Under conditions of water stress, plants produce a hormone that coordinates the closure of stomata to restrict water loss through transpiration.

Which of the following statements regarding the mechanism of abscisic acid (ABA) mediated stomatal closure are correct?

1. ABA binds to specific receptors on the cell surface membranes of guard cells, triggering an influx of calcium ions ($C{a}^{2+}$) into the cytoplasm.
2. The resulting rise in cytosolic $C{a}^{2+}$ concentration activates proton pumps to actively transport hydrogen ions ($H^{+}$) out of the guard cells, hyperpolarising the membrane.
3. The outward movement of potassium ions ($K^{+}$) and anions from the guard cells increases the water potential ($\psi$) inside the cells, leading to osmotic water loss and flaccidity.