o-Phenylenediamine-induced DNA damage and mutagenicity in tobacco seedlings is light-dependent

Of the three isomers of the aromatic amine phenylenediamine. (PDA), only o- PDA, but not m- and p-PDA, induced DNA damage (as measured by the Comet ass ay), and somatic mutations in the leaves of the chlorophyll-deficient teste r strain Nicotiana tabacum var. xanthi. With increasing light intensity (0, 30, 80 or 140 mu mol m(-2) s(-1) photosynthetic photon fluence, rate) duri ng a 72 h mutagenic treatment of tobacco seedlings, o-PDA-induced DNA damag e and the yield of somatic mutations were significantly increased. The pero xidase inhibitor diethyldithiocarbamate (DEDTC) repressed o-PDA-induced DNA damage. The effect of light is caused by the light-dependent increase of p eroxidase activity and the accumulation of hydrogen peroxide, which partici pate in the metabolic activation of the promutagen o-PDA to mutagenic produ ct(s). In contrast, DNA damage induced by the direct-acting alkylating muta gen ethyl methanesulphonate was the same whether treatment was in the light or in the dark, and was not repressed by the peroxidase inhibitor DEDTC. ( C) 2001 Elsevier Science B.V. All rights reserved.