How does salicylic acid induce systemic resistance
against pathogens? (5)
There are several ways in which salicylic acid can induce systemic resistance against pathogens:
1. Activation of defense pathways: Salicylic acid acts as a signaling molecule that can activate a cascade of defense responses in plants, known as the salicylic acid pathway. This signaling pathway triggers the expression of various defense-related genes, leading to the production of antimicrobial compounds and reinforcement of the plant cell walls.
2. Induction of phytoalexins: Salicylic acid can stimulate the synthesis and accumulation of phytoalexins, which are antimicrobial compounds produced by plants in response to pathogen attack. Phytoalexins can directly inhibit the growth and reproduction of pathogens, enhancing the plant's resistance to infection.
3. Priming of the immune system: Salicylic acid can prime the plant's immune system, making it more responsive and ready to defend against subsequent pathogen attacks. Priming involves the pre-activation of defense mechanisms in anticipation of future threats. This allows for a faster and stronger response to pathogens, providing enhanced resistance.
4. Systemic acquired resistance (SAR): Salicylic acid plays a critical role in the induction of systemic acquired resistance, a durable and broad-spectrum defense response in plants. When a pathogen attacks a particular part of a plant, salicylic acid is produced and transported to other parts of the plant systemically. This signal alerts the whole plant to prepare for potential future attacks and activates systemic defense mechanisms.
5. Interference with pathogen enzymes: Salicylic acid can interfere with the activity of certain pathogen enzymes that are important for the infection process. By inhibiting these enzymes, salicylic acid can disrupt the pathogen's ability to establish and spread infection within the plant. This creates a hostile environment for the pathogen and significantly reduces its virulence.
Salicylic acid induces systemic resistance against pathogens through the following mechanisms:
1. Signaling pathway activation: Salicylic acid acts as a signal molecule, triggering the activation of defense pathways in plants. It binds to and modulates the activity of several proteins involved in the plant's immune response, including receptor-like kinases and transcription factors.
2. Induction of defense-related genes: Salicylic acid stimulates the expression of various defense-related genes, including pathogenesis-related (PR) genes. These genes encode proteins that directly contribute to the plant's defense against pathogens, such as enzymes that degrade cell walls, antimicrobial peptides, and proteins involved in the production of toxic compounds.
3. Reinforcement of physical barriers: Salicylic acid promotes the reinforcement of physical barriers in plants, such as the cell wall and cuticle. It stimulates the deposition of callose, a protective material that strengthens cell walls and acts as a barrier against pathogen invasion.
4. Enhanced production of antimicrobial compounds: Salicylic acid triggers the synthesis of antimicrobial compounds, such as phytoalexins and volatile organic compounds (VOCs). These compounds have direct toxic effects on pathogens or indirectly inhibit their growth and spread.
5. Systemic acquired resistance (SAR) priming: Salicylic acid induces a phenomenon called systemic acquired resistance, where the entire plant becomes more resistant to secondary infections by pathogens. It does this by priming the plant's immune system, making it more responsive and prepared to launch a faster and stronger defense upon subsequent pathogen attacks.
These mechanisms collectively contribute to the ability of salicylic acid to induce systemic resistance against pathogens in plants.