Slow, weak voltage-dependent S-type anion efflux channel involved in maintenance of anion homeostasis. Cl(-) efflux through SLAC1 causes membrane depolarization, which activates outward- rectifying K1 channels, leading to KCl and water efflux to reduce turgor further and cause stomatal closure, that reduces water loss and promotes leaf turgor. Essential for stomatal closure in response to CO(2), abscisic acid (ABA), ozone O(3), light/dark transitions, humidity change, calcium ions, hydrogen peroxide H(2)O(2), reactive oxygen species (ROS), and nitric oxide.