Jiří Velemínský

The mutagenic activity of 1-alkyl-1-nitrosoureas and 1-alkyl-3-nitro-1-nitrosoguanidines

Abstract The mutagenic activities of five 1-alkyl-1-nitrosoureas and six 1-alkyl-3-nitro-1-nitrosoguanidines were tested and compared on Arabidopsis thaliana . All the nitrosoureas tested were active, whereas only methyl and ethyl derivatives of nitrosogunidines were. There was a tendency for the mutagenic effectiveness to decrease with increasing number of C-atoms in the alkl group. The nitrosoamides tested had a much higher mutagenic efficiency than X-rays, i.e. at the same level of induced mutations they caused less sterility. The possible reasons for the activity of nitrosoguanidines in Arabidopsis and their lack of mutagenic activity in barley are briefly discussed.

Monitoring the genotoxicity of soil extracts from two heavily polluted sites in Prague using the Tradescantia stamen hair and micronucleus (MNC) assays.

We have taken soil samples from two sites in Prague, the capital of the Czech Republic, that are heavily polluted by motor vehicles. As a negative control, soil samples from a recreational site in Prague with no motor vehicle traffic were used. Soil samples from these sites were extracted with water or 5% dimethylsulphoxide (DMSO) for 24 h and cuttings of Tradescantia clone 4430 were immersed for 12 h at 25 degrees C in the extraction solutions. As a positive control Tradescantia plants have been treated with the promutagenic arylamine o-phenylenediamine at the same treatment conditions. None of the tested soil extractions significantly increased the frequency of somatic mutations in the stamen hair assay. By contrast, a 5% DMSO soil extract from one of the tested sites (entrance of the Letná tunnel) significantly increased the frequency of micronuclei (MNC) in the pollen mother tetrad cells. A repetition of the treatment 14 days later also resulted in an increase in the frequency of MNC, however the increase was not statistically significant. This study was conducted for the International Programme on Plant Bioassays.

Mechanisms of inhibition of N-nitroso compounds-induced mutagenicity

In this review we describe the mechanisms of the inhibitory effects of various chemical agents towards the mutagenicity of N-nitroso compounds, including direct-acting mutagens such as N-nitroso derivatives of alkylureas, alkylnitroguanidines and alkylurethanes, and promutagenic nitrosamines. Possible mechanisms by which the inhibitors may exert their effects outside and inside the target cells include chemical and enzymatic deactivation of the mutagen, inhibition of metabolic activation of nitrosamines, scavenging mutagenic products, inhibition of cellular uptake, induction of detoxifying mechanisms, protecting nucleophilic centers in DNA and modulating DNA repair.

Inhibition of dimethylnitrosamine-induced mutagenesis in Arabidopsis thaliana by diethyldithiocarbamate and carbon monoxide

Diethyldithiocarbamate and carbon monoxide markedly inhibited the frequency of embryonic and chlorophyll mutations induced by the metabolism-requiring mutagen dimethylnitrosamine in the higher plant Arabidopsis thaliana. In contrast, the monoamine oxidase substrates, tryptamine, benzylamine and 2-phenylethylamine, had no such effect. The mutagenicity of a direct-acting mutagen, N-methyl-N-nitrosourea, was not altered by these inhibitors or substrates.

Somatic mutations in tobacco plants after chronic exposure to maleic hydrazide and its diethanolamine and potassium salts

Abstract Chronic exposure to the plant-growth regulator and herbicide maleic hydrazide (MH) and its diethanolamine or potassium salts was highly mutagenic in a double heterozygous chlorophyll mutant of Nicotiana tabacum.

Mutational events after recurrent or chronic exposures of mutagenic and promutagenic N-nitroso compounds to a heterozygous tobacco tester strain

Recurrent exposures (17 administrations in 37 days) to the direct-acting mutagens N-methyl-N-nitrosourea and N-ethyl-N-nitrosourea and a chronic exposure (38 days) to the metabolism-requiring mutagen dimethylnitrosamine markedly increased the frequency of somatic mutations in a double heterozygous chlorophyll mutant ofNicotiana tabacum, whereas exposure to N-methyl-N′-nitro-N-nitrosoguanidine was ineffective.

Transient expression of heterologous model gene in plants using Potato virusX-based vector

To optimize the efficiency of expression of foreign proteins using Potato virus X (PVX) -- based vector, the gene for the coat protein (CP) of other virus (Potato virusA, PVA) was cloned into the vector, propagated in E. coli and subsequently inoculated or agroinfected into the host plants. Host range studies showed that the best host plant is N. benthamiana. By means of RT PCR the presence and the stability of the construct were tested. Both ELISA and Western blot analysis were applicable for expressed protein detection. Expression level of PVA CP achieved approximately 5--10 per mille of total soluble proteins. The results demonstrated that agroinfection is the most suitable method for the propagation of our model gene using PVX--based vectors.

