title: Making sense out of Ca(2+) signals: their role in regulating stomatal movements.
abstract: Plant cells maintain high Ca(2+) concentration gradients between the cytosol and the extracellular matrix, as well as intracellular compartments. During evolution, the regulatory mechanisms, maintaining low cytosolic free Ca(2+) concentrations, most likely provided the backbone for the development of Ca(2+)-dependent signalling pathways. In this review, the current understanding of molecular mechanisms involved in Ca(2+) homeostasis of plants cells is evaluated. The question is addressed to which extent the mechanisms, controlling the cytosolic Ca(2+) concentration, are linked to Ca(2+)-based signalling. A large number of environmental stimuli can evoke Ca(2+) signals, but the Ca(2+)-induced responses are likely to differ depending on the stimulus applied. Two mechanisms are put forward to explain signal specificity of Ca(2+)-dependent responses. A signal may evoke a specific Ca(2+) signature that is recognized by downstream signalling components. Alternatively, Ca(2+) signals are accompanied by Ca(2+)-independent signalling events that determine the specificity of the response. The existence of such parallel-acting pathways explains why guard cell responses to abscisic acid (ABA) can occur in the absence, as well as in the presence, of Ca(2+) signals. Future research may shed new light on the relation between parallel acting Ca(2+)-dependent and -independent events, and may provide insights in their evolutionary origin.
authors.affiliation: Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Biosciences, Biocenter, Würzburg University, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany. roelfsema@botanik.uni-wuerzburg.de
authors.forename: M Rob G
authors.initials: MR
authors.lastname: Roelfsema
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D017920:Antiporters / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D027682:Cation Transport Proteins / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006706:Homeostasis; D054046:Plant Stomata / Q000502:physiology*
chemical_list: D017920:Antiporters; D027682:Cation Transport Proteins; C027614:calcium-hydrogen antiporters; D000040:Abscisic Acid; D000252:Calcium-Transporting ATPases; D002118:Calcium