Cross-talks between Ca2+/CaM and H2O2 in abscisic acid-induced antioxidant defense in leaves of maize plants exposed to water stress

Here we examined whether Ca2+/Calmodulin (CaM) is involved in abscisic acid (ABA)-induced antioxidant defense and the possible relationship between CaM and H2O2 in ABA signaling in leaves of maize (Zea mays L.) plants exposed to water stress. An ABA-deficient mutant vp5 and its wild type were used for the experimentation. We found that water stress enhanced significantly the contents of CaM and H2O2, and the activities of chloroplastic and cytosolic superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR), and the gene expressions of the CaM1, cAPX, GR1 and SOD4 in leaves of wild-type maize. However, the increases mentioned above were almost arrested in vp5 plants and in the wild-type plants pretreated with ABA biosynthesis inhibitor tungstate (T), suggesting that ABA is required for water stress-induced H2O2 production, the enhancement of CaM content and antioxidant defense. Besides, we showed that the up-regulation of water stress-induced antioxidant defense was almost completely blocked by pretreatment with Ca2+ inhibitors, CaM antagonists and reactive oxygen (ROS) manipulators. Moreover, the analysis of time course of CaM and H2O2 production under water stress showed that the increase in CaM content preceded that of H2O2. These results suggested that Ca2+/CaM and H2O2 were involved in the ABA-induced antioxidant defense under water stress, and the increases of Ca2+/CaM contents triggered H2O2 production, which inversely affected the contents of CaM. Thus, a cross-talk between Ca2+/CaM and H2O2 may play a pivotal role in the ABA signaling.