Mutagenic synergy between paraoxon and plant-activated m-phenylenediamine or 2-acetoxyacetylaminofluorene

Paraoxon (diethyl‐p‐nitrophenylphosphate) is the toxic, but non‐mutagenic metabolite of the organo‐phosphorus ester insecticide parathion. Although this agent has been used as a deacetylase inhibitor in many studies, we discovered a mutagenic synergy when paraoxon was incubated with plant‐activated m‐phenylenediamine (mPDA) or with direct‐acting 2‐acetoxyacetylaminofluorene (2AAAF) and S. typhimurium tester strains. Using non‐toxic concentrations of plant‐activated mPDA and paraoxon a 10‐fold increase in the mutant yield of S. typhimurium was observed. The mutagenicity of the plant‐activated mPDA product required that O‐acetyltransferase (OAT) be expressed by the S. typhimurium tester strain. However, the paraoxon‐dependent mutagenic synergy was observed using the direct‐acting arylamine metabolite, 2AAAF, with strains YG1024, TA98 and TA98/1,8‐DNP6 regardless of their OAT activity. This mutagenic synergy is dependent upon the presence of an activated acetylated form of the arylamine. The data presented here demonstrate that this mutagenic synergy is limited to paraoxon and not to the parent compound (parathion) or to a major metabolite of parathion (p‐nitrophenol).

The influence of streptomycin on the frequency of induced chromosome aberrations

Abstract1.Působení vysokými až subletálními dosemi streptomycinu (0,5 m Mol, 1 m Mol) neindukovalo žádné průkazné zvýšení frekvence chromosomálních aberací v metafázi a v anafázi a telofázi. Jediné průkazné zvýšení frekvence aberantních anafází a telofází bylo zjištěno po působení 1 m Mol streptomycinu (30°C, 48hod. restituce). Zvýšení je hlavně podmíněno výskytem lagging chromosomů a bylo tedy výsledkem poruchy vřeténka a ne chromosomální aberací. To bylo prokázáno neprůkazností zvýšení frekvence aberantních metafází při stejném působení. V diskusi jsou zdůrazněny nevýhody hodnocení frekvence chromosomálních aberací v anafázi a telofázi.2.Simultánní působení nízkých dosí streptomycinu (0,005, 0,0005 m Mol) a ethylalkoholu snížilo frekvenei chromosomálních aberací ve srovnání s frekvencí po působení samotného ethylalkoholu.3.Předpůsobení s 0,05 m Mol streptomycinu po dobu 2 hod. snížilo frekvenci chromosomálních aberací, indukovamých ethylalkokolem.Summary1.Treatment with high to sublethal doses of streptomycin (1 m Mol, 0.5 m Mol) did not induce any significant increase in chromosome aberrations at the metaphase and at the ana- and telophase. The only significant increase in aberrant ana- and telophases was observed as a consequence of treatment with 1 m Mol streptomycin (30 °C, 48 hrs recovery). This increase was mainly caused by the presence of lagging chromosomes and was therefore the result of spindle damage and not of chromosome aberrations. This fact was verified by the nonsignificance of the increase in aberrant metaphases under the same treatment. The disadvantages of evaluation of chromosome aberrations in ana- and telophase are stressed in the discussion.2.Simultaneous treatment with low doses of streptomycin (0.005, 0.0005 m Mol) and ethanol showed a decrease in the frequency of chromosome aberrations compared with their frequency after ethanol treatment alone.3.Pretreatment with 0.05 m Mol streptomycin for 2 hrs reduced the number of chromosome aberrations, induced by ethanol.AbstractВлияние стрептомицина на частоту индуцированных хромосомных перестроек сказывается следующим образом:1.Действие высокими (до сублетальных) дозами стрептомицина (0,5 мМол, 1 мМол) пе вызвало никакого достоверного повышения частоты хромосомных абберраций в метафзах и в ана- и телофазах. Единственное достоверное повышение частоты абберрантных ана- и телофаз установлено после воздействия 1 мМол стрептомицина (30° Ц, 48 часов реституции). Повышение обусловлено прежде всего появлением опаздывающихся хромосом (lagging chromosomes), является, следовательно, результатем нарушения веретена и не хромосомных абберраций. Данный факт доказан недостоверностью повышения частоты абберрантных метафаз при том же воздействии.2.Симультанное действие низких доз стрептомицина (0,005; 0,0005 мМол) и этилалкоголя снизило частоту хромосомных абберраций по сравнению с частотой после воздействия одним этилалкоголем.3.Более высокие дозы стрептомицина (0,5; 0,05 мМол) тоже вызвали снижение частоты хромосомных абберраций, однако, это снижение может быть вызвано торможением митоза.4.Преднарительное воздействие 0,05 мМол стрептомицином в течение 2 часов снизило частоту хромосомных абберраций, вызванных этилалкоголем.5.Последствие стрептомицином не вызвало никакого достоверного снижения частоты хоомосомных абберраций.

Mutagenicity of 3-azido-1,2-propanediol and 9-(3-azido-2-hydroxypropyl)-adenine in repair deficient strains of Escherichia coli

The mutagenicity of two non-aromatic organic azido compounds, 3-azido-1,2-propanediol (AG) and 9-(3-azido-2-hydroxypropyl)-adenine (AHPA), was studied in E. coli repair deficient strains uvrA6, uvrA6 + umuC36, uvrA6+ umuC122::Tn5, polA1, tagA1+ alkA1, ada and dam3. The mutagenicity of both agents was markedly enhanced by defects of UvrABC excinuclease (uvrA6) and was independent of umuC function of the SOS error-prone pathway. Neither azido compound promoted umuDC operon expression. The mutagenicity of AG in tag A1, alkA1 and ada mutants does not differ from that found in the wild-type strain. The expression of both ada and alkA genes was not elevated by AG. Experiments on polA1 and dam3 mutants suggest that DNA polymerase I as well as the mutHLS mismatch repair pathway does not contribute to the removal of putative DNA lesions induced by AG.