Which of the following serves as a mitotic spindle poison?

Options

A. `Ca^(2+)`
B. `Mg^(2+)`
C. Tubulin
D. Colchicine

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks for a substance that acts as a mitotic spindle poison. This means we need to identify a compound that disrupts the formation or function of the mitotic spindle during cell division.

2. **Identifying Options:**
The options provided are calcium, magnesium, tubulin, and colchicin. We need to analyze each option to determine which one is known to affect the mitotic spindle.

3. **Analyzing the Options:**
- **Calcium:** This is an essential ion in various cellular processes but does not act as a mitotic spindle poison.
- **Magnesium:** Similar to calcium, magnesium is important for many cellular functions but is not known to interfere with the mitotic spindle.
- **Tubulin:** Tubulin is a protein that makes up the microtubules of the spindle apparatus. While it is essential for spindle formation, it is not a poison.
- **Colchicin:** This is a compound derived from the plant Colchicum autumnale. It is known to inhibit the formation of spindle fibers by preventing the polymerization of tubulin into microtubules.

4. **Conclusion:**
Based on the analysis, colchicin is the only option that serves as a mitotic spindle poison. It disrupts the normal function of the spindle apparatus, leading to cell cycle arrest during metaphase.

5. **Final Answer:**
The mitotic spindle poison is **colchicin**.

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