Analysis of LMW RNA profiles of Frankia strains by staircase electrophoresis.

An optimized technique of polyacrylamide gel electrophoresis, Staircase Electrophoresis (SCE), was applied to determine the stable Low Molecular Weight RNA (LMW RNA) profiles of 25 Frankia strains from diverse geographic origins and host specificity groups as well as species from other actinomycete genera. Application of the technique permits the rapid identification of Frankia strains and their differentiation from other actinomycetes. The isolates used in this study were grouped in eight clusters, each comprising strains with identical LMW RNA profiles. Comparison of these results with others obtained from DNA sequences or DNA hybridization methods suggest a high degree of complexity in the genus Frankia. Application of SCE to profile LMW RNA should in the future facilitate biodiversity studies of Frankia and discrimination of new species.

Plant species diversity as a driver of early succession in abandoned fields: a multi-site approach.

Succession is one of the most studied processes in ecology and succession theory provides strong predictability. However, few attempts have been made to influence the course of succession thereby testing the hypothesis that passing through one stage is essential before entering the next one. At each stage of succession ecosystem processes may be affected by the diversity of species present, but there is little empirical evidence showing that plant species diversity may affect succession. On ex-arable land, a major constraint of vegetation succession is the dominance of perennial early-successional (arable weed) species. Our aim was to change the initial vegetation succession by the direct sowing of later-successional plant species. The hypothesis was tested that a diverse plant species mixture would be more successful in weed suppression than species-poor mixtures. In order to provide a robust test including a wide range of environmental conditions and plant species, experiments were carried out at five sites across Europe. At each site, an identical experiment was set up, albeit that the plant species composition of the sown mixtures differed from site to site. Results of the 2-year study showed that diverse plant species mixtures were more effective at reducing the number of natural colonisers (mainly weeds from the seed bank) than the average low-diversity treatment. However, the effect of the low-diversity treatment depended on the composition of the species mixture. Thus, the effect of enhanced species diversity strongly depended on the species composition of the low-diversity treatments used for comparison. The effects of high-diversity plant species mixtures on weed suppression differed between sites. Low-productivity sites gave the weakest response to the diversity treatments. These differences among sites did not change the general pattern. The present results have implications for understanding biological invasions. It has been hypothesised that alien species are more likely to invade species-poor communities than communities with high diversity. However, our results show that the identity of the local species matters. This may explain, at least partly, controversial results of studies on the relation between local diversity and the probability of being invaded by aliens.

Mutagenic evaluation of the pesticides captan, folpet, captafol, dichlofluanid and related compounds with the mutants TA102 and TA104 of Salmonella typhimurium.

A mutagenic evaluation of captan, folpet, captafol, dichlofluanid and related compounds was carried out using the Salmonella/mammalian microsome test using strains TA102 and TA104. These strains contain A-T base pairs at the site of the mutation in contrast to the other Salmonella tester strains that detect mutagens damaging G-C base pairs. In addition, the excision repair system of the TA102 strain is still intact. Captan and folpet were mutagenic in strain TA104, captafol was mutagenic in strain TA102, whereas the remaining test compounds (dichlofluanid, tetrahydrophthalimide and thiozolidine-4-carboxylic acid) were not mutagenic in either strain. In conclusion, we consider it of value to add these two strains to those already used in the Ames test in order to increase confidence in our ability to detect mutagens and to shed further light on their mechanism of action.

Influence of bacterial growth of the overnight culture on the captan- and folpet-induced reversion in the Ames test.

The influence of the stage of bacterial growth of the overnight culture on captan- and folpet-induced reversion in the Ames test was investigated. Tests were performed in order to determine both the number of viable bacteria at different intervals of bacterial growth--in the presence or absence of captan and folpet--and also the number of revertants. Captan or folpet were tested at 5 micrograms per plate, a concentration which had previously showed a mutagenic effect to the TA100 strain. The highest induced reversion was obtained when the bacterial culture used had entered the stationary-phase after 10-14 h, with a titre of at least 10(8) viable cells per ml.

Mutagenic evaluation of trichlorfon using different assay methods with Salmonella typhimurium.

Evaluation of the mutagenicity of trichlorfon pesticide was carried out with strains TA1535, TA100, TA97, TA98 and TA104 of Salmonella typhimurium by means of several assay methods: (i) spot test; (ii) standard plate incorporation test; (iii) plate incorporation test with preincubation; (iv) fluctuation test and (v) fluctuation test with preincubation, with and without post-mitochondrial liver fraction (S9) from Wistar rats pretreated with phenobarbital and 5,6-benzoflavone as a metabolic activation system. Trichlorfon induced base-pair substitution mutations, and its mutagenic activity was decreased by the addition of S9 mix. The fluctuation test and fluctuation test with preincubation were the most sensitive assay methods for detecting the mutagenicity of trichlorfon.

The effect of antibiotics on the infective viability of an alder (Alnus glutinosa L. Gaertn.) crushed nodule inoculum.

