Plants have two categories of defence mechanisms against pathogens: structural and biochemical. Structural defences are either pre-existing barriers like waxy coatings or induced after infection, like formation of necrosis around infection sites. Biochemical defences also have pre-existing and induced types, such as inhibitors that are constitutively present or phytoalexins whose production increases after infection to inhibit pathogens. Important induced biochemical defences include phytoalexins, hypersensitive response, and increased defensive enzyme production.

1. Types Of Defence Mechanism In Plants
Discussed by-
Dr Vishnupriya Sharma
Department of Botany
Allahabad / Prayagraj

2. Types Of Defence Mechanism In Plants
Types of Defence Mechanism in plants can be classified into two broad
categories
A. Structural defence Mechanism
B. Biochemical defence Mechanism

3. Structural defence Mechanism
Structural defence Mechanism is divided into two categories
A. Pre existing defence Mechanism (Constitutive Defence Mechanism)
Outer/Structural Barriers Internal Structural Barriers
B. Post infection defence Mechanism (Induced Defence Mechanism
Histological Defence
Structure Cellular Defence
Structure
Cytoplasmic
Defence Structure
Necrotic Or
Hypersenstive
Defence Structure

4. Biochemical Defence Mechanism
Pre existing Biochemical defence
Mechanism
Defence induced by pathogen/Active
Biochemical defence Mechanism
1. Inhibitors released by the plant in its
environment
2. Inhibitors Present in plant cells before
infection
3. Defence through lack of essential
factors-a.lack of recognition between
host and pathogen b.lack of host of
receptors and sensitive sites for toxins
c. lack of essential nutrients for
pathogens
1. Defence through increased levels of
phenolic compounds and phytoalexins
2. Hypersensitive reaction
3. Inactivation of pathogen enzymes
4. Detoxification of pathogenic toxins
5. Induced synthesis of enzyme PAL
phenylalanine ammonia lyase

5. Phytoalexins

6. Biosynthesis and Mode Of Action

7. Important Phytoalexins