Plant Lemna Gibba Research Articles

Phytoremediation, recovery and toxic effects of ionic gadolinium using the free-floating plant Lemna gibba

The biosorption and recovery of ionic gadolinium (Gd) from contaminated water by the free-floating duckweed Lemna gibba was studied. The highest non-toxic concentration range was determined as (6.7 mg L-1). The concentration of Gd in the medium and in the plant biomass was monitored and a mass balance was established. Tissue Gd concentration of Lemna increased with increasing Gd concentration of the medium. The bioconcentration factor was up to 1134 and in nontoxic concentrations up to 2.5 g kg-1 Gd tissue concentration was reached. Lemna ash contained 23.2 g Gd kg-1. Gd removal efficiency from the medium was 95%, however, only 17–37% of the initial Gd content of the medium accumulated in Lemna biomass, an average of 5% remained in the water, and 60–79% was calculated as a precipitate. Gadolinium-exposed Lemna plants released ionic Gd into the nutrient solution when they were transferred to a Gd-free medium. The experimental results revealed that in constructed wetlands, L. gibba is able to remove ionic Gd from the water and can be suitable for bioremediation and recovery purposes.

Identification of the Mechanism Involved in the Removal Potetial of Textile Pollutants by the Aquatic Plant Lemna gibba L.

Identification of the Mechanism Involved in the Removal Potetial of Textile Pollutants by the Aquatic Plant Lemna gibba L.

Physiological and biochemical effect of silver on the aquatic plant Lemna gibba L.: Evaluation of commercially available product containing colloidal silver

This paper aims to evaluate the effects of a product containing colloidal silver in the aquatic environment, using duckweed Lemna gibba as a model plant. Therefore, growth parameters, photosynthetic pigments content and protein content as physiological indices were evaluated. Changes in the content of non-enzymatic antioxidants and activity of several antioxidant enzymes, alongside with the accumulation of hydrogen peroxide and lipid peroxidation end-products were assessed to explore the potential of colloidal silver to induce oxidative stress. The commercially available colloidal silver product contained a primary soluble form of silver. The treatment with colloidal silver resulted in significant physiological and biochemical changes in L. gibba plants and a consequent reduction of growth. Accumulation of silver caused altered nutrient balance in the plants as well as a significant decrease in photosynthetic pigments content and protein concentration. The antioxidative response of L. gibba plants to treatment with colloidal silver was inadequate to protect the plants from oxidative stress caused by metal accumulation. Silver caused concentration-dependent and time-dependent hydrogen peroxide accumulation as well as the elevation of lipid peroxidation levels in L. gibba plants. The use of commercially available products containing colloidal silver, and consequent accumulation of silver, both ionic and nanoparticle form in the environment, represents a potential source of toxicity to primary producers in the aquatic ecosystem.

Inhibitory effects of silver nanoparticles on photosystem II performance in Lemna gibba probed by chlorophyll fluorescence

Toxic effects of silver nanoparticles (AgNPs) on photosynthetic processes and biomass were investigated in aquatic plant Lemna gibba, and the plants were exposed to different concentrations of AgNPs for 7 days. At 7 day of exposure, a direct negative impact on the physiological state of plant was indicated by the decrease of chlorophyll (Chl) synthesis, the deterioration of photosynthetic activity and the change in biomass. When L. gibba was treated to 1 mg L−1 of AgNPs, total Chl content and the biomass decreased respectively by 66 and 51% compared to the control (P < 0.05). Under this condition, the alteration of photosystem II (PSII) photochemical reactions was indicated by a significant change compared to control of different studied fluorescence parameters value: FV/FM (35%), ET/RC (63%), VJ (61%), qP (57%) and NPQ (102%). Therefore, Chl a fluorescence measurements showed strong evidence of inhibitory effects on energy transfer from light harvesting complexes to reaction centers, the deterioration of the PSII water splitting system and the inactivation of PSII reaction centers at 1 mg L−1. In conclusion, our results demonstrated that AgNPs induced an inhibitory mechanism on photosynthetic processes and biomass of L. gibba plant.

Effects of superparamagnetic iron oxide nanoparticles on photosynthesis and growth of the aquatic plant Lemna gibba.

