How these phenolics help in plant defence....?

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2. “Role of phenols in plant
defence”
Presented By:
Mr. Basavaraj, V. T.
PALB 6293
Sr. M. Sc.(Agri.)
Department of Plant Pathology
UAS, GKVK, Bengaluru
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3. Sequence of Seminar
 Introduction
 What are phenolics…?
 Biosynthesis of phenolics
 Significance of phenolics
 Case Study
 Conclusion
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Major pathways of secondary-metabolite biosynthesis and their inter-
relationship with primary metabolism
Taiz and Zeiger (2010)

6. SECONDARY METABOLITES
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Terpenes
Terpenes derived from
the C5 precursor
Isopentenyl diphosphate
(IPP)
• Monoterpenes
• Diterpenes
• Triterpenes,
• Sesquiterpenes
• Steroids,
• Saponines
Phenolics
Phenolics-shikimate
pathway or
acetate/melonate
pathway
Flavanoids
Polyacetylene
Polyketides
Phenylpropanoids
Nitrogen containing
compounds
Alkaloids-derived from
amino acids
Alkaloids
Non protein amino acids
Amines, amides
Cyanogenic glycosides

7. What are phenolic compounds?
 The terms ‘phenol’ and ‘polyphenol’ can be defined chemically
as substances that possess an aromatic ring bearing one (phenol)
or more (polyphenol) hydroxyl substituents
 Synthesized via two different routes:
 Shikimate pathway (plants)
 Acetate-melonate pathway (fungi and bacteria)
Solubility:
 Most of plant phenolics soluble in polar organic solvents
 Phenolic glycosides are water soluble
 Many serves as defence compounds against herbivore and
pathogens
 Attracts pollinators and seed dispersal7

8. • Phenolic compounds:-
o Widely distributed secondary metabolites,
o Ubiquitously present in the plant kingdom.
o Active and passive forms of defence.
o Functions in plants: structure, protection and
interaction with biotic and abiotic factors
 The first step of the defence mechanism in plants
involves a rapid accumulation of phenols at the
infection site (Matern and Kneusal, 1988).
 The role of phenolic compounds in defence is related
to their antimicrobial, antinutritional or
unpalatable properties.
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9. Cont…
 Environmentally induced as well as genetically controlled
 One mean of self-protection
 Classes of phenolic compounds
 Simple hydroxybenzoic acid,
 Free and conjugated hydroxycinnamic acids,
 Coumarins,
 Flavonoids and
 Stilbenes etc., involved in defence
 The types of phenol that are implicated in defence differ greatly
and that depends on plant species
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10. Occurrence of phenolics
 They are usually found as esters or glycosides rather than as free
compounds.
 Polyphenols (relatively hydrophilic) accumulate in
 Central vacuoles of guard cells,
 Epidermal cells and
 Subepidermal cells of leaves and shoots
 Some are found covalently linked to the plant cell wall (lignin) and
some found in waxes (related to lipidic structures) or on the external
surfaces (cuticle) of plant organs (Vincenzo et al., 2006).
 Biosynthesis of phenolic compounds occurs at various sites in plant
cells, such as the chloroplasts and endoplasmic reticulum membrane.
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11. Biosynthesis of phenolics
Taiz and Zeiger (2010)
• Shikimic acid pathway converts simple carbohydrates into aromatic amino acids.
• Cinnamic acid formed from phenylalanine by phenylalanine ammonia lyase (PAL)
enzyme
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12. Important enzymes
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Polyphenol oxidases
Peroxidases
PAL
(Phenylalanine
Ammonia Lyase)
• Oxidises phenols to quinones-
bactericidal and fungicidal
• Oxidative detoxification of pathogen
phytotoxins
• Increases polymerization of the
phenols into lignins- the complex
phenols
• Key enzyme for the synthesis of
phenols, phytoalexins and other
defence related chemicals.

13. Significance of phenolic compounds
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UV sunscreens
Signal compounds
Pigmentation
Plant growth
Plant defence

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15.  Phenolic compounds act as a screen inside
the epidermal cell layer by making
adjustments to the antioxidant systems at
both cell and whole organism level.
 Flavonols are involved in UV screening
due to their strong absorbance in UV-A (325-
400nm) and UV-B(280-325nm) wavelengths.
UV sunscreens
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16. Phenolics as signal compounds
 Polyphenols enter the soil mainly as leachates - directly affect the
rates of decomposition and nutrient cycling.
 Allelopathic effects -Examples:
1. p-Hydroxy benzoic acid , p-coumaric acid (present in leaves),
2. Quercetin, juglone (present in leaves, bark and root exudates)
3. Catechin , sorgoleone (found in rhizosphere and root exudates)
 Symbiosis– Legumes & Rhizobium nodulation by flavonoid
Apigenin, luteolin
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17.  Role of flavonoids is to serve as visual signals by
 Acting as pigments in fruits and flowers
 To attract animals as pollinators in flowers,
 To attract animals to eat the fruits and help in seed dispersal
 Anthocyanins and anthocyanidins - red, blue and purple colours
in plants.
 Chalcones and aurones are two classes of flavonoids that
contribute to yellow flower colour in a number of plants.
Eg: yellow carnation (chalcone isosalipurposide).
Carnation
Phenolics as pigments
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18. Phenolics and plant growth
 Cell wall integrity and shape – wall bound phenolic acids like p-
coumaric and ferulic acid acts as reservoir of phenylpropanid units
for lignin biosynthesis.
 Flavanoids have role in functional pollen development in petunia
plants.
Phenolic turgorins - gallic acid and gentisic acid found in the pulvini in
Mimosa pudica L.
-Nyctinastic leaf movement
 Seed germination and dormancy
Ferulic acid inhibits germination of seeds of Raphanus sativus
Coumarinic acid found more in rapidly germinating Melilotus alba
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19. Phenolics and plant defence
Phytoanticipi
ns
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Phytoalexins

