To increase the length of grape stalks gibberellin are applied. The mechanism of action of gibberellin exploited in this case is its

Options

A. ability to increase length of apex.
B. ability to increase in the length of the axis.
C. ability to avoid apical dominance.
D. all of these.

Answer

To solve the question regarding the mechanism of action of gibberellin in increasing the length of grape stalks, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Gibberellin**:
- Gibberellin is a plant hormone that plays a crucial role in promoting growth. It is known for its ability to stimulate various growth processes in plants.

**Hint**: Remember that gibberellins are a class of plant hormones that promote growth and development.

2. **Function of Gibberellin**:
- One of the primary functions of gibberellin is to increase the length of the internodes (the sections of stem between the nodes). This is particularly important in plants like grapes, where longer stalks are desirable.

**Hint**: Focus on the role of gibberellin in elongating plant structures, especially internodes.

3. **Apical Dominance**:
- Apical dominance refers to the phenomenon where the main central stem of the plant grows more strongly than the side stems. Gibberellin can influence this process, but its primary role in this context is not to avoid apical dominance but to promote elongation.

**Hint**: Consider how gibberellin interacts with other hormones related to growth and dominance in plants.

4. **Evaluating the Options**:
- The question provides several options regarding the mechanism of gibberellin:
- Ability to increase the length of apex (incorrect)
- Ability to increase in the length of the axis (correct)
- Ability to avoid apical dominance (incorrect)
- All of these (incorrect)

**Hint**: Carefully analyze each option based on the known functions of gibberellin.

5. **Conclusion**:
- The correct answer is the "ability to increase in the length of the axis," as this directly relates to the application of gibberellin to enhance grape stalk length.

**Hint**: Summarize the key function of gibberellin that relates to the question.

### Final Answer:
The mechanism of action of gibberellin exploited in this case is its **ability to increase in the length of the axis**.