Assuntos
Cotilédone/genética , Testes de Mutagenicidade/métodos , Nicotiana/genética , Plantas Tóxicas , Cotilédone/efeitos dos fármacos , Reparo do DNA/efeitos dos fármacos , Reparo do DNA/genética , Genes de Plantas/efeitos dos fármacos , Metanossulfonato de Metila/toxicidade , Metilnitrosoureia/toxicidade , Mutagênicos/toxicidade , Plantas Geneticamente Modificadas , Sensibilidade e Especificidade , Nicotiana/efeitos dos fármacosRESUMO
Two transgenic clones X3 and X15 of Nicotiana tabacum var. Xanthi, heterozygous in two genes (a1 and a2) for chloroplast differentiation and transformed with the E. coli DNA repair gene ada cloned downstream from the 1' direction of the dual mas promoter, differed in the expression of the ada gene, in the number of copies of integrated T-DNA and in the response to the mutagenic action of alkylating and non-alkylating agents. The X3 genome contained four copies and the X15 genome one copy of T-DNA, nevertheless the expression of the ada gene, measured by the activity of O6-alkylguanine DNA alkyltransferase (ATase), was about six times higher in X15 than in X3. ATase activity in both clones was highest in extracts from callus whereas very low (X15) or no (X3) activity was detected in leaf extracts. This may explain the lack of difference between X15 and non-transformed tobacco (NTX) in the frequency of N-methyl-N-nitrosourea (MNU)-induced somatic mutations in leaves. In contrast, the frequency of somatic mutations in X3 was about 2-5 times higher than in NTX and X15 after the same doses of MNU, methyl methanesulfonate, maleic hydrazide and gamma-rays. Alteration of plant gene(s) essential in mutation pathway(s) by insertion of T-DNA or by somaclonal variation may explain the higher sensitivity of the X3 clone.
Assuntos
Alquilantes/toxicidade , Proteínas de Escherichia coli , Escherichia coli/genética , Raios gama , Hidrazida Maleica/toxicidade , Mutagênicos/toxicidade , Nicotiana/genética , Plantas Tóxicas , Alquilantes/metabolismo , Proteínas de Bactérias/genética , Sequência de Bases , Células Cultivadas , Clonagem Molecular , DNA Recombinante , Genes Bacterianos , Hidrazida Maleica/metabolismo , Metiltransferases/metabolismo , Dados de Sequência Molecular , Mutagênicos/metabolismo , O(6)-Metilguanina-DNA Metiltransferase , Plantas Geneticamente Modificadas , Nicotiana/efeitos dos fármacos , Nicotiana/metabolismo , Nicotiana/efeitos da radiação , Fatores de Transcrição , Transformação GenéticaRESUMO
UV-irradiation (254 nm, 10 or 20 J/cm2) of p-aminobenzoic acid (PABA) and p-aminosalicylic acid (NaPAS) potentiated their antimutagenicity towards N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis in Salmonella typhimurium. Their inhibitory action towards the formation of the mutagen N-methyl-N-nitrosourea from the nitrosation mixture of N-methylurea and nitrite was also increased by UV-irradiation. In contrast, UV-irradiated PABA exhibited no inhibitory effects towards the mutagenicity of sodium azide or 3-azidoglycerol. Neither PABA nor NaPAS nor their UV-irradiation products were themselves mutagenic in the Ames assay.
