THE CONTROL OF SPECIFICITY IN GUARD-CELL SIGNAL-TRANSDUCTION

Stomatal guard cells have proven to be an attractive system for dissec ting the mechanisms of stimulus-response coupling in plants. In this r eview we focus on the intracellular signal transduction pathways by wh ich extracellular signals bring about closure and opening of the stoma tal pore. It is proposed that guard cell signal transduction pathways may be organized into functional arrays or signalling cassettes that c ontain elements common to a number of converging signalling pathways. The purpose of these signalling cassettes may be to funnel extracellul ar signals down onto the ion transporters chat control the fluxes of i ons that underlie stomatal movements. Evidence is emerging that specif icity in guard cell signalling may be, in part, encoded in complex spa tio-temporal patterns of increases in the concentration of cytosolic-f ree calcium ([Ca2+](cyt)). It is suggested that oscillations in [Ca2+] (cyt) may generate calcium signatures that encode information concerni ng the stimulus type and strength. New evidence is presented that sugg ests that these calcium signatures may integrate information when many stimuli are present.