Which one of the plant growth regulators would you use if you are asked to
quickly ripen a fruit.

Answer

To answer the question of which plant growth regulator is used to quickly ripen a fruit, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Purpose**: The question asks for a plant growth regulator that can quickly ripen fruit. This indicates that we are looking for a substance that promotes the ripening process.

2. **Understand Plant Growth Regulators**: Plant growth regulators (PGRs) are chemicals that influence the growth and development of plants. They include auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

3. **Focus on Ripening**: Among these regulators, ethylene is known for its role in the ripening of fruits. It is a gaseous hormone that is produced in larger quantities in fruits as they begin to ripen.

4. **Mechanism of Action**: Ethylene works by promoting the expression of genes that synthesize enzymes necessary for the ripening process. These enzymes help in the breakdown of starches into sugars, softening of the fruit, and development of color and flavor.

5. **Conclusion**: Therefore, the plant growth regulator that is used to quickly ripen a fruit is **ethylene**.

### Final Answer:
The plant growth regulator used to quickly ripen a fruit is **ethylene**.

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