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

Abstract

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 (I(Kin)) was highly activated, whereas the outward K+ current (I(Kout)) was inactivated. In contrast, hypertonic conditions inactivated the l(Kin) while activating I(Kout). Single-channel recording analyses indicated that an alteration in channel opening frequency was responsible for regulating I(Kin) and I(Kout) under different osmotic conditions. Further studies correlate osmoregulation of I(Kin) with the pattern of organization of actin filaments, which may be a critical component in the osmosensing pathway in plant cells.