Salinity-induced decrease in NADPH oxidase activity in the maize leaf blade elongation zone

We reported previously that salinity-induced elongation constraints in the expansion zone of maize leaves are associated with reduced reactive oxygen species (ROS) production and could be alleviated by the addition of ROS. The NaCl effect was salt-specific and not osmotic. This paper explores the causes for such reduction. The decrease in ROS levels under salinity was not accompanied by increases in soluble apoplastic antioxidant activities such as superoxide dismutase, peroxidases and ascorbate. In experimental systems devoid of cell walls (protoplasts and membrane fractions) superoxide anion (O2−) production was inhibited by 50 and 100 mM NaCl, 50 μM DPI, 10 mM EGTA, and 5 mM verapamil, a Ca2+ channel inhibitor. Inhibitory effects of NaCl and reduced Ca2+ supply were also observed in in gel assessment of O2−-generating activity. The main activity band excised from the ND-PAGE was recognized by an antibody against the C-terminal portion of the tomato gp91phox homolog. These results indicate the radical dotO2−-generating activity negatively affected by NaCl was compatible with that of plasma membrane NADPH oxidase.