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Plant Defenses against Pathogens

How plant defend against pathogens
by

Irene Kao

on 13 November 2012

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Transcript of Plant Defenses against Pathogens

Plant Defenses Against Pathogens Hyper Sensitive Response Systemic Acquired
Resistance What is it? How does it work? Relationship between the 2 Defense Responses. How to stop the infection? What happens when infected... What is it? First Line of Defense Gene-for-Gene Recognition Types of Pathogens Defense Virulent Pathogens are pathogens that plant have little to no specific defense against.

Avirulent Pathogens are strains of pathogens that does not kill but mildy harm the host plant. Hyper-sensitive response is the death of tissue and cells near the infected area to restrict the spread of pathogens.

After sealing the infected area off, the infected cells inside will destroy each other.

Note: This only occurs once a plant has been infected by a pathogen. This is why only some parts of the leaves are "sick". When pathogenic elicitor binds to a R protein. It alternates the permeability of the plasma member and stimulates productions of phtoalexins (toxic compounds).

Pathogenesis-relate (PR) proteins, enzymes that hydrolyze components in the cell walls of the pathogens, are also produced.

The infection also stimulates the cross-linking of molecules within the cell wall and the decomposition of lignin, which are responses that set up a local barricade that slows the spread of the pathogen to other parts of the plant. Systemic Acquired Resistance is a defence mechanism resulted from a warning signal, "sound the alarm", produced by the plant undergoing Hyper-Sensitive Response.

Systemic Acquired Resistance allows the plant to protect against a diversity of pathogens for days before it's even infected. Methylsalicylic acid is produced at the infected site, carried by phyloem to the rest of the plant where it is convereted to Salicylic acid in remote areas.

Salicylic acid signals the production of PR proteins by activating the STP for it.

The STP activated also induces resistance to pathogenic attacks, thereby Acquired resistance. Physical barriers such as epidermis of the primary plant body and periderm of the secondary plant body. Fault: viruses, bacteria and spores can still enter through the natural openings of (i.e. stromata) and wounds. Second Line of Defense If pathogens bypass the first line of defense a second line of defense activates.

A chemical attack enhanced by plants ability to recognize certain pathogens.

Fault: some diseases can suppress plants defense system. Recognition of pathogen derived molecules by disease resistant (R) genes 1 R protein recognizes only 1 corresponding pathogen molecule encoded by avirulent (Avr) gene. Elicitors are recognized by R proteins, triggers STP leading to defense response in Hyper Sensitive Response on a Leaf
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