Consider the following events involved in stomatal opening
1. Turgor pressure of guard cells increases
2. `K^(+)` ions move into guard cells
3. Formation of malic acid
4. Water moves into guard cells
What is the correct sequence of these events leading to opening of stomata ?

Options

A. 2-4-3-1
B. 3-2-4-1
C. 2-3-4-1
D. 3-1-2-4

Answer

To determine the correct sequence of events leading to the opening of stomata, we can analyze the given statements step by step based on the potassium malate theory. Here’s how the sequence unfolds:

1. **Formation of Malic Acid**: The process begins with the formation of malic acid in the guard cells. This occurs when the pH of the guard cells increases due to the uptake of H+ ions, which stimulates the hydrolysis of starch into phosphoenolpyruvate, and subsequently into oxaloacetic acid, which is then converted to malic acid.

2. **K+ Ions Move into Guard Cells**: After the formation of malic acid, the malic acid dissociates into malate ions and H+ ions. The H+ ions are actively transported into the guard cells, which leads to the exchange of K+ ions that move into the guard cells from the surrounding cells.

3. **Water Moves into Guard Cells**: The influx of K+ ions increases the osmotic concentration inside the guard cells. This causes water to move into the guard cells by osmosis, further increasing the turgor pressure within them.

4. **Turgor Pressure of Guard Cells Increases**: As water enters the guard cells, they become turgid due to the increased turgor pressure. This turgidity causes the guard cells to bow outward, leading to the opening of the stomatal pore.

Thus, the correct sequence of events is:
3 → 2 → 4 → 1

### Final Answer:
The correct sequence of events leading to the opening of stomata is:
1. Formation of malic acid (3)
2. K+ ions move into guard cells (2)
3. Water moves into guard cells (4)
4. Turgor pressure of guard cells increases (1)