Mechanism of cytokinin action: There are enough evidences to prove that cytokinin stimulate cell division by affecting nucleic acid metabolism and protein synthesis. Though exact mechanism of their action is not known, it has been found that cytokinins increase internal production of sugar and other solutes, thereby retarding yellowing of leaves due to senescence. In addition, cytokinins affect synthesis of some specific enzymes necessary for synthesis of specific amino acids and check protein degradation during senescence.