Locomotion behavior testing as a complementary tool in Collembola avoidance assays with neurotoxic insecticides

This study aimed (1) to assess the ability of collembolans Folsomia candida to avoid soils contaminated with three seed dressing insecticides imidacloprid, clothianidin, and fipronil; (2) to assess the effects of the insecticides on collembolans' locomotion behavior; (3) to check if changes in the locomotion behavior would explain the avoidance/preference responses; and (4) to evaluate the possibility to use locomotion behavior as toxicity biomarker of the tested insecticides. Avoidance and locomotion behavior assays with collembolans F. candida were performed with commercial seed dressing formulations of three insecticides (imidacloprid, clothianidin, and fipronil). Results showed no avoidance behavior at any concentration, while a "preference" was observed with increasing concentrations of the three tested insecticides. Significant reductions in the locomotion of exposed collembolans were observed at ≥ 1 mg kg-1 for imidacloprid (18-38%) and fipronil (29-58%) and ≥ 4 mg kg-1 for clothianidin (10-47%). At the higher insecticide concentrations, the collembolans had their trajectories restricted to smaller areas, with a tendency for circular movements. Our results confirm that the "preference" for contaminated soils with neurotoxic substances is likely due to locomotion inhibition impairing the ability of organisms to escape. This effect highlights that only avoidance assays may be not sufficient to assure the safety of some substances and confirm the potential of locomotion behavior as a sensitive toxicity biomarker for neurotoxic insecticides.

Ecotoxicity of Diazinon and Atrazine Mixtures after Ozonation Catalyzed by Na+ and Fe2+ Exchanged Montmorillonites on Lemna minor

The toxicity of two pesticides, diazinon (DAZ) and atrazine (ATR), before and after montmorillonite-catalyzed ozonation was comparatively investigated on the duckweed Lemna minor. The results allowed demonstrating the role of clay-containing media in the evolution in time of pesticide negative impact on L. minor plants. Pesticides conversion exceeded 94% after 30 min of ozonation in the presence of both Na+ and Fe2+ exchanged montmorillonites. Toxicity testing using L. minor permitted us to evaluate the change in pesticide ecotoxicity. The plant growth inhibition involved excessive oxidative stress depending on the pesticide concentration, molecular structure, and degradation degree. Pesticide adsorption and/or conversion by ozonation on clay surfaces significantly reduced the toxicity towards L. minor plants, more particularly in the presence of Fe(II)-exchanged montmorillonite. The results showed a strong correlation between the pesticide toxicity towards L. minor and the level of reactive oxygen species, which was found to depend on the catalytic activity of the clay minerals, pesticide exposure time to ozone, and formation of harmful derivatives. These findings open promising prospects for developing a method to monitor pesticide ecotoxicity according to clay-containing host-media and exposure time to ambient factors.

Role of Silica on Clay-Catalyzed Ozonation for Total Mineralization of Bisphenol-A

Catalytic ozonation for the total mineralization of bisphenol-A (BPA) from aqueous solution was investigated in the presence of various silica-based catalysts such as mesoporous silica, acid-activated bentonite (HMt) and montmorillonite-rich materials (Mt) ion-exchanged with Na⁺ and Fe²⁺ cations (NaMt and Fe(II)Mt). The effects of the catalyst surface were studied by correlating the hydrophilic character and catalyst dispersion in the aqueous media to the silica content and BPA conversion. To the best of our knowledge, this approach has barely been tackled so far. Acid-activated and iron-free clay catalysts produced complete BPA degradation in short ozonation times. The catalytic activity was found to strongly depend on the hydrophilic character, which, in turn, depends on the Si content. Catalyst interactions with water and BPA appear to promote hydrophobic adsorption in high Si catalysts. These findings are of great importance because they allow tailoring silica-containing catalyst properties for specific features of the waters to be treated.

Insight into natural medium remediation through ecotoxicity correlation with clay catalyst selectivity in organic molecule ozonation

The oxidative degradation of diazinon (DAZ) and diclofenac sodium (DCF) in aqueous media was comparatively investigated and correlated with the mortality of Artemia salina in the presence of clay catalysts. For this purpose, montmorillonites (Mt) exchanged with Na⁺ and Fe²⁺ cations (NaMt and Fe(II)Mt), acid activated bentonites and hydrotalcite were used as clay catalysts. Surface interaction and adsorption on the clay surface were found to govern the catalyst dispersion in aqueous media and both activity and selectivity in ozonation. These catalysts' features were correlated with the ecotoxicity of ozonised reaction mixtures as expressed in terms of mortality rates of Artemia salina. DAZ and DCF display specific intrinsic ecotoxicity that evolves differently during ozonation according to the catalyst. The ecotoxicity was found to strongly depend on the distribution of the ozonation intermediates, which, in turn, was narrowly correlated with the acid-base properties of the catalyst surface. These valuable findings allow the prediction of the behaviour of the clay-containing media in natural remediation.