Toxicity of superparamagnetic iron oxide nanoparticles (SPION) was investigated in Lemna gibba plants exposed for 7days to Fe3O4 (SPION-1), Co0.2Zn0.8Fe2O4 (SPION-2), or Co0.5Zn0.5Fe2O4 (SPION-3) at 0, 12.5, 25, 50, 100, 200 or 400µgmL(-1). At<400µgmL(-1) of SPION exposure, toxicity was indicated by decrease of chlorophyll content, deterioration of photosystem II (PSII) functions, strong production of reactive oxygen species (ROS), and inhibition of growth rate based on fresh weight (52-59%) or frond number (32-49%). The performance index of PSII activity was the most sensitive biomarker of PSII functions and decreased by 83, 86, and 79% for SPION-1, SPION-2, and SPION-3, respectively. According to the change of these biomarkers, the exposure of SPION suspensions to L. gibba caused several alterations to the entire plant cellular system, which may come from both the uptake of nanoparticles and metal ions in the soluble fraction. Our results, based on the change of several biomarkers, showed that these SPION have a complex toxic mode of action on the entire plant system and therefore affects its viability. Therefore, the plant model L. gibba was shown to be a sensitive bioindicator of SPION cellular toxicity and thus can be used in the development of a laboratory bioassay toxicity testing.

Silver nanoparticle toxicity effect on growth and cellular viability of the aquatic plant Lemna gibba

The toxicity effect of silver nanoparticles (AgNPs) on growth and cellular viability was investigated on the aquatic plant Lemna gibba exposed over 7 d to 0, 0.01, 0.1, 1, and 10 mg/L of AgNPs. Growth inhibition was demonstrated by a significant decrease of frond numbers dependent on AgNP concentration. Under these conditions, reduction in plant cellular viability was detected for 0.1, 1, and 10 mg/L of AgNPs within 7 d of AgNPs treatment. This effect was highly correlated with the production of intracellular reactive oxygen species (ROS). A significant increase of intracellular ROS formation was triggered by 1 and 10 mg/L of AgNP exposure. The induced oxidative stress was related to Ag accumulation within L. gibba plant cells and with the increasing concentration of AgNP exposure in the medium. The authors' results clearly suggested that AgNP suspension represented a potential source of toxicity for L. gibba plant cells. Due to the low release capacity of free soluble Ag from AgNP dissolution in the medium, it is most likely that the intracellular uptake of Ag was directly from AgNPs, triggering cellular oxidative stress that may be due to the release of free Ag inside plant cells. Therefore, the present study demonstrated that AgNP accumulation in an aquatic environment may represent a potential source of toxicity and a risk for the viability of duckweeds.

Bio-accumulation and toxicity of lead (Pb) in Lemna gibba L (duckweed)

The vascular aquatic plant Lemna gibba (duckweed) was exposed during seven days to lead (Pb) at concentrations ranging from 50 to 300 mg/L in a greenhouse with controlled photoperiod and temperature. The effects of Pb on growth of Lemna gibba were examined during 13 days in the same experimental design. The maximum accumulation of lead by Lemna gibba occurs during the third day in the 50 mg/L test, and at the sixth day, lead in all test concentrations produces approximately a 100% inhibitory effect on duckweed growth. In all tests, the maximum relative growth rates were achieved on the third day and then, the toxicity effects were: 59.3% total soluble starch reduction; 94.7% total soluble proteins reduction; 246% increase in total soluble amino acids; 50% increase in total soluble sugars and an 18.2% increase in total phenols. This experiment showed that the transfers of Pb from nutritive solution to plants were fast. Nevertheless, Pb produced toxic effects on Lemna gibba; however duckweed was able to remove Pb at the experimental concentrations used.

Toxicity and removal of heavy metals (cadmium, copper, and zinc) by Lemna gibba

Effects of cadmium, copper, and zinc on the aquatic plant Lemna gibba were determined under controlled conditions; in parallel their removal from the growth medium was followed. The results showed that the three heavy metals affected growth, a physiological stress index defined as the ratio of Chlorophyll to phaeophytin (D665/D665a), and the contents of proline. After 4 days, 10 −3–10 −1 mg/L Cd inhibited growth by 25–100%, reduced D665/D665a by 35–89%, and increased proline content by 44–567%. Under the same conditions, 10 −4–10 −1 μg/L Cu inhibited growth by 36–75%, reduced D665/D665a by 19–81%, and increased proline content by 67–288%. Comparable concentrations of Zn had little effect. However, higher concentrations (4, 30, and 50 mg/L) inhibited growth by 50–79%. Also, 0.1 and 30 mg/L induced a small reduction of D665/D665a (−3.8% and −22%) and an increase in proline contents (+144% and +177%). When it was observed, proline accumulation was always transient and the maximum was reached after 4 days. Monitoring metal concentration in the medium showed that L. gibba was able to remove metals from the medium. Zn and Cu removal was biphasic, it was rapid during the first 2 days (> 60% reduction) and slow (10–20%) during the following 8 days. For Cd, removal was linear and depended on the initial concentration. It reached approximately 90% after 6 or 8 days for initial concentrations of 10 −1 and 10 −3 mg/L, respectively.

