Constitutive defenses are always present in plants, even when they are not under attack. These defenses include:
* Physical barriers: The outermost layer of plant cells, called the cell wall, is a tough, rigid structure that helps to protect the cell from damage. The cell wall also contains a variety of antimicrobial compounds that can kill or inhibit the growth of pathogens.
* Chemical defenses: Plants produce a wide variety of chemical compounds that can inhibit the growth of or kill pathogens. These compounds include:
* Phytoalexins: These are antimicrobial compounds that are produced in response to infection.
* Phenolics: These are compounds that are toxic to many pathogens.
* Terpenes: These are volatile compounds that can repel pathogens or inhibit their growth.
* Enzymes: Plants produce a variety of enzymes that can degrade the cell walls of pathogens or interfere with their metabolism.
* Proteins: Plants produce a variety of proteins that can bind to pathogens and prevent them from entering the plant cells.
Inducible defenses are defenses that are activated only when a plant is under attack. These defenses include:
* Systemic acquired resistance (SAR): This is a defense response that is triggered by infection with a pathogen and results in the activation of defense mechanisms throughout the plant.
* Hypersensitive response (HR): This is a defense response that results in the rapid death of plant cells at the site of infection, which helps to prevent the pathogen from spreading.
* RNA silencing: This is a defense mechanism that involves the production of small RNAs that can silence the expression of genes in pathogens.
The combination of constitutive and inducible defenses allows plants to mount a robust and effective defense against a wide variety of pathogens. These defenses are essential for plant survival in the face of a constant barrage of attacks from microorganisms.