Toxic Responses of Palladium Accumulation in Duckweed (Lemna minor): Determination of Biomarkers

Palladium (Pd) is a trace metal of the platinum group elements, representing an emerging contaminant for the environment. It is of great interest to characterize the bioaccumulation and toxicity of Pd to improve our toxicological knowledge for this contaminant. Under standardized toxicity testing conditions, we analyzed Pd accumulation and toxicity effects on the duckweed Lemna minor exposed to nominal concentrations from 2 to 50 µM. The inhibitory effect was significant (p < 0.05) from 8 µM of Pd, starting with 9.5% of growth inhibition and a decrease of 1 cm for the root size. Under 12.5 μM of Pd, the bioaccumulated Pd of 63.93 µg/g fresh weight inhibited plant growth by 37.4%, which was caused by a strong oxidative stress in the cytosol and organelles containing DNA. Under 25 and 50 μM of Pd, bioaccumulated Pd was able to deteriorate the entire plant physiology including chlorophyll synthesis, the photosystem II antenna complex, and the photochemical reactions of photosynthesis. In fact, plants treated with 50 μM Pd accumulated Pd up to 255.95 µg/g fresh weight, causing a strong decrease in total biomass and root elongation process. Therefore, we showed several growth, physiological, and biochemical alterations which were correlated with the bioaccumulation of Pd. These alterations constituted toxicity biomarkers of Pd with different lowest-observed-effect dose, following this order: root size = growth inhibition < catalase activity = carotenoid content = reactive oxygen species production = total thiols < chlorophyll a/b = variable fluorescence to maximal fluorescence intensity ratio = absorbed-light energy transfer from the chlorophyll a antenna to the photosystem II reaction center = performance index of photosystem II activity < V_J . Therefore, the present study provides insight into the toxicity mechanism of Pd in L. minor plants under standardized testing conditions. Environ Toxicol Chem 2021;40:1630-1638. © 2021 SETAC.

Functionalized Glutathione on Chitosan-Genipin Cross-Linked Beads Used for the Removal of Trace Metals from Water

Functionalized glutathione on chitosan-genipin cross-linked beads (CS-GG) was synthesized and tested as an adsorbent for the removal of Fe(II) and Cu(II) from aqueous solution. The beads were characterized by several techniques, including Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), CNS elementary analysis, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The effect of several parameters such as the pH, the temperature, and the contact time was tested to optimize the condition for the adsorption reaction. The beads were incubated in aqueous solutions contaminated with different concentrations of Fe(II) and Cu(II) (under the range concentration from 10 to 400 mg·L-1), and the adsorption capacity was evaluated by inductively coupled plasma optical emission spectrometry (ICP-OES). The adsorption equilibrium was reached after 120 min of incubation under optimal pH 5 for Fe(II) and after 180 min under optimal pH 6 for Cu(II). According to the Langmuir isotherm, the maximum adsorption capacities (q max) for Fe(II) and Cu(II) were 208 mg·g-1 and 217 mg·g-1, respectively. Our results showed that the adsorption efficiency of both metals on CS-GG beads was correlated with the degree of temperature. In addition, the adsorption reaction was spontaneous and endothermic, indicated by the positive values of ΔG 0 and ΔH 0. Therefore, the present study demonstrated that the new synthesized CS-GG beads had a strong adsorption capacity for Fe(II) and Cu(II) and were efficient to remove these trace metals from aqueous solution.

Cadmium accumulation and toxicity affect the extracytoplasmic polyphosphate level in Chlamydomonas reinhardtii

Cadmium is a non-essential metal and highly toxic for biological functions. Depending on the dose of Cd²⁺, the biochemical response will differ. In this study, we investigated the level of extracytoplasmic polyphosphate (polyP) when Chlamydomonas reinhardtii was exposed to the effect of CdCl₂. When compared to control cells, Cd²⁺-treated cells to 400-600 µM showed a decrease in the growth rate from 0.78 to 0.38 d^-1 for the strain CC-125, and a decrease from 0.81 to 0.32-0.35 d^-1 for CC-503. This indicated a strong toxicity effect on the population growth of cells during 72 h. In addition, the results demonstrated the decrease in the synthesis and/or the degradation of polyP that was correlated with the accumulation of Cd²⁺ in both algal strains. Furthermore, the level of polyP decreased in relation to the decrease of F_V/F_M value. The toxicity of Cd²⁺ induced a high level of cell necrosis for CC-503, and the level of polyP could not be recovered at 72 h. In response to the toxic effects of Cd²⁺, the observed formation of palmelloid colonies by CC-125 cells was correlated with the recovery of the polyP level. Nevertheless, both algal strains were able to accumulate significant amount of Cd²⁺ in their biomass. Therefore, our study demonstrated a distinct impact of Cd²⁺ on the metabolism of polyP (synthesis and/or degradation), which was dependent on the concentration of CdCl₂ and the Chlamydomonas strain. Based on this study, the level of polyP can be used as a biomarker of Cd²⁺ toxicity at 24-48 h, even with the cell wall-deficient strain CC-503.

