Purification and initial characterization of ubiquitin from the higher plant, Avena sativa

Ubiquitin is a highly conserved, 76-amino acid polypeptide recently demonstrated to be involved in ATP-dependent protein degradation in mammalian cells. From immunoblot analyses with anti-human-ubiquitin antibodies we have detected the presence of free ubiquitin in green leaves, etiolated shoots, and dry seeds of the higher plant, oats (Avena sativa L.). We also find that crude oat extracts contain protease(s) that rapidly degrade both oat and human ubiquitin (t1/2 approximately 10 min at 27 degrees C). This proteolysis apparently cleaves ubiquitin at the carboxyl-terminal glycine dipeptide and results in inactivation of the molecule with respect to ligation but does not affect its mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Using homogenization conditions that preclude this proteolysis (low pH and the addition of the protease inhibitor p-chloromercuribenzoate) and immunoblotting as an assay for the protein, a procedure for the purification of ubiquitin from etiolated oat shoots was developed. Characterization of purified oat ubiquitin by absorption spectra, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing, radioimmunoassay with anti-human-ubiquitin antibodies, and kinetic analyses using the ubiquitin activating enzyme isolated from rabbit liver indicates that this protein is remarkably similar to the mammalian form. Small differences between the oat and human proteins have been observed by amino acid compositional analyses indicating that the two forms are not totally homologous. Immunoblotting of crude oat extracts has revealed the presence of high molecular weight proteins recognized by anti-ubiquitin antibodies that represent ubiquitin-protein conjugates formed in vivo. Taken together, these data provide evidence that higher plants contain a ubiquitin-dependent proteolytic pathway that is mechanistically identical to that present in animals.     

Conjugation of ubiquitin to proteins from green plant tissues

Conjugation of the polypeptide ubiquitin to endogenous proteins was studied in oat (Avena sativa L.) plants, and particularly in green tissues. Conjugating activity in leaf extracts was different from that in root extracts, and in both was less than in etiolated tissue. The conjugates were identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and their formation was both time- and ATP-dependent and had a pH optimum of about 8.2. The assay had a high affinity for ATP with a probable K_m of less than 50 micromolar. The ubiquitin conjugating system was also shown to be present in isolated chloroplasts, and ubiquitin could be conjugated to endogenous proteins of lyzed chloroplasts in which the ATP concentrations were reduced by preincubation or desalting. SDS-PAGE analysis led to the suggestion that the large and small subunits of ribulose-1,5-bisphosphate carboxylase (RuBPCase) may be able to be ubiquitinated, and we have shown that ubiquitin can stimulate the in vitro breakdown of ¹²⁵I-labeled RuBPCase. These results invite the speculation that ubiquitin may be involved in the regulation of protein turnover in green plants.     

In vitro phytochrome dark reversion process

Thermal reversion of the far-red absorbing form of phytochrome to the red absorbing form in darkness has been investigated in crude and partially purified isolates from a number of etiolated and light grown higher plants. The influence of temperature, aging and urea on the rate of reversion was also determined.

Phytochrome isolated from all higher plants underwent reversion. The reversion proceeded in at least 2 distinct stages; a short rapid initial phase being followed a slow phase which continued for many hours. Reversion rate was highest in phytochrome isolated from green leaves of parsnip (Pastinacea sativa) and lowest in that isolated from etiolated oats (Avena sativa). Although the rate of reversion could be changed by modifying the tertiary structure of the protein component, the large differences in rate appeared to be characteristic of the plant source. Observed in vitro rates of reversion are slower than those occurring in vivo. Removal of other buffer solubilized material during purification had little effect on the rate of reversion of phytochrome isolated from etiolated material.

     

Identification of a highly conserved domain on phytochrome from angiosperms to algae

A monoclonal antibody (Pea-25) directed to phytochrome from etiolated peas (Pisum sativum L., cv Alaska) binds to an antigenic domain that has been highly conserved throughout evolution. Antigenic cross-reactivity was evaluated by immunoblotting sodium dodecyl sulfate sample buffer extracts prepared from lyophilized tissue samples or freshly harvested algae. Pea-25 immunostained an approximately 120-kilodalton polypeptide from a variety of etiolated and green plant tissues, including both monocotyledons and dicotyledons. Moreover, Pea-25 immunostained a similarly sized polypeptide from the moss Physcomitrella, and from the algae Mougeotia, Mesotaenium, and Chlamydomonas. Because Pea-25 is directed to phytochrome, and because it stains a polypeptide about the size of oat phytochrome, it is likely that Pea-25 is detecting phytochrome in each case. The conserved domain that is recognized by Pea-25 is on the nonchromophore bearing, carboxyl half of phytochrome from etiolated oats. Identification of this highly conserved antigenic domain creates the potential to expand investigations of phytochrome at a cellular and molecular level to organisms, such as Chlamydomonas, that offer unique experimental advantages.     

