Question

Which of the following plant growth regulators promotes internode elongation prior to flowering in cabbage ?

• A. Ethephon
• B. Abscisic acid
• C. Gibberellin
• D. Indole butyric acid

Hint:

To remember the primary function of Gibberellins, associate the word "Gibberellin" directly with "Giant growth" and "Bolting". Whenever you see keywords like "internode elongation in rosette plants", "cabbage", or "bolting prior to flowering", the correct answer is invariably Gibberellin ($\text{GA}_3$).

Answer 1

The Correct Option is C

Step 1: Understand the question.
We need the hormone that makes internodes elongate just before flowering in cabbage, a rosette plant.
Step 2: Recall bolting.
The sudden stretching of internodes before flowering in rosette plants is called bolting.
Step 3: Link bolting to gibberellin.
Gibberellin triggers rapid cell division and elongation in the sub-apical region, causing this bolting. So gibberellin is the answer.
Step 4: Reject Ethephon.
Ethephon releases ethylene which ripens fruit and causes abscission, but it does not cause bolting.
Step 5: Reject Abscisic acid.
Abscisic acid is a growth inhibitor and stress hormone that opposes gibberellin, so it cannot elongate internodes.
Step 6: Reject IBA and conclude.
Indole butyric acid is an auxin used mainly for rooting, not for bolting. Therefore gibberellin is responsible.
\[ \boxed{\text{Gibberellin}} \]