Microwave-facilitated extraction of furanocoumarins onto paper substrates: an imaging technique to analyse spatial distribution and abundance in leaves.

An impediment to studying the implications of fine-scale variation in the distribution of secondary compounds within plants has been an inability to map their distribution. Conventional approaches require fine-scale dissections, followed by extraction and analysis, a strategy which is often limited by the large number of extractions required and by the difficulty in quantifying compounds in very small samples. A method has been developed which allows the microwave-facilitated transfer of furanocoumarins from fresh leaves to two-dimensional substrates (phase separation paper). The fluorescence of these compounds under UV light is enhanced by treatment with base, which probably opens the lactone ring of the compounds. The developed prints are then photographed under UV light and the images analysed with commonly available software programs. Images so obtained for furanocoumarins in wild parsnip foliage revealed that the total fluorescence from extracted furanocoumarins is correlated with the amount of furanocoumarins remaining in the leaf. Thus, the images provide information not only on spatial distribution but also quantitative data.