Capillary zone electrophoresis for analysis of phytochelatins and other thiol peptides in complex biological samples derivatized with monobromobimane

Long-term impact of cadmium in protonema cultures of Physcomitrella patens

Antioxidative responses of axenic protonema cultures of the moss Physcomitrella patens exposed to 10 μM Cd over 40 d were studied. Cd treatment suppressed growth by ca. 75% with concomitant browning of some filaments and suppression of chlorophyll autofluorescence but had no impact on tissue water content. Despite this negative growth responses which could be related to enhanced ROS formation (as detected using fluorescence staining reagents for total ROS, hydroperoxides and lipid peroxidation), some metabolites revealed strong elevation by Cd which could contribute to attenuation of long-term Cd stress (elevation of ascorbic, malic and citric acids). Molar ratio of malate to Cd was 12.7 and citrate to Cd 2.5, thus potentially contributing to Cd chelation. Interestingly, GSH/GSSG pool and nitric oxide formation remained unaltered by Cd. Accumulation of Cd reached 82 μg/g DW with bioaccumulation factor of 73. Data indicate that Cd induces elevation of potentially protective metabolites even after prolonged exposure though they do not prevent oxidative stress sufficiently.

Nitric oxide affects cadmium-induced changes in the lichen Ramalina farinacea

Metabolic responses of epiphytic lichen Ramalina farinacea to cadmium (Cd) and/or nitric oxide (NO) scavenger (cPTIO) were studied. Accumulation of Cd and other metallic nutrients was not affected by cPTIO while total and absorbed amounts differed. Cd-induced NO formation was suppressed by cPTIO but ROS signal was synergistically enhanced, confirming that NO is essential to keep ROS under control. This excessive ROS generation could be a reason for depleted amount of all fatty acids, including SFAs, MUFAs and PUFAs. Total content of fatty acids reached 3.89 mg/g DW in control with linoleic (40%), palmitic (24%), oleic (12.8%) and stearic (8%) acids as major compounds: interestingly, shift in relative ratio of saturated (from 40 to 35% of total FAs) versus polyunsaturated fatty acids (from 42 to 48% of total FAs) was observed. Glutathione was suppressed by all treatments but Krebs acids were almost unaffected by cPTIO, indicating no regulatory role of NO in their accumulation. On the contrary, Cd-induced elevation in NO signal was related to increase in ascorbate and proline content while cPTIO suppressed it, indicating a tight relation between NO and these metabolites. Data are compared also with algae and vascular plants to show similarities between various life lineages.

Metal-induced oxidative stress in terrestrial macrolichens

Short-term (24 h) responses of Cladonia arbuscula subsp. mitis and Cladonia furcata to copper (CuII) or chromium (CrIII) excess (10 or 100 μM) were compared. C. arbuscula accumulated more Cu and Cr at higher metal doses but both species revealed depletion of K and/or Ca amount. Not only Cu but also Cr typically elevated reactive oxygen species (ROS) formation (fluorescence microscopy detection of total ROS and hydrogen peroxide) and depleted nitric oxide (NO) signal, with Cu showing more negative impact on lipid peroxidation (BODIPY 581/591 C11 staining reagent). Metals and staining reagents also affected anatomical responses and photobiont/mycobiont visibility. Principally different impact of Cu and Cr was observed at antioxidative metabolites level, indicating various ways of metal-induced ROS removal and/or metal chelation: Cu strongly depleted glutathione (GSH) and stimulated phytochelatin 2 (PC2) content while ascorbic acid accumulation was depleted by Cu and stimulated by Cr. Subsequent experiment with GSH biosynthetic inhibitor (buthionine sulfoximine, BSO) revealed that 48 h of exposure is needed to deplete GSH and BSO-induced depletion of GSH and PC2 amounts under Cu or Cr excess elevated ROS but depleted NO. These data suggest close relations between thiols, NO and appearance of oxidative stress (ROS generation) under metallic stress also in lichens.

Metabolic responses of terrestrial macrolichens to nickel

Short-term (24 h) responses of Cladonia arbuscula subsp. mitis (formerly known as Cladina and this name is used to distinguish the tested species) and Cladonia furcata to nickel (Ni²⁺) excess (10 or 100 μM) were compared. Cladonia accumulated more Ni at higher Ni dose (1.717 mg total Ni/g DW), K amount was unaffected and Ca amount decreased in Cladina only. Fluorescence microscopy detection of total/general ROS and hydrogen peroxide showed Ni-stimulated increase in both species being more pronounced in Cladonia and in mycobiont partner mainly. Nitric oxide visualization (diaminonaphthalene staining) also revealed elevation in response to Ni that could contribute to synthesis of protective metabolites: they may include ascorbic acid or reduced glutathione which increased in Ni-exposed Cladina or Cladonia, respectively. Only low content of phytochelatin 2 was detected in Ni-treated Cladonia and the role in Ni chelation is not apparent. Among aliphatic organic acids, content of citric or succinic acid was not or slightly affected by Ni, production of malic acid dropped by ca. 50% in both species and α-ketoglutaric acid showed the opposite behavior in the tested species. Data indicate that even short-term Ni treatments induce metabolic changes and symptoms of oxidative stress in lichens, confirming that nickel is not non-toxic metal as frequently visible from standard biochemical assays of basic physiology. Ascorbic acid and GSH rather than aliphatic organic acids seem to contribute to Ni tolerance.