The effect of various antibiotic substances, mainly penicillin, streptomycin, tetracycline and chloramphenicol respectively, on the infective viability of an alder crushed nodule inoculum towards the host plant has been studied. Penicillin was inocuous in respect of both plant and nodule endophyte. Its use did not prevent the formation of nitrogen-fixing partnership. The other antibiotics tested showed a harmful effect either inhibiting infection (streptomycin) or causing death in most plants (tetracycline and chloramphenicol). The use of penicillin in isolation trials of the alder nodule endophyte is suggested.

Cytogenetic effects of permethrin in cultured human lymphocytes.

The pyrethroid insecticide permethrin was tested for its ability to induce sister chromatid exchanges (SCE), micronuclei (MN) and structural chromosome aberrations (CA) in cultured human peripheral blood lymphocytes. Permethrin was tested in the range of 5-500 micrograms/ml in the absence and in the presence of a rat liver activation system (S9 mix). Small elevations in the SCE frequencies were found and even though statistically significant may have no biological meaning, the more so since there was no dose-effect relationship. Permethrin induced both MN and CA when it was evaluated in the absence of a metabolic activation system. Nevertheless, it cannot be said that S9 mix suppressed the activity in itself. The effect of permethrin seemed to be time of exposure dependent. Permethrin could be characterized as a S-phase independent agent with greater potential for inducing chromosomal damage than sister chromatid exchanges.

Induction of structural chromosome aberrations in human lymphocyte cultures and CHO cells by permethrin.

The pyrethroid insecticide permethrin was tested for its ability to induce structural chromosome aberrations (CA) in human lymphocyte cultures and CHO cells, in order to confirm the clastogenic effect of itself and to compare the response of the two different cell types. Permethrin was tested in the range of 50-200 micrograms/ml in human lymphocyte cultures and in the range of 20-100 micrograms/ml in CHO cells. In both lymphocyte and CHO cultures, assays were performed in the absence and in the presence of a rat liver activation system (S9 mix). In the absence of S9 mix, two experiments with different duration of the treatment were carried out. Permethrin induced CA in both cultures when it was evaluated in the absence of a metabolic activation system. The activity of a given concentration of permethrin seemed to be decreased more by the reduction of the time of exposure than by the presence of S9 mix. Aberrations induced by permethrin were mainly chromosome-type aberrations in both cultures. Thus, permethrin can be characterised as an S-phase independent clastogenic agent. The response of both lymphocyte and CHO cultures was similar, indicating that both systems showed the same sensitivity for detecting the clastogenicity in vitro of permethrin.

[Predictive value of short-term assays of chemical carcinogenesis]. / Valor predictivo de los ensayos de corta duración sobre carcinogénesis química.

Many agents of our surroundings are mutagenic, and a significant number of the mutagenic agents are carcinogenic. It is then useful to evaluate the short-term screening test allowing to predict the carcinogenic effect of chemicals. The authors make a summary about the predictive value of the existing assays, and write about the need of the systematic use of a convenient battery of tests to detect carcinogenicity in every product to which the human being may be exposed.

A study of the capacity of soils to induce nodules in Alnus glutinosa (L.) Gaertn. and Myrica gale L., with special reference to the specificity of the endophytes.

One hundred soil samples from sites in North, Centre and West of Spain were examined for their capacity to induce nodules in alder (Alnus glutinosa) and bog myrtle (Myrica gale). Soils from A. glutinosa communities particularly from places where Myrica was absent, were checked for their infectivity towards M. gale. There was a good correlation between the results, since there was not one single sample which could induce nodules in Myrica which did not do the same in alder. The nodules formed on M. gale plants grown in soils collected from alder habitats showed acetylene-reducing activity at a level comparable to that described in the literature, in the case of other Myrica species. Considering together the results now obtained and in previous work, the possibility of cross-inoculation between M. gale and A. glutinosa, is again put forward and it is thus held that no specificity can be assigned, for the time being, to the respective endophytes.

Analysis of cytogenetic damage induced in CHO cells by the pyrethroid insecticide fenvalerate.

A synthetic pyrethroid insecticide, fenvalerate, was tested for its ability to induce chromosome aberrations (CA) and sister chromatid exchanges (SCE) in CHO cells. Fenvalerate was assayed both in the presence and in the absence of a rat liver activation system (S9-mix). Our results indicate that fenvalerate in the presence of S9-mix is able significantly to increase the frequency of CA, while in the SCE test this increase occurred both in the presence and in the absence of S9-mix. In addition, fenvalerate affected the cell cycle, causing a decrease in the mitotic index (MI) and in the proliferative rate index (PRI).

[Mutagenic evaluation of the urine of rats treated with oils implicated in the toxic oil syndrome using bacterial tests]. / Evaluación mutagénica de orina de ratas tratadas con aceites implicados en el síndrome tóxico mediante ensayos bacterianos.

The mutagenic activity of the urine of pregnant rats treated with toxic oil syndrome-related rape seed oil or with edible oil was evaluated by means of the Ames and Green tests. It was found that the urine of the pregnant rats treated with "Jen" oil, that was related to the toxic oil syndrome, was mutagenic.