Enzyme activity inhibition of the ABA-inducible copper amine oxidase AtCuAOδ reverses most of the ABA-mediated stomatal closure in Arabidopsis.

Plant copper amine oxidases (CuAOs) catalyze the oxidation of polyamines to aminoaldehydes producing ammonia and hydrogen peroxide (H2O2). The involvement of H2O2 derived by CuAO-driven polyamine oxidation in stomatal closure induced by stress hormones has been observed in different plants. Previous study showed that two loss-of-function mutants of the Arabidopsis thaliana CuAOδ (At4g12290) were unresponsive to ABA-induced stomatal closure. Here we investigated the role of the vacuolar AtCuAOδ in the ABA-mediated stomatal closure by pharmacological approaches. Present data based on RT-qPCR studies show that AtCuAOδ expression is up-regulated by ABA treatments with a 2-to 4-fold increase of expression levels depending on ABA concentration (from 1 to 100 µM) as soon as 3 h from the onset of treatment. This induction peaked at 6 h with a 4-fold increase at 100 μM ABA. The well-known inhibitors of CuAO enzyme activity, 2-bromoethylamine and aminoguanidine, as well as the H2O2 scavenger N,N1-dimethylthiourea reversed most of the ABA-induced stomatal closure in WT plants. Our results, consistently with previous data, suggest that the vacuolar AtCuAOδ is a necessary component in the network orchestrating the ABA-mediated regulation of stomatal closure via H2O2 production, cooperating with the other ABA-induced ROS enzymatic sources involved in this event.