Characterization and inducibility of a scopoletin-degrading enzyme from sunflower

The role of an enzyme, tentatively identified as a peroxidase, in the metabolism of the coumarin phytoalexin scopoletin has been investigated in sunflower. When sunflower leaf discs were fed with 0.05 mM scopoletin the coumarin was initially slowly metabolized by glycosylation. After a delay of 24 hr scopoletin then rapidly disappeared and this could not be accounted for by the accumulation of extractable metabolites. Instead, the disappearance of scopoletin was associated with the increased activity of a peroxidase which metabolized the coumarin to a coloured insoluble metabolite. The scopoletin-peroxidase was purified 222-fold and had a M-r of 46 000 and was associated with peroxidase activity toward esculetin and guaiacol, but not ayapin, In leaves, the activity of the scopoletin-peroxidase was increased locally around wound sites and its activity could be elevated al more distant sites by treatment with CuCl2 or salicylic acid. The scopoletin-peroxidase activity was also identified in peas, tobacco and potato. (C) 1997 Elsevier Science Ltd. All rights reserved.