Osmo-sensitive and stretch-activated calcium-permeable channels in Vicia faba guard cells are regulated by actin dynamics.
In responses to a number of environmental stimuli, changes of cytoplasmic [Ca(2+)](cyt) in stomatal guard cells play important roles in regulation of stomatal movements. In this study, the osmo-sensitive and stretch-activated (SA) Ca(2+) channels in the plasma membrane of Vicia faba guard cells are identified, and their regulation by osmotic changes and actin dynamics are characterized. The identified Ca(2+) channels were activated under hypotonic conditions at both whole-cell and single-channel levels. The channels were also activated by a stretch force directly applied to the membrane patches. The channel-mediated inward currents observed under hypotonic conditions or in the presence of a stretch force were blocked by the Ca(2+) channel inhibitor Gd(3+). Disruption of actin filaments activated SA Ca(2+) channels, whereas stabilization of actin filaments blocked the channel activation induced by stretch or hypotonic treatment, indicating that actin dynamics may mediate the stretch activation of these channels. In addition, [Ca(2+)](cyt) imaging demonstrated that both the hypotonic treatment and disruption of actin filaments induced significant Ca(2+) elevation in guard cell protoplasts, which is consistent with our electrophysiological results. It is concluded that stomatal guard cells may utilize SA Ca(2+) channels as osmo sensors, by which swelling of guard cells causes elevation of [Ca(2+)](cyt) and consequently inhibits overswelling of guard cells. This SA Ca(2+) channel-mediated negative feedback mechanism may coordinate with previously hypothesized positive feedback mechanisms and regulate stomatal movement in response to environmental changes.
Zhang
Wei
W
State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100094, China.
Fan
Liu-Min
LM
Wu
Wei-Hua
WH
D008841:Actin Cytoskeleton / Q000502:physiology*; D001464:Barium / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D015220:Calcium Channels / Q000502:physiology*; D017136:Ion Transport / Q000502:physiology; D009995:Osmosis; D011523:Protoplasts / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D031307:Vicia faba / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*
D015220:Calcium Channels; D001464:Barium; D002118:Calcium