opening of stomata

• opening of stomata is promoted by high light intensity, low mesophyll co2 levels and high humidity
• blue light is absorbed by blue light photoreceptors which activate an ATP-powered proton-pump (H+-ATPase) in the plasma membrane of guard cell
• ATPs generated by the LDR of photosynthesis in guard cell are hydrolyzed to provide energy to drive the proton pump. As protons are pumped out from the guard cell, the cell becomes increasingly negatively charged. The inward potassium ion channels are activated and potassium ions diffuse from the subsidiary cells through the channel down this electrochemical gradient into the guard cell. Chloride ions then enters to balance the charge.
• the accumulation of potassium ions causes the water potential in the guard cell to become more negative. Water enters by osmosis down a water potential gradient from neighbouring subsidiary cells into the guard cells. The guard cells becomes turgid. The volume of the cells increases and guard cells expand
• the increased turgor pressure causes the guard cells to curve outward and the stomatal pore opens