Phospholipase Dδ is involved in nitric oxide-induced stomatal closure

Nitric oxide (NO) has recently emerged as a second messenger involved in the complex network of signaling events that regulate stomatal closure. Little is known about the signaling events occurring downstream of NO. Previously, we demonstrated the involvement of phospholipase D (PLD) in NO signaling during stomatal closure. PLD delta, one of the 12 Arabidopsis PLDs, is involved in dehydration stress responses. To investigate the role of PLD delta in NO signaling in guard cells, we analyzed guard cells responses using Arabidopsis wild type and two independent pld delta single mutants. In this work, we show that pld delta mutants failed to close the stomata in response to NO. Treatments with phosphatidic acid, the product of PLD activity, induced stomatal closure in pld delta mutants. Abscisic acid (ABA) signaling in guard cells involved H2O2 and NO production, both required for ABA-induced stomatal closure. pld delta guard cells produced similar NO and H2O2 levels as the wild type in response to ABA. However, ABA- or H2O2-induced stomatal closure was impaired in pld delta plants. These data indicate that PLD delta is downstream of NO and H2O2 in ABA-induced stomatal closure.