Development of the HPLC-ELSD method for the determination of phytochelatins and glutathione in Perilla frutescens under cadmium stress conditions

A rapid, accurate and simple method was developed for the simultaneous determination of glutathione (GSH) and phytochelatins (PCs) by high-performance liquid chromatography (HPLC) with an evaporative light-scattering detector. GSH, phytochelatin 2 (PC2), PC3, PC4, PC5 and PC6 can be separated with baseline separation within 9 min using a Venusil AA column (250 mm × 4.6 mm i.d., 5 µm particle sizes). Acetonitrile and water containing 0.1% trifluoroacetic acid (0.1%) were employed as the mobile phase for the gradient elution. The drift tube temperature and flow rate of the carrier gas (N2) were 50°C and 1.5 l min-1, respectively. Under optimum conditions, good linear regression equations of six analytes were obtained with the detection limits ranging from 0.2 to 0.5 µg ml-1. The proposed method has been applied successfully for the quantification of GSH and PCs in Perilla frutescens (a cadmium hyperaccumulator) under cadmium stress. The recoveries were between 82.9% and 115.3%.

Accumulation and toxicity of organochlorines in green microalgae

Toxicity of mine dump effluent containing five hexachlorocyclohexane (α, β, γ, δ and ε-HCH, sum 159.4 μg/L) and two trichlorobenzene (TCB, sum 65.2 μg/L) isomers to two microalgae (Scenedesmus quadricauda and Coccomyxa subellipsoidea) was studied over 24 h exposure and also with 2- and 10-fold diluted stock solution (i.e. 1×, 0.5× and 0.1× strength). Individual isomers revealed rather dose-dependent accumulation typically higher in Scenedesmus than in Coccomyxa (max. sum of HCH 14.99 μg/g DW with bioaccumulation factor 94) and δ-HCH was dominant isomer. TCB isomers showed low accumulation in algae. 0.1× dose elevated chlorophylls and carotenoids in Coccomyxa while enzymatic activities (SOD, CAT, and APX), thiols (glutathione and phytochelatin 2) and ascorbic acid were rather elevated by 1× dose in both species. Malic acid, rather than citric acid, increased in response to 0.5× and 1× concentration. Sum of fatty acids was higher in Coccomyxa than in Scenedesmus with palmitic, oleic, linoleic and α-linolenic acids being dominant compounds in both species. Detailed profiling revealed that saturated and monounsaturated fatty acids increased in Coccomyxa while polyunsaturated fatty acids in Scenedesmus in response to increasing dose of organochlorines. Accumulation of organochlorines and metabolic responses in algae are reported here for the first time.

Calcium availability but not its content modulates metal toxicity in Scenedesmus quadricauda

Impact of calcium nutrition (pre-culture on solid medium with standard or elevated Ca dose, i. e. 0.17 and 4.40mM marked as low and high Ca) on acute metal toxicity (Cd, Mn and Pb, 24h of exposure to 10µM) in freshwater green alga Scenedesmus quadricauda was studied. Surprisingly, Ca content differed only slightly between low and high Ca samples and applied metals rather suppressed its amount. Na content was higher in metal-exposed high Ca samples, indicating that Ca/Na ratio may affect accumulation of metals. Content of heavy metals increased in order Cd < Mn < Pb and high Ca samples contained less metal than low Ca samples at least in absorbed fraction. Accumulation of ascorbic acid and thiols (GSH - glutathione and PC2 - phytochelatin 2) was affected mainly by Cd, GSH also by Mn and PC2 by Pb with often significant differences between low Ca and high Ca samples. Calcium nutrition also affected responses of algae to metals at the level of antioxidative enzyme activities (SOD, APX, and CAT) and elevated values were typically found in high Ca samples while ROS (hydrogen peroxide and superoxide radical) were mainly depleted in Mn treatment. These data confirm that Ca nutrition affects accumulation of metals in algae and metabolic parameters as observed in vascular plants but, unlike them, rather Ca/Na ratio than absolute Ca content seems to regulate the uptake of metals.

