Oriented cell division plays a critical role in plant growth and development. In the Arabidopsis root apical meristem, it ensures the correct distribution and tissue allocation of different cell types by guiding cells to divide in a specific direction, thereby maintaining meristem stability and function. Despite its importance in regulating root apical meristem development, the mechanisms controlling the onset and duration of oriented cell division remain largely unexplored. In this thesis, we employed chemical genetics, classical genetics and single-cell transcriptomics to investigate the regulation of oriented cell division and its impact on the size of the Arabidopsis root apical meristem.