Effects of potentised substances on growth rate of the water plant Lemna gibba L.

This study investigated, whether the growth rate of Lemna gibba L. (duckweed) can be influenced by the application of homeopathic potencies of gibberellic acid, kinetin, argentum nitricum, and lemna minor. Duckweed was grown in either potencies (14x-30x, decimal steps) or water controls (unsuccussed and succussed) over seven days. Frond (leaf-like structure) growth was measured using a non-destructive image analysis system. Growth rates were calculated for three time intervals (0-7, 0-3, 3-7 days). Five to six independent, randomized and blinded experiments were analysed for each of the four tested substances. Water control experiments were performed repeatedly to test the reliability of the experimental set-up (systematic negative controls). The systematic negative control experiments did not yield any significant effects. Hence, false positive results could be excluded. The test system had a low coefficient of variation (1.5%). Out of the four tested substances gibberellic acid had the most pronounced effect (p=0.0002, F-test) on the main outcome parameter frond growth rate (r(area) day 0-7). Potency levels 15x, 17x, 18x, 23x and 24x reduced growth rate of Lemna gibba (p<0.05 against the pooled water control, LSD test). Lemna gibba may be considered as a suitable test organism for further studies on the efficacy of homeopathic potencies. Evidence accumulates, that adjacent potency levels may strongly differ in their biological activity. Potential consequences for therapeutical application might be worth investigating.

Detection of microcystin contamination by the measurement of the variability of the in vivo chlorophyll fluorescence in aquatic plant Lemna gibba

In recent years, chlorophyll fluorescence analysis has become one of the most powerful and widely used techniques available to plant ecophysiologists. In this work, the chlorophyll fluorescence is used in order to evaluate the biotic stress induced by exposure to cyanobacterial toxins (microcystins). Experiments were carried on the aquatic plant Lemna gibba exposed to various concentrations of a microcystins (0.01, 0.03, 0.05, 0.07, 0.15, 0.22 and 0.3 μg equivalent MC-LR.mL −1) during 5 h. The reversibility of the stress changes was also studied following 24 h of treatment. The efficiency and the utility of this biophysical technique were compared to biochemical analysis priory used to evaluate the plant stress induced by such contamination. The results showed that there is a concentration-dependent effect on the measured in vivo chlorophyll fluorescence with significant differences between the control and all concentrations except for 0.01 μg equivalent MC-LR.mL −1. The reversibility tested showed also that after avoiding the contact with the microcystins, the chlorophyll fluorescence measurements were not significantly different from the control. The results showed that if the contact with the microcystins is short and not repeated plants may not suffer from a significant stress. We concluded that this simple and rapid technique based on the variable fluorescence, could be recommended and applied to test the plant stress caused by cyanobacterial toxins.

Phytotoxic effects of cyanobacteria extract on the aquatic plant Lemna gibba: Microcystin accumulation, detoxication and oxidative stress induction

The occurrence of toxic cyanobacteria in the aquatic environment constitutes a serious risk for the ecological balance and the functioning of ecosystems. The presence of cyanotoxins in ecosystems could have eventual adverse effects on aquatic plants, which play an important biological role as primary producers. The original aim of this study was to investigate microcystin (MC) accumulation, detoxication and oxidative stress induction in the free-floating aquatic vascular plant Lemna gibba (Duckweed, Lemnaceae). Experiments were carried out with a range of MC levels, obtained from toxic Microcystis culture extracts (0.075, 0.15, 0.22 and 0.3 μg equiv. MC-LR mL −1). During chronic exposure of the plant to MC, we examined the growth, photosynthetic pigment contents and also the physiological behavior related to toxin accumulation, possible biodegradation and stress oxidative processes of L. gibba. For the last reason, changes in peroxidase activity and phenol compound content were determined. This is a first report using phenol compounds as indicators of biotic stress induced by MC contamination in aquatic plants. Following MC exposure, a significant decrease of plant growth and chlorophyll content was observed. Also, it was demonstrated that L. gibba could take up and bio-transform microcystins. A suspected MC degradation metabolite was detected in treated Lemna cells. In response to chronic contamination with MCs, changes in the peroxidase activity and qualitative and quantitative changes in phenolic compounds were observed after 24 h of plant exposure. The physiological effects induced by chronic exposure to microcystins confirm that in aquatic ecosystems plants coexisting with toxic cyanobacterial blooms may suffer an important negative ecological impact. This may represent a sanitary risk due to toxin bioaccumulation and biotransfer through the food chain.

