Absorption and luminescence spectroscopy of mass-selected flavin adenine dinucleotide mono-anions.

We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using photo-induced dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0 eV (210-550 nm). The S0 → S2 transition is strongly blue shifted relative to aqueous solution, supporting the view that this transition has a significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima cannot be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions in vacuo. The gas-phase Stokes shift for S1 is 3000 cm-1, which is considerably larger than any previously reported for other molecular ions and consistent with a significant displacement of the ground and excited state potential energy surfaces. Consideration of the vibronic structure is thus essential for simulating the absorption and luminescence spectra of flavins.

Toxicity testing of fifteen non-crop plant species with six herbicides in a greenhouse experiment: implications for risk assessment.

Estimation of risk to plants not targeted by herbicides when used in agricultural or forestry situations requires appropriate data on multiple species. Currently, many questions remain unresolved as to the adequate type and number of species to be tested. This paper presents the result of a unique greenhouse experiment where testing was performed with 15 non-crop plant species sprayed with 6 herbicides. The herbicides were chosen because of their different modes of action and because they are widely used in several countries. The plants favoured were species commonly found in field margins of Europe and/or North America. This dataset (called thereafter Danish/Canadian) was compared to the crop species that had been submitted to the US EPA for the same herbicides. In general, the selected plant species in the Danish/Canadian database were easy to grow and maintain in the greenhouse. The Danish/Canadian plants were overall more sensitive than the species tested in the US EPA data, yielding to a 5% protection threshold (HC5(50)) that was always more conservative. There was a large variability in plant responses among herbicides. Recommendations are provided on species that should and should not be used for risk assessment of non-target plants.

Relationships between sulfonylurea herbicide treatment of host plants and the performance of herbivorous insects.

Previous work had shown that the sulfonylurea herbicide chlorsulfuron affected the survival of a herbivorous insect species dwelling on a sub-lethally exposed host plant. Further experiments have been conducted to establish whether this negative effect was a single occurrence characteristics for the specific insect-plant interaction and the specific herbicide tested. Three insect-plant interactions were tested for the effects of selected sulfonylurea herbicides, i.e. metsulfuron-methyl, chlorsulfuron and tribenuron-methyl. The species pairs tested were Pieris brassicae/Brassica napus, Gastrophysa polygoni/Fallopia convolvulus and Sitobium avenae/Triticum aestivium. No significant effects on survival and relative growth rate of P brassicae or G polygoni were found when treating the host plants with sulfonylurea herbicides. However, the host plants had a significantly reduced root and shoot growth rate when treated with herbicide. Treating T aestivium with the recommended field rate of metasulfuron-methyl did not cause any change in development time, growth rate or fecundity of S avenae feeding on the host plants. The data presented suggest that the increased mortality observed for G polygoni larvae feeding on chlorsulfuron-treated host plants observed earlier was characteristic for this herbicide and for the specific plant-insect interaction only.

Toxicity and bioaccumulation of copper to black bindweed (Fallopia convolvulus) in relation to bioavailability and the age of soil contamination.

The use of ecotoxicity test results obtained in the laboratory for prediction of effects of potentially toxic concentrations of chemicals in the field is hampered by several factors differing between the laboratory and the field situations. One important factor is the binding of test chemicals to soil, which is affected by the age of the contamination and soil type. The present study investigated the effect of contamination age by introducing an aging period of 1 to 12 weeks between mixing the test substance, copper sulfate, in with soil and introducing the test plant, Fallopia convolvulus (L.) A. Löve. Copper accumulation, emergence of cotyledons, and growth were assessed and related to total (boiling with HNO(3)) and 0.01 M CaCl(2)- and DTPA-extractable soil copper concentrations. Aging of the copper-contaminated soil had only small effects on bioaccumulation of copper, copper toxicity, and extractable soil copper fractions. Soil copper had no effect on emergence of cotyledons. Estimated EC(50) values for shoot and root growth averaged 280 mg Cu/kg. Effects on growth in these laboratory-treated soils were much more severe than in a study performed in soil from an old copper-contaminated field site. Neither CaCl(2)- nor DTPA-extractable copper fractions could explain all of the differences in effects between aged spiked soil and field soil. The accumulation pattern for roots and shoots of F. convolvulus indicated that excessive copper was accumulated and adsorbed mainly by the fine roots, whereby the copper concentrations of other plant parts were kept low until the plant was no longer able to maintain this regulation. An internal threshold for effects on growth of about 20 mg Cu/kg shoot dry weight was estimated, coinciding with a soil copper concentration of approximately 200 mg/kg.

Effects of soil copper on black bindweed (Fallopia convolvulus) in the laboratory and in the field

The present study aims to identify factors of importance to the extrapolation from laboratory toxicity test to field effects using copper and black bindweed as a model. In the laboratory the influence of Cu on seed germination and seedling survival was studied in both soil spiked with Cu in the laboratory and soil collected at a Cu-polluted site. Maternal effects were also studied. We found that seeds from Cu-stressed plants germinated more readily after a short, cold storage than control seeds, but no differences were found after a longer storage. The low germination of control seeds compared to maternal treated seeds could not be attributed to differences in thickness of the seed coat. Germination was slightly stimulated at 232 mg Cu kg-1. At the highest Cu level (i.e. 1,330 mg Cu kg-1) only 5% of the seeds germinated. Mortality of the seedlings increased with increasing Cu concentration reaching 40% at 391 mg Cu kg-1. At higher concentrations mortality decreased. Germination was not affected in laboratory tests with soil from a Cu-polluted site, but the biomass of the plants decreased with increasing Cu concentration. The distribution of the plants on a Cu-polluted site was registered in relation to soil Cu concentration. Cu was analyzed using three different extractors, i.e. HNO3, CaCl2, and DTPA. The distribution of the plant in the field was predicted from calculated lifetime effect of a given Cu soil concentration based on the laboratory tests. The results revealed that growth is more sensitive in the field than should be expected from laboratory tests due to several stressors in the former situation. Bioavailability was lower in the field soil but this was counteracted by the increased effect. Incorporating bioavailability in the prediction of field effects thus reduced the fit of the model and bioavailability measures could not be further evaluated.

Effects of copper sulfate on black bindweed (Polygonum convolvulus L.).

Seedlings of black bindweed (Polygonum convolvulus L.) were transplanted to soil contaminated with copper sulfate at different dosages. These plants were followed until maturity under greenhouse conditions, and measures of mortality, growth, and reproduction were obtained from harvests 21, 34, and 105 days after the transplant. It was found that application of 125 mg Cu2+ kg-1 resulted in 1.7% lifetime mortality increasing to 100% at 500 mg kg-1. The mortality was dependent on exposure time. No further mortality was observed after 50 days. The population consisted of a relatively tolerant and a sensitive group. This was indicated by differences in lifetime of plants treated with 500 mg kg-1 and by a diversification in biomass of individuals dying from treatment with 315 mg kg-1. The plants surviving treatment had reduced biomass and seed production at dosages above 200 mg kg-1.