- Systemic Acquired Resistance (SAR) is a plant defense mechanism that confers long-lasting protection against a broad spectrum of pathogens. It involves the accumulation of pathogenesis-related (PR) proteins in response to salicylic acid (SA) signaling. - SAR is triggered by initial infection at a local site and protects the entire plant. It provides an alternative to toxic chemicals for controlling plant diseases in a sustainable way. - Key events in SAR include the production of SA at the infection site, transmission of the SAR signal systemically, and accumulation of PR proteins that contribute to broad-spectrum resistance against future infections.

2. SAR
(SYSTEMIC ACQUIRED
RESISTANCE)
SUBMITTED TO:-
DR.SURJYA KANTA BEURA SUBMITTED BY :-
PROFESSOR AND HEAD. UDAYENDU BARIK
DEPT. OF PLANT PARHOLOGY M.Sc.(ag) Ist year
OUAT,BHUBANESWAR admsn. no – 18122l10
dept. of plant pathology
ouat,bhubaneswar

3. CONTENT
Introduction
Basics of Systemic Acquired Resistance (SAR)
History of SAR
Importance of SAR in plant diseases management
Mechanisms of SAR
PR Proteins in SAR
Conclusion

6.  Systemic Acquired Resistance (SAR) is a plant defense mechanism of induced
defense that confers long-lasting protection against a broad spectrum of
microorganisms & pest.
 Presently disease control is largely based on the use of hazardous
chemicals viz., fungicides, bactericides and insecticides for either direct or
indirect disease management.
 The hazardous natures of the products on the environment, human and animal
health strongly necessitates to search for new safer means of disease control.
 SAR have high potential to diminish the use of toxic chemicals in the
agriculture and has emerged as an alternative, non-conventional, non-biocidal
and eco-friendly approach for plant protection and hence for sustainable
agriculture.
 SAR requires the signal molecule salicylic acid (SA) and is associated
with accumulation of pathogenesis-related proteins, which are thought to
contribute to resistance (Dube, 2017).
INTRODUCTION

7. PLANT DEFENCE
Passive defenses Active defenses
Physical
barriers
Chemical
barriers
Rapid
defense
Delayed
defense
 Wax
 Cuticle
 Cell wall
 Stomata
 Lenticels
 pH
 Phytoanticipins
 Membrane
permeability loss
 Oxidative burst
 Fortification cell wall
 HR
 Phytoalexin –
production
PR- Proteins
Induced Systemic
Resistance (ISR)
 Systemic Acquired
Resistance (SAR)
(Choi & Hwang, 2011)

8. BASICS OF EVENTS IN AN INCOMPTIBLE HOST-
INTERACTION

9. What is induced resistance ???
The induced resistance can be defined as an increased expression of
natural defense mechanisms of plants against different pathogens.
LAR ISR SAR

10. o A distinct signal transduction pathway that plays an important role in the
ability of plants to defend themselves against pathogens…..
o Significant phenomenon recognized by Chester in 1933.
o Concept of SAR proposed by Ronald Ross in 1961.
o Infection of plants with necrotizing pathogens (causing HR) often results in
enhanced resistance to subsequent infections by a variety of bio-tropic
pathogens.
o SAR requires the signal molecule salicylic acid (SA) and is associated with
accumulation of Pathogenesis Related proteins, which are thought to
contribute to resistance.
o Resistance triggered in the plant during its life time is Acquired Resistance.
 Local (LAR) confined to few cells or tissues
 Systemic (SAR) having been moved through out the plant
SAR (Systemic AcquiredResistance)

11. Broad
spectrum
Expression of
PR-Protein
Involvement
SA Signaling
Necrotic
lesions(PP) as
inducing agent
Establishment
SAR depend on
plant & inducing
factor

12. History of SAR
Year Name Contribution
1901 Ray & Beauverie The natural phenomenon of resistant in response to pathogen infection
or plant immunity
1932 Carbonne &
Kalaljev
Showed that acquired resistant also depends on the general fitness of the
host
1933 Chester Documented the idea of PhysiologicalAcquired Immunity
1961 A. F. Ross Published the first systemic study of SAR
He coined the term “Systemic acquired resistance”
1970 V
an et al. Showed that viral infection of tobacco induced the accumulation of a distinct
set of proteins, called pathogenesis-related proteins (PR proteins)
1979 Ray White observed that PR protein accumulation and resistance to TMV could be
induced by treatment of tobacco with salicylic acid (SA), aspirin (acetyl SA), or
benzoic acid
1991 Ward et al. Studied steady-state mRNA levels from at least nine families of genes were
shown to be coordinately induced in uninfected leaves of inoculated plants;
these gene families are now known as SAR genes
1993 Gaffney et al A requirement for SA as an endogenous signal for SAR was proven with using
a bacterial gene, nahG, encoding salicylate hydroxylase, which removes SA by
conversion tocatechol

13. o SA dependent
o Necrosis reaction
present
o Signaling molecules SA
o Less elastic
o Against biotrophs
o Continuous irritation is
not required
o PR-proteins involved
o SA independent
o Necrosis reaction
absent
o Signaling molecules
JA, Ethylene
o More elastic
o Against necrotrophs
and insects
o Continuous irritation
is required
o Defense genes
involved
SAR ISR

14. Importance of SAR in plant diseases management
o SAR can also be transmitted to the next generation progeny.
o Its provides a broad-range resistance against
pathogens.
o Leads to pathogenesis-related (PR) gene expression.
fungal, bacterial and viral
o Its ability to immunize susceptible plants implies that genetic potential
for resistance is in all types of plants.
o The significant practical aspects of SAR is the discovery of chemical inducers of
plant defense.
o New generation fungicides act as a plant defense system. (rather than killing
pathogen.) ICGA-245704, a benzothiadiazole (BTH) (Alfa-Aesar) & Dichloro-
isonicotinic acid (DCINA) compound (plant-activator) switches SAR in plant.

