The Mechanism Of ABA-And Water Stress-Induced Apoplastic H₂O₂ Accumulation In Maize Leaves

In maize(Zea mays L.)cells, the sources of apoplast hydrogen peroxide (H₂O₂) induced by abscisic acid (ABA) and water stress have been proposed. The histochemical and cytochemical localization of ABA and water stress-induced H₂O₂ production in leaves of maize were examined, using 3,3-diaminobenzidine (DAB) and cerium chloride (CeCl₃) staining, respectively. Pretreatment with the NADPH oxidase inhibitors diphenylene iodonium (DPI) and imidazole, the peroxidases (POD) inhibitors NaCN and NaN₃, polyamine oxidases (PAO) inhibitors quinacrine and guazatine, reduced H₂O₂ accumulation induced by ABA and water stress. Among them, NADPH oxidase inhibitors mostly arrested the production of apoplastic H₂O₂ compared to those of the other two enzymes. Further studies showed that exogenous ABA treatment and water stress could enhance the activities of plasma membrane (PM) NADPH oxidase, cell wall POD, apoplast PAO significantly. These results suggested that exogenous ABA treatment and water stress can lead to significant increases in H₂O₂ accumulation in apoplast through up-regulating the activities of the PM NADPH oxidases, cell wall POD and apoplast PAO, and the PM NADPH oxidase play a major role.With the same techniques described above, the apoplastic accumulation of H₂O₂ induced by water stress was arrested in the ABA biosynthesis inhibitor (tungstate)-pretreated maize plants, suggesting that ABA could be a key inducer of apoplasic H₂O₂ production. The activities of PM NADPH oxidase, cell wall POD and apoplast PAO in the tungstate-pretreated maize plants exposed to water stress were descreased significantly compared to those in the non-tugstate pretreated maize plants, suggesting that ABA accumulation induced by water stress participats in the activation of the three enzymes. Those results suggested that endogenous ABA accumulation induced by water stress can lead to the increases in apoplast H₂O₂ through up-regulating the activities of the PM NADPH oxidases, cell wall POD, apoplast PAO.