Influence of sulphate on the reduction of cadmium toxicity in the microalga Chlamydomonas moewusii

Cadmium is considered as one of the most hazardous metals for living organism and ecosystems. Environmental factors play an important role since they alter the toxicity of metals by varying the bioavailability of these elements for the organisms. The aim of the present study was to investigate, using the freshwater microalga Chlamydomonas moewusii, the existence of an interaction between cadmium and sulphate as a factor that varied the toxicity of this metal. Different cell parameters such as cell growth, content of chlorophylls and biosynthesis of phytochelatins (PCs) were determined. A two-way ANOVA showed that the interaction had a significant effect size of 21% (p<0.001) for the growth of this microalga and around of a 6% on the content of chlorophylls/cell. The effect of this inhibition was that when the concentration of sulphate increased, a lower toxic effect of cadmium on the growth and on the content of chlorophylls was observed. In addition, the increase of sulphate concentration allowed the biosynthesis of a higher amount of PCs and/or PCs with higher chain length. This higher biosynthesis was responsible for the reduction of the toxic effect of cadmium and explained the interaction.

Effect of cadmium on selected physiological and morphological parameters in metallicolous and non-metallicolous populations of Echium vulgare L

Cadmium tolerance of three populations of Echium vulgare L., naturally occurring on two Zn-Pb waste deposits (metallicolous populations M1, M2) and on an uncontaminated site (non-metallicolous population, NM) was investigated. The plants were cultivated in hydroponics at 0, 5, 15, 30, or 50μM Cd for 14 days. Although Cd reduced the content of photosynthetic pigments indifferently in the three populations, plant growth parameters and root viability analyses confirmed different Cd tolerances decreasing in the order M1>M2>NM in the populations studied. Organic acids (tartrate, malate, citrate, succinate) were not responsible for the elevated Cd tolerance of the metallicolous populations, although malate and citrate might participate in Cd detoxification in the roots of the M1 and M2. Phytochelatin concentrations were higher in the roots of M1 and M2 populations of E. vulgare, suggesting their role in Cd detoxification and different Cd tolerances.

Sulphate, more than a nutrient, protects the microalga Chlamydomonas moewusii from cadmium toxicity

Sulphur is an essential macroelement that plays important roles in living organisms. The thiol rich sulphur compounds, such as cysteine, γ-Glu-Cys, glutathione and phytochelatins participate in the tolerance mechanisms against cadmium toxicity. Plants, algae, yeasts and most prokaryotes cover their demand for reduced sulphur by reduction of inorganic sulphate. The aim of this study was to investigate, using a bifactorial experimental design, the effect of different sulphate concentrations in the nutrient solution on cadmium toxicity in the freshwater microalga Chlamydomonas moewusii. Cell growth, kinetic parameters of sulphate utilization and intracellular concentrations of low-molecular mass thiol compounds were determined. A mathematical model to describe the growth of this microalga based on the effects of sulphate and cadmium was obtained. An ANOVA revealed an interaction between them, 16% of the effect sizes was explained by this interaction. A higher amount of sulphate in the culture medium allowed a higher cadmium tolerance due to an increase in the thiol compound biosynthesis. The amount of low-molecular mass thiol compounds, mainly phytochelatins, synthesized by this microalga was significantly dependent on the sulphate and cadmium concentrations; the higher phytochelatin content was obtained in cultures with 4 mg Cd/L and 1mM sulphate. The maximum EC50 value (based on nominal cadmium concentration) reached for this microalga was 4.46 ± 0.42 mg Cd/L when the sulphate concentration added to the culture medium was also 1mM. An increase in the sulphate concentration, in deficient environments, could alleviate the toxic effect of this metal; however, a relative excess is also negative. The results obtained showed a substrate inhibition for this nutrient. An uncompetitive model for sulphate was chosen to establish the mathematical model that links both factors.

Intracellular speciation and transformation of inorganic mercury in marine phytoplankton

Metal speciation is closely related to toxicity in aquatic organisms, but quantitative study of mercury transformation has rarely been reported. In this study, the ability of three marine phytoplankton species, including a green alga Chlorella autotrophica, a flagellate Isochrysis galbana and a diatom Thalassiosira weissflogii, to convert inorganic mercury were examined. We found that all algae tested were able to transform Hg(II) into dissolved gaseous mercury (DGM), phytochelatin (PC) complexes and metacinnabar (β-HgS). The most tolerant species, T. weissflogii, generally produced the highest level of PCs and β-HgS. Attributed to the highest DGM production ability, C. autotrophica accumulated the least Hg, but was the most sensitive due to low PC induction and β-HgS formation. Of the added Hg(II), less than 5% was reduced to DGM per day in all species. Of the intracellular Hg, <20% and 20-90% were chelated by PCs and transformed into β-HgS, respectively. These results suggest that intracellular biotransformation might be more important than bioavailability regulation in Hg(II) detoxification in marine phytoplankton.

