The production of coumarin phytoalexins in different plant organs of sunflower ( Helianthus annuus L.)

Abstract

Summary The production and excretion of the coumarins scopoletin, its 7-O-glucoside scopolin, and ayapin were studied in whole sunflower plants and isolated organs, using a previously reported abiotic elicitation system (Gutierrez et al., 1995). The kinetics of coumarin accumulation in tissue and their excretion to the incubation medium was similar but the amount detected in the medium was from 4 to 10 times higher, indicating that these compounds are largely excreted after their synthesis. Differendy from socopoletin and ayapin, scopolin was only produced in hypocotyls and roots of seedlings. Differences among sunflower cultivars with respect to their capacity for coumarin synthesis have been found. Evidence was also obtained that following treatment with abiotic elicitors coumarin phytoalexins may be synthesized in the aerial part of the plant and then translocated to the root where they are exported into the root medium. Analysis of coumarin content in the incubation medium 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.