Systemic resistance is a type of induced plant defense mechanism that provides protection against a broad range of pathogens and pests. It is triggered when a plant is exposed to a pathogen or other stress factor, such as herbivory, and results in increased resistance not only in the site of infection, but also in other parts of the plant that were not directly affected.
Systemic resistance can be either local or systemic acquired resistance. Local acquired resistance occurs when a plant is exposed to a pathogen and develops resistance at the site of infection, while systemic acquired resistance occurs when a plant is exposed to a pathogen and develops resistance throughout the entire plant.
The mechanism of systemic resistance involves the activation of signal transduction pathways that lead to the production of defense-related proteins, such as pathogenesis-related (PR) proteins and enzymes, and the accumulation of phytohormones, such as salicylic acid, jasmonic acid, and ethylene. These defense-related proteins and phytohormones help to limit the spread of the pathogen and reduce the damage caused by the infection.
Systemic resistance is not only triggered by pathogen attack but also by beneficial microbes such as rhizobacteria and mycorrhizae that induce systemic resistance in plants. This mechanism is called induced systemic resistance (ISR), and it involves the activation of similar defense responses to systemic acquired resistance.
Overall, systemic resistance is an important plant defense mechanism that provides long-lasting protection against a broad range of pathogens and pests. It plays a critical role in plant immunity and has potential applications in the development of sustainable agricultural practices.