Herbicidal Effects of Statin Pharmaceuticals inLemna gibba

Statin pharmaceuticals, heavily prescribed in the treatment of hypercholesterolemia, are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme-A reductase (HMGR). In plants, these compounds also inhibit HMGR, which regulates cytosolic isoprenoid biosynthesis in the mevalonic acid (MVA) pathway. Phytotoxicity was evaluated in the higher aquatic plant Lemna gibba exposed to atorvastatin and lovastatin for 7-days by measuring the concentrations of sterols and ubiquinone; products downstream in the MVA pathway. The efficiency of the parallel and unaffected methylerythritol phosphate pathway (MEP) was also evaluated by measuring the end product, plastoquinone. Statin treatment caused an accumulation of plastoquinone, and unexpectedly, ubiquinone, an artifact likely due to metabolite sharing from the plastidial MEP pathway. Statins were, however, highly phytotoxic to L. gibba and HPLC-UV analysis of plant extracts showed significantly decreased concentrations of both stigmasterol and beta-sitosterol, which are critical components of plant membranes and regulate morphogenesis and development. EC10 values for atorvastatin and lovastatin were as small as 26.1 and 32.8 microg/L, respectively. However, hazard quotients indicated that statins present little risk to the model higher aquatic plant Lemna gibba at environmentally relevant concentrations, even though pathway-specific endpoints were 2-3 times more sensitive than traditional gross morphological endpoints typically used in risk assessment.

Identification of six differentially expressed genes in response to copper exposure in the aquatic plant Lemna gibba (duckweed)

Aquatic plants are susceptible to metal pollution and provide an entry point for metals, such as copper, into the aquatic biosphere. Exposure of the aquatic plant Lemna gibba to copper has been associated with the production of reactive oxygen species (ROS) and oxidative damage, caused in large part by the ability of this metal to redox cycle. In particular, copper-mediated production of ROS, a known group of signaling molecules, triggers numerous defense responses in L. gibba. Therefore, the objective of the present study was to examine to what extent acute copper exposure alters gene expression. First, the kinetics of copper uptake was assessed to determine if assimilation occurred within the short exposures needed to induce gene expression. Subsequently, using differential display polymerase chain reaction, we identified six genes with expressions that were putatively altered in response to copper. Differential expression was confirmed by northern hybridization analysis and showed that copper causes an accumulation of transcripts that encode for callose synthase, heat shock protein 90, serine decarboxylase, and the biotin carboxylase subunit of acetyl-coenzyme A carboxylase. Conversely, copper caused a decline in transcript levels for genes encoding the HAP5 subunit of the heme-activated protein (HAP) transcription factor in addition to the chloroplast nucleoid DNA-binding protein CND41. Interestingly, the expressions of these genes are sensitive to cellular ROS levels. We believe that these gene products provide valuable information regarding the molecular mechanisms of copper toxicity.

A pilot study of constructed wetlands using duckweed ( Lemna gibba L.) for treatment of domestic primary effluent in Israel

Constructed wetlands are well known as highly efficient system to treat wastewater from different sources. This treatment system is cost-effective for reuse in desert areas. A continuous flow, free water surface (FWS) pilot wetland using the duckweed plant Lemna gibba L. was constructed at the Blaustein Institute for Desert Research in Kiryat Sde Boker of the Negev, Israel, and operated on domestic primary effluents. Water quality and system efficiency were observed during the experiment for reuse purposes. Results indicated that, hydraulic residence time averaged 4.26±0.61 d, average influent flow rate was 0.234±0.027 m 3/d and hydraulic load 0.22±0.03 m/d. Hydraulic efficiency in the system was high and allowed good settling conditions. Suspended solids and organic matter removals were the highest and effluent concentrations were 13.1±9.7 and 40.3±11.9 mg/l for TSS and total BOD 5, respectively. Nitrogen removal was lower (10–20%) but slightly increased with higher nitrogen loads. Therefore, nitrogen content in the plants was high (4.3±0.5%/kg dry plant). Phosphorus removal was negligible. High removal for fecal coliform (∼95%) and effluent turbidity (>50%) were also observed.

