Copper amine oxidase and phospholipase D act independently in abscisic acid (ABA)-induced stomatal closure in Vicia faba and Arabidopsis

Recent evidence has demonstrated that both copper amine oxidase (CuAO; EC 1.4.3.6) and phospholipase D (PLD; EC 3.1.4.4) are involved in abscisic acid (ABA)-induced stomatal closure. In this study, we investigated the interaction between CuAO and PLD in the ABA response. Pretreatment with either CuAO or PLD inhibitors alone or that with both additively led to impairment of ABA-induced H2O2 production and stomatal closure in Vicia faba. ABA-stimulated PLD activation could not be inhibited by the CuAO inhibitor, and CuAO activity was not affected by the PLD inhibitor. These data suggest that CuAO and PLD act independently in the ABA response. To further examine PLD and CuAO activities in ABA responses, we used the Arabidopsis mutants cuao zeta and pld alpha 1. Ablation of guard cell-expressed CuAO zeta or PLD alpha 1 gene retarded ABA-induced H2O2 generation and stomatal closure. As a product of PLD, phosphatidic acid (PA) substantially enhanced H2O2 production and stomatal closure in wide type, pld alpha 1, and cuao zeta. Moreover, putrescine (Put), a substrate of CuAO as well as an activator of PLD, induced H2O2 production and stomatal closure in WT but not in both mutants. These results suggest that CuAO and PLD act independently in ABA-induced stomatal closure.