chlorophyll-a and metsulfuron-methyl

Physiological effects of metsulfuron-methy on Elodea nuttallii was studied. The growth status, the photosynthetic pigments content and activities of anti-oxidation enzymes of Elodea nuttallii were examined with different contents of metsulfuron-methyl in cultural solution. The results showed that metsulfuron-methy could stimulate the sprout bourgeoning but restrained the growth of frond remarkably. At lower concentrations, metsulfuron-methy could increase the content of chlorophyll at the beginning, but inhibited the syntheses of chlorophyll ultimately and reduced the plant's photosynthetic capacity. Activities of CAT and POD increased at first and then decreased, while SOD activities increased all the time. With higher concentration and longer treatment time, the activities of anti-oxidation enzymes would decrease. It is indicated that metsulfuron-methy can arise the formation and accumulation of reactive oxygen species in Elodea nuttalii, and induce activities of anti-oxidation enzymes. When stress intensity exceeds a certain value, the activities of anti-oxidation enzymes will be inhibited and reactive oxygen species can not be removed in time and will finally result in oxidative damages to the plant. This may be an important toxicity mechanism of this kind of herbicide to aquatic plants.

Topics: Arylsulfonates; Catalase; Chlorophyll; Dose-Response Relationship, Drug; Environmental Monitoring; Herbicides; Hydrocharitaceae; Peroxidase; Photosynthesis; Reactive Oxygen Species; Superoxide Dismutase; Time Factors

The influence of the acetolactate synthase inhibitor metsulfuron-methyl on the operation of the photosynthetic apparatus was examined on 4-weeks-old climate chamber-grown Solanum nigrum plant. To have an indication on the relative performance of the photosynthetic apparatus of ALS-treated plants, the level of carbon dioxide (CO(2)) fixation, the relative quantum efficiency of photosystem I (Phi(PSI)) or photosystem II (Phi(PSII)) electron transport and leaf chlorophyll content were assessed for both control and treated plants at 2, 4 and 7 days after application of the herbicide. Results indicated a progressive inhibition of the level of CO(2) fixation, the relative quantum efficiency of photosystem I (Phi(PSI)) and II (Phi(PSII)) electron transport and the leaf chlorophyll content already 2 days after application of the herbicide. The linear relationship between the photosystem I and II was unaltered by herbicidal treatment and was sustained under conditions where large changes in pigment composition of the leaves occurred. It appears that the stress-induced loss of leaf chlorophyll is not a catastrophic process but rather is the consequence of a well-organised breakdown of components. Under photorespiratory and non-photorespiratory conditions, the relationship between the index of electron transport flow through photosystem I and II and the rate of CO(2) fixation is altered so that electron transport becomes less efficient at driving CO(2) fixation.

Topics: Acetolactate Synthase; Arylsulfonates; Chlorophyll; Electron Transport; Herbicides; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Plant Leaves; Solanum nigrum

The highest concentrations of herbicides measured in flowing surface waters are often only present for short periods of time. These herbicide pulses can reach concentrations that would affect aquatic plants if present over a long time. The aim of this study was to assess the effect of a 3-h herbicide pulse relative to the effects of long-term (4 and 7 days) exposure of six herbicides with different sites of action and different K(ow) on the growth of the floating macrophyte Lemna minor. The herbicides were the two photosynthetic inhibitors: diquat and terbuthylazine, the inhibitors of acetolactate syntase (ALS), imazamox and metsulfuron-methyl and the microtubule assembly inhibitors propyzamide and pendimethalin. The log K(ow) ranged from -4.6 to 5.2. For imazamox, metsulfuron-methyl, propyzamide and pendimethalin a 3-h pulse induced the effect on area-specific growth as did a 4-day exposure at an approximate 10-fold higher concentration. For diquat and terbuthylazine a concentration closer to a factor of 100 or more was needed for a 3-h pulse to induce an effect similar to that of a 4-day exposure. For diquat, the low pulse-effect was most likely due to a slow uptake of the hydrophilic ion (log K(ow) = -4.6), as no effect was observed on chlorophyll fluorescence within 8 h after exposure. The chlorophyll fluorescence parameters are expected to respond quickly to a PSI inhibitor as diquat. For terbuthylazine, fluorescence measurements showed an effect on photosynthesis within 1h of exposure, and reached a minimum after 3 h. Recovery was fast, and initial fluorescence was restored within 24 h. Hence, the small pulse effect on area-specific growth was due to rapid recovery of photosynthesis. In contrast to terbuthylazine, the stop in area-specific growth observed for the ALS-and microtubule assembly inhibitors, took up to 4 days to recover from. Such a long recovery time after a pulse of only 3 h indicate that at realistic pulse exposures of up to a day or two, pulse-effects will approach the effects obtained in long-term studies. When investigating the effects of pulse exposures on aquatic plants, we should therefore focus more on non-photosynthetic inhibitors, which might not appear in pulses in as large concentrations as the PSII inhibitors investigated up till now, but whose effect, even in a shorter pulse, can be more damaging.

