[The mechanism of ABA-induced apoplastic H2O2 accumulation in maize leaves]

In maize (Zea mays L.) cells, the sources of apoplast hydrogen peroxide (H(2)O(2)) induced by abscisic acid (ABA) has been proposed. Histochemical and cytochemical localization of ABA-induced H(2)O(2) production in leaves of maize was examined, using 3, 3-diaminobenzidine (DAB) and cerium chloride (CeCl(3)) staining respectively. Pretreatment with two different inhibitors for each enzymes, with diphenylene iodonium (DPI) and imidazole against NADPH oxidase, NaCN and NaN(3) against peroxidases (POD), and quinacrine and guazatine against polyamine oxidases (PAO), reduced H(2)O(2) accumulation induced by ABA. Among them, NADPH oxidase inhibitors arrested the production of apoplastic H(2)O(2) most strongly (Figs.1,2). Further studies showed that exogenous ABA treatment could enhance the activities of plasma membrane (PM) NADPH oxidase, cell wall POD and apoplast PAO significantly. Moreover, the activity of PM NADPH oxidase kept increasing before 1.5 h, while the other two enzymes began to decrease at 0.5 h within 2 h by ABA treatment (Fig.3). The results suggest that exogenous ABA treatment can lead to significant increases in H(2)O(2) accumulation in apoplast through up-regulating the activities of the PM NADPH oxidases, cell wall POD and apoplast PAO, of which the first one plays a central role in ABA-induced apoplastic H(2)O(2) accumulation.