TRANSGENIC PERIWINKLE TISSUES OVERPRODUCING CYTOKININS DO NOT ACCUMULATE ENHANCED LEVELS OF INDOLE ALKALOIDS

Cytokinins play a critical role in several aspects of plant growth, me tabolism and development. We previously reported that adding cytokinin s to the culture medium of a suspension-cultured cell line of periwink le increased the accumulation of indole alkaloids, and our aim was to compare the effect of exogenously-applied cytokinins with that of elev ated levers of endogenous cytokinins on indole alkaloid production. We used an Agrobacterium tumefaciens strain yielding a plasmid with the isopentenyl transferase gene under control of its own promoter. Co-cul ture of suspension cells with the bacteria caused a severe stress resp onse leading to cell necrosis. Therefore, we failed to transform this material but we succeeded in transforming periwinkle cotyledons. We ve rified that callus cultures generated from the isopentenyl transferase -transgenic cotyledons accumulated high cytokinin concentrations. Trea ting normal callus cultures (generated from untransformed cotyledons) with cytokinins enhanced their alkaloid production. By contrast, the e nhanced concentration of endogenous cytokinins in transgenic calli did not increase indole alkaloid production, and thus did not mimic the e ffect of exogenously-applied cytokinins. Hypothesis to explain this di screpancy are discussed.