Effect of mercury on the polyphosphate level of alga Chlamydomonas reinhardtii

In this study, the accumulation and toxicity effect of 1-7 μM of Hg was determined during 24-72 h on two strains of Chlamydomonas reinhardtii, CC-125 and CC-503 as a cell wall-deficient mutant, by monitoring the growth rate and the maximum quantum yield of Photosystem II. In addition, the level of extracytoplasmic polyphosphates (polyP related to the cell wall) was determined to understand the polyP physiological role in Hg-treated algal cells. The results showed that the polyP level was higher in the strain CC-125 compared to CC-503. When algal cells were exposed to 1 and 3 μM of Hg, the accumulation of Hg was correlated with the degradation of polyP for both strains. These results suggested that the degradation of polyP participated in the sequestration of Hg. In fact, this mechanism might explain at 72 h the recovery of the polyP level, the efficiency of maximum PSII quantum yield, the low inhibition of growth rate, and the low accumulated Hg in algal biomass. Under the effect of 5 and 7 μM of Hg, the degradation of polyP was complete and could not be recovered, which was caused by a high accumulation and toxicity of Hg already at 24 h. Our results demonstrated that the change of polyP level was correlated with the accumulation and effect of Hg on algal cells during 24-72 h, which can be used as a biomarker of Hg toxicity. Therefore, this study suggested that extracytoplasmic polyP in C. reinhardtii contributed to the cellular tolerance for Hg.

Effect of cadmium accumulation on green algae Chlamydomonas reinhardtii and acid-tolerant Chlamydomonas CPCC 121

Cadmium is one of the most dangerous metals found in wastewater since exposure to low concentrations are highly toxic for cellular functions. In this study, the effect of cadmium accumulation on Chlamydomonas reinhardtii and acid-tolerant strain CPCC 121 was investigated during 48 h under 100-600 μM of Cd and two pH conditions (4 and 7). The toxicity of accumulated Cd was determined by the change of cellular and photosynthetic parameters. Obtained results showed that the maximum capacity of Cd accumulation in algal biomass was reached for both strains at 24 h of exposure to 600 μM of Cd. Under this condition, C. reinhardtii showed a higher uptake of Cd compared to the strain CPCC 121, inducing a stronger cellular toxic impact. Chlamydomonas CPCC 121 showed a tolerance for Cd due to the exclusion of Cd at the cell wall surface, which was higher at pH 4 than pH 7. TEM images and EDX spectrum of Cd distribution within the cell confirmed the role of the cell wall as a barrier for Cd uptake. Although Cd²⁺ concentration was the highest in the medium, CPCC 121 was the most tolerant at pH 4, but was not enough efficient to be considered for the phycoremediation of Cd. At neutral pH, the efficiency of C. reinhardtii for the removal of Cd was limited by its toxicity, which was dependent to the concentration of Cd in the medium and the time of exposure.

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 7 days to Fe3O4 (SPION-1), Co0.2Zn0.8Fe2O4 (SPION-2), or Co0.5Zn0.5Fe2O4 (SPION-3) at 0, 12.5, 25, 50, 100, 200 or 400 µg mL(-1). At < 400 µg mL(-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.

Different toxicity mechanisms between bare and polymer-coated copper oxide nanoparticles in Lemna gibba

In this report, we investigated how the presence of a polymer shell (poly(styrene-co-butyl acrylate) alters the toxicity of CuO NPs in Lemna gibba. Based on total Cu concentration, core-shell CuO NPs were 10 times more toxic than CuO NPs, inducing a 50% decrease of growth rate at 0.4 g l(-1) after 48-h of exposure while a concentration of 4.5 g l(-1) was required for CuO NPs for a similar effect. Toxicity of CuO NPs was mainly due to NPs solubilization in the media. Based on the accumulated copper content in the plants, core-shell CuO NPs induced 4 times more reactive oxygen species compared to CuO NPs and copper sulfate, indicating that the presence of the polymer shell changed the toxic effect induced in L. gibba. This effect could not be attributed to the polymer alone and reveals that surface modification may change the nature of NPs toxicity.

Effect of soluble copper released from copper oxide nanoparticles solubilisation on growth and photosynthetic processes of Lemna gibba L

Copper oxide nanoparticles (CuO NPs) are used as a biocide in paints, textiles and plastics. Their application may lead to the contamination of aquatic ecosystems, where potential environmental effects remain to be determined. Toxic effects may be related to interactions of NPs with cellular systems or to particles' solubilisation releasing metal ions. In this report, we evaluated CuO NPs and soluble copper effects on photosynthesis of the aquatic macrophyte Lemna gibba L to determine the role of particle solubility in NPs toxicity. When L. gibba plants were exposed 48 h to CuO NPs or soluble copper, inhibition of photosynthetic activity was found, indicated by the inactivation of Photosystem II reaction centers, a decrease in electron transport and an increase of thermal energy dissipation. Toxicity of CuO NPs was mainly driven by copper ions released from particles. However, the bioaccumulation of CuO NPs in plant was shown, indicating the need to evaluate organisms of higher trophic level.

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.

Alteration of chromium effect on photosystem II activity in Chlamydomonas reinhardtii cultures under different synchronized state of the cell cycle

The inhibitory effect of chromium (Cr) on photosystem II (PSII) activity was investigated in the green alga Chlamydomonas reinhardtii during different phases of the cell cycle. Algae were cultivated in continuous light or a light/dark cycle (16:8 h) to obtain a synchronously dividing cell culture. The cell division phases were determined with the DNA-specific fluorescent probe SYBR green using flow cytometry. The effect of Cr on PSII activity was investigated after a 24-h treatment with algal cultures having different proportions of newly divided cells (G(0)/G(1)), dividing cells at the DNA replication phase (S), and dividing cells at the mitosis phase (G(2)/M). Using chlorophyll a fluorescence parameters based on PSII electron transport capacity in dark- (Φ(M)II) and light-adapted (Φ'(M)II) equilibrium state, we found that the effect of Cr differs depending on the stage of the cell cycle. When algal cultures had a high proportion of cells actively dividing (M phase), the toxic effect of Cr on PSII activity appeared to be much higher and PSII quantum yield was decreased by 80 % compared to algal cultures mainly in the G(0)/G(1) phase. Therefore, the inhibitory effect of Cr on photosynthesis appears to be different according to the cell cycle state of the algal population.

