PLANT DEFENSE
MECHANISMS
WHATEVER CONCERNS
PLANT DEFENSE OR
RESISTANCE, IT IS
CONTROLLED BY GENES
OF THE PLANT AND
PATHOGEN
NONHOST
RESISTANCE

THE MOST COMMON CASE:
APPLE TREE CANNOT BE
INFECTED BY PATHOGENS
SPECIFIC TO TOMATO AND VICE
VERSA
PARTIAL, POLYGENIC,
QUANTITATIVE OR
HORIZONTAL RESISTANCE




RESULT OF MORE OR MANY
MINOR GENES
PRESENT IN ALL PLANTS
DIFFERENT LEVELS AGAINST
DIFFERENT PATHOGENS
BASICALLY AGAINST
NECROTROPHIC OR
SEMIBIOTROPHIC PATHOGENS AS
BOTRYTIS, FUSARIUM, SCLEROTINIA
ETC.
RACE-SPECIFIC,
MONOGENIC OR VERTICAL
RESISTANCE
RESULT OF ONE MAJOR GEN
 USUALLY AGAINST BIOTROPHIC
PATHOGENS AS DOWNY
MILDEWS, POWDERY MILDEWS
AND RUSTS
 GEN TO GEN THEORY

PREEXISTING STRUCTURAL
DEFENSE

WAX, CUTICLE, STRUCTURE OF
CELL WALL, STOMATA AND
LENTICELS, PRESENCE OF
THICK-WALLED TISSUES
(SCLERENCHYMA) ETC.
PREEXISTING CHEMICAL
DEFENSE

RELEASED INTO ENVIRONMENT:
FUNGITOXIC EXUDATES,
PHENOLIC COMPOUNDS (EG.
RED AND YELLOW ONION
CANNOT BE INFECTED BY
SMUDGE, WHEREAS WHITE ONE
CAN BE INFECTED BECAUSE OF
LACKING CATECHOL),
COUMARINS
PREEXISTING CHEMICAL
DEFENSE

INHIBITORS IN PLANT CELLS
BEFORE INFECTION:
TANNINS, CATECHIN, SAPONINS
(EG.TOMATINE, AVENACINE),
LOW MOLECULAR PROTEINS –
PHYTOCYSTATINS, LECTINS,
GLUCANASES AND CHITINASES
CONTAINED IN SURFACE CELLS
DEFENSE THROUGH LACK
OF ESSENTIAL FACTORS
LACK OF RECOGNITION
BETWEEN HOST AND
PATHOGEN
 LACK OF HOST RECEPTORS AND
SENSITIVE SITES FOR TOXINS
 LACK OF ESSENTIAL
SUBSTANCES FOR THE
PATHOGEN

INDUCED STRUCTURAL
AND BIOCHEMICAL
DEFENSES
INDUCED STRUCTURAL
AND BIOCHEMICAL
DEFENSES
RECOGNITION OF THE
PATHOGENS BY THE HOST
PLANT:
- PATHOGEN ELICITORS
- HOST PLANT RECEPTORS
=> MOBILIZATION OF DEFENSES
AND TRANSMISSION OF ALARM
SIGNAL

INDUCED STRUCTURAL
DEFENSES

CYTOPLASMIC DEFENSE
REACTION

CELL WALL DEFENSE
STRUCTURES
CELL WALL DEFENSE
STRUCTURES
INDUCED STRUCTURAL
DEFENSES - HISTOLOGICAL
DEFENSE STRUCTURES:

CORK LAYERS
INDUCED STRUCTURAL
DEFENSES - HISTOLOGICAL
DEFENSE STRUCTURES:

CORK LAYERS
INDUCED STRUCTURAL
DEFENSES - HISTOLOGICAL
DEFENSE STRUCTURES:
TYLOSES
- DEPOSITION
OF GUMS
-
INDUCED STRUCTURAL
DEFENSES - HISTOLOGICAL
DEFENSE STRUCTURES:

ABSCISSION LAYERS
NECROTIC STRUCTURAL
DEFENSE REACTION
NECROTIC STRUCTURAL
DEFENSE REACTION
HYPERSENSITIVE
REACTION
INDUCED BIOCHEMICAL
DEFENSES

ACTIVE OXYGEN SPECIES:
SUPEROXIDE (O -2), HYDROGEN
PEROXIDE (H2O2) AND
HYDROXYL RADICAL (OH)
INDUCED BIOCHEMICAL
DEFENSES
REINFORCEMENT OF HOST CELL
WALLS BY
 CALLOSE
 GLYCOPROTEINS (EXTENSIN)
 PHENOLIC COMPOUNDS
(SUBERIN, LIGNIN)
 MINERAL ELEMENTS (SILICON,
CALCIUM)
INDUCED BIOCHEMICAL
DEFENSES
PRODUCTION OF
ANTIMICROBIAL SUBSTANCES
IN ATTACKED CELLS:
PATHOGENESIS RELATED
PROTEINS

INDUCED BIOCHEMICAL
DEFENSES
PRODUCTION OF SECONDARY
METABOLITES:
 PHENOLIC COMPOUNDS LIKE
CHLOROGENIC ACID, CAFFEIC
ACID AND FERULIC ACID
 PHENOL OXIDIZING ENZYMES –
QUINONES (MORE TOXIC THAN
ORIGINAL COMPOUND)
INDUCED BIOCHEMICAL
DEFENSES
PRODUCTION OF SECONDARY
METABOLITES:
 PHYTOALEXINS – PHASEOLIN,
PISATIN, GOSSYPOL, CAPSIDIOL
ETC.
 ELICITORS OF PHA ARE
RELEASED FROM PATHOGEN
CELL WALL BY HOST ENZYMES
OR PRODUCET BY HOST CELL
ITSELF

DETOXIFICATION OF
PATHOGEN TOXINS BY
PLANTS

E.G. HC TOXIN, PYRICULARIN
IMMUNIZATION OF PLANTS
AGAINST PATHOGENS

PLANTIBODIES
SYSTEMIC ACQUIRED
RESISTANCE
DEFENSE THROUGH
GENETICALLY
ENGINEERING DISEASERESISTANT PLANTS
PLANT-DERIVED GENES:
 E.G. Hml GENE FOR ENZYME
INACTIVATING HC TOXIN
 GENES ACTIVATED BY AVR
GENES OF PATHOGENS
 ANTIVIRAL GENES

DEFENSE THROUGH
GENETICALLY
ENGINEERING DISEASERESISTANT PLANTS



PATHOGEN-DERIVED GENES
SEE VIROLOGY
GENE FROM ASPERGILLUS NIGER
FOR H2O2 GENERATING GLUCOSE
OXIDASE INCREASES RESISTANCE
AGAINST P. INFESTANS, A. SOLANI
DEFENSE THROUGH
GENETICALLY
ENGINEERING DISEASERESISTANT PLANTS



PATHOGEN-DERIVED GENES
T4 GENE FOR LYSOZYME
DEGRADING CELL WALL OF SOME
BACTERIA AND FUNGI
GENE FOR CHITINASE FROM T.
HARZIANUM AGAINST APPLE
SCAB
RNA SILENCING