Diseased celery infected with the fungus Sclerotinia sclerotiorum had greatly increased levels of three phytoalexin furocoumarins, namely psoralen, 5-MOP, and 8-MOP, which are responsible for skin photosensitivity. Storage of freshly harvested celery at 4 °C resulted in clear signs of fungal infection, from latent fungus, appearing within 23-29 days, with concomitant increases in total furocoumarin levels from 1.84 ppm (wet weight) to 43.82 ppm and with occasional samples as high as 95.52 ppm. Psoralen, the most active of the DNA photoalkylating furocoumarins, increased during storage from <0.06 to 14.14 ppm and on occasions 24.24 ppm. A combination of HPLC, TLC, and an extremely sensitive photobiological assay was used to obtain these results, which are discussed in relation to possible health consequences.

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The photobiological properties of a novel, naturally occurring furoisocoumarin isolated from coriander and named coriandrin are described. Photosensitized lethal and mutagenic effects in bacteria indicate that it is more active than psoralen. It is a weak frameshift mutagen in the dark. Mammalian cells in tissue culture are photosensitized more actively with coriandrin than with psoralen even though preliminary evidence from interrupted radiation experiments and DNA analysis suggest that coriandrin does not form DNA interstrand crosslinks. Sister chromatid exchanges were induced with a unit dose of 1.1 x 10(-2) with coriandrin; the value for psoralen is 3 x 10(-3). Coriandrin appears to be metabolized more rapidly than furocoumarins by liver mixed function oxidases. Skin photosensitizing activity is very weak compared with psoralen, a surprising observation considering its potency in biological test systems.

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