Cadmium toxicity on the freshwater microalga Chlamydomonas moewusii Gerloff: Biosynthesis of thiol compounds

Cadmium (Cd) toxicity and production of different thiols (phytochelatins, glutathione, gamma-Glu-Cys and cysteine) were studied in the microalga Chlamydomonas moewusii exposed to different concentrations of this metal (1, 2, 4, 6, 8, and 10 mg/L) for 96 h. The inhibitory effect of Cd on growth was demonstrated. The value of EC50 (metal concentration which reduces the population growth to 50% of the control) obtained for this microalga was estimated at 4.1 +/- 0.8 mg/L of Cd after 96 h of exposure. The amount of thiol compounds synthesized by C. moewusii changed with Cd concentration. Cysteine concentrations were significantly higher compared to those of gamma-Glu-Cys and glutathione in all the Cd concentrations assayed. The amino acid cysteine reached its higher levels in those cultures in which a decrease in the concentration of phytochelatins (PCs) was observed. Both cysteine and glutathione concentrations showed significant differences along the Cd concentrations assayed, while the amount of gamma-Glu-Cys detected remained stable. The PCs detected were of two, three, and four subunits. The level of PC(2) was higher than that of PC(3) and PC(4). PC(4) was detected only in the cultures exposed to the Cd concentrations of 1 and 2 mg/L, in which the synthesis of phytochelatins was higher. A rapid increase in the production of PC(2) and PC(3) was observed up to a Cd concentration of 2 mg/L, after which their levels began to decrease. Phytochelatins were not detected in cultures without Cd (controls) and in those exposed to the maximum Cd concentration (10 mg/L), in which cell growth was completely inhibited.

Separation and quantification of monothiols and phytochelatins from a wide variety of cell cultures and tissues of trees and other plants using high performance liquid chromatography

The HPLC method presented here for the quantification of metal-binding thiols is considerably shorter than most previously published methods. It is a sensitive and highly reproducible method that separates monobromobimane tagged monothiols (cysteine, glutathione, gamma-glutamylcysteine) along with polythiols (PC(2), PC(3), PC(4) and PC(5)) within 23min from a wide variety of samples. Total run time of the method is 35min. Detection limits for thiols is 33fmol for 10microlL injection. This method will be applicable to study the metal detoxification mechanisms for a wide variety of cell cultures and tissues of plants and trees including algae, Arabidopsis, crambe, rice, and red spruce.

Recent developments in CE and CEC of peptides

The article brings a comprehensive survey of recent developments and applications of high-performance capillary electromigration methods, zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC, and electrochromatography, to analysis, preparation, and physicochemical characterization of peptides. New approaches to the theoretical description and experimental verification of electromigration behavior of peptides and to methodology of their separations, such as sample preparation, adsorption suppression, and detection, are presented. Novel developments in individual CE and CEC modes are shown and several types of their applications to peptide analysis are presented: conventional qualitative and quantitative analysis, purity control, determination in biomatrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid and sequence analysis, and peptide mapping of proteins. Some examples of micropreparative peptide separations are given and capabilities of CE and CEC techniques to provide important physicochemical characteristics of peptides are demonstrated.

Determination and characterization of phytochelatins by liquid chromatography coupled with on line chemical vapour generation and atomic fluorescence spectrometric detection

Liquid chromatography (LC) coupled on line with UV/visible diode array detector (DAD) and cold vapour generation atomic fluorescence spectrometry (CVGAFS) has been developed for the speciation, determination and characterization of phytochelatins (PCs). The method is based on a bidimensional approach, e.g. on the analysis of synthetic PC solutions (apo-PCs and Cd(2+)-complexed PCs) (i) by size exclusion chromatography coupled to UV diode array detector (SEC-DAD); (ii) by the derivatization of PC -SH groups in SEC fractions by p-hydroxymercurybenzoate (PHMB) and the indirect detection of PC-PHMB complexes by reversed phase liquid chromatography coupled to atomic fluorescence detector (RPLC-CVGAFS). MALDI-TOF/MS (matrix assisted laser desorption ionization time of flight mass spectrometry) analysis of underivatized synthetic PC samples was performed in order have a qualitative information of their composition. Quantitative analysis of synthetic PC solutions has been performed on the basis of peak area of PC-PHMB complexes of the mercury specific chromatogram and calibration curve of standard solution of glutathione (GSH) complexed to PHMB (GS-PHMB). The limit of quantitation (LOQ) in terms of GS-PHMB complex was 90 nM (CV 5%) with an injection volume of 35 microL, corresponding to 3.2 pmol (0.97 ng) of GSH. The method has been applied to analysis of extracts of cell cultures from Phaeodactylum tricornutum grown in Cd-containing nutrient solutions, analysed by SEC-DAD-CVGAFS and RPLC-DAD-CVGAFS.