Effects of 25 pharmaceutical compounds to Lemna gibba using a seven‐day static‐renewal test

Antibiotics are known to have antichloroplastic properties, but their effects on aquatic higher plants are virtually unknown. In order to address this issue, 25 pharmaceuticals, including 22 antibiotics, were assessed for phytotoxicity to the aquatic higher plant Lemna gibba. A 7-d static-renewal test was used, and plants were treated with 0, 10, 30, 100, 300, and 1,000 microg/L of pharmaceutical-containing growth media. Phytotoxicity was assessed using multiple growth and biochemical endpoints. Effective concentration (EC)50, EC25, and EC10 values as well as tests for significant differences between treatments and controls lowest-observed-effect concentration (LOECs) were calculated for each endpoint. Twelve different classes of antibiotics were assessed; however, only members of the fluoroquinolone, sulfonamide, and tetracycline classes of antibiotics displayed significant phytotoxicity. The most toxic members of each of these classes tested were lomefloxacin, sulfamethoxazole, and chlortetracycline, with wet weight EC25 values of 38, 37, and 114 microg/L, respectively. Injury symptoms were comparatively uniform and consistent among chemical classes while degree of phytotoxicity varied considerably. Both of these criteria varied markedly between classes. Wet mass was consistently the most sensitive endpoint above 100 microg/L; conversely, frond number was the most sensitive below 100 microg/L. Pigment endpoints were significantly less sensitive than growth endpoints.

Similar stress responses are elicited by copper and ultraviolet radiation in the aquatic plant Lemna gibba: implication of reactive oxygen species as common signals.

Metals and ultraviolet (UV) radiation are two environmental stressors that can cause damage to plants. These two types of stressors often impact simultaneously on plants and both are known to promote reactive oxygen species (ROS) production. However, little information is available on the potential parallel stress responses elicited by metals and UV radiation. Using the aquatic plant Lemna gibba, we found that copper and simulated solar radiation (SSR, a light source containing photosynthetically active radiation (PAR) and UV radiation) induced similar responses in the plants. Both copper and SSR caused ROS formation. The ROS levels were higher when copper was combined with SSR than when applied with PAR. Higher concentrations of copper plus PAR caused toxicity as monitored by diminished growth and chlorophyll content. This toxicity was more pronounced when copper was combined with SSR. Because the generation of ROS was also higher when copper was combined with SSR, we attributed this enhanced toxicity to elevated levels of ROS. In comparison to PAR-grown plants, SSR treated plants exhibited elevated levels of superoxide dismutase (SOD) and glutathione reductase (GR). These enzyme levels were further elevated under both PAR and SSR when copper was added at concentrations that generated ROS. Interestingly, copper treatment in the absence of SSR (i.e. copper plus PAR) induced synthesis of the same flavonoids as those observed in SSR without copper. Finally, addition of either dimethyl thiourea or GSH (two common ROS scavengers) lowered in vivo ROS production, alleviated toxicity and diminished induction of GR as well as accumulation of UV absorbing compounds. Thus, the potential of ROS being a common signal for acclimation to stress by both copper and UV can be considered.

Quantitative structure‐activity relationship for the photoinduced toxicity of polycyclic aromatic hydrocarbons to the luminescent bacteria Vibrio fischeri

Sunlight can greatly enhance the toxicity of polycyclic aromatic hydrocarbons (PAHs). Photosensitization reactions (e.g., generation of singlet-state oxygen) and photomodification reactions (e.g., photooxidation of PAHs to more toxic species) are both pathways of photoinduced toxicity of PAHs. Previously, a quantitative structure-activity relationship (QSAR) was developed for PAHs showing that a photosensitization factor (PSF) and photomodification factor (PMF) can be additively combined to describe photoinduced toxicity. That QSAR model was developed for the photoinduced toxicity of 16 PAHs to the higher plant Lemna gibba. The objective of this study was to apply the QSAR model developed for L. gibba to another organism. The organism chosen was the luminescent marine bacteria Vibriofischeri. Toxicity data used for the QSAR model were inhibition of luminescence and inhibition of growth of V. fischeri. Both short-term (15 min) and long-term (18 h) assays of toxicity were used. Light did not impact on PAH toxicity in the short-term assay, and thus the QSAR model did not correlate well with these data. Conversely, light greatly enhanced toxicity when the long-term assay was employed. The PMFs for the PAHs from the L. gibba QSAR showed a moderate correlation to bacterial toxicity in the long-term assay, whereas the PSFs showed only a weak correlation to toxicity. As was the case for L gibba, summing the PMF and the PSF resulted in a strong correlation to toxicity that had predictive value. Thus, a QSAR model derived for plants accurately described the toxicity of PAHs to a bacterial species. This indicates that the bipartite mechanism of PAH-photoinduced toxicity may be applicable to other organisms.

