124. A plant that survives a local pathogen infection, often develops increased resistance to a subsequent attack
by a mechanism called:
(1) Systemic Acquired Resistance
(2) DAMP-triggered immunity
(3) Hypersensitive response
(4) Heat Shock Response

Detailed Explanation:

Question:
A plant that survives a local pathogen infection, often develops increased resistance to a subsequent attack by a mechanism called:

✅ Correct Answer: (1) Systemic Acquired Resistance

What is Systemic Acquired Resistance (SAR)?

Systemic Acquired Resistance (SAR) is a whole-plant resistance response that occurs after a local infection by a pathogen. Once a plant successfully fends off a localized attack, it activates a signaling network that “primes” the rest of the plant to defend against future invasions — even in parts that were never infected.

Think of it as the plant’s version of immune memory.

Key Features of SAR:

• Triggered by: Localized pathogen infection, often associated with a hypersensitive response.

• Signaling molecules: Salicylic acid (SA) plays a key role in transmitting the defense signal throughout the plant.

• Effect: Induces pathogenesis-related (PR) genes, which encode proteins that boost the plant’s immune system.

• Long-lasting protection: SAR can protect against a broad spectrum of pathogens and last for days to weeks.

Why SAR is Important in Agriculture:

• Enhances disease resistance naturally, reducing the need for chemical pesticides.

• Can be induced artificially using compounds like salicylic acid analogs or beneficial microbes.

• Contributes to sustainable and resilient crop protection strategies.

Explanation of Incorrect Options:

• (2) DAMP-triggered immunity
  Refers to immune responses initiated by Damage-Associated Molecular Patterns, but this is typically an immediate, local defense mechanism—not systemic.

• (3) Hypersensitive response (HR)
  This is a local cell death response that restricts pathogen spread at the infection site. HR often precedes SAR but does not provide systemic resistance by itself.

• (4) Heat Shock Response
  A mechanism to cope with heat stress, involving heat shock proteins (HSPs), not pathogen defense.

Conclusion:

When a plant fights off a local infection, it doesn’t just stop there — it goes on alert across the entire system. This “immunization effect” is due to Systemic Acquired Resistance (SAR), a powerful mechanism that equips plants for future pathogen encounters. It’s an incredible example of plant defense evolution.

✅ Correct Answer: (1) Systemic Acquired Resistance