Question

Which of the following hormones is synthesized from methionine?

• A. Auxin
• B. Gibberellin
• C. Cytokinin
• D. Ethylene

Hint:

For exams, it's very useful to remember the amino acid precursors for hormones:

\textbf{Tryptophan} \(\rightarrow\) \textbf{Auxin}
\textbf{Methionine} \(\rightarrow\) \textbf{Ethylene}
These two are the most commonly asked pairings.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The question asks to identify the plant hormone whose biosynthetic pathway starts with the amino acid methionine.
Step 2: Detailed Explanation:
Let's review the primary precursors for the major plant hormones:

Auxin (specifically Indole-3-acetic acid, IAA) is primarily synthesized from the amino acid tryptophan.

Gibberellin is a terpenoid, synthesized from geranylgeranyl pyrophosphate (GGPP) via the MEP or MVA pathway. It is not derived from an amino acid.

Cytokinin is a derivative of the purine base adenine.

Ethylene (C₂H₄) is a simple gaseous hormone. Its biosynthesis in plants starts with the amino acid methionine. Methionine is converted to S-adenosylmethionine (SAM), then to 1-aminocyclopropane-1-carboxylic acid (ACC) by ACC synthase, and finally to ethylene by ACC oxidase.

Step 3: Final Answer:
Based on the biosynthetic pathways, ethylene is the plant hormone synthesized from methionine.