A 37-kDa peroxidase secreted from liverworts in response to chemical stress

Comparison of 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) and perfluorooctane sulfonate (PFOS) accumulation and toxicity in mung bean

With the regulation of perfluorooctanesulfonate (PFOS), 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA) has been used as a potential PFOS alternative in electroplating. In this study, the uptake, translocation and phytotoxicity of PFOS and 6:2 Cl-PFESA in mung bean (Vigna radiata (Linn.) Wilczek.) were investigated. The uptake kinetics of PFOS and 6:2 Cl-PFESA fit the Michaelis-Menten equation well, suggesting that the uptake is a carrier-mediated process. The root concentration factor (RCF) of 6:2 Cl-PFESA (34.55 mL g^-1 dw) was 1.27 times that of PFOS (27.11 mL g^-1 dw), and the translocation factor (TF) of 6:2 Cl-PFESA (0.177) was 1.07 times that of PFOS (0.165). Exposure to 6:2 Cl-PFESA and PFOS both resulted in the inhibition of mung bean seedling development. Treatment with 6:2 Cl-PFESA and PFOS led to the concentration-dependent elevation of malondialdehyde (MDA), carbonyl groups, and phosphorylated histone H2AX (γ-H2AX) levels in mung bean roots. The MDA and carbonyl group contents induced by 6:2 Cl-PFESA were 1.10-1.35 and 1.03-1.14 times, respectively, those of PFOS. The hydroxyl free radical (·OH) levels in mung bean roots after exposure to PFOS and 6:2 Cl-PFESA were elevated significantly, and the ·OH levels induced by 6:2 Cl-PFESA were higher than those induced by PFOS. Hydroxyl free radical levels were positively correlated with the MDA and carbonyl group contents in mung bean roots (p < 0.05). The dynamic changes in some antioxidative enzyme activities in mung bean seedlings were determined, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). The results demonstrated the phytotoxicities of 6:2 Cl-PFESA and PFOS to mung bean in the early developmental stage. 6:2 Cl-PFESA is more harmful to mung beans than PFOS. The production of hydroxyl radical is the mechanism that causes the toxicity of PFOS and 6:2 Cl-PFESA toward plants.

Effect of Salicylic Acid Pre-Treatment after Long-Term Desiccation in the Moss Syntrichia ruralis (Hedw.) Web. and Mohr

The main objective of this research was to examine the effects of exogenous salicylic acid (SA) and to study the seasonal variation of the chlorophyll a fluorescence parameters and antioxidant enzymatic activities in desiccation-tolerant moss species Syntrichia ruralis (Hedw.) Web. and Mohr. Aqueous 0.001 M SA solution was sprayed on the moss cushions collected from semi-arid sandy grassland, Hungary in three seasons (spring, summer, autumn). These cushions were kept under the observation for 10 Days. Chlorophyll a fluorescence parameters, i.e., maximum photochemical quantum yield of PS II (Fv/Fm), effective photochemical quantum yield of PS II (ΦPSII), non-photochemical quenching (NPQ), and antioxidant enzymatic activities, i.e., ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (POD), and protein content were determined. The results showed the increase of Fv/Fm in spring and autumn season while ΦPSII was reduced significantly during spring and summer season after treatment with SA compared to control. SA-treated mosses showed higher values of non-photochemical quenching (NPQ) during the spring and autumn season than in summer. Activities of enzyme APX and CAT were found to increase in SA-treated except POD activity. In SA-treated moss cushions, lower protein content was found. It can be concluded that seasonal variation has been observed in chlorophyll fluorescence and antioxidant system after long term of desiccation in S. ruralis species that could be because of SA and might be due to fluctuations in conditions of their habitat, duration of light intensity, temperature and precipitation.

