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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 CdCl 2 in maize roots, and examine the relationship between MAPK activation and ROS production under CdCl 2 treatment. Using in-gel kinase assays, immunoprecipitation, and immunoblot analysis, we identified 43 and 45 kDa ERK-like MAPKs in response to CdCl 2. Further analysis revealed that ZmMPK3-1 and ZmMPK6-1 correspond to the 43 and 45 kDa MAPKs, respectively. In addition, CdCl 2 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. • Cadmium activates 43 and 45 kDa ERK-like MAPKs in maize roots. • ZmMPK3-1 and ZmMPK6-1 correspond to the 43 and 45 kDa MAPKs, respectively. • Cadmium induces ROS production prior to the activation of ZmMPK3-1 and ZmMPK6-1. • Inhibition of ROS attenuates Cd-activation of ZmMPK3-1 and ZmMPK6-1. • Cadmium up-regulates expression of ZmRBOHs , but not ZmMPK3-1 and ZmMPK6-1. [ABSTRACT FROM AUTHOR]