An assessment of the roles of furanocoumarins in Heracleum lanatum

Abstract

Several naturally occurring furanocoumarins such as xanthotoxin cause cell damage by complexing with DNA in the presence of long-wave UV light. Heracleum lanatum, an Umbellifer, contains high concentrations of such compounds in the leaves but survives in sunlight and is a food source for insects, fungi, and man. Microscopic investigations and feeding experiments carried out in long-wave UV show that although the compounds are normally isolated in the petiolar oil ducts, the plant can tolerate xanthotoxin uptake in the transpiration stream. Aphids living on Heracleum take up and bind xanthotoxin fed via a cut stem but are unaffected over short term. Such tolerance in plant and aphid may be due to limited cell divisions during the test, but the biochemical basis of tolerance in growing Heracleum is not known. Various fungi, including pathogens of Umbellifers, show differing sensitivities to xanthotoxin plus UV, perhaps because of differing uptake rates and growth habits.