Both mitogen-activated protein kinase (MAPK) cascades and reactive oxygen species (ROS) are critical to signaling in eukaryotes. Cadmium induces MAPK activation and ROS production in plants. This study aims to identify specific MAPKs activated by CdCl2 in maize roots, and examine the relationship between MAPK activation and ROS production under CdCl2 treatment. Using in-gel kinase assays, immunoprecipitation, and immunoblot analysis, we identified 43 and 45 kDa ERK-like MAPKs in response to CdCl2. Further analysis revealed that ZmMPK3-1 and ZmMPK6-1 correspond to the 43 and 45 kDa MAPKs, respectively. In addition, CdCl2 induced ROS production prior to the activation of ZmMPK3-1 and ZmMPK6-1. Inhibition of ROS attenuated Cd-activation of ZmMPK3-1 and ZmMPK6-1, whereas inhibition of MAPK signaling did not disturb Cd-induced ROS production. Collectively, these results indicate that, in maize roots, cadmium stress activates ZmMPK3-1 and ZmMPK6-1 via ROS induction. (C) 2019 Elsevier Inc. All rights reserved.