Abstract

Leaf injury of the ozone-sensitive tobacco cultivar Bel W 3 caused by ozone treatments was prevented to a large extent by root application of putrescine, spermidine or spermine. The titres of soluble free and conjugated putrescine and spermidine were concomitantly increased two- to three-fold after putrescine or spermidine application. The amounts of putrescine and spermidine associated with cell wall or membrane pellet fractions were elevated four to six times above levels of control plants. In order to establish whether the protective effect of polyamines against ozone damage may be caused by their proposed radical scavenging properties, the reactivities of polyamines and putrescine conjugates towards hydroxyl, tert-butoxyl, sulphite radicals and superoxide anions were determined. Free polyamines showed relatively low rate constants with all types of radicals. Only putrescine conjugates with the effective radical scavengers caffeic, ferulic and p-coumaric acid had consistently high rate constants. It is concluded that scavenging of radicals by free polyamines cannot explain the protection against ozone damage observed after exogenous application.