The metabolic precursor for the synthesis of ethylene is

Options

A. citric acid
B. `alpha`- ketoglutaric acid
C. methionine
D. succinic acid

Answer

To determine the metabolic precursor for the synthesis of ethylene, we can analyze the given options step by step:

1. **Identify the options**: The options provided are:
- A) Citric Acid
- B) Alpha-Keto Glutaric Acid
- C) Methionine
- D) (Another mention of Citric Acid)

2. **Evaluate each option**:
- **Option A: Citric Acid**: This compound is primarily involved in the Krebs cycle and is produced from the fermentation of glucose. It does not play a direct role in the synthesis of ethylene. Therefore, this option is incorrect.
- **Option B: Alpha-Keto Glutaric Acid**: This compound is important in amino acid metabolism and the Krebs cycle but is not a precursor for ethylene synthesis. Thus, this option is also incorrect.
- **Option C: Methionine**: This amino acid is known to be a direct precursor for the synthesis of ethylene in plants. Ethylene is synthesized from S-adenosylmethionine (SAM), which is derived from methionine. Therefore, this option is correct.
- **Option D: Citric Acid** (again): As previously mentioned, this option is incorrect for the same reasons stated above.

3. **Conclusion**: The correct answer is **C) Methionine**, as it is the metabolic precursor for the synthesis of ethylene.