Ionic flux of guard cells directly connected with expenditure of energy is

Options

A. Outward movement of protons
B. Outward movement of malate
C. Inward movement of `K^(+)`
D. Inward movement of Cl.

Answer

To solve the question regarding the ionic flux of guard cells and its connection to energy expenditure, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of Guard Cells**:
- Guard cells regulate the opening and closing of stomata, which are small openings on the surfaces of leaves. This regulation is crucial for gas exchange and transpiration in plants.

2. **Identify Ion Movement in Guard Cells**:
- During stomatal opening, guard cells take up potassium ions (K+) and other ions, which leads to an increase in turgor pressure. Conversely, during stomatal closure, ions are expelled.

3. **Examine Energy Expenditure**:
- The movement of ions across the guard cell membrane is not a passive process. It requires energy, primarily in the form of ATP, to pump protons (H+) out of the guard cells.

4. **Proton Pumping Mechanism**:
- The outward movement of protons (H+) is facilitated by proton pumps (H+-ATPases) in the guard cell membrane. This pumping creates a proton gradient, which is essential for the secondary active transport of other ions.

5. **Evaluate the Options**:
- **Outward movement of protons**: This is directly linked to energy expenditure as it requires ATP.
- **Outward movement of malate**: This is not directly linked to energy expenditure.
- **Inward movement of potassium ions**: This is a result of the proton gradient but does not directly expend energy.
- **Inward movement of chlorine**: Similar to potassium, this is not directly linked to energy expenditure.

6. **Conclusion**:
- The correct answer is the **outward movement of protons**, as it directly involves the expenditure of energy.

### Final Answer:
The ionic flux of guard cells directly connected with expenditure of energy is the **outward movement of protons**.

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