Genotoxic effects of chromium onpolytene chromosomes of Chironomus riparius Meigen 1804 (Diptera, Chironomidae)

Abstract Genotoxic effect as tested of chronic exposure to three different concentrations of Chromium (III) on polytene chromosomes of larvae of Chironomus riparius (syn. Chironomus thummi) from the embryonic stage to the IV larval instar for two successive generations. In chromosomes AB, CD, EF and G significant differences of chromosome aberrations were found between exposed and control larvae as well as changes in functional activity (induction of novel puffs not corresponding to those induced during normal larval development in arms A, B, C and E, telomeric and centromeric decondensations especially at telomeres of chromosome G and arm C.). No significant differences were found between the effects of the three treatments nor between the two generations. In chromosome G the Balbiani Ring system (where some permanently active regions are involved in transcription of salivary proteins) appeared as a model for studying the response of the genome to Cr (III) treatment. In approximately one-third of the cells of the exposed larvae, the activity of the Balbiani rings BRc and BRb was reversed. In 10% of the cells of both generations of treated larvae, deletion or collapse of BRc was observed. Pomponlike G chromosomes were present in 6% of the cells. This type of chromoosme appeared either in a very decondesed or in a highly condensed state. In 5 % of the treated larvae the apical region of the chromosome G folded back so that the nucleolar organizer region appeared as if it was at the end of the chromosome. These structural and functional chromosomal changes are interpreted as a reaction of the genome to stressful rearing conditions.