UV-INDUCED PEROXIDASE AND PHENYLALANINE AMMONIA-LYASE ACTIVITY AND PHASEOLLIN ACCUMULATION IN LEAVES OF PHASEOLUS-VULGARIS L - IN RELATION TO ETHYLENE

Attached or detached leaves of bean (P. vulgaris L.) were irradiated with short-wave UV light (254 nm) which resulted in increased ethylene production, increased activity of soluble and ionically bound peroxidase, increased activity of phenylalanine ammonia-lyase [PAL] and an accumulation of phaseolin [a phytoalexin], accompanied by bronzing of these leaves. In order to evaluate the role of ethylene in this process, plants were pretreated with 0.5 mM aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, or with 0.45 mM 5-methyl-7-chloro-4-ethoxycarboxylmethoxy-2,1,3-benzothiodiazole (DU), a presumed inhibitor of ethylene action. Both compounds showed an inhibitory effect on UV-induced ethylene production. DU stimulated UV-induced peroxidase activity, whereas AVG seemed to decrease UV-induced peroxidase activity. DU and AVG had only a weak inhibitory effect on UV-induced PAL activity. Both compounds retarded slightly the accumulation of phaseollin and the appearance of necrotic symptoms in UV-irradiated bean leaves. Ethephon treatment (500 or 1000 ppm) failed to induce the accumulation of phaseollin in attached or detached leaves of bean. The role of ethylene in UV-induced peroxidase and PAL activity and accumulation of phaseollin in bean leaves is discussed.