Plant defense mechanism, types of plant defense mechanism, Cinnamic acid introduction, cinnamic acid synthesis, role of cinnamic acid in plant defense mechanism, salicylates introduction, synthesis of salicylates, role of salicylates in plant defense mechanism, salicylate act as signal phytohormone.

1. Plant defense system: Cinnamic acid
and Salicylates - Mode of action
Jasmine Juliet .R,
Biotechnology Department
Agricultural college and
Research & Institute
Madurai.

2. Defense mechanism in plants
 Plants represent a rich source of nutrients for many organisms
including fungi, bacteria, virus, nematodes, insects and vertebrates.
 Plants lacking an immune system comparable to animals.
 Plants have developed a stunning array of structural, chemical and
protein based defenses designed to detect invading organisms and
stop them before they are able to cause extensive damage.
 Each plant species is affected by approximately 100 different
kinds of fungi, bacteria, Viruses and nematodes.

4. Plant defense mechanism
• Plants employ complex defense mechanisms against
microbial infection that involves:
1) Recognition of the invader,
2) Activation of signal transduction pathways,
3) The production of proteins and
4) The production of metabolites with different
roles in defense.

5. Cinnamic acid - Introduction
• Cinnamic acid is an organic compound with the
formula C6H5CH=CHCOOH.
• It is a white crystalline compound that is slightly soluble in water, and
freely soluble in many organic solvents.
• Cinnamic acid classified as an unsaturated carboxylic acid, it occurs
naturally in a number of plants.
• It exists as both a cis and a trans
isomer, trans form is more common.
Cinnamic acid chemical structure

6. Cinnamic acid - Introduction
• Cinnamic acid is one of the most important phenolic acids.
• Cinnamic acid is converted in flowering plants by different
enzymes to diverse defense compounds.
• Cinnamic acid can induce the expression of defense-related genes.
• Cinnamic acid (CA) is one of the basic phenylpropanoid with
antioxidant activity, produced by plants in response to stressful
conditions.

7. Role of cinnamic acid in plant defense
mechanism
• Stress induced phenylpropanoids are derived from
Cinnamic acid and is a basic nucleus for the synthesis of
numerous phenylpropanoids induced under adverse
environmental conditions.
• Cinnamic Acid and its derivatives are appeared as an
antioxidant and antibacterial activities in plants in response
to stressful conditions.
• Cinnamic Acid was used as a plant growth regulator under
saline conditions..

9. Simplified scheme of the shikimate and phenylpropanoid pathways
Enzyme name Abbreviation:
CS, chorismate synthase; CM, chorismate mutase;
ICS, isochorismate synthase; B2H, benzoic acid-2-hydroxylase;
PAL, phenylalanine ammonia lyase; C4H, cinnamic acid 4-hydroxylase;
4CL, 4 coumarate CoA ligase; CHS, chalcone synthase;
CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase;
C3H, p-coumarate-3-hydroxylase;
COMT, caffeate O-methyltransferase; CCR, cinnamoyl-CoA reductase;
CAD, cinnamyl alcohol dehydrogenase.

10. Role of cinnamic acid in plant defense
mechanism by lignification
• The cinnamate (CA) 4-hydroxylase (C4H) is a cytochrome P450
that catalyzes, phenylpropanoid pathway, leading to the synthesis of
lignin, pigments, and many defense molecules.
• The process of lignification is observed in systemic acquired
resistance.
• Lignification may contribute resistance in many different ways.
• Incorporation of lignin into plant cell wall strengthen it
mechanically and make it more resistant to degradation by
enzymes secreted by an invading pathogen.

13. Role of cinnamic acid in plant defense
mechanism - Hydroxycinnamates
• Hydroxycinnamates: Derivatives of cinnamic acid.
• Hydroxy cinnamates have antioxidant properties.
Examples are:
 Caffeic acid: coffee, apples, blueberries.
 Coumaric acid: spinach, cereals.
 Curcumin: Curcuma spp. (turmeric, Jiang Huang, E Zhu).
 Ferulic acid: coffee, cereals, citrus juices.
 Sinapic acid: broccoli and other brassicas, citrus juices.

14. Role of cinnamic acid in plant defense
mechanism
• The cinnamic acids have higher levels of reactive oxygen
scavenging activity.

15. Salicylate in plant defense mechanism -
Introduction
• Plants possess specialized structures, chemicals and sophisticated
mechanisms to defend themselves from pathogens.
• Understanding these defense mechanisms and pathways are critical for
developing innovative approaches to protect crop plants from diseases.
• Plant defense pathways involve a number of signaling compounds that
regulate the production of defense-related chemicals.
• These pathways are strongly connected with salicylic acid (SA),
ethylene (ET), jasmonic acid (JA) and abscisic acid (ABA).

17. Salicylates - Introduction
• Salicylic acid is a monohydroxybenzoic acid. It has the formula C7H6O3.
• This colourless crystalline organic acid is widely uised in organic synthesis an
functions as a plant hormone.
• It is derived from the metabolism of salicin.
• In addition to serving as an important active
metabolite of aspirin (acetylsalicylic acid), it is probably best known for its use
as a key ingredient in topical anti-acne products.
• The salts and esters of salicylic acid are known as salicylates.
• It is on the World Health Organization's List of Essential Medicines, the safest
and most effective medicines needed in a health system.

18. Salicylates - Introduction
• The salts and esters of salicylic acid are known as salicylates.
• It is on the World Health Organization's List of Essential
Medicines, the safest and most effective medicines needed in
a health system.

19. Salicylates - History
• White willow (Salix alba) is a natural source of salicylic acid.
• Hippocrates, Galen, Pliny the Elder and others knew that willow bark could
ease pain and reduce fevers.
• It was used in Europe and China to treat pain and reduce fevers. This
remedy is mentioned in texts.
• Native Americans use an infusion of the bark for fever and other
medicinal purposes.
• In 2014, archaeologists identified traces of salicylic acid on 7th century
pottery fragments found in east central Colorado.

20. Salicylates - History
• The Reverend Edward Stone, a vicar from Chipping Norton, Oxfordshire, England,
noted in 1763 that the bark of the willow was effective in reducing a fever.
• The active extract of the bark, called salicin, after the Latin name for the white
willow (Salix alba), was isolated and named by the German chemist Johann
Andreas Buchner in 1828.
• A larger amount of the substance was isolated in 1829 by Henri Leroux,
a French pharmacist.
• Raffaele Piria, an Italian chemist, was able to convert the substance into a sugar
and a second component, which on oxidation becomes salicylic acid.
• Salicylic acid was also isolated from the herb meadowsweet by German researchers
in 1839.

21. White willow (Salix alba) is a natural source of salicylic acid.

22. Salicylic acid synthesis
• Plants have two pathways for SA production, the isochorismate (IC)
pathway and the phenylalanine ammonia-lyase (PAL) pathway.
• Enzymes involved in SA biosynthesis are abbreviated as follows:
AAO aldehyde oxidase,
BA2H benzoic acid 2-hydroxylase,
CM chorismate mutase,
ICS isochorismate synthase,
IPL isochorismate pyruvate lyase,
 PAL phenylalanine ammonia-lyase.

24. C4H and branching in the upper phenylpropanoid pathway.
PAL, Phe ammonia-lyase; 4CL, 4-hydroxycinnamate CoA ligase;
AOPP, amino-β-phenyl-propionic acid is an inhibitor of PAL
MDCA, methylene dioxocinnamic acid is an inhibitor of 4CL
Salicylic acid synthesis

25. Structures of salicylic acid and its derivates.
SA, salicylic acid; SAG, SA 2-O-β-D-glucoside;
SGE, SA glucose ester; MeSA, methyl salicylate;
MeSAG, methyl salicylate 2-O-β-D-glucose.

27. Salicylates – Mode of action
• Salicylic acid (SA) is an essential trigger of plant
disease resistance.
• In plants, Salicylic Acid is synthesized from cinnamic
acid via benzoic acid or from isochorismate by the
action of an isochorismate synthase.
• Salicylic Acid is an important defense hormone
against several pathogens in flowering plants

29. Salicylates – Mode of action
• Salicylic acid is a phenolic phytohormone and is found in plants
with roles in plant growth
development, photosynthesis, transpiration, ion uptake and
transport.
• Salicylic acid is involved in endogenous signaling, mediating in
plant defense against pathogens.
• It plays a role in the resistance to pathogens by inducing the
production of pathogenesis-related proteins.

30. Salicylates – Mode of action
• Salicylate is involved in the systemic acquired resistance in which
a pathogenic attack on one part of the plant induces resistance in
other parts.
• The signal can also move to nearby plants by salicylic acid being
converted to the volatile ester methyl salicylate.
• Methyl salicylate is taken up by the stomata of the nearby plant,
and once deep in the leaf, is converted back to salicylic acid to
induce the immune response.

33. Salicylate in plant defense mechanism -
Conclusion
• Salicylic acid is act as bactericidal and an antiseptic.
• Salicylates including salicylic acid (SA) are one of the major
defense-signaling hormones (jasmonates are the others).
• Plants that are deficient in SA synthesis or signaling are much
more susceptible to many microbial pathogens, particularly
biotrophic or hemibiotrophic pathogens.

34. Thank you