Which one of the following of the plant growth substances is not a growth promoter.

Options

A. IAA
B. Gibberellins
C. Kinetin
D. Abscisic acid

Answer

To determine which plant growth substance is not a growth promoter, we need to analyze the given options: IAA, Ziberlins, Kinetin, and Abscisic Acid.

**Step 1: Identify the substances.**
- IAA (Indole-3 Acetic Acid)
- Ziberlins (Gibberellins)
- Kinetin
- Abscisic Acid (ABA)

**Step 2: Classify the substances.**
Plant growth substances can be classified into two categories: growth promoters and growth inhibitors.

**Step 3: Analyze each substance:**
- **IAA (Indole-3 Acetic Acid)**: This is an auxin, which is a type of growth promoter. It is involved in processes such as apical dominance, cell elongation, and differentiation.

- **Ziberlins (Gibberellins)**: These are also growth promoters. They stimulate stem elongation, seed germination, and other growth processes.

- **Kinetin**: This is a type of cytokinin, which promotes cell division and delays senescence, making it a growth promoter as well.

- **Abscisic Acid (ABA)**: This is known as a stress hormone and is primarily an inhibitor. It is responsible for processes such as stomatal closure and promoting senescence.

**Step 4: Conclusion**
Among the options provided, Abscisic Acid (ABA) is the only substance that is not a growth promoter; instead, it acts as a growth inhibitor.

**Final Answer: Abscisic Acid (ABA)**

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