Rearrangements in the salivary gland chromosomes of Chironomus riparius Mg. (Diptera, Chironomidae) following exposure to lead

The effect of lead (Pb) nitrate on the structural and functional organization of the polytene chromosomes of Chironomus riparius larvae was examined. No specimens with standard polytene chromosomes were found in the material treated with different concentrations of Pb ions. The polytene chromosomes of all individuals exposed to Pb showed various somatic chromosome rearrangements (heterozygous inversions, deletions, duplications and deficiencies), which were not detected in the studied controls. Deletions in chromosome G occurred in a high frequency resulting in the formation of so called "pompons". The activity of Balbiani rings (BRs) and nucleolar organizer (NOR) significantly decreased with increasing the concentrations of Pb ions. The number of BRc/BRb showing little or no activity (-/-) increased following exposure of the F2 generation to low and high concentrations of Pb ions. Sections of the polytene chromosomes where somatic aberrations were concentrated are considered as "weak" sites. It was shown that in these sites were distributed repetitive DNA elements (Alu and Hinf) that might be activated by stress agents and generated many chromosome rearrangements. It is evident that lead nitrate has a marked genotoxic effect on the salivary polytene chromosomes of Chironomus riparius.