Different mechanisms of plant defense.

1. HOW PLANT DEFEND THEMSELVES AGAINST
PATHOGENS
Zohaib ul Hassan (Plant Pathology)
zuhaib1144@gmail.com
+92 343 6331144
University College of Agriculture, University of Sargodha
Sargodha, Pakistan

2. HOW PLANTS DEFEND THEMSELVES
AGAINST PATHOGENS
PLANT:
Plants, also called green plants , are multi cellular, auto-
trophic eukaryotes of the kingdom Plantae.
MAJOR PLANT PATHOGENS:
A. Bacteria
B. Virus
C. Fungi
D. Nematodes

3. PLANT CAN DEFEND THEMSELVES
1. Structural characteristics
Physical barriers & inhibit the pathogen from gaining
entrance.
2. Bio-Chemical Reaction:
Different substances produce by plant cells or tissues.
(inhibit the growth of pathogen in it).
Plant resistance:
Generally controlled by the genes.

4. RESISTANCE
Ability of host/plant to overcome or exclude the attack of
pathogen.
Resistance is of different types:
1. Monogenic
2. Polygenic
3. Systemic acquired resistance

6. When pathogen attack on plant.
The genes of pathogen are activated (produce all their weapons of
attack e.g. enzymes, toxins etc.)
To infect the plant.
Plant show resistance in different ways
 Polygenic
 Monogenic
 Induced

7. NON-HOST RESISTANCE
Unsuccessful plant/pathogen interactions
Pathogen---- >Non-Host
e.g. Apple trees are not infected by tomato pathogens

8. POLYGENIC RESISTANCE
• Many genes include in such type of resistance.
 Some plant genes code for the chemical substances.
 Toxic to pathogens or neutralize the toxin of pathogen.
• Some structural genes also present which slow down the
entry of pathogen.

9. Plant defense (polygenic)
• Different chemical substances
• Pre-existing defense structures
• Chemicals and different defense structures made after
attack of pathogen or A-biotic stress.

10. Polygenic resistance
• Plant pathogen attack.
• Plant shows resistance partially or incompletely.
• Different genes are involved.
• Polygenic, quantitative, multi-genic, horizontal, durable,
field or minor gene resistance.

11. Monogenic, r-gene resistance
• Host Plant:
Have one resistance genes per pathogen capable of
attacking it.
• “each pathogen carries matching genes for
a-virulence (A) for each of the R genes of the host plant.”
Pathogen Host
A-virulence gene in pathogen
Trigger the R-gene in the host.
• Host will show the resistance

12. The Hypersensitive Response
• Localized induced cell defense.
• Limiting the growth of the pathogen.
• initiated by the recognition by the plant of specific
pathogen-produced signal molecules, known as elicitors.

15. Preexisting structures
• Waxes
• Cuticle
• Stomata
• Cell wall (toughness,hardness)

16. Preexisting chemical defenses
• Resistance of a plant against pathogen attacks also
depends on the substances produced in its cells before or
after infection.
• These chemicals inhibits the growth of pathogen/
suppress the pathogen infection.
• In some cases these chemicals check the disease ,when
physical barriers are absent.

17. Inhibitors released by plants in its
environment
• Fungitoxic exudates:
• inhibit the germination of spores of fungi Botrytis
and Cercospora, respectively, in tomato.(leaves)
• onion smudge, caused by the fungus Colletotrichum
circinans
Reduced by phenolic compounds protocatechuic
acid and catechol.

18. Inhibitors Present in Plant Cells before
Infection
• In young fruits, leaves and stems
• Several phenolic compounds,tannins, and some fatty
acid-like compounds such as dienes.
• Resistance to Botrytis spp.
• Also determine the host range of fungus e.g; the presence
or absence of saponin in a host and of saponinase in a
fungus determines the host range of the fungus.

19. DEFENSE THROUGH LACK OF
ESSENTIAL FACTORS
• Lack of Recognition between Host and Pathogen
• recognition factors (specific molecules or structures)
that can be recognized by pathogen.
It is thought that Various types of oligosacchrides,
polysacchrides and proteins are involved in it. (but
actual factor is still unknown).

20. Lack of Host Receptors and Sensitive
Sites for Toxins
• Pathogen (usually fungus produces) host-specific toxins.
• Specific toxins  specific receptor (symptoms)
• Lack of host receptors and sensitive sites for toxins
No symptoms will produce

21. INDUCED STRUCTURAL AND
BIOCHEMICAL DEFENSES
• Recognition of the Pathogen by the Host Plant
• Pathogen Elicitors
A. Non specific elicitors:
• ( toxins, glycoproteins, carbohydrates, fatty acids,
peptides and enzymes like proteases, pectnases)
B. Specific elicitor:
• (avr gene products, hrp gene products, and
suppressor molecules).

22. • Host receptors
Recognize the elicitor , which trigger its defense
mechanism.
• it induces the expression of all defense related
genes tested and also induced resistance.

23. INDUCED STRUCTURAL DEFENSES
• cytoplasmic defense reaction:
• Defense structures formed, involve the cytoplasm of the
plant.
• cell wall defense structures:
• Involve the walls of invaded cells.
• Histological defense structures:
• Deeper into the plant.
• necrotic or hypersensitive defense reaction:

24. Histological Defense Structures
• Formation of Cork Layers:
• Formation of Abscission Layers:
• Formation of Tyloses:
• Present in xylem. Tyloses have cellulosic walls and may,
by their size and numbers, clog the vessel
completely.
• Defense through the Hypersensitive Response:
• As soon as the pathogen establishes contact with the cell,
the nucleus moves toward the invading pathogen and
soon disintegrates.

25. IMMUNIZATION OF PLANTS AGAINST
PATHOGENS
• Defense through Plantibodies:
• Such antibodies, encoded by animal genes but produced
in and by the plant, are called plantibodies.
• Mostly present in transgenic plants.

26. SYSTEMIC ACQUIRED RESISTANCE
• Generalized resistance in response to infection.
• By a pathogen or
• Treatment with certain natural or synthetic chemical
compounds.
• Systemic acquired resistance acts nonspecifically.
• Reduces the severity of disease.

27. Defense Mechanisms in plants