Sites of toxicity of specific photooxidation products of anthracene to higher plants: inhibition of photosynthetic activity and electron transport in Lemna gibba L. G-3 (duckweed).

Sites of toxicity of polycyclic aromatic hydrocarbons (PAHs) were examined to determine if inhibition of photosynthetic activity could be correlated to whole-organism toxicity. The inhibition of photosynthesis was observed by detecting the induction kinetics of endogenous chlorophyll a (Chl a) fluorescence. Anthracene (ANT) photooxidation products were applied to the aquatic higher plant Lemna gibba L. G-3 at concentrations ranging from 0.01 to 10 ppm. The impact on Chl a fluorescence was found to correlate with whole-organism toxicity for the 13 PAH compounds tested in this in vivo study. The mechanism of toxic action starts with inhibition of photosystem I (PSI) or the cytochrome-b6/f complex, followed by photooxidative damage to photosystem II (PSII). To study the effects of oxygenated ANTs on photosynthesis in vivo, the IC(50)s for F(V)/F(M) (PSII activity) and F(Q)/F(M) (activity downstream from PSII) were determined. The IC(50)s for a decrease of F(Q)/F(M) for all 13 chemicals were on average twofold lower than those for F(V)/F(M). F(V)/F(M) was found to be a measure of acute toxicity, whereas F(Q)/F(M) was found to be a measure of chronic toxicity. Thus, Chl a fluorescence by use of the whole organism was able to detect the impacts of photomodified ANT products and indicate a site of action for the chemicals.

Chlorophyll fluorescence as a bioindicator of effects on growth in aquatic macrophytes from mixtures of polycyclic aromatic hydrocarbons

AbstractChlorophyll‐a fluorescence induction is a rapid technique for measuring photosynthetic electron transport in plants. To assess chlorophyll‐a fluorescence as a bioindicator of effects of polycyclic aromatic hydrocarbon mixtures, chlorophyll‐afluorescence parameters and plant growth responses to exposure to the wood preservative creosote were examined in the aquatic plants Lemna gibba and Myriophyllum spicatum. Exposure to creosote inhibited growth of L. gibba (EC50 = 7.2 mg/L total polycyclic aromatic hydrocarbons) and M. spicatum (EC50 = 2.6 mg/L) despite differences in physiology. Creosote also diminished maximum PSII efficiency (Fv/Fm) (EC50 = 36 and 13 mg/L for L. gibba and M. spicatum) and the effective yield of photosystem II photochemistry (ΔF/F′m) (EC50 = 13 and 15 mg/L for L. gibba and M. spicatum). The similarity between growth and chlorophyll‐a fluorescence EC50s and slopes of the response curves suggests a close mechanistic link between these end points. The predictive power of chlorophyll‐a fluorescence as a bioindicator of whole‐organism effects applied to complex contaminant mixtures is discussed.

Chlorophyll fluorescence as a bioindicator of effects on growth in aquatic macrophytes from mixtures of polycyclic aromatic hydrocarbons.

Chlorophyll-a fluorescence induction is a rapid technique for measuring photosynthetic electron transport in plants. To assess chlorophyll-a fluorescence as a bioindicator of effects of polycyclic aromatic hydrocarbon mixtures, chlorophyll-a fluorescence parameters and plant growth responses to exposure to the wood preservative creosote were examined in the aquatic plants Lemna gibba and Myriophyllum spicatum. Exposure to creosote inhibited growth of L. gibba (EC50 = 7.2 mg/L total polycyclic aromatic hydrocarbons) and M. spicatum (EC50 = 2.6 mg/L) despite differences in physiology. Creosote also diminished maximum PSII efficiency (Fv/Fm) (EC50 = 36 and 13 mg/L for L. gibba and M. spicatum) and the effective yield of photosystem II photochemistry (deltaF/Fm') (EC50 = 13 and 15 mg/L for L. gibba and M. spicatum). The similarity between growth and chlorophyll-a fluorescence EC50s and slopes of the response curves suggests a close mechanistic link between these end points. The predictive power of chlorophyll-a fluorescence as a bioindicator of whole-organism effects applied to complex contaminant mixtures is discussed.