Chironomids (Diptera) and their salivary gland chromosomes as indicators of trace-metal genotoxicity.

摘要

The long-term impact of pollution in freshwater aquatic environments can be assessed realistically only if the mutagenic effects of pollutants on organisms inhabiting aquatic biotopes are evaluated. To do this, the larvae of Chironomids (Diptera) can serve as suitable indicators of potential environmental genotoxicity. These larvae exhibit aberrations in their polytene chromosomes, which, when analyzed, indicate an early response to toxicity more efficiently than morphological analysis, up to now the usual technique. Chironomids have excellent salivary gland chromosomes with well-defined bands and permanent somatic pairing, where there are two important regions of active transcription - Balbiani rings (BRs) and Nucleolar organizers (NOR). We have described the responses of different Chironomid species in two situations: in the field and in the laboratory, where we performed Cr, Al, Pb and Cu trace-metal-exposure experiments with Chironomus riparius. In both situations, the genome response consisted in a statistically significant increase in somatic chromosome aberrations and decrease in BR and NOR activity to levels lower than those of larvae under standard conditions. The main chromosome aberrations consisted in inversions, amplifications, deletions and deficiencies. Deletions in the chromosome G in C. riparius transformed it into a pompon-like structure. Chromosome aberrations were not randomly distributed: they occurred mainly in sites with repetitive DNA elements that have a highly interspersed location in the C. riparius genome. Hence C. riparius is the species most likely to produce aberrations and can be used as a model for cost-effective monitoring of the early genomic response to trace metals and other stress agents.