15. Signal generation and transmission In SAR
Ideal Charactristics of Transported Signal:
o Induce a defensive response
o Produced or released at the site of attack
o Translocated from the attacked to the systemic tissue
o Accumulate in the systemic tissue before resistance expression takes place
(Choi & Hwang, 2011)

16. MECHANISM OF SAR
(A-)
(R-)

17.  Pathogenesis related proteins (PRs) are assigned an important role
in plant defense against pathogenic constraints and in general
adaptation to stressful environment.
 These proteins are accumulated 7-10 days after infection and indicate
the attainment of SAR.
 It is accumulated in the intercellular spaces (first line of defence) and
vacuole (second line of defence by lytic enzyme).
Pathogenesis-Related (PR) Proteins in SAR

18. Accumulation of PR Proteins in SAR
(Pieterse and Van Loon, 2004)
Cytoplasma

19. Low-
molecular
Proteins
(5-75 ) kDa
Stable at low
pH (< 3)
Thermostable
& Highly
resistant to
proteases
Contains four α-
helices and β-
strands
arranged
antiparallel
between helices
Established in all
plant organs–
leaves, stems,
roots, flowers
Feature:
Antifungal,
Antibacterial,
Insecticidal &
Antiviral action
Biochemical
and structural
characteristics
of PR Proteins

20. Classification and Properties of families of PR proteins
Family Type member Properties Targeted Pathogen Site
PR-1 Tobacco PR-1a Antifungal Active against Oomycetes
PR-2 Tobacco PR-2 β-1,3-Glucanase Cell wall Glucan of fungi
PR-3 Tobacco P, Q class (I,II, IV,V,VI,VI)
Chitinase Cell wall chitin of fungi
PR-4 Tobacco ‘R’ Chitinase class I,II Cell wall Chitin of fungi
PR-5 Tobacco S Thaumatin-like, Active against Oomycetes
PR-6 Tomato Inhibitor I Proteinase-inhibitor Active on Nematodes + Insect
PR-7 Tomato P69 Endoproteinase Microbial cell wall dissolution
PR-8 Cucumber chitinase Chitinase class III Cell wall Chitin of fungi +
Mucopeptide wall of bacteria
PR-9 Tobacco ‘lignin-
forming peroxidase’
35
Peroxidase Antimicrobial activity by
catalyzing oxidative cross-linking
protein and phenolic in cell wall
leading to physical barrier
AND MANY MORE FAMILIES………..

21. Plant Inducer organism SAR Systemic protection against SAR gene
Arabidopsis
Turnip crinkle virus
Pseudomonas syringae
Fusarium oxysporum
+
+
+
+
Pseudomonas syringae
Turnip crinkle virus
Pseudomonas syringae
Peronospora parasitica
PR-1, PR-2
Sugarcane Colletotrichum falcatum + Colletotrichum falcatum
PAL,
Peroxidase,
Polyphenol
oxidase
Rice Pseudomonas syringae + Magnaporthe grisea Lip oxygenase
Tobacco
Tobacco mosaic virus
Tobacco necrosis virus
Thielaviopsis basicola
Pseudomonas fluorescens
+
+
+
+
Thielaviopsis basicola
Phytophthora parasitica
Peronospora tabacina
Pseudomonas tabaci
PR-1, PR-2,
PR-3, PR-4,
PR-5, PR-1g
PR-8,
Potato
Phytophthora infestans
Phytophthora cryptogea
+ Phytophthora infestans β- 1,3-glucanase
Tomato Phytophthora infestans + Phytophthora infestans Chitinase
Plants exhibiting SAR
(Sticher, 1997)

22. SIGNALS FOR SYSTEMIC ACQUIRED RESISTANCE
Electrical
Signals
Reactive
Oxygen Species
Lipid-Based Signal
Molecule
Natural Organic
Compounds
Inorganic
Compounds
oSalicylic Acid (SA)
o Jasmonic Acid (JA)
oMethyl ester JA (MeJA) o
Methyl ester SA (MeSA) o
Ethylene
o Systemin
o Riboflavin
o Phosphate salts
o Silicon
o Synthetic compounds
BABA (β-aminobutyric acid)
INA (2,6 – dichloroisonicotinic acid )
BTH/ ASM (Benzo-(1, 2, 3)-thiadiazole-7-
carbothioic acid S-methyl ester )
o H2 O2
o DPI (Diphenylene iodonium)
o dir 1
o LTPs
o eds 1
o pad 4
o SABP 2
o Pin2 mRNA
(Sticher, 1997)

23. CONCLUSION
SAR is effective against a broad range of pathogens and parasites,
including fungi, bacteria and viruses.
Salicylic acid is not a translocated signal responsible for inducing SAR
but is required in signal transduction.
Methyl salicylate, lipid signaling, peptide signaling, Green-leaf volatiles
are the transported signals in SAR.
SA, MeSA, JA, BTH/ASM, INA, BABA and H2O2 plays important role in
building broad-spectrum disease resistance against many plant diseases.
Over expression of an essential regulatory gene (NPR 1) leads to the
generation of broad-spectrum disease resistance in plant which is also
known as systemic acquired resistance.