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Selective effects of chemical mutagens on the chromosomes of Vicia faba as influenced by segment transpositions
232
ist INTERNATIONAL CONFERENCE, ASILOMAR
41 RIEGER, R., Zentralinstitut ffir Genetik und Kulturpflanzenforschung der Akademie der Wissenschaften, Gatersleben (German Democratic Republic).
Selective effects of chemical mutagens on the chromosomes of Vicia
faba as influenced by segment transpositions Newly synthesized karyotypes of V. faba with all chromosomes easily interdistinguishable due to interchanges and inversions have been used to study the intrachromosomal distribution of chromatid aberrations induced by energy-rich radiation or chemical mutagens. X-rays, E3H~thymidine, E3H~uridine, various alkylating agents, hydroxylanfine, ethanol, mitomycin C, maleic hydrazide and N-methyl-N-nitrosourethane were among the agents tested for selective effects on certain regions of the chromosomes. Preferential localization of induced chromatid aberrations was found after application of all agents with the exception of N-methyl-N-nitrosourethane and X-rays. Aberration clustering occurred in or immediately adjacent to chromosome segments which represent constitutive heterochromatin. Which of these segments showed up as an aberration 'hotspot' depended on the mutagen applied. Transposition of potential hotspot regions to other places in the karyotype indicates that the hotspot character of at least some segments is influenced by their position in the karyotype and may be wiped out or induced by appropriate segment positioning. Hotspots localized in structurally identical chromosomes in different karyotypes may also become influenced by their karyotypical background, i.e., certain structural features of the other chromosomes contained in the complement, and may then react to the treatment with quantitatively modified aberration accumulation. The same is true for the spectrum of induced chromatid aberrations. Appropriate karyotype repatterning may furthermore modify the mutagen-sensitivity of the chromosome complement. All these findings are indications of the complex processes involved in the production of chromosome structural changes which deserve attention in environmental mutagen testing.
42 RINEHART, ROBERT R., MURRAY J. TOWLE, FRANK J. RATTY AND EDWARD MACK,
California State University at San Diego, Calif. (U.S.A.).
The mutagenicity of oxides of nitrogen and methylbenzeneamine in
Salmonella typhimurium The mutagenic effects of exposing Salmonella typhimurium to various concentrations of oxides of nitrogen were investigated. In general, it was found that 2400 ppm of NO~ induced an approximate io-fold increase in histidine reversion frequencies and a 23% decrease in cell survival after 30 min of treatment. Exposures of 377 ppm NO~ induced a i6-fold increase in mutations after I-h treatment; 37.7 ppm NO2 induced a 4.8-fold increase after a 3-h treatment and 11.3 ppm NO~ produced a 54% increase in mutations after a 24-h treatment. No significant decreases in cell survival frequencies were associated with the lower NO~ concentrations used. Methylbenzene-
ist INTERNATIONAL CONFERENCE, ASILOMAR
41 RIEGER, R., Zentralinstitut ffir Genetik und Kulturpflanzenforschung der Akademie der Wissenschaften, Gatersleben (German Democratic Republic).
Selective effects of chemical mutagens on the chromosomes of Vicia
faba as influenced by segment transpositions Newly synthesized karyotypes of V. faba with all chromosomes easily interdistinguishable due to interchanges and inversions have been used to study the intrachromosomal distribution of chromatid aberrations induced by energy-rich radiation or chemical mutagens. X-rays, E3H~thymidine, E3H~uridine, various alkylating agents, hydroxylanfine, ethanol, mitomycin C, maleic hydrazide and N-methyl-N-nitrosourethane were among the agents tested for selective effects on certain regions of the chromosomes. Preferential localization of induced chromatid aberrations was found after application of all agents with the exception of N-methyl-N-nitrosourethane and X-rays. Aberration clustering occurred in or immediately adjacent to chromosome segments which represent constitutive heterochromatin. Which of these segments showed up as an aberration 'hotspot' depended on the mutagen applied. Transposition of potential hotspot regions to other places in the karyotype indicates that the hotspot character of at least some segments is influenced by their position in the karyotype and may be wiped out or induced by appropriate segment positioning. Hotspots localized in structurally identical chromosomes in different karyotypes may also become influenced by their karyotypical background, i.e., certain structural features of the other chromosomes contained in the complement, and may then react to the treatment with quantitatively modified aberration accumulation. The same is true for the spectrum of induced chromatid aberrations. Appropriate karyotype repatterning may furthermore modify the mutagen-sensitivity of the chromosome complement. All these findings are indications of the complex processes involved in the production of chromosome structural changes which deserve attention in environmental mutagen testing.
42 RINEHART, ROBERT R., MURRAY J. TOWLE, FRANK J. RATTY AND EDWARD MACK,
California State University at San Diego, Calif. (U.S.A.).
The mutagenicity of oxides of nitrogen and methylbenzeneamine in
Salmonella typhimurium The mutagenic effects of exposing Salmonella typhimurium to various concentrations of oxides of nitrogen were investigated. In general, it was found that 2400 ppm of NO~ induced an approximate io-fold increase in histidine reversion frequencies and a 23% decrease in cell survival after 30 min of treatment. Exposures of 377 ppm NO~ induced a i6-fold increase in mutations after I-h treatment; 37.7 ppm NO2 induced a 4.8-fold increase after a 3-h treatment and 11.3 ppm NO~ produced a 54% increase in mutations after a 24-h treatment. No significant decreases in cell survival frequencies were associated with the lower NO~ concentrations used. Methylbenzene-