Antigibberellin is

Options

A. Cycocel
B. Plastoquinone
C. IAA
D. Ubiquinone.

Explanation

**Step-by-Step Solution:**

1. **Understanding Antigibberellin**: Antigibberellin refers to substances that inhibit the effects of gibberellins, which are plant hormones that promote growth.

2. **Identifying the Correct Option**: The question provides four options: psychocell, plastoquinone, IAA (indole acetic acid), and ubiquinone. We need to identify which of these acts as an antigibberellin.

3. **Analyzing Each Option**:
- **Psychocell**: This is known to act as an antigibberellin and is also referred to as a dwarfing agent. It reduces plant growth, making it the correct answer.
- **Plastoquinone**: This is an electron acceptor in photosystem II and does not have any antigibberellin activity, so it is incorrect.
- **IAA (Indole Acetic Acid)**: This is a naturally occurring auxin that promotes growth and does not act as an antigibberellin, making it incorrect.
- **Ubiquinone**: Also known as coenzyme Q10, it is involved in cellular respiration but does not exhibit antigibberellin activity, so it is incorrect.

4. **Conclusion**: Based on the analysis, the only correct option that acts as an antigibberellin is **psychocell**.

**Final Answer**: Psychocell is the correct answer as it acts as an antigibberellin.

---