Cross-talks between Ca 2+ /CaM and H 2 O 2 in abscisic acid-induced antioxidant defense in leaves of maize plants exposed to water stress

Here we examined whether Ca 2+ /Calmodulin (CaM) is involved in abscisic acid (ABA)-induced antioxidant defense and the possible relationship between CaM and H 2 O 2 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 H 2 O 2 , 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 H 2 O 2 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 Ca 2+ inhibitors, CaM antagonists and reactive oxygen (ROS) manipulators. Moreover, the analysis of time course of CaM and H 2 O 2 production under water stress showed that the increase in CaM content preceded that of H 2 O 2 . These results suggested that Ca 2+ /CaM and H 2 O 2 were involved in the ABA-induced antioxidant defense under water stress, and the increases of Ca 2+ /CaM contents triggered H 2 O 2 production, which inversely affected the contents of CaM. Thus, a cross-talk between Ca 2+ /CaM and H 2 O 2 may play a pivotal role in the ABA signaling.