Inhibition of NADPH oxidase increases defense enzyme activities and improves maize seed germination under Pb stress

Contaminated soil accumulated high levels of Pb, which shows great risk to human health and crop growth. To alleviate Pb impaired seed germination and seedling growth, effects of three methods were compared. Here, effects of the heavy metal chelator EDTA, reactive oxygen species (ROS) scavenger (e.g. dimethylthiourea/DMTU, glutathione and melatonin), and specific inhibitors of NADPH oxidase or NOX (e.g. imidazole/IMZ and diphenylene iodonium/DPI), on maize seed germination and seedling growth were examined under Pb stress. IMZ and DPI increased seed germination by 1-2-fold under Pb stress, compared with less than 50% for ROS scavengers, while EDTA decreased germination. Pb-induced H2O2 accumulation was reduced more dramatically by IMZ than DMTU. Compared with DMTU, Pb-impaired SOD and CAT enzyme can be reversed more significantly by IMZ. Thus, inhibiting the NOX was more efficient than using ROS scavengers for improving seed germination under Pb stress. Compared with EDTA and ROS scavenger, IMZ and DPI treatment cannot protect seedling growth under Pb stress. In addition, IMZ is cheap and highly efficient, making it suitable for improving seed germination in Pb-polluted soil.