The action of light on the formation of stilbenes and the induction of stilbene synthase in dark-grown and light-grown callus of peanut (Arachis hypogaea) was investigated over the wavelength range from 250 to 400 nm. Ultraviolet light of 260-270 nm had a significant and selective effect on the formation of resveratrol and isopentenylresveratrol. The callus responded by the production of stilbene synthase, with maximal activity appearing 4 h after irradiation with a fluence rate of 1 W m(-2) (270 nm) applied for 10 min. At lower fluence rates, maximal responses in enzyme activity were shifted to longer induction periods. The efficiency of the biosynthetic pathway, and the form and maxima of enzyme profiles depended on the duration of exposure. We failed to demonstrate any significant influence of red light at low energy irradiation (672 nm, 726 nm and 753 nm).

A peanut (Arachis hypogaea L.) cell-suspension culture susceptible to selective induction of stilbene formation was established. The principles of defense responses of the whole plant were found to be retained in the artificial system. The suspension culture was characterized by its growth curve and by various biochemical parameters. In the stationary phase, reached 8 d after transfer to a new medium, the formation of stilbenes and stilbene synthase could be induced without altering the levels of other enzymes. Eighteen hours after applying an artificial elicitor (ultraviolet-C light) or 4 h after eliciting with a crude preparation of Phytophthora cambivora cell walls, phenylalanineammonia-lyase activity was increased eightfold and stilbene-synthase activity 20-fold. The activity of phenylalanine ammonia-lyase reached its peak at a slightly different time from that of stilbene synthase. The main products of L-phenylalanine metabolism in the induced cells were resveratrol, 3,3',5-trihydroxy-4'-methoxystilbene and isopentenylresveratrol. Likewise, feruloyl-CoA reductase, as a parameter of lignin formation, was enhanced following induction, albeit with a different time course and with a less steep increase than found for phenylalanine ammonia-lyase and stilbene synthase.

ABSTlRACFCultured cells of Picea excelsa capable of forming sdlbenes and flavanoids have been established. Unlike needles of intact plants continin piceatannol (3,3',4',5-tetrahydroxystilbene) Stilbene synthase is the key enzyme on the way to fungostatic stilbene derivatives characterized as phytoalexins (6, 8, 1 1). Chalcone synthase initiates the route to a flavanone and thus to other phytoalexins, e.g the one having a pterocarpan skeleton (7). Both enzymes function with the same substrates, malonyl-CoA and pcoumaroyl-CoA, and have in common mechanistic details of catalysis, i.e. nucleophilic attack of anion of acetyl-CoA at the ester group of the aromatic substrate (7, 12, 18). They fold, however, the intermediary polyketide chain topologically in a different way and apply different mechanisms of cyclization.It was, therefore, ofinterest to compare the two enzymes when occurring in the same species. The primary purpose ofthe present study was to determine whether the two catalytic activities were due to a single protein modulated by specific cofactors or to two different proteins.The data presented provide evidence that, although stilbene synthase and chalcone synthase resemble each other in several aspects, they are two proteins not related immunologically.

Callus cultures were established from cotyledons of Arachis hypogaea. The cultured cells were shown to produce stilbene synthase (resveratrol-forming) if the cells were irradiated with 254 nm UV light. The lag period after which the stilbene synthase activity appeared was similar for cultured cells and intact cotyledons.