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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

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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