THE PRODUCTION OF COUMARIN PHYTOALEXINS IN DIFFERENT PLANT ORGANS OF SUNFLOWER (HELIANTHUS-ANNUUS L)

The production and excretion of the coumarins scopoletin, its 7-O-gluc oside scopolin, and ayapin were studied in whole sunflower plants and isolated organs, using a previously reported abiotic elicitation syste m (Gutierrez et al., 1995). The kinetics of-coumarin accumulation in t issue and their excretion to the incubation medium was similar but the amount detected in the medium was from 4 to 10 times higher, indicati ng that these compounds are largely excreted after their synthesis. Di fferently from socopoletin and ayapin, scopolin was only produced in h ypocotyls and roots of seedlings. Differences among sunflower cultivar s with respect to their capacity for coumarin synthesis have been foun d. Evidence was also obtained that following treatment with abiotic el icitors coumarin phytoalexins may be synthesized in the aerial part of the plant and then translocated to the root where they are exported i nto the root medium. Analysis of coumarin content in the incubation me dium is the simplest and most convenient experimental approach to the study of coumarin phytoalexin production in sunflowers. Data presented confirm earlier observations, indicating that their synthesis must be induced, being tissue-dependent and developmentally regulated.