1.Guard cells respond cell-autonomously to physiological stimulation,allowing cell biological analyses of stomatal opening and closing in response to various stimuli.
2.Guard cells respond to most of the classically known hormonal stimuli in plants,illustrating that presently unidentified but essential plant receptors and early signalling mechanisms function in these cells.
3.A network of ion channels in the plasma membane and tonoplast of guard cells has been characterized that,together with metabolic responses,controls stomatal movements (see Figure 1).Being targets of early signaling branches these ion channels provide effective probes to identify and characterize upstream regulators.
4.Stomatal aperture regulates plant CO2 intake and water loss,thus critically influencing growth and water stress responsiveness.In addition,powerful techniques have recently been developed and adapted for guard cell signal transduction studies,allowing interdisciplinary,molecular genetic,cell biological,second messenger,biophysical,physiological and genomic analyses.