The most efficient precursor of ethylene is

• (a) Adenine
• (b) Thiocarbamate
• (c) Zeation
• (d) Methionine

The most efficient precursor of ethylene is (d) Methionine. This amino acid plays a crucial role in the biosynthesis of ethylene in plants.

Why Methionine?

Methionine is important because it is involved in the production of S-adenosylmethionine (SAM), which is a key compound in the ethylene synthesis pathway.

Other Options Explained

• Adenine: Primarily a component of nucleotides and does not directly contribute to ethylene production.
• Thiocarbamate: Not commonly associated with ethylene synthesis.
• Zeation: This term is not widely recognized in the context of ethylene precursors.

In summary, methionine is the most effective precursor for ethylene, making it vital for various plant processes, including fruit ripening and response to stress.