Modulation of the light-harvesting chlorophyll antenna size in Chlamydomonas reinhardtii by TLA1 gene over-expression and RNA interference

Truncated light-harvesting antenna 1 (TLA1) is a nuclear gene proposed to regulate the chlorophyll (Chl) antenna size in Chlamydomonas reinhardtii. The Chl antenna size of the photosystems and the chloroplast ultrastructure were manipulated upon TLA1 gene over-expression and RNAi downregulation. The TLA1 over-expressing lines possessed a larger chlorophyll antenna size for both photosystems and contained greater levels of Chl b per cell relative to the wild type. Conversely, TLA1 RNAi transformants had a smaller Chl antenna size for both photosystems and lower levels of Chl b per cell. Western blot analyses of the TLA1 over-expressing and RNAi transformants showed that modulation of TLA1 gene expression was paralleled by modulation in the expression of light-harvesting protein, reaction centre D1 and D2, and VIPP1 genes. Transmission electron microscopy showed that modulation of TLA1 gene expression impacts the organization of thylakoid membranes in the chloroplast. Over-expressing lines showed well-defined grana, whereas RNAi transformants possessed loosely held together and more stroma-exposed thylakoids. Cell fractionation suggested localization of the TLA1 protein in the inner chloroplast envelope and potentially in association with nascent thylakoid membranes, indicating a role in Chl antenna assembly and thylakoid membrane biogenesis. The results provide a mechanistic understanding of the Chl antenna size regulation by the TLA1 gene.

A flavin binding cryptochrome photoreceptor responds to both blue and red light in Chlamydomonas reinhardtii

Cryptochromes are flavoproteins that act as sensory blue light receptors in insects, plants, fungi, and bacteria. We have investigated a cryptochrome from the green alga Chlamydomonas reinhardtii with sequence homology to animal cryptochromes and (6-4) photolyases. In response to blue and red light exposure, this animal-like cryptochrome (aCRY) alters the light-dependent expression of various genes encoding proteins involved in chlorophyll and carotenoid biosynthesis, light-harvesting complexes, nitrogen metabolism, cell cycle control, and the circadian clock. Additionally, exposure to yellow but not far-red light leads to comparable increases in the expression of specific genes; this expression is significantly reduced in an acry insertional mutant. These in vivo effects are congruent with in vitro data showing that blue, yellow, and red light, but not far-red light, are absorbed by the neutral radical state of flavin in aCRY. The aCRY neutral radical is formed following blue light absorption of the oxidized flavin. Red illumination leads to conversion to the fully reduced state. Our data suggest that aCRY is a functionally important blue and red light-activated flavoprotein. The broad spectral response implies that the neutral radical state functions as a dark form in aCRY and expands the paradigm of flavoproteins and cryptochromes as blue light sensors to include other light qualities.

Polyclonal antibodies against the TLA1 protein also recognize with high specificity the D2 reaction center protein of PSII in the green alga Chlamydomonas reinhardtii

The Chlamydomonas reinhardtii DNA-insertional transformant truncated light-harvesting antenna 1 (tla1) mutant, helped identify the novel TLA1 gene (GenBank Accession # AF534570-71) as an important genetic determinant in the chlorophyll antenna size of photosynthesis. Down-regulation in the amount of the TLA1 23 kDa protein in the cell resulted in smaller chlorophyll antenna size for both photosystems (in Tetali et al. Planta 225:813-829, 2007). Specific polyclonal antibodies, raised against the recombinant TLA1 protein, showed a cross-reaction with the predicted 23 kDa TLA1 protein in C. reinhardtii protein extracts, but also showed a strong cross-reaction with a protein band migrating to 28.5 kDa. Questions of polymorphism, or posttranslational modification of the TLA1 protein were raised as a result of the unexpected 28.5 kDa cross-reaction. Work in this paper aimed to elucidate the nature of the unexpected 28.5 kDa cross-reaction, as this was deemed to be important in terms of the functional role of the TLA1 protein in the regulation of the chlorophyll antenna size of photosynthesis. Immuno-precipitation of the 28.5 kDa protein, followed by LC-mass spectrometry, showed amino acid sequences ascribed to the psbD/D2 reaction center protein of PSII. The common antigenic determinant between TLA1 and D2 was shown to be a stretch of nine conserved amino acids V-F-L(V)LP-GNAL in the C-terminus of the two proteins, constituting a high antigenicity "GNAL" domain. Antibodies raised against the TLA1 protein containing this domain recognized both the TLA1 and the D2 protein. Conversely, antibodies raised against the TLA1 protein minus the GNAL domain specifically recognized the 23 kDa TLA1 protein and failed to recognize the 28.5 kDa D2 protein. D2 antibodies raised against an oligopeptide containing this domain also cross-reacted with the TLA1 protein. It is concluded that the 28.5 kDa cross-reaction of C. reinhardtii protein extracts with antiTLA1 antibodies is due to antibody affinity for the GNAL domain of the D2 protein and has no bearing on the identity or function of the TLA1 protein.

