The Role of Induced Systemic Resistance in Plant Immunity
Introduction
Induced Systemic Resistance (ISR) is a defensive mechanism in plants that is activated in response to certain types of pathogens or beneficial microbes. This resistance is not localized to the site of infection or colonization, but rather is systemic, meaning it protects the entire plant. ISR is a complex process involving numerous signaling pathways and a variety of plant hormones, including jasmonic acid, salicylic acid, and ethylene.
Mechanism of Induced Systemic Resistance
The ISR mechanism is triggered when plant roots come into contact with specific beneficial soil microbes, such as plant growth-promoting rhizobacteria (PGPR) and mycorrhizal fungi. These microbes produce certain molecules or change the environment in a way that is recognized by the plant, leading to the activation of the ISR response.
The recognition of these microbes or their products leads to changes in the plant's cellular metabolism and the activation of defense-related genes. This results in the production of antimicrobial compounds and proteins, as well as changes in the plant's cell wall and other structural defenses. The ISR response also involves the production of plant hormones, including jasmonic acid, salicylic acid, and ethylene, which play key roles in signaling and coordinating the defense response.
Role of Plant Hormones in ISR
Plant hormones play a crucial role in the ISR response. They act as signaling molecules, coordinating the plant's defense response and regulating the expression of defense-related genes.
Jasmonic Acid
Jasmonic acid is a plant hormone that plays a key role in the ISR response. It is produced in response to wounding, insect attack, and microbial infection, and it regulates the expression of a wide range of defense-related genes. In the context of ISR, jasmonic acid is thought to play a role in signaling the presence of beneficial microbes and initiating the defense response.
Salicylic Acid
Salicylic acid is another plant hormone that is crucial for the ISR response. It is produced in response to pathogen attack and is involved in both local and systemic defense responses. Salicylic acid regulates the expression of a range of defense-related genes and is thought to play a role in the recognition of beneficial microbes and the activation of the ISR response.
Ethylene
Ethylene is a gaseous plant hormone that plays a role in a variety of plant processes, including fruit ripening, leaf abscission, and the response to stress. In the context of ISR, ethylene is thought to play a role in signaling the presence of beneficial microbes and coordinating the defense response.
Benefits of ISR in Agriculture
The ISR response has significant potential for use in sustainable agriculture. By harnessing the power of beneficial soil microbes to induce a systemic defense response in crops, farmers can potentially reduce their reliance on chemical pesticides. This could have significant benefits for the environment, as well as for the health and safety of farm workers and consumers.