Question

Discus the role of K${}^{+}$ in the mechanism by which water moves into guard cells. With the help of a labelled diagram describe briefly the closing and opening mechanism in stomata of plants such as common grass.

Answer 1

Stomatal opening and closing is caused by the absorption and removal of water into and from the guard cells respectively.

Opening: Huge amounts of potassium ions accumulate in the guard cells which increases the solute potential and hence the water potential is dropped. This causes water from neighboring cells to enter the guard cell and they become turgid or swollen. In this condition, the stomatal pore is opened.

Closing: This is the opposite phenomenon of opening as it occurs when water is removed from the guard cells and they become flaccid. $K^{+}$ ions move out of the cell. This causes the stomatal pore to close. This occurs in the absence of light or when rates of photosynthesis are low. In this condition, the stomatal pore is closed.