ABSTRACT
knowledge of the role of cytokinins in controlling cell division is of paramount importance for both fundamental and applied biology. This chapter discusses cytokinin regulation of the cell cycle in nonhabituated and nontumorous plant cells. The stimulatory effect of cytokinins on cell division was initially observed in in vitro cultured tobacco pith tissue and confirmed with other tissues, cells, and protoplasts of a variety of plants. The demonstration of cytokinins controlling the cell cycle in intact plants requires the use of either plants grown under conditions resulting in suboptimal cytokinin production or the analysis of tissues deficient in cytokinins. In normal plants some organs, such as the correctively inhibited axillary buds, are deficient in cytokinins. The endogenous cytokinin level is usually high in mitotically active tissues, including root and shoot meristems, procambium, and cambium. Cytokinins arc intimately involved in the regulation of the cell cycle in both cultured cells and meristems of intact plants.