Phylogenomic analysis of the Chlamydomonas genome unmasks proteins potentially involved in photosynthetic function and regulation

Chlamydomonas reinhardtii, a unicellular green alga, has been exploited as a reference organism for identifying proteins and activities associated with the photosynthetic apparatus and the functioning of chloroplasts. Recently, the full genome sequence of Chlamydomonas was generated and a set of gene models, representing all genes on the genome, was developed. Using these gene models, and gene models developed for the genomes of other organisms, a phylogenomic, comparative analysis was performed to identify proteins encoded on the Chlamydomonas genome which were likely involved in chloroplast functions (or specifically associated with the green algal lineage); this set of proteins has been designated the GreenCut. Further analyses of those GreenCut proteins with uncharacterized functions and the generation of mutant strains aberrant for these proteins are beginning to unmask new layers of functionality/regulation that are integrated into the workings of the photosynthetic apparatus.

Effect of aluminum on cellular division and photosynthetic electron transport in Euglena gracilis and Chlamydomonas acidophila

The present study investigated aluminum's effect on cellular division and the photosynthetic processes in Euglena gracilis and Chlamydomonas acidophila at pH 3.0, at which Al is present mostly as Al(3+), AlSO(4) (+), and Al(SO(4))(2) (-). These algal species were exposed to 100, 188, and 740 microM Al, and after 24 h cell-bound Al was significantly different from control only for the highest concentration tested. However, very different effects of Al on algal cellular division, biomass per cell, and photosynthetic activity were found. Aluminum stimulated cell division but decreased at some level biomass per cell in C. acidophila. Primary photochemistry of photosynthesis, as Photosystem II quantum yield, and energy dissipation via nonphotochemical activity were slightly affected. However, for E. gracilis, under the same conditions, Al did not show a stimulating effect on cellular division or photosynthetic activity. Primary photochemical activity was diminished, and energy dissipation via nonphotochemical pathways was strongly increased. Therefore, when Al is highly available in aquatic ecosystems, these effects may indicate very different response mechanisms that are dependent on algal species.

Mechanism of REP27 protein action in the D1 protein turnover and photosystem II repair from photodamage

The function of the REP27 protein (GenBank accession no. EF127650) in the photosystem II (PSII) repair process was elucidated. REP27 is a nucleus-encoded and chloroplast-targeted protein containing two tetratricopeptide repeat (TPR) motifs, two putative transmembrane domains, and an extended carboxyl (C)-terminal region. Cell fractionation and western-blot analysis localized the REP27 protein in the Chlamydomonas reinhardtii chloroplast thylakoids. A folding model for REP27 suggested chloroplast stroma localization for amino- and C-terminal regions as well as the two TPRs. A REP27 gene knockout strain of Chlamydomonas, termed the rep27 mutant, was employed for complementation studies. The rep27 mutant was aberrant in the PSII-repair process and had substantially lower than wild-type levels of D1 protein. Truncated REP27 cDNA constructs were made for complementation of rep27, whereby TPR1, TPR2, TPR1+TPR2, or the C-terminal domains were deleted. rep27-complemented strains minus the TPR motifs showed elevated levels of D1 in thylakoids, comparable to those in the wild type, but the PSII photochemical efficiency of these strains was not restored, suggesting that the functionality of the PSII reaction center could not be recovered in the absence of the TPR motifs. It is suggested that TPR motifs play a role in the functional activation of the newly integrated D1 protein in the PSII reaction center. rep27-complemented strains missing the C-terminal domain showed low levels of D1 protein in thylakoids as well as low PSII photochemical efficiency, comparable to those in the rep27 mutant. Therefore, the C-terminal domain is needed for a de novo biosynthesis and/or assembly of D1 in the photodamaged PSII template. We conclude that REP27 plays a dual role in the regulation of D1 protein turnover by facilitating cotranslational biosynthesis insertion (C-terminal domain) and activation (TPR motifs) of the nascent D1 during the PSII repair process.

Validation of photosynthetic-fluorescence parameters as biomarkers for isoproturon toxic effect on alga Scenedesmus obliquus

Photosynthetic-fluorescence parameters were investigated to be used as valid biomarkers of toxicity when alga Scenedesmus obliquus was exposed to isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] effect. Chlorophyll fluorescence induction of algal cells treated with isoproturon showed inactivation of photosystem II (PSII) reaction centers and strong inhibition of PSII electron transport. A linear correlation was found (R2>or=0.861) between the change of cells density affected by isoproturon and the change of effective PSII quantum yield (PhiM'), photochemical quenching (qP) and relative photochemical quenching (qP(rel)) values. The cells density was also linearly dependent (R2=0.838) on the relative unquenched fluorescence parameter (UQF(rel)). Non-linear correlation was found (R2=0.937) only between cells density and the energy transfer efficiency from absorbed light to PSII reaction center (ABS/RC). The order of sensitivity determined by the EC-50% was: UQF(rel)>PhiM'>qP>qP(rel)>ABS/RC. Correlations between cells density and those photosynthetic-fluorescence parameters provide supporting evidence to use them as biomarkers of toxicity for environmental pollutants.

