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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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