Figure 1.

Paraquat redox cycling and generation of reactive oxygen species (ROS). (A) Paraquat cycles between oxidation states by accepting an election from reducing equivalents such as NAD(P)H, and donating an electron to oxygen (O₂). (B) Electron donation to O₂ results in the formation of superoxide (${\mathrm{O}}_2^{●–}$), the precursor of other ROS. Superoxide dismutase catalyzes the conversion of ${\mathrm{O}}_2^{●–}$ to hydrogen peroxide (H₂O₂), whereas (C) iron-catalyzed Fenton-like reactions convert H₂O₂ to the hydroxyl radical (^●OH) (Gray et al., 2007; Reczek et al., 2017) .