DNA damage checkpoints delay mitotic cell-cycle progression in response to DNA stress, stalling the cell cycle to allow time for repair. CDKB is a plant-specific cyclin-dependent kinase (CDK) that is required for the G2/M transition of the cell cycle. In Arabidopsis, DNA damage leads the degradation of CDKB2, and the subsequent G2 arrest gives cells time to repair damaged DNA. G2 arrest also triggers transition from the mitotic cycle to endoreduplication, leading to the presence of polyploid cells in many tissues. In contrast, in rice (Oryza sativa), polyploid cells are found only in the endosperm. It was unclear whether endoreduplication contributes to alleviating DNA damage in rice(Oryza sativa). Here, we show that DNA damage neither down-regulatesOrysa;CDKB2;1 nor induces endoreduplication in rice. Furthermore, we found increased levels ofOrysa;CDKB2;1 protein upon DNA damage. These results suggest that CDKB2 functions differently in Arabidopsis and rice in response to DNA damage. Arabidopsis may adopt endoreduplication as a survival strategy under genotoxic stress conditions, but rice may enhance DNA repair capacity upon genotoxic stress. In addition, polyploid cells due to endomitosis were present inCDKB2;1knockdown rice, suggesting an important role forOrysa;CDKB2;1 during mitosis.