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

A Sensitive Response Index Selection for Rapid Assessment of Heavy Metals Toxicity to the Photosynthesis of Chlorella pyrenoidosa Based on Rapid Chlorophyll Fluorescence Induction Kinetics

Heavy metals as toxic pollutants have important impacts on the photosynthesis of microalgae, thus seriously threatening the normal material circulation and energy flow of the aquatic ecosystem. In order to rapidly and sensitively detect the toxicity of heavy metals to microalgal photosynthesis, in this study, the effects of four typical toxic heavy metals, chromium (Cr(VI)), cadmium (Cd), mercury (Hg), and copper (Cu), on nine photosynthetic fluorescence parameters (φ_Po, Ψ_Eo, φ_Eo, δ_Ro, Ψ_Ro, φ_Ro, F_V/F_O, PI_ABS, and S_m) derived from the chlorophyll fluorescence rise kinetics (OJIP) curve of microalga Chlorella pyrenoidosa, were investigated based on the chlorophyll fluorescence induction kinetics technique. By analyzing the change trends of each parameter with the concentrations of the four heavy metals, we found that compared with other parameters, φ_Po (maximum photochemical quantum yield of photosystem II), F_V/F_O (photochemical parameter of photosystem II), PI_ABS (photosynthetic performance index), and S_m (normalized area of the OJIP curve) demonstrated the same monotonic change characteristics with an increase in concentration of each heavy metal, indicating that these four parameters could be used as response indexes to quantitatively detect the toxicity of heavy metals. By further comparing the response performances of φ_Po, F_V/F_O, PI_ABS, and S_m to Cr(VI), Cd, Hg, and Cu, the results indicated that whether it was analyzed from the lowest observed effect concentration (LOEC), the influence degree by equal concentration of heavy metal, the 10% effective concentration (EC₁₀), or the median effective concentration (EC₅₀), the response sensitivities of PI_ABS to each heavy metal were all significantly superior to those of φ_Ro, F_V/F_O, and S_m. Thus, PI_ABS was the most suitable response index for sensitive detection of heavy metals toxicity. Using PI_ABS as a response index to compare the toxicity of Cr(VI), Cd, Hg, and Cu to C. pyrenoidosa photosynthesis within 4 h by EC₅₀ values, the results indicated that Hg was the most toxic, while Cr(VI) toxicity was the lowest. This study provides a sensitive response index for rapidly detecting the toxicity of heavy metals to microalgae based on the chlorophyll fluorescence induction kinetics technique.

Chromium effects on photosynthetic electron transport in pea (Pisum sativum L.)

MAIN CONCLUSION

Components of the photosynthetic electron transport chain in pea (Pisum sativum L.) leaves under in vivo conditions showed the following sensitivity to the inhibitory action of chromium(VI): intersystem electron transport > photosystem I > photosystem II. Inhibitory effects of chromium (VI) (K2Cr2O7, Cr) on the light reactions of photosynthesis were studied in vivo in Pisum sativum L. by using Multi-function Plant Efficiency Analyser (M-PEA-2). Photosynthetic parameters related to photosystem (PS) II, PSI and intersystem electron carriers were calculated from the light-induced kinetics of prompt chlorophyll a fluorescence (OJIP transient), delayed chlorophyll a fluorescence (DF), and 820 nm modulated reflection (MR). We showed that the I2 step of DF induction is sensitive to inhibition of the Q0 site of the cytochrome b6f complex. Such parameters as δRo of the JIP test related to the functional state of photosynthetic reactions beyond the PQ pool, Vred of the MR induction assigned to the overall rate of P700+ and plastocyanin reduction, and I2 step of the DF induction were significantly altered in the presence of low-dose Cr(VI). Moderate doses of Cr affected mainly PSI-related parameters including Vox and ΔMR parameters of the MR induction, whereas high-dose treatment influenced JIP test parameters φPo(= FV/FM) and ψEo related to PSII. The obtained results showed that the earliest Cr(VI) effect on the photosynthetic electron transport chain manifests itself by inhibition of the intersystem electron transport, rather, at the level of the cytochrome b6f complex. Inhibitory effects of Cr on PSI were more pronounced than those on PSII. Sensitivity of the used kinetic parameters toward the functional state of photosynthetic reactions makes this approach suitable for early diagnostics of toxic action of pollutants on plants.

