Cytokinins are plant-specific chemical hormones. They encourage cell division, or cytokinesis, in plant roots and shoots and are essential for controlling the plant cell cycle and a variety of developmental processes. They influence apical dominance, axillary shoot growth, and leaf senescence in addition to being primarily responsible for cell division in plant roots and branch systems.
The majority of cytokinins are typically produced in the roots from adenine. For healthy growth and cell differentiation, they travel upward in the xylem tissue and into the leaves and fruits. All types of complex plants, bacteria, mosses, and fungi contain the majority of these hormones. Cytokinins come in over 200 different varieties, both natural and synthetic.
The first cytokinin discovered was an adenine (aminopurine) derivative called "agonist" (6-furfurylaminopurine), which was isolated as a DNA degradation product.
Cytokinins work in conjunction with auxin to delay senescence, at least in its early stages. Senescence is characterized by the yellowing of individual leaves, which happens as a result of the destruction of chlorophyll and the breakdown of proteins. By maintaining the protein and chlorophyll content of the leaf as well as the structure of the chloroplast, cytokinins prevent yellowing.
Commercially, cytokinins are employed to keep greens from yellowing during storage. In horticultural tissue culture, high auxin and low cytokinin conditions result in the formation of roots, whereas low auxin and high cytokinin conditions result in the growth of shoots.