Isoflavonoid formation as an indicator of UV stress in bean (Phaseolus vulgaris L.) leaves

Induction of the isoflavonoid pigment, coumestrol (3,9-dihydroxy-6H-benzofuro-(3,2-c)(1) benzopyran-6-one), in primary leaves of beans (Phaseolus vulgaris L. var Saxa) by ultraviolet (UV) radiation was used as a quantifiable marker for UV damage to a plant system. Coumestrol was induced only by wavelengths below 300 nanometers and its formation could be reversed by treatment with white, but not red light after the UV irradiation period. Formation of coumestrol by UV could also be prevented over a period of 14 hours by simultaneous irradiation with blue light provided that the blue fluence rate was high enough. The results suggest that coumestrol formation is mediated via UV-induced pyrimidine dimer formation in the plant DNA and the photorepair properties of blue light are discussed with respect to possible increases in solar UV due to stratospheric ozone depletion