How do stomata open?
Stomata sense environmental cues, like light, to open. These cues start a series of reactions that cause their guard cells to fill with water. Lets follow a scenario where the sun is rising and a cotton plant is signaled to open its stomata: • Signal received: The blue light at dawn is the signal that is recognized by a receptor on the guard cell. • The receptor signals the H+-ATPases on the guard cells plasma membrane to start pumping protons (H+) out of the guard cell. This loss of positive charge creates a negative charge in the cell. • Potassium ions (K+) enter the guard cell through channels in the membrane, moving toward its more negative interior. • As the potassium ions accumulate in the guard cell, the osmotic pressure is lowered. • A lower osmotic pressure attracts water to enter the cell. • As water enters the guard cell, its hydrostatic pressure increases. • The pressure causes the shape of the guard cells to change and a pore is formed, allowing gas exchange. SIDE VIEW OF
