The following statements refer to the observations made by a student, upon using 2,6-dichloroisonicotinic acid (INA) to induce systemic acquired resistance (SAR) in tobacco. INA treatment:

A. Enhances salicylic acid concentration in plants.
B. Does not enhance salicylic acid concentration in plants.
C. Fails to activate SAR in nahG-expressing plants.
D. Activates SAR in nahG-expressing plants.

Which one of the following options represents the combination of all correct statements?

Correct option is D

Correct Answer: (4) B and D

Explanation: 2,6-Dichloroisonicotinic acid (INA) and SAR (Systemic Acquired Resistance)

INA is a synthetic analog of salicylic acid (SA) and is known to induce SAR (Systemic Acquired Resistance) in plants without directly increasing endogenous SA levels.

Let's examine each statement:

A."Enhances salicylic acid concentration in plants."

Incorrect

• INA does not increase endogenous salicylic acid (SA) levels.

• It is a functional mimic of SA, activating the same defense pathways without boosting SA production.

B."Does not enhance salicylic acid concentration in plants."

Correct

• This is true. INA acts independently of SA synthesis, and thus does not elevate SA levels in plants.

C."Fails to activate SAR in nahG-expressing plants."

Incorrect

• nahG plants express a bacterial gene that degrades salicylic acid (SA), preventing SA-dependent SAR.

• However, INA can still activate SAR in these plants because it bypasses the need for SA.

• So this statement is incorrect.

D."Activates SAR in nahG-expressing plants."

Correct

• Since INA mimics SA, it can activate SAR even in SA-deficient (nahG) plants.

• This is a well-documented observation in plant immunity studies.