Rapid Chlorophyll a Fluorescence Transients of Lemna minor Leaves as Indication of Light and Exogenous Electron Carriers Effect on Photosystem II Activity

By using saturating flash, we investigated the change in the rapid fluorescence rise when Lemna minor leaf was exposed to different light conditions and treated with exogenous electron acceptors (methyl viologen and duroquinone) and electron donor (hydroxylamine). Investigation was carried out by using combined pulse amplitude modulated fluorometer and plant efficiency analyzer system, which were employed simultaneously to provide different light conditions and to induce rapid fluorescence rise respectively. We have shown that when leaf of L. minor was exposed to different conditions of illumination, rapid fluorescence rise was greatly influenced by the electron transport functions beyond quinone A-plastoquinone reduction. This was indicated by the change in both fluorescence yield and appearance time of the different transients. When exogenous electron donor (hydroxylamine) and acceptors (methyl viologen and duroquinone) were applied in in vivo condition, we showed that rapid fluorescence rise represented a reliable indicator of PSII-PSI electron transport state and energy dissipation process.

Rapid chlorophyll a fluorescence transient of Lemna gibba leaf as an indication of light and hydroxylamine effect on photosystem II activity

Rapid chlorophyll fluorescence transient induced by saturating flash (3000 micromol of photons m-2 s-1) was investigated when Lemna gibba had been exposed to light (100 micromol of photons m-2 s-1) causing the Kautsky effect or in low light intensity unable to trigger PSII photochemistry. Measurements were made by using, simultaneously, a pulse amplitude modulated fluorometer and plant efficiency analyzer system, either on non-treated L. gibba leaf or those treated with different concentrations of hydroxylamine (1-50 mM) causing gradual inhibition of the water splitting system. When any leaf was exposed to continuous light during the Kautsky effect, a rapid fluorescence transient may reflect current activity of photosystem II within the photosystem II complex. Under those conditions, a variation of transition steps appearing over time was related to a drastic change to the photosystem II functional properties. This value indicated that the energy dissipation through non-photochemical pathways was undergoing extreme change. The change of rapid fluorescence transient, induced under continuous light, when compared to those obtained under very low light intensity, confirmed the ability of photosystem II to be capable to undergo rapid adaptation lasting about two minutes. When the water splitting system was inhibited and electron donation partially substituted by hydroxylamine, the adaptation ability of photosystem II to different light conditions was lost. In this study, the change of rapid fluorescence kinetic and transient appearing over time was shown to be a good indication for the change of the functional properties of photosystem II induced either by light or by hydroxylamine.

Inhibition of photosystem II photochemistry by Cr is caused by the alteration of both D1 protein and oxygen evolving complex

The effect of chromium (Cr) on photosystem II (PSII) electron transport and the change of proteins content within PSII complex were investigated. When Lemna gibba was exposed to Cr during 96 h, growth inhibition was found to be associated with an alteration of the PSII electron transport at both PSII oxidizing and reducing sides. Investigation of fluorescence yields at transients K, J, I, and P suggested for Cr inhibitory effect to be located at the oxygen-evolving complex and Q(A) reduction. Those Cr-inhibitory effects were related to the change of the turnover of PSII D1 protein and the alteration of 24 and 33 kDa proteins of the oxygen-evolving complex. The inhibition of the PSII electron transport and the formation of reactive oxygen species induced by Cr were highly correlated with the decrease in the content of D1 protein and the amount of 24 and 33 kDa proteins. Therefore, functional alteration of PSII activity by Cr was closely related with the structural change within PSII complex.

Photosynthetic parameters as indicators of trinitrotoluene (TNT) inhibitory effect: change in chlorophyll a fluorescence induction upon exposure of lactuca sativa to TNT

Trinitrotoluene, as a compound of conventional explosive, may cause inhibitory effect on terrestrial plants. When Lactuca sativa was exposed to different concentrations of trinitrotoluene (32-1000 mg/kg), photosynthetic process was investigated by using rapid chlorophyll fluorescence kinetic and pulse modulated fluorometry. The decrease of chlorophyll a variable fluorescence was seen to be caused by the deactivation of photosystem II reaction centers. We found for rapid variable fluorescence to be a useful indicator to evaluate the inhibitory effect of trinitrotoluene on photosystem II primary photochemistry and electron transport. The fluorescence parameters, related to the reduction state of photosystem II and to non-photochemical dissipation of light energy, showed a strong relation between the inhibitory effect of photosystem II activity and concentration of trinitrotoluene. The change of photosynthetic fluorescence parameters induced by trinitrotoluene was a reliable indication of the plant physiological state. We proposed for the reduction state of photosystem II and the non-photochemical energy dissipation to be a useful tool in bioassay toxicity testing of trinitrotoluene polluted soil.

