Fig. 6.

Postulated properties of two independent vacuolar ion channels. The first is the Ca²⁺-sensitive, PAO-inhibited channel involved in ABA signaling and in the pressure sensitivity. The second system is responsible for the fast hypoosmotic transient, responding to inward water flow by activation of an ion channel. It is likely to involve an aquaporin as a sensor, signaling water flow by asymmetric deformation of the aquaporin protein. The aquaporin may become ion-permeable as a result or, alternatively, may signal its deformation to an associated ion channel, thereby activating it.