The first cytokinin was isolated by

Options

A. Darwin
B. Evins
C. Miller and Skoog
D. Leopoid

Answer

### Step-by-Step Solution:

1. **Understanding Cytokinins**: Cytokinins are a class of plant hormones that play a crucial role in regulating plant growth and development. They are known to promote cell division and are involved in various physiological processes in plants.

2. **Historical Context**: The first cytokinin was isolated in the mid-20th century. This period was significant for plant physiology as researchers were exploring various plant hormones and their effects.

3. **Isolation of Cytokinin**: The first cytokinin was isolated by a scientist named **Miller** in **1955**. This isolation was done from **herring sperm**, which is notable for containing high levels of nucleic acids.

4. **Naming of Cytokinin**: The compound isolated by Miller was later named **kinetin**. Kinetin is known for its ability to promote cell division, which is also referred to as cytokinesis.

5. **Function of Cytokinins**: Cytokinins have several important functions in plants:
- They promote cell division.
- They work in opposition to auxins (another class of plant hormones).
- They inhibit apical dominance, allowing lateral buds to grow in the presence of an apical bud.
- They delay senescence (aging) of leaves, thus prolonging their life.

6. **Conclusion**: Therefore, the correct answer to the question of who first isolated cytokinin is **Miller**, and it was done in collaboration with **Skoog**.

### Final Answer:
The first cytokinin was isolated by **Miller** in **1955** from herring sperm.

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