Role of cytokinins in adventitious root formation

Adventitious rooting is an innate de novo process that allows the propagation of many economically important plant species through vegetative means. Cytokinins are known to promote the cell division in meristem. Quite often, it has been reported that when the ratio of cytokinin: auxin is large, it primarily induces bud formation; however, when the ratio of cytokinin: auxin is low, it promotes root formation. It has been experimentally observed that plant roots in which the cytokinin signaling is suppressed show faster growth and development compared to wild-type roots becoming longer and ramified. Exogenous application of cytokinin inhibits root elongation. It happens due to a decrease in the number of dividing cells and size of root meristem. Overall, it has been noticed that the synthesis of cytokinin is essential during root formation. Cytokinins may strongly inhibit rooting; nonetheless, they maybe at low concentrations enhance adventitious root (AR) formation. In the present chapter, we have tried to compile the information on the role of phytohormones in the AR formation with special emphasis on relationship of cytokinin-mediated regulation of AR formation.