Voltage-dependent K+ channels as targets of osmosensing in guard cells.

Guard cell turgor responds to the osmogradient across the plasma membrane and controls the stomatal aperture. Here, we report that guard cells utilize voltage-dependent K+ channels as targets of the osmosensing pathway, providing a positive feedback mechanism for stomatal regulation. When exposed to a hypotonic condition, the inward K+ current (IKin) was highly activated, whereas the outward K+ current (IKout) was inactivated. In contrast, hypertonic conditions inactivated the IKin while activating IKout. Single-channel recording analyses indicated that an alteration in channel opening frequency was responsible for regulating IKin and IKout under different osmotic conditions. Further studies correlate osmoregulation of IKin with the pattern of organization of actin filaments, which may be a critical component in the osmosensing pathway in plant cells.