Changes in the room-temperature emission spectrum of chlorophyll during fast and slow phases of the Kautsky effect in intact leaves

Changes in the room-temperature emission spectrum of chlorophyll (Chl) were analyzed using fast diode-array recordings during the Kautsky effect in mature and in greening barley leaves. In mature leaves, the comparison of F(O) (basal level of fluorescence yield at transient O) and F(M) (maximum level of fluorescence yield at transient M) spectra showed that the relative amplitude of total variable fluorescence was maximal for the 684 nm Photosystem II (PSII) band and minimal for the 725 nm Photosystem I band. During the increase from F(O) to F(M), a progressive redshift of the spectrum of variable fluorescence occurred. This shift reflected the different fluorescence rise kinetics of different layers of chloroplasts inside the leaf. This was verified by simulating the effect of screening on the emission spectrum of isolated chloroplasts and by experiments on greening leaves with low Chl content. In addition, experiments performed at different greening stages showed that the presence of uncoupled Chl at early-greening stages and light-harvesting complex II (LHCII) at later stages have detectable but minor effects on the shape of room-temperature emission spectra. When strong actinic light was applied to mature green leaves, the slow fluorescence yield, which declined from F(M) to F(T) (steady-state level of fluorescence yield at transient T), was accompanied by a slight redshift of the 684 nm PSII band because of nonphotochemical quenching of short-wavelength-emitting Chl ascribed to LHCII.

Determination of photosynthetic and enzymatic biomarkers sensitivity used to evaluate toxic effects of copper and fludioxonil in alga Scenedesmus obliquus

Modulated PAM fluorometry and Plant Efficiency Analyser methods were used to investigate photosynthetic fluorescence parameters of alga Scenedesmus obliquus exposed to inhibitory effect of fungicides copper sulphate and fludioxonil (N-(4-nitrophenyl)-N'-propyl-uree). The change of those parameters were studied when alga S. obliquus have been exposed during 48 h to different concentrations of fungicides (1, 2 and 3 mgl(-1)). Under the same condition, enzymatic activities of catalase, ascorbate peroxidase, glutathione reductase and glutathione S-transferase were investigated to evaluate antioxidative response to fungicides effects. The change of sensitivity of those parameters was dependent to the mode of fungicide action, their concentration and time of exposure. For copper effects, the most indicative photosynthetic biomarkers were parameters Q(N) as non-photochemical fluorescence quenching, Q(Emax) as the proton induced fluorescence quenching and ABS/RC as the antenna size per photosystem II reaction center. Copper induced oxidative stress was indicated by increased activity of catalase serving as the most sensitive and valuable enzymatic biomarker. On the other hand, fludioxonil effect on photosynthetic parameters was very negligible and consequently not very useful as biomarkers. However, fludioxonil induced strong antioxidative activities associated with cytosol enzymes, as we found for catalase, ascorbate peroxidase and glutathione S-transferase activities. By obtained results, we may suggest for the activation of those enzymes to be sensitive and valuable biomarkers of oxidative stress induced by fludioxonil. Determination of biomarkers sensitivity may offer advantages in providing real criteria to use them for ecotoxicological diagnostic studies.

Protochlorophyllide phototransformation in the bundle sheath cells of Zea mays

The protochlorophyllide transformation process was investigated by using comparative analysis of 77 K fluorescence spectral changes occurring in isolated bundle sheath (BS) cells of etiolated Zea mays leaves after being exposed to a 200 ms saturating flash. Deconvolution analysis of the fluorescence spectra showed essential differences in the ratio of protochlorophyll(ides) and chlorophyll(ides) spectral forms indicating for BS cells to have a characteristic pathway of protochlorophyllide transformation. Bundle sheath cells showed a high ratio between non-photoactive protochlorophyll(ide)-F632 and photoactive protochlorophyllide-F655. In those cells, the 200 ms flash triggered a preferential formation of chlorophyll(ide)-F675 which remained stable in the dark for at least 90 min. Isolated BS cells showed an accumulation of chlorophyll(ide)-F675 resulting in the formation of inactive photosystem II. However for mesophyll cells of intact leaves, it was found to have a high ratio between photoactive and non-photoactive protochlorophyll(ide), showing the succession of chlorophyll(ide) forms usually known in C(3) plants. Protochlorophyllide phototransformation pathway in BS cells related to early stages of plastid differentiation triggered by light may indicate specific conditions for PSII assembly process leading to inactive PSII forms.

Oxyfluorfen toxic effect on S. obliquus evaluated by different photosynthetic and enzymatic biomarkers

The effect of oxyfluorfen was investigated when alga Scenedesmus obliquus has been exposed to different concentrations (7.5, 15, and 22.5 microg x L(-1)) at 12, 24, and 48 hours of exposure. Toxicity test was done by using 13 biomarkers concerning growth rate, chlorophyll content and indicators of photosynthetic and antioxidant enzyme activities. The change of the 13 parameters showed a great variation of sensitivity indicating differences in parameters' suitability to be used as biomarkers when alga culture was exposed to oxyfluorfen toxicity. The order of sensitivity between those biomarkers was: Antenna size (ABS/RC) > Chlorophyll content > Catalase (CAT) > Operational PSII quantum yield (phiS(PSII)) > Glutathione S-transferase (GST) > Functional plastoquinone pool (Q(PQ)) > Glutathione reductase (GR) > Growth rate > Nonphotochemical quenching (QN) > Proton gradient quenching (Q(Emax)) > Ascorbate peroxidase (APX) > Photochemical quenching (Q(p)) > Maximum PSII quantum yield (Phi(PSII)). The effect of oxyfluorfen on the changes of those parameters was interpreted as a result of herbicide mode of action at molecular level of alga cellular system. This study indicated for some photosynthetic and enzymatic biomarkers to be useful indicators of toxicity effect induced in non-target alga species. Determination of biomarkers' sensitivity order may facilitate their selection to be used in environmental risk assessment of polluted water.