Activity of Redox Enzymes in the Thallus of Anthoceros natalensis

Anthocerotophyta (hornworts) belong to a group of ancient nonvascular plants and originate from a common ancestor with contemporary vascular plants. Hornworts represent a unique model for investigating mechanisms of formation of stress resistance in higher plants due to their high tolerance to the action of adverse environmental factors. In this work, we demonstrate that the thallus of Anthoceros natalensis exhibits high redox activity changing under stress. Dehydration of the thallus is accompanied by the decrease in activities of intracellular peroxidases, DOPA-peroxidases, and tyrosinases, while catalase activity increases. Subsequent rehydration results in the increase in peroxidase and catalase activities. Kinetic features of peroxidases and tyrosinases were characterized as well as the peroxidase isoenzyme composition of different fractions of the hornwort cell wall proteins. It was shown that the hornwort peroxidases are functionally similar to peroxidases of higher vascular plants including their ability to form superoxide anion-radical. The biochemical mechanism was elucidated, supporting the possible participation of peroxidases in the formation of reactive oxygen species (ROS) via substrate-substrate interactions in the hornwort thallus. It has been suggested that the ROS formation by peroxidases is an evolutionarily ancient process that emerged as a protective mechanism for enhancing adaptive responses of higher land plants and their adaptation to changing environmental conditions and successful colonization of various ecological niches.

Toxic effects of chlortetracycline on maize growth, reactive oxygen species generation and the antioxidant response

The toxicity of chlortetracycline (CTC) on maize (Zea mays L.) growth and reactive oxygen species (ROS) generation was studied. The root and shoot lengths and fresh weights of maize seedlings were inhibited by CTC treatment (p < 0.05). Root length was more sensitive than other parameters with the EC10 value of 0.064 mg/L. The spin trapping technique followed by electron paramagnetic resonance (EPR) analysis was used to quantify the ROS production. The ROS generated in maize roots after exposure to CTC was identified as hydroxyl radical (*OH). The EPR signal intensity correlated positively with the logarithm of CTC concentrations exposed (p < 0.05). The dynamic changes of malondialdehyde (MDA) contents and the antioxidative enzyme activities in maize roots were also determined. As compared to the control group, CTC was found to significantly increase MDA content. Treatment of maize roots with the *OH scavenger sodium benzoate (SB) reduced the MDA content and enhanced the antioxidative enzyme activities. The results demonstrated the harmfulness of CTC at high dose to maize in the early developmental stage, and clarified that the inducement of *OH is one of the mechanisms of CTC toxicity.

Cell wall peroxidases in the liverwort Dumortiera hirsuta are responsible for extracellular superoxide production, and can display tyrosinase activity

In our earlier work, we showed that the liverwort Dumortiera hirsuta produces an extracellular oxidative burst of superoxide radicals during rehydration following desiccation stress. The oxidative burst is a common early response of organisms to biotic and abiotic stresses, with suggested roles in signal transduction, formation of protective substances such as suberin, melanin and lignin and defense against pathogens. To discover which enzymes are responsible for the extracellular superoxide production, we isolated apoplastic fractions from D. hirsuta, surveyed for the presence of potential redox enzymes, and performed non-denaturing polyacrylamide gel electrophoresis activity stains. Various isoforms of peroxidase (EC 1.11.1.7) and tyrosinase (o-diphenolase) (EC 1.10.3.1) were present at significant levels in the apoplast. In-gel activity staining revealed that some peroxidases isoforms could produce superoxide, while tryosinases could readily metabolize 3,4-dihydroxy phenyl l-alanine (l-dopa) into melanins. Interestingly, some peroxidase isoforms could oxidize the native tyrosinase substrate l-dopa at significant levels, even in the absence of hydrogen peroxide, while others could do so only in the presence of hydrogen peroxide. In D. hirsuta, peroxidases may play an important role in melanin formation. Possible functions for these diverse oxidases in liverwort biology are discussed.

Quickly-released peroxidase of moss in defense against fungal invaders

Mosses (Bryophyta) are nonvascular plants that constitute a large part of the photosynthesizing biomass and carbon storage on Earth. Little is known about how this important portion of flora maintains its health status. This study assessed whether the moss, Physcomitrella patens, responds to treatment with chitosan, a fungal cell wall-derived compound inducing defense against fungal pathogens in vascular plants. Application of chitosan to liquid culture of P. patens caused a rapid increase in peroxidase activity in the medium. For identification of the peroxidase(s), matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF)/MS, other methods and the whole-genome sequence of P. patens were utilized. Peroxidase gene knock-out mutants were made and inoculated with fungi. The peroxidase activity resulted from a single secreted class III peroxidase (Prx34) which belonged to a P. patens specific phylogenetic cluster in analysis of the 45 putative class III peroxidases of P. patens and those of Arabidopsis and rice. Saprophytic and pathogenic fungi isolated from another moss killed the Prx34 knockout mutants but did not damage wild-type P. patens. The data point out the first specific host factor that is pivotal for pathogen defense in a nonvascular plant. Furthermore, results provide conclusive evidence that class III peroxidases in plants are needed in defense against hostile invasion by fungi.

