Cytokinins, a class of plant-specific hormones, play a central role in cell cycle regulation and developmental programs. Due to the lack of biosynthetic and signaling mutants, the regulatory roles of cytokinins have not been well understood. This study genetically engineered cytokinin oxidase (CKX) expression in transgenic tobacco plants to reduce their endogenous cytokinin content. The results showed that cytokinin-deficient plants developed stunted shoots with smaller apical meristems, prolonged plastochrones, and reduced leaf cell production, indicating an absolute requirement of cytokinins for leaf growth. In contrast, root meristems of transgenic plants were enlarged and gave rise to faster-growing and more branched roots. These findings suggest that cytokinins are important regulatory factors for plant meristem activity and morphogenesis, with opposing roles in shoots and roots. The study also demonstrated that cytokinins control both root growth rate and the generation of new root meristems. The results provide insights into the regulatory functions of cytokinins and highlight the potential of manipulating CKX gene expression to modulate growth characteristics and yield parameters in crop plants.Cytokinins, a class of plant-specific hormones, play a central role in cell cycle regulation and developmental programs. Due to the lack of biosynthetic and signaling mutants, the regulatory roles of cytokinins have not been well understood. This study genetically engineered cytokinin oxidase (CKX) expression in transgenic tobacco plants to reduce their endogenous cytokinin content. The results showed that cytokinin-deficient plants developed stunted shoots with smaller apical meristems, prolonged plastochrones, and reduced leaf cell production, indicating an absolute requirement of cytokinins for leaf growth. In contrast, root meristems of transgenic plants were enlarged and gave rise to faster-growing and more branched roots. These findings suggest that cytokinins are important regulatory factors for plant meristem activity and morphogenesis, with opposing roles in shoots and roots. The study also demonstrated that cytokinins control both root growth rate and the generation of new root meristems. The results provide insights into the regulatory functions of cytokinins and highlight the potential of manipulating CKX gene expression to modulate growth characteristics and yield parameters in crop plants.