From Cell Division to Stress Tolerance: The Versatile Roles of Cytokinins in Plants

Cytokinins are plant hormones that are essential for plant growth and development and are involved in a variety of processes. They are synthesized by the modification of adenine with an isoprenoid chain, resulting in cytokinins such as isopentenyladenine and zeatin. The levels of these hormones are regulated by conjugation, degradation and oxidation processes that modulate their activity. Cytokinins are perceived by cells through specific receptors that, when activated, trigger signaling cascades responsible for regulating the expression of genes critical for development. In addition, cytokinins interact with other hormones, such as auxins, to coordinate plant growth and architecture. They are transported by the xylem and phloem, allowing them to be distributed to different parts of the plant and to regulate processes such as cell division, morphogenesis and inhibition of leaf senescence, thereby prolonging the vegetative phase. Cytokinins also play a role in plant responses to biotic and abiotic stresses. They influence the expression of defense genes against pathogens and pests and adjust plant metabolism and growth in response to adverse conditions such as drought and salinity. Cytokinins interact in an integrated manner with other stress hormones, such as abscisic acid and ethylene, to coordinate plant responses to environmental challenges. In agriculture, the manipulation of cytokinins, whether by external application or genetic modification, shows great potential for increasing crop yields and improving plant resistance to stress. Advances in molecular biology and gene editing offer new opportunities to precisely modify these functions. This review elucidates recent research on cytokinins, covering their mechanisms of action, interactions with other hormones, and applications in agriculture.