Application of Brassica napus hairy root cultures for phenol removal from aqueous solutions

Phenolic compounds present in the drainage from several industries are harmful pollutants and represent a potential danger to human health. In this work we have studied the removal of phenol from water using Brassica napus hairy roots as a source of enzymes, such as peroxidases, which were able to oxidise phenol. These hairy roots were investigated for their tolerance to highly toxic concentrations of phenol and for the involvement of their peroxidase isoenzymes in the removal of phenol. Roots grew normally in medium containing phenol in concentrations not exceeding 100 mg l(-1), without the addition of H(2)O(2). However, roots were able to remove phenol concentrations up to 500 mg l(-1), in the presence of H(2)O(2), reaching high removal efficiency, within 1h of treatment and over a wide range of pH (4-9). Hairy roots could be re-used, at least, for three to four consecutive cycles. Peroxidase activity gradually decreased to approximately 20% of the control, at the fifth cycle. Basic and near neutral isoenzymes (BNP) decreased along time of recycling while acidic isoenzymes (AP) remained without changes. Although both group of isoenzymes would be involved in phenol removal, AP showed higher affinity and catalytic efficiency for phenol as substrate than BNP. In addition, AP retained more activity than BNP after phenol treatment. Thus, AP appears to be a promising isoenzyme for phenol removal and for application in continuous treatments. Furthermore, enzyme isolation might not be necessary and the entire hairy roots, might constitute less expensive enzymatic systems for decontamination processes.

Oxidation of Polyphenols by Extracellular Peroxidase in Suspension Cell Culture of Liverwort Heteroscyphus planus

Peroxidase secretion and activity in the oxidation of polyphenols bisphenol A (BPA, 2,2-bis(4-hydroxyphenyl)propane) and lignin model compound (LMC, guaiacylglycerol-β-guaiacylether) were observed in a suspension cell culture of liverwort Heteroscyphus planus. When BPA was co-incubated in a suspension cell culture of liverwort for 5 days, it was depleted by approximately 63%. Oxidation of BPA was observed in culture filtrates of liverwort, and most of the oxidation products were insoluble higher molecular-weight compounds (30%). The oxidative degradation products of BPA and LMC were analyzed by GC-MS and were identified by comparing their retention time and MS spectra with those of the authentic compounds. BPA was degraded to 4-isopropenylphenol and p-hydroxyacetophenone. The formation of these products was examined using [2H14]-BPA. The lignin model compound was degraded to guaiacol, vanillin, coniferyl alcohol and ferulic acid. Biphenyl dehydrodimer was detected in both the reaction mixtures of the suspension cell culture and the culture filtrates incubated with the LMC. The dimer was identified as 1,1′-(4,4′-dihydroxy-3,3′-dimethoxy-5,5′-biphenylene)- bis[8-(2″-methoxyphenoxy)-7,9-propanediol] by 1D and 2D NMR analysis. The activity of secreted peroxidase in the suspension cell culture (0.045 U/mL) was slightly enhanced by addition of LMC (0.059 U/mL), p-cresol (0.064 U/mL), and 2,6-dimethoxyphenol (0.082 U/mL) 7 days after the beginning of incubation.

Structural motifs of syringyl peroxidases predate not only the gymnosperm-angiosperm divergence but also the radiation of tracheophytes

* The most distinctive variation in the monomer composition of lignins in vascular land plants is that found between the two main groups of seed plants. Thus, while gymnosperm lignins are typically composed of guaiacyl (G) units, angiosperm lignins are largely composed of similar levels of G and syringyl (S) units. * However, and contrary to what might be expected, peroxidases isolated from basal (Cycadales and Ginkgoales) and differentially evolved (Coniferales and Gnetales) gymnosperms are also able to oxidize S moieties, and this ability is independent of the presence or absence of S-type units in their lignins. * The results obtained led us to look at the protein database to search for homologies between gymnosperm peroxidases and true eudicot S-peroxidases, such as the Zinnia elegans peroxidase. * The findings showed that certain structural motifs characteristic of eudicot S-peroxidases (certain amino acid sequences and beta-sheet secondary structures) predate the gymnosperm-angiosperm divergence and the radiation of tracheophytes, since they are found not only in peroxidases from basal gymnosperms, ferns and lycopods, but also in peroxidases from the moss Physcomitrella patens (Bryopsida) and the liverwort Marchantia polymorpha (Marchantiopsida), which, as typical of bryophytes, do not have xylem tissue nor lignins.

