Cytokinin interaction with free radical metabolism and senescence: Effects on endogenous lipoxygenase and purine oxidation

A typical system comprising xanthine‐xanthine oxidase, which produces superoxide free radicals, significantly increased endogenous levels of the senescence‐associated lipoxygenase enzyme while cytokinin reversed this effect. It is suggested that in its interaction with free radicals cytokinin may have a dual effect: a) it may inhibit purine oxidation by the formation of a 2,8 dihydroxy purine which lowers the substrate affinity of xanthine oxidase; b) it may act as a direct free radical scavenger by virtue of H abstraction from the α‐carbon atom in the amine bond.