Plant Defense Systems
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Transcript of Plant Defense Systems
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Plant defense systems
A.BharaniDeepan
13-513-301
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Constitutively produced
chemicals
Plant Defenses
Physical barriers
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Pre-defense chemicals like secondary
metabolites are already accumulated in
plants.
Terpenoids, alkaloids, glucosinolates,
phytoecdysones, saponins, cardiac glycosides.
CONSTITUTIVE RESISTANCE
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Induced resistance
Induction of synthesis of a toxinalready present in low amount
Biosynthesis of phytoalexins,
proteinase inhibitors, PR proteins
Hypersensitive reaction
Defense process
that is triggered
only by pathogen
attack. It includes:
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Mechanical defense
Presence of Cutin, suberin& Waxes in the Cuticle and
periderm.
Lignification - strengthens
the cell wall by forming a
ramified network
throughout the matrix thus
anchoring the cellulose
microfibrils more firmly.
Lignin protects the
microfibrils on the walls
from chemical, physical and
biological attack
http://localhost/var/www/apps/conversion/Lecture%20notes/Defense-Related%20Proteins%20of%20Higher%20Plants_files/Figure2.gif -
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DEFENSE ROLE OF PHENOLICS IN
PLANTS
Allelopathic effects : Juglone
Feeding deterrents : Gallotannins,Quercetin, glycoside (Flavonol)
Anti-fungal agents : Luteone(isoflavone), Protocatechuic acid,
Phloridzin
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Phytoalexin : Isoflavans
Phenyl propanoids : Coniferyl alcohol
Furocoumarins : Psoralab
Pterocarpans : Pisatin
Stilbenes: Resveratrol, styrylpyrones,arylpyrones
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TANNINS
Impart resistance to plants from microbes and animal
predators.
By precipitation of salivary proteins, tannin renders animaltissue unpalatable.
Grazing animals do not consume plants with tannin
content more than 2% (dry weight basis).
Protein component of viruses are made inactive by tannins
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Terpenes
Several sesquiterpenes play well
defined and essential roles in higher
and lower plants including furanoid
phytoalexins, lactone antifeedantsand numerous antibiotics
Triterpenoid compounds fromazadirachtin has insecticidal
properties
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Compound Insects Mode of Action
Pyrethroids Many insects Neurotoxins
Citronellol Leaf hopper Oviposition deterrent
Iridoid Many insects
Lepidopterangrasshoppers
Antifeedant
Sesquiterpene lactone
(Alantolactone)
Lepidopterans Flour
beetles
Antibiosis
Gossypol H. virescens
Spodopteralittoralis
Toxic
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Phytoecdysteroids
Ecdysone inhibit molting in insects.
Stimulate secretion of phenol oxidase, which
make the newly formed cuticle harder before
it expands.
As a result the mouthparts get buried and the
insect is unable to feed on plants
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Pathogenesis-related proteins(PR
proteins)
Protective plant proteins specifically induced inpathological or related situations are called
"pathogenesis-related proteins.
phytoalexin, isoflavone reductase
proteins accumulated in seeds and fruits are consideredto have a constitutive defense function against microbial
pathogens and invertebrate pests in addition to their
storage function.
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Compatible interaction disease
Incompatible interaction resistance
3 aspects of response:
1.Hypersensitive
2.Local
3.Systemic
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Hypersensitive reaction (HR)
Characterized by localized and rapid cell death at the site of
infection to prevent pathogen spread
During HR, reactive oxygen species are produced that causeslocal cell death and necrosis within 24 hrs
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Systemic Response or SystemicAcquired Resistance (SAR)
SAR takes 24-48 h to start, can last for months
Involves gene activation and a transmitted signal
Genesinduced:
Chitinases 1,3-Glucanases
PRproteins
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P IP model Polygalacturonares secreted by fungal hypae
PG inhibiting proteins present in plant cell wall
PGs release oligogalacturonoides which interact with receptor of the
plant
Transduction of the oligogalacturonoide signals result in the
expression of plant defense protein
Chitinase, glucanse and phytoalexins are secreted by the plant
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Biosynthetic pathways for SecondaryMetabolites
Shikimic acid
AcetateMevalonate
AcetateMalonate
Amino acidRelated
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THANK YOU