In eukaryotic cells, changes in electrical/chemical signaling and osmotic pressure are important cellular events that control plant development and physiology. These factors depend on the movement of ions between compartments, controlled by membrane proteins (channels, pumps, and exchangers). The guard cell of stomata unquestionably possesses two major membranes: the plasma membrane and the vacuolar membrane. My current work aims to understand how the ion flux network between these two membranes controls gas exchange.