Chromium hazard and risk assessment: New insights from a detailed speciation study in a standard test medium

Despite the consensus about the importance of chemical speciation in controlling the bioavailability and ecotoxicity of trace elements, detailed speciation studies during laboratory ecotoxicity testing remain scarce, contributing to uncertainty when extrapolating laboratory findings to real field situations in risk assessment. We characterized the speciation and ecotoxicological effects of chromium (Cr^III and Cr^VI ) in the International Organization for Standardization (ISO) medium for algal ecotoxicity testing. Total and dissolved (< 0.22 μm) Cr concentrations showed little variability in media spiked with Cr^VI , whereas dissolved Cr concentration decreased by as much as 80% over a 72-h time period in medium amended with Cr^III . Analyses by ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) highlighted the absence of redox interconversion between Cr^III or Cr^VI both in the presence and absence of algal cells (Raphidocelis subcapitata). Furthermore, the concentration of ionic Cr^III dropped below detection limits in less than 2 h with the corresponding formation of carbonate complexes and Cr hydroxides. Precipitation of Cr^III in the form of colloidal particles of variable diameters was confirmed by nanoparticle (NP) tracking analysis, single particle ICP-MS, and single particle counting. In terms of time-weighted dissolved (< 0.22 μm) Cr concentration, Cr^III was 4 to 10 times more toxic than Cr^VI . However, Cr^III ecotoxicity could arise from interactions between free ionic Cr^III and algae at the beginning of the test, from the presence of Cr-bearing NPs, or from a combination of the 2. Future ecotoxicological studies must pay more attention to Cr speciation to reliably compare the ecotoxicity of Cr^III and Cr^VI . Environ Toxicol Chem 2018;37:983-992. © 2017 SETAC.

Bioaccumulation and subcellular partitioning of Cr(III) and Cr(VI) in the freshwater green alga Chlamydomonas reinhardtii

Chromium occurs in aquatic environments under two main redox forms, namely Cr(III) and Cr(VI), with different geochemical and biochemical properties. Cr(VI) readily crosses biological membranes of living organisms and once inside the cells it undergoes a rapid reduction to Cr(III). The route of entry for the latter form is, however, poorly known. Using the radioactive tracer ⁵¹Cr we compared the accumulation (absorption and adsorption) of the two Cr forms by the green unicellular alga Chlamydomonas reinhardii after 1h and 72h of exposure to 100nM of either Cr(III) or Cr(VI) at pH 7. Both Cr forms had similar accumulation, with a major part in the extracellular (adsorbed) fraction after 1h and a major part of total accumulated Cr in the intracellular (absorbed) fraction after 72h. We also investigated the intracellular partitioning of Cr using an operational fractionation scheme and found that both Cr forms had similar distributions among fractions: Cr was mostly associated with organelles (23±12% after 1h and 37±7% after 72h) and cytosolic heat-stable proteins and peptides (39±18% after 1h and 35±3% after 72h) fractions. Further investigations using a metallomic approach (SEC-ICP-MS) were performed with the heat-stable proteins and peptides fraction to compare the distribution of the two Cr forms among various biomolecules of this fraction. One Cr-binding biomolecule (∼28kDa) appeared after 1h of exposure for both Cr species. After 72h another biomolecule of lower molecular weight (∼0.7kDa) was involved in binding Cr and higher signal intensities were observed for Cr(VI) than for Cr(III). We show, for the first time, that both Cr(III) and Cr(VI) have similar fate within algal cells, supporting the tenet that a unique redox form occurs within cells.

Effect of chromium oxide (III) nanoparticles on the production of reactive oxygen species and photosystem II activity in the green alga Chlamydomonas reinhardtii

With the growth of nanotechnology and widespread use of nanomaterials, there is an increasing risk of environmental contamination by nanomaterials. However, the potential implications of such environmental contamination are hard to evaluate since the toxicity of nanomaterials if often not well characterized. The objective of this study was to evaluate the toxicity of a chromium-based nanoparticle, Cr2O3-NP, used in a wide diversity of industrial processes and commercial products, on the unicellular green alga Chlamydomonas reinhardtii. The deleterious impacts of Cr2O3-NP were characterized using cell density measurements, production of reactive oxygen species (ROS), esterase enzymes activity, and photosystem II electron transport as indicators of toxicity. Cr2O3-NP exposure inhibited culture growth and significantly lowered cellular Chlorophyll a content. From cell density measurements, EC50 values of 2.05±0.20 and 1.35±0.06gL(-1) Cr2O3-NP were obtained after 24 and 72h of exposure, respectively. In addition, ROS levels were increased to 160.24±2.47% and 59.91±0.15% of the control value after 24 and 72h of exposition to 10gL(-1) Cr2O3-NP. At 24h of exposure, the esterase activity increased to 160.24% of control value, revealing a modification of the short-term metabolic response of algae to Cr2O3-NP exposure. In conclusion, the metabolism of C. reinhardtii was the most sensitive to Cr2O3-NP after 24h of treatment.