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Protein kinase CK2, which consists of two α and two β subunits, plays an essential role in plant development and is implicated in plant responses to abiotic stresses, including salt and heat. However, the function of CK2 in response to heavy metals such as cadmium (Cd) has not yet been established. In this study, the transgenic line CKB4ox , which overexpresses CKB4 encoding the CK2β subunit and has elevated CK2 activity, was used to investigate the potential role of CK2 in response to Cd stress in Arabidopsis thaliana . Under Cd stress, CKB4ox showed reduced root growth and biomass accumulation as well as decreased chlorophyll and proline contents compared with wild type. Furthermore, increased Cd accumulation and a higher H 2 O 2 content were found in CKB4ox , possibly contributing to the inhibition of CKB4ox growth under Cd stress. Additionally, altered levels of Cd and H 2 O 2 were found to be associated with decreased expression of genes involved in Cd efflux, Cd sequestration and H 2 O 2 scavenging. Taken together, these results suggest that elevated expression of CKB4 and increased CK2 activity enhance the sensitivity of plants to Cd stress by affecting Cd and H 2 O 2 accumulation, including the modulation of genes involved in Cd transport and H 2 O 2 scavenging. This study provides direct evidence for the involvement of plant CK2 in the response to Cd stress. [ABSTRACT FROM AUTHOR]