Plant Defense: Definition, Types, & Examples

What is Plant Defense?

Plants defend against herbivores with mechanical wounding, barriers, secondary metabolites, and attraction of parasitoids.

Mechanism of Plant Defense

i. Hydrogen Peroxide

When a plant is attacked by fungus, it pinches the cell wall, further disrupting it and in response to that, plant liberate hydrogen peroxide. This is the defense mechanism of plant. There are various ways, the first one is where hydrogen peroxide will stop the cell wall from getting disrupted.

To dissociate the plants, pathogens will require enzymes like pectinase and other enzymes to disintegrate the cell wall. Thus, the enzyme liberated by the fungal pathogen has to be halted or its action has to be terminated, which is done by the hydrogen peroxide.

Its mechanism can be explained from the following steps. Once the hydrogen peroxide is liberated, it further will reach the area where it would be working on, the cell wall.

Hydrogen peroxide will interact peroxidase enzyme which will disintegrate pectinase. Thus, pectinase will not be able to damage the cell wall and the problem is solved. Another mechanism of hydrogen peroxide is liberating the phytoalexins, which are the antiviral proteins. These phytoalexins stop synthesis of protein within cells, when the plants is invaded by a pathogen, in this case fungus.

The fungus, also liberates certain chemicals, which makes the fungus known that there is a pathogen in the vicinity. In the plasma membrane, hydrogen peroxide, transfers the message through a response, that there is a cell which is invaded.

After mrna is formed it moves to cytoplasm from nucleus, where ribosomes will carry out synthesis of protein and phytoalexins will be generated, which will act like antiviral proteins.

If in the cell, phytoalexins is available, synthesis of protein will be stopped and eventually, even the pathogen’s growth will be ceased, thus the pathogen will be banished.

ii. Barriers

Along with the fibrous, which aids in providing defensive structure, lignin also possess the same characteristics. Lignin exists on wood and is usually seen on plants which have been invaded by pathogen.

The area which is invaded by the pathogen is stitched or covered by the callose, which inhibits the movement so as the eliminate the risk of infection to the other parts and restriction in movement will also help to ensure that none of the materials have been replicated or used by the pathogen for replication.

The removal of dead parts of the plants like the leaf is done by ethylene, which inhibits the infection by eliminating that complete infected area, so that it doesn’t spread further and the whole plant does not have to be chopped off. Plants also possess tannins and galls, which captivates the foreign particle, present in the plant.

Tannins quarantine the chemicals and the foreign antigen away from each other. Gall is the place where the cells which are invaded, undergo inflammation and possess tannins.

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