The Roles And Signaling Of H₂O₂ And Calcium/Calmodulin In The ABA-Induced Antioxidant Defense In Leaves Of Maize Plants

The histochemical and cytochemical localization of abscisic acid (ABA)-induced H₂O₂ production in leaves of maize (Zea mays L.) plants were examined, using 3,3-diaminobenzidine (DAB) and CeCl₃ staining, respectively. H₂O₂ generated in response to ABA treatment was detected within 0.5 h in major and minor veins of the leaves and maximized at about 2-4 h, and then declined. ABA-induced H₂O₂ accumulation was observed only in apoplast of the mesophyll cells, and the greatest accumulation occurred in the walls of mesophyll cells facing large intercellular spaces. Meanwhile, the applications of NADPH oxidase inhibitor and ROS scavengers showed that NADPH oxidase is required for ABA-induced H₂O₂ accumulation, and H₂O₂ involves ABA-induced the increase in the activities of the chloroplastic and cytosolic antioxidant enzymes, such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR).The histochemical and cytochemical localization of water stress-induced H₂O₂ production in leaves of ABA-deficient vp5 mutant and wild-type maize plants were also examined. H₂O₂ generated in response to water stress treatment was detected within 1 h and maximized at about 2-4 h, and then declined. Water stress led to the H₂O₂ accumulation of apoplast, chloroplast, mitochondrion, peroxisome and xylem vessels of wild-type maize leaves. The results from histochemical detection show that pretreatment with the NADPH oxidase inhibitor DPI and the ROS scavengers CAT and SOD almost completely arrested the increase of water stress-induced H₂O₂ production in the leaves of wild-type maize. Meanwhile, the results from cytochemical localization showed that these manipulators also almost completely arrested the increase of H₂O₂ accumulation in the apoplast, but did not affect the increase of water stress-induced H₂O₂ accumulation in chloroplasts, mitochondrian, peroxisomes. These results indicate that NADPH oxidase is involved in water stress-induced H₂O₂ accumulation in apoplast and H₂O₂ accumulation in intracellular do not depend on apoplast H₂O₂ accumulation. Furthermore, H₂O₂ accumulation in apoplast is a major source of water stress-induced H₂O₂ accumulation in...