Enhancing a search for traditional medicinal plants with anthelmintic action by using wild type and stress reporter Caenorhabditis elegans strains as screening tools

Traditional healers in Sarawak, Malaysia, use plants such as Picria fel-terrae, Linariantha bicolor and Lansium domesticum to treat gastrointestinal infections. This study aimed to test whether their nematocidal activities could be confirmed in vitro using highly standardised Caenorhabditis elegans models. We applied eight different ethanol solubilised plant extracts and two commercial anthelmintic drugs to larval and adult stages of C. elegans in vitro. Seven C. elegans strains were evaluated, one wild type and six strains with GFP-tagged stress response pathways to help characterise and compare the pathways affected by plant extracts. Our in vitro screen confirmed that both of the commercial anthelmintic drugs and five of the eight traditionally used plant extracts had significant nematocidal activity against both larval and adult C. elegans. The most effective extracts were from P. fel-terrae. The plant extracts triggered different stress response pathways from the commercial anthelmintic drugs. This study showed that using traditional knowledge of plant medicinal properties in combination with a C. elegans in vitro screen provided a rapid and economical test with a high hit rate compared with the random screening of plants for nematocidal activities. The use of transgenic C. elegans strains may allow this approach to be refined further to investigate the mode of action of active extracts.     

Loss of phytochrome photoreversibility in vitro: I. Extraction and partial purification of killer

Crude pea (Pisum sativum L. var. Alaska) phytochrome extracts contain a substance, “Killer,” which interacts with the far red-absorbing form of phytochrome causing a net loss of spectrophotometrically detectable phytochrome in vitro. Killer is absent from crude extracts of Avena phytochrome, is separable from pea phytochrome by gel filtration, and is alcohol-extractable from etiolated pea seedlings. Killer activity in alcohol extracts behaved, during partial purification, in a manner identical to that derived from pea phytochrome preparations. The mass extraction and partial purification of Killer are described.     

Toxicity of crude extracts from several terrestrial plants to barnacle larvae on mangrove seedlings

This study involved the use of terrestrial plant extracts as substitutes for toxic chemicals to control the major fouling organisms of mangroves, the barnacles. In terms of the solvents used to obtain the plant crude extracts, ethyl acetate was best, ethyl alcohol next and pure water worst, except in the case of Allium cepa (AC), where pure water was better than ethyl alcohol. For different plants, different solvents resulted in different poisonous effects, and plants belonging to different classes showed different levels of activities. In particular, using ethyl acetate crude extracts, Allium sativum (AS), AC and Capsicum annuum (CA) caused massive death of barnacle larvae at a low concentration in the shortest time. The less poisonous organic solvents were able to extract more active materials, and this was advantageous in enhancing the effect. For pure water crude extracts, AC and Zingiber officinale were best, but for 95% ethyl alcohol crude extracts, AS and AC were best. For ethyl acetate crude extracts, the effects of AS, AC and CA were better. Different solvent extracts of AC with 12 h of exposure all had LC₅₀ values <100 mg/L. The concentrations of the effective plant crude extracts used were close to, or even lower than, those used for pesticides referred to in the literature.     

Molecular cloning of a cysteine synthase cDNA from Citrullus vulgaris (watermelon) by genetic complementation in an Escherichia coli Cys− auxotroph

We have isolated cDNA clones encoding cysteine synthase (CSase, EC 4.2.99.8), which catalyzes the terminal step in cysteine biosynthesis, by direct genetic complementation of a Cys^? mutation in Escherichia coli with an expression library of Citrullus vulgaris (watermelon) cDNA. The library was constructed from 8-day-old etiolated seedlings of C. vulgaris in the λZAPII vector, converted to a plasmid library by in vivo excision, and then used for transformation of cysteine auxotroph E. coli NK3, which lacks the cysK and cysM loci. The complementing cDNA containing a 560 by 5′-untranslated region encodes a polypeptide of 325 amino acids of M_r 34342. The translational product reacted with an antibody raised against CSase A of Spinacia oleracea. CSase and β-pyrazolealanine synthase activities were demonstrated in vitro in extracts from E