Recombinagenic activity of four compounds in the standard and high bioactivation crosses of Drosophila melanogaster in the wing spot test

The wing somatic mutation and recombination test (SMART) using Drosophila m elanogaster was employed to determine the recombinagenic and mutagenic acti vity of four chemicals in an in vivo eukaryotic system. Two different cross es involving the wing cell markers mwh and flr(3) were used: the standard c ross and a high bioactivation cross. The high bioactivation cross is charac terized by a high constitutive level of cytochromes P450 which leads to an increased sensitivity to a number of promutagens and procarcinogens. Three- day-old larvae derived from both crosses were treated chronically with the oxidizing agent potassium chromate and with the three procarcinogens cyclop hosphamide, p-dimethylaminoazobenzene and 9,10-dimethylanthracene. From bot h crosses two types of progeny were obtained: marker-heterozygous and balan cer-heterozygous. The wings of both genotypes were analysed for the occurre nce of single and twin spots expressing the mwh and/or flr(3) mutant phenot ypes. In the marker-heterozygous genotype the spots can be due either to mi totic recombination or to mutation. In contrast, in the balancer-heterozygo us genotype only mutational events lead to spot formation, all recombinatio n events being eliminated. The oxidizing agent potassium chromate was equal ly and highly genotoxic in both crosses. Surprisingly, the promutagen cyclo phosphamide also showed equal genotoxicity in both crosses, whereas p-dimet hylaminoazobenzene was negative in the standard cross, but clearly genotoxi c in the high bioactivation cross. 9,10-Dimethylanthracene showed a rather weak genotoxicity in the high bioactivation cross. Analyses of the dose-res ponse relationships for mwh clones recorded in the two wing genotypes demon strated that all four compounds are recombinagenic. The fraction of all gen otoxic events which are due to mitotic recombination ranged from 83% (9,10- dimethylanthracene) to 99% (p-dimethylaminoazobenzene). These results demon strate that the wing spot test in Drosophila is most suited to the detectio n of recombinagenic activity of genotoxic chemicals.