Calcium-based signalling systems in guard cells

Calcium is a ubiquitous intracellular signal responsible for controlling nu merous cellular processes in both plants and animals. As an example, Ca2+ h as been shown to be a second messenger in the signal transduction pathways by which stomatal guard cells respond to external stimuli. Regulated increa ses in the cytosolic concentration of free calcium ions([Ca2+](cyt)) in gua rd cells have been observed to be a common intermediate in many of the path ways leading to either opening or closing of the stomatal pore. This observ ation has prompted investigations into how specificity is encoded in the Ca 2+ signal. It has been suggested that the key to generating stimulus-specif ic calcium signatures lies in the ability to access differentially the cell ular machinery controlling calcium influx and release from intracellular st ores. Several important components of the calcium-based signalling pathways have been identified in guard cells including cADPR, phospholipase C-InsP( 3), InsP(6) and H2O2. These data suggest that the pathways for intracellula r mobilization of Ca2+ are evolutionarily conserved between plants and anim als.