Studies on the photobiological activity of two naturally occurring furochromones, visnagin and khellin, in Chlamydomonas reinhardtii.

Irradiation of arg-1 cells of the green alga Chlamydomonas reinhardtii with UV-A in the presence of visnagin (10 microg/ml) produced weak mutagenic effects when a fluence rate of 5.1 W/m2 and fluences of 1.5-36.7 kJ/m2 were applied. A maximum number of revertants was obtained at approximately 9.2 kJ/m2. When a fluence rate of 20.4 W/m2 was used the photomutagenicity of visnagin was markedly enhanced with fluences of > or = 36.7 kJ/m2. In survival experiments with a fluence rate of 5.1 W/m2 the surviving fraction decreased continuously to approximately 4%. In experiments with a fluence rate of 20.4 W/m2, however, higher survival rates were observed compared at equal UV-A doses. Visnagin was much less phototoxic and photomutagenic than bergapten when compared at equimolar concentrations and equal UV-A doses. Re-irradiation with UV-A in the absence of unbound visnagin did not alter survival and mutagenicity which had been induced by the first treatment. The mutation frequency plotted versus the UV-A fluence exhibited second-order kinetics. Khellin showed only marginal photosensitizing capacity and no significant mutagenicity up to a concentration of 100 microg/ml and a total UV-A fluence of 73.4 kJ/m2.