Topics: Aniline Compounds; Araceae; Arylsulfonates; Benzamides; Chlorophyll; Chromatography, Liquid; Diquat; Dose-Response Relationship, Drug; Fluorescence; Fresh Water; Herbicides; Imidazoles; Mass Spectrometry; Photosynthesis; Time Factors; Triazines

The s-triazine herbicide terbutylazine, an inhibitor of photosystem II, is often found in surface waters in concentrations < 1 microg L(-1), but concentrations up to 13 microg L(-1) have been measured. To study the effect on the aquatic flora, we tested the sensitivity of 10 aquatic macrophyte species and a natural epiphyte community in a 2-week laboratory multispecies test at constant terbutylazine concentrations and two irradiance regimes. The data were described by a log-logistic concentration-response model and species sensitivity distributions (SSDs) were created from the EC50 and EC10 values. The 5% hazard concentration (HC5) of the EC10-based SSD for terbutylazine was 1 and 3 microg L(-1); hence the low chronic terbutylazine concentrations measured in the environment are not likely to affect the macrophyte community. To compare the species sensitivity between different groups of herbicides, SSDs were constructed from a published study on the sulfonylurea metsulfuron-methyl, an inhibitor of acetolactate synthase. There was no correlation between species-specific sensitivity to the two herbicides; hence, the combined exposure of different herbicides might affect the macrophyte community more broadly rather than seriously affecting a few susceptible species. Evaluating the standard procedure of leaving at least a factor of 100 between the EC50 of standard tests on Lemna sp. and the predicted environmental concentration seems to be protective for at least 95% of the macrophyte species for both terbutylazine and metsulfuron-methyl.

Topics: Arylsulfonates; Chlorophyll; Chlorophyll A; Environmental Exposure; Fresh Water; Herbicides; Magnoliopsida; Risk Assessment; Species Specificity; Triazines

The aim of this study was to investigate the short-term (2 weeks) effects of the herbicide metsulfuron methyl alone and in combination with the insecticide cypermethrin in freshwater enclosures (80 l). We used a factorial design with four levels of herbicide (0, 1, 5, 20 microg/l) and two levels of insecticide (0 and 0.05 microg/l). The root growth of the macrophyte species Elodea canadensis and Myriophyllum spicatum decreased following exposure to the lowest concentration of metsulfuron methyl tested. Metsulfuron methyl exposure resulted in a decreased pH in the aquatic enclosure at the lowest concentration tested, which is most likely a further indication of decreased macrophyte primary production. The biomass of periphytic algae growing on the leaves of M. spicatum increased in the enclosures exposed to metsulfuron methyl. The species composition of the periphytic algae differed significantly from the controls in the enclosures exposed to 20 microg/l of the herbicide. The increased biomass of periphytic algae on the leaves of the macrophytes is probably an indirect effect of the herbicide exposure. The exposure to metsulfuron methyl possibly induced a leakage of nutrients from the macrophyte leaves, which promoted an increased algal growth. The exposure to metsulfuron methyl did not alter the biomass or the species composition of the phytoplankton community. The zooplankton communities in the enclosures were dominated by rotifers, which were not affected by the exposure to cypermethrin. However, a cypermethrin exposure of 0.05 microg/l initially decreased the abundance of copepod nauplii. Ten days after exposure, the abundance of nauplii was significantly higher in the insecticide-exposed enclosures compared with the non-exposed enclosures. This might be an indication of a sub-lethal stress response, which either increased the number of offspring produced or induced an increased hatching of copepod resting stages. No combined effects of the herbicide and insecticide exposure, either direct or indirect, were observed in the enclosure study. Significant effects on the macrophytes were observed following exposure to 1 microg metsulfuron methyl per litre in the enclosure study. Furthermore, a single species laboratory assay indicated that the shoot elongation of E. canadensis decreased following exposure to >or=0.1 microg metsulfuron methyl per litre. These concentrations are well within the range of expected environmental concentrations, thus this study s

Topics: Animals; Arylsulfonates; Biomass; Chlorophyll; Chlorophyll A; Drug Interactions; Ecosystem; Environment, Controlled; Environmental Exposure; Fresh Water; Herbicides; Hydrocharitaceae; Insecticides; Models, Biological; Multivariate Analysis; No-Observed-Adverse-Effect Level; Phytoplankton; Plant Roots; Pyrethrins; Saxifragaceae; Toxicity Tests, Acute; Water Pollutants, Chemical; Zooplankton