Effects of heavy metals and nitroaromatic compounds on horseradish glutathione S-transferase and peroxidase

Glutathione S-transferase (GST) and peroxidase (POX) activities have a direct relation to the effect of stress on plant metabolism. Changes in the activities of the enzymes were therefore studied. Horseradish hairy roots were treated by selected bivalent ions of heavy metals (HMs) and nitroaromatic compounds (NACs). We have shown differences in GST activity when assayed with substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB). The conjugation of DCNB catalysed by GST was inhibited in all roots treated with HMs as compared to non-treated roots, whereas NACs caused induction of the activity in dependence on the exposition time and concentration of compounds. The conjugation of CDNB by GST was not affected to the same extent. The increase of GST activity was determined in cultures treated by nickel (0.1 mM) and diaminonitrotoluenes (DANTs, 0.1 mM) for 6 h, whereas the roots treated by 2,4,6-trinitrotoluene (TNT), 4-amino-2,6-dinitrotoluene (ADNT) and dinitrotoluene (DNT, 1.0 mM) needed 27 h treatment to induce the activity. The POX activity of cultures treated by HMs was inhibited to 17-35% in comparison to non-treated cultures. The POX activity of roots treated by TNT (0.1 and 1.0 mM) for 6 and 27 h and by ADNT (0.1 and 1.0 mM) for 6 h was inhibited. A partial increase of POX activity was measured in roots treated by all NACs for 27 h. The content of oxidized glutathione (GSSG) and reduced glutathione (GSH) in the roots differed significantly. It was followed as a symptom of the stress reaction of the plant metabolism to the effect of NACs and HMs.

Phytoremediation of polyaromatic hydrocarbons, anilines and phenols

Phytoremediation technologies based on the combined action of plants and the microbial communities that they support within the rhizosphere hold promise in the remediation of land and waterways contaminated with hydrocarbons but they have not yet been adopted in large-scale remediation strategies. In this review plant and microbial degradative capacities, viewed as a continuum, have been dissected in order to identify where bottle-necks and limitations exist. Phenols, anilines and polyaromatic hydrocarbons (PAHs) were selected as the target classes of molecule for consideration, in part because of their common patterns of distribution, but also because of the urgent need to develop techniques to overcome their toxicity to human health. Depending on the chemical and physical properties of the pollutant, the emerging picture suggests that plants will draw pollutants including PAHs into the plant rhizosphere to varying extents via the transpiration stream. Mycorrhizosphere-bacteria and -fungi may play a crucial role in establishing plants in degraded ecosystems. Within the rhizosphere, microbial degradative activities prevail in order to extract energy and carbon skeletons from the pollutants for microbial cell growth. There has been little systematic analysis of the changing dynamics of pollutant degradation within the rhizosphere; however, the importance of plants in supplying oxygen and nutrients to the rhizosphere via fine roots, and of the beneficial effect of microorganisms on plant root growth is stressed. In addition to their role in supporting rhizospheric degradative activities, plants may possess a limited capacity to transport some of the more mobile pollutants into roots and shoots via fine roots. In those situations where uptake does occur (i.e. only limited microbial activity in the rhizosphere) there is good evidence that the pollutant may be metabolised. However, plant uptake is frequently associated with the inhibition of plant growth and an increasing tendency to oxidant stress. Pollutant tolerance seems to correlate with the ability to deposit large quantities of pollutant metabolites in the 'bound' residue fraction of plant cell walls compared to the vacuole. In this regard, particular attention is paid to the activities of peroxidases, laccases, cytochromes P450, glucosyltransferases and ABC transporters. However, despite the seemingly large diversity of these proteins, direct proof of their participation in the metabolism of industrial aromatic pollutants is surprisingly scarce and little is known about their control in the overall metabolic scheme. Little is known about the bioavailability of bound metabolites; however, there may be a need to prevent their movement into wildlife food chains. In this regard, the application to harvested plants of composting techniques based on the degradative capacity of white-rot fungi merits attention.