Which of the following effects is brought about by gibberellins but not by auxins?

Options

A. stimulation of cambial activity
B. stimulation of fruit development
C. inhibition of leaf abscission
D. breaking of dormancy in leaf buds

Answer

To determine which effect is brought about by gibberellins but not by auxins, we need to understand the roles of both plant growth regulators.

### Step-by-Step Solution:

1. **Understanding Gibberellins and Auxins**:
- Both gibberellins and auxins are types of plant hormones (also known as phytohormones) that regulate various aspects of plant growth and development.

2. **Functions of Auxins**:
- Auxins are primarily involved in promoting cell elongation, apical dominance, and root development. They play a significant role in agricultural and horticultural practices.

3. **Functions of Gibberellins**:
- Gibberellins are known for promoting stem elongation, seed germination, and breaking dormancy in seeds and buds. They are also involved in stimulating cambial activity, which contributes to secondary growth in plants.

4. **Identifying the Unique Effect of Gibberellins**:
- The question asks for an effect that is specific to gibberellins and not auxins.
- Among the options provided:
- Stimulation of cambial activity (not unique to gibberellins)
- Stimulation of root development (not unique to gibberellins)
- Inhibition of leaf abscission (not unique to gibberellins)
- Breaking of dormancy in leaf buds (specific to gibberellins)

5. **Conclusion**:
- The correct answer is "breaking of dormancy in leaf buds," as this effect is specifically associated with gibberellins and not auxins.

### Final Answer:
The effect brought about by gibberellins but not by auxins is **breaking of dormancy in leaf buds**.