Final answer:
Salicylic acid in plants is typically observed during a pathogen attack. It is crucial for activating plant defense mechanisms, including the hypersensitive response and systemic acquired resistance. Studies underline its role in the oxidative burst, which helps signal defense responses to pathogenic challenges. Therefore, correct option is A.
Step-by-step explanation:
Salicylic acid is typically observed in plants during a pathogen attack. It is an important molecule that contributes to both local and systemic responses when plants are challenged by pathogens.
Salicylic acid is key to the activation of a plant’s defense mechanisms and is associated with the hypersensitive response that quickly leads to the death of infected plant cells to prevent the spread of infection.
This defense strategy also includes systemic acquired resistance (SAR), where chemicals like salicylic acid help to prime other parts of the plant to respond more effectively to future attacks.
Recent studies have revealed salicylic acid's role in the plant immune response, including its implication in the oxidative burst, which is a rapid production of reactive oxygen species that serves as a signal for the activation of defense genes.
When a pathogen triggers this burst of reactive oxygen species, salicylic acid accumulates in affected tissues, helping to fortify the plant's defense system against the pathogen.