Involvement of superoxide radical in signal transduction regulating stomatal movements.

Stomatal movements are regulated by alternate phase transition in the lipophilic domains of membrane initiated by blue light through activation of plasmalemma redox system. ABA blocks the blue light activated redox reactions leading to the accumulation of superoxide (O2.-) radical inducing melting of the membrane and increased fluidity. Phenolic compounds which reverse the ABA effects reduce O2.- radical and thereby reverse phase transition in lipophilic domains of membrane. Stomatal movements thus appear to be regulated by blue light activated redox reactions involving formation of O2.- radical and its reduction by the reducing equivalents available in the GCPs.