effect of reactive oxygen species on ethylene production induced by osmotic stress in etiolated mungbean seedling

After 10 h osmotic stress in 25% polyethylene glycol (PEG6000) solution (-1.8 MPa) at 25 °C in darkness, the etiolated mungbean seedlings were transferred to pure water for recovery. The ethylene release rate and the level of reactive oxygen species (ROS), including superoxide radical (O2-) and hydrogen peroxide (H2O2), were investigated during the recovery process. The results showed that ethylene production rate and amount of ROS increased dramatically after osmotic stress, and a close correlation was observed between ethylene release rate and concentrations of ROS. Inhibitors of ethylene biosynthesis, aminoethoxyvinylglycine (AVG) or aminooxyacetic acid (AOA), could reduce the ethylene release rate, but had no significant influence to the content of O2- and H2O2. As well as, silver thiosulfate (STS), an inhibitor of ethylene action, exhibited no obvious effect to the concentration of ROS, showing stress-inducible ethylene was not the cause for the increase of stress-inducible ROS. On the other hand, exogenous generator of superoxide radical (methylviologen, MV, or sodium dithionite, Na2S2O4) could enhance the ethylene production evidently, which could be inhibited by exogenous scavenger of superoxide radical (superoxide dismutase, SOD, or 1, 4-diazabicyclo (2,2,2) octane, DABCO). However, either exogenous H2O2 or catalase (CAT) had no significant influence on ethylene production. The results suggested that it was superoxide radical but not H2O2which was involved directly in osmotic stress-inducible ethylene biosynthesis. The dual-role of superoxide radical on stress ethylene biosynthesis was also discussed.