Effects of Methanol on Photosynthetic Processes and Growth of Lemna gibba¶

Effects of methanol on growth and photosynthetic activity of Lemna gibba exposed under continuous illumination were examined. As a higher plant, L. gibba appeared to be much more sensitive to methanol inhibitory effect compared with some algae (Theodoridou et al. [2002] Biochim. Biophys. Acta, 1573, 189-198). We found that stimulatory or inhibitory effects were strongly dependent on the methanol concentration and the time of exposure. When the exposure was up to 0.2% methanol, the growth rate of biomass was improved by 50%. However, stimulatory effect of methanol appeared to be smaller when plants were exposed for 48 h compared with 24 h. Increase in biomass induced by methanol was not based on the increase in primary photosynthetic process but rather on accommodation of energy dissipation during photosynthesis. Inhibitory effect on the growth of L. gibba already observed for 0.5% methanol was strongly associated with the increase in the nonphotochemical energy dissipation. The ratio between biomass and methanol concentration appeared to determine the stimulatory or the inhibitory effect. Suggested explanations for the stimulatory and the inhibitory effects are presented.

Evaluation of the effects of diuron and its derivatives on Lemna gibba using a fluorescence toxicity index

The herbicide diuron (DCMU) [3-(3,4-dichlorophenyl)-1,1-dimethylurea] is largely used in agricultural practices which contribute to water pollution in large areas. Its degradation induced by light or microbial activity is known to be a slow process, and may result in the accumulation of DCMU derivatives in the environment. In this report we used the yield of PSII variable fluorescence of Lemna gibba affected by the DCMU derivatives DCPMU [1-(3,4-dichlorophenyl)-3-methylurea], DCPU [1-(3,4-dichlorophenyl)urea], and DCA [3,4-dichloroaniline] to calculate the fluorescence toxicity index. We found the fluorescence toxicity index to be a useful parameter to evaluate the inhibitory effect on PSII electron transport in L. gibba exposed to DCMU and its derivatives. The variations observed for the inhibitory effect between DCMU and its derivatives seem to be caused by the modification of the dimethylurea group within the DCMU molecule. The fluorescence toxicity index demonstrated a strong quantitative dependency between the inhibitory effect of PSII electron transport and pollutant concentrations. We propose the fluorescence toxicity index to be a useful tool for future bioassays in evaluating the quality of water polluted with herbicides that induce an inhibition to PSII photochemistry.

Evaluation of different algal species sensitivity to mercury and metolachlor by PAM-fluorometry

In this study, the pulse-amplitude-modulation (PAM)-fluorometric method was used to evaluate the difference in the sensitivity to mercury (Hg) and metolachlor of six algal species: Ankistrodesmus falcatus, Selenastrum capricornutum, Chlorella vulgaris, Nannoplankton (PLS), Microcystis aeruginosa and Pediastrum biwae. We found that the fluorescence parameters (phiM, the maximal photosystem II (PSII) quantum yield, phi'M, the operational PSII quantum yield at steady state of electron transport, Q(P), the photochemical quenching value, and Q(N), the non-photochemical quenching value) were appropriate indicators for inhibitory effects of mercury but only phi'M and Q(N) were useful for metolachlor. The examined algal species showed very different levels of sensitivity to the effect of Hg and of metolachlor. The most sensitive species to Hg and metolachlor were respectively M. aeruginosa and A. falcatus, while the least sensitive were C. vulgaris and P. biwae. We interpreted these differences by the action mode of pollutants and by the different metabolism properties and morphological characteristics between algal species. These results related to fluorescence parameters may offer useful tool to be used in bioassay for different pollutants. Heterogeneous algal sensitivity to the same pollutant suggests the need to use a battery of species to evaluate the effects of mixtures of pollutants in aquatic systems.

Spectroscopic analysis of desiccation-induced alterations of the chlorophyllide transformation pathway in etiolated barley leaves

Effects of water deficit on the chlorophyllide (Chlide) transformation pathway were studied in etiolated barley (Hordeum vulgare) leaves by analyzing absorption spectra and 77-K fluorescence spectra deconvoluted in components. Chlide transformations were examined in dehydrated leaves exposed to a 35-ms saturating flash triggering protochlorophyllide (Pchlide) and Chlide transformation processes. During the 90 min following the flash, we found that dehydration induced modifications of Chlide transformations, but no effect on Pchlide phototransformation into Chlide was observed. During this time, content of NADPH-Pchlide oxydoreductase in leaves did not change. Chlide transformation process in dehydrated leaves was characterized by the alteration of the Shibata shift process, by the appearance of a new Chlide species emitting at 692 nm, and by the favored formation of Chl(ide) A(668)F(676). The formation of Chl(ide) A(668)F(676), so-called "free Chlide," was probably induced by disaggregation of highly aggregated Chlide complexes. Here, we offer evidence for the alteration of photoactive Pchlide regeneration process, which may be caused by the desiccation-induced inhibition of Pchlide synthesis.