH).Phenolic compounds are chemically

heterogenous groups.

Some are water soluble and some aresoluble in organic solvents.


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Two basic pathways of phenolicssynthesis are-

Shikhimic acid pathway (in plants ,fungi and bacteria)

Malonic acid pathway (in fungi and

bacteria)


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Classification ofPhenolicsSimple phenolic compound

On the basis of their structure-

1. Simple phenylpropanoid

2. Phenylpropanoid lactones

3.

Benzoic derivatives phenoliccompound


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Complex phenolic compound

ex. Lignin, flavonoids,anthocyanins, tannins


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LigninHighly branched phenylpropanoid

compound.

The lignin is generally boundcovalently to the polysaccharide andthe cellulose.


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Thus difficult to isolate & so structurenot been correctly elucidated.

Made up of three phenylpropanoidphenols.

-Coniferyl

-Coumaryl

-Sinapyl


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These components are addedenzymatically that involves the use of

the free radicals. Structural analysisgenerally showed the C-O-C, C-Cbonding in the three dimensional

orientation.


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Lignin works as a protective agent inplant by-

1. Providing the physical strength thatrepels the herb feeder.

2. By binding to the protein andcellulose and so reducing theirdigestibility in their feeders.

3. By accumulating at the site ofwounding and infection.


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FlavonoidsThe largest class of the phenolics.

The structure generally consists of the

15 carbons.

Out of which 12 present as the twobenzene ring and the rest three are

present as the bridge carbons.


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Flavonoids GroupsGenerally there are four major classes

of the flavonoids-

1.Anthocynin

2.Flavones

3.Flavonols

4.Isoflavones


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N-containing compoundNitrogen containing compound include

antiherbivore defenses like alkaloids,

cyanogenic glycosides.N-containing compound are

synthesized from common amino acid.

Examples- alkaloids, cyanogenicglycosides, glucosinolates and nonprotein amino acid.


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Function of phenolicsSimple phenolics protect plant against

herbivore and fungi.

Furanocoumarins is activated by light.

Activate Furanocoumarins insert itselfinto DNA and bind to pyrimidine ring,

block transcription and repair and leadto death of insect. This mechanism isknown as Photo toxicity.


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There are certain simple phenolicswhich on release from leaves, roots

and decaying litter affect neighbouringplants.

Ex. Caffeic acid and ferulic acid inhibit

growth and germination of many plantsAllelopathy: investigation of effect of

these phenolic on neighbouring plant.


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AlkaloidsAlkaloids are found in species of

vascular plants.

Alkaloids have a pharmacologicaleffect on vertebrate animals.

Several type of alkaloids are derived

from ornithine.Alkaloids provide defense against

predators(generally mammals)


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At lower dose these compounds arepharmacologically useful but high dose

of alkaloid lead to death in humans.ex.-morphine, cocaine, nicotine,caffeine

On cellular level many alkaloidinterfere with components of nervoussystem.


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Cyanogenic glycosidesThese compound itself are not toxic

but readily broken down to give off

toxic substances when the plant iscrushed.

Cyanogenic glycosides release HCN.

These are widely distributed in plantslike legumes, grasses, rose family.


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Have protective function in certain

plant however some herbivore haveadapted to feed on these glycosides.


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GlucosinolatesGlucosinolates breakdown to release

volatile defensive substances.

These are found principally incrucifers.

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Groups and Function of Secondary Metabolites

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