20.  Phytoanticipins are the low molecular weight antimicrobial
compounds that are present in plants before infection by
microorganisms or are produced after infection solely from pre-existing
constituents (Van Etten et al., 1995).
 J. C. Walker, K. P. Link and H. R. Angell (1929) reported that
catechol and protocatechuic acid in pigmented onion are resistant to
Colletotrichum circinans.
Susceptible Resistant
Phytoanticipins
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21. Preformed phenolics
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Phenolic compounds Plant Pathogen
Catechol,
Protocatechuic
acid
Onion Colletotrichum
circinans- onion
smudge
Benzaldehyde Potato Botrytis cineria
Proanthocynidins Barley Fusarium spp.
5- Pentadecylresorcinol Mango Alternaria alternata
Chlorogenic acid Peach Monilinia fructicola- brown rot

22. Phytoalexins
 Greek word - Phyto = “plant” and alexin = “to ward off”
 Low-molecular-weight antimicrobial compounds that are both
synthesized by and accumulated in cells after exposure to
microorganisms.
 The concept of phytoalexin theory of disease resistance was first
propounded by Muller and Borger, 1940.
 Phytoalexins have been reported mostly in dicotyledons and in
few monocots such as rice and oat.
 Isoflavonoids are common in the Leguminosae
 Stilbenes have been detected in Vitaceae and Leguminosae
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23. Phenolic compounds – Post
invasion
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Phenolic
compound
Plant Pathogen
Pisatin Pea Nectria haematococca
Glyceollin I Soybean Phytopthora megasperma
Avenanthramide A Oats Puccinia coronata f.sp. avenae
Luteolinidin Sorghum Colletotrichum graminicola
Pterostilbene Grapes Plasmopara viticola
Isoflavanoid Green bean Colletotrichum
lindemuthianum

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25. Objective: To investigate the defence response of patchouli
inoculated with virulent Ralstonia solanacerum
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26. Fig. 1. Changes in peroxidase (POD) activity in the leaves and stems of patchouli
inoculated with R. solanacearum. (a) Upper leaves; (b) upper stems; (c) lower leaves;
(d) lower stems.
(Jain-Hui et al., 2017)
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27. Fig. 3. Changes in super oxidide dismutase (SOD) activity in the leaves and stems of
patchouli inoculated with R. solanacearum. (a) Upper leaves; (b) upper stems;
(c) lower leaves; (d) lower stems.
(Jain-Hui et al., 2017)
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28. Isoenzymatic bands of peroxidase
(POD) from patchouli inoculated with
R. solanacearum. Arrows depict all
detected POD isoenzymes.
Isoenzymatic bands of superoxide
dismutase (SOD) from patchouli
inoculated with R. solanacearum. Arrows
denote all detected SOD isoenzymes.
(Jain-Hui et al., 2017)
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29. Objective: To study the effect of Brotomax treatment on phenolic
compounds and inhibitory effect of phenolic compounds on in vitro
growth of Phytophthora sp.
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30. Effect of Brotomax on total phenols level in different organs of
the olive
(Rio et al., 2003)
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After 170 DAA, Increase in 15.6% in leaves and 8.8% in stem over control
Untreated Treated

31. Distribution of total phenols in olive stem tissues.
Levels of tyrosol, catechin and oleuropein (mg/ 100 g FW) in olive cortex stem
(Rio et al., 2003)31
Cortex to pith: 2.4 times and in cortex 16.9% increase over control
Tyrosol: 30.9%, Catechin: 10.3% and oleuropien: 24.6% increase over control
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32. Inhibition (%) of Phytophthora sp. growth with leaf, stem, root, cortex and pith
extracts from untreated and 0.3% Brotomax treated olive plants at 170 days
after anthesis
(Rio et al., 2003)
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Phenolic
compound
IC 50 (g/L)
Tyrosol 2.7 ± 0.3
Catechin 3.3 ± 0.2
oleuropein 4.0 ± 0.2
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33. Objective: To study the effects of UV irradiation on levels of
naringin and tangeretin in the peel of Citrus aurantinum fruits
before and after infection with Pencillium digitatum.
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34. Fig. 1: Effects of naringin (A) at 1 g/L ( ) and 5 g/L ( ), and tangeretin (B)
at 1 g/L ( ) and 0.1 g/L ( ) on the growth of P. digitatum. The controls are
represented by( ).
(Arcas et al., 2000) 34
IC 50 value for naringin and tangeretin was 10.4 ± 0.2 and 2.4 ± 0.2 g/L respectively.
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35. Irradiation time (hours)
Effect of UV irradiation and inoculation after irradiation with
P. digitatum on naringin (A) and tangeretin (B) levels.
(Arcas et al., 2000) 35
7%
55%
Irradiation time (hours)
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0 1 2

36. Fig. 3: UV irradiation effect on P. digitatum growth.
(Arcas et al., 2000) 36
Days after
inoculation
Per cent inhibition
1 hour
irradiation
2 hour
irradiation
2 40 43
3 16 45
4 17 45
5 3 38
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37.  Advantages
 Ubiquitous in plants
 Highly fungitoxic
 The oxidized phenolics are much more inhibitory in nature
 defence role in biotic and abiotic stress
 Limitations
 Although several kinds of phenolics are found in plants, they
may not accumulate to fungitoxic levels during pathogenesis
 Successful pathogensovercome thefungitoxicphenolics by
several methods and can cause disease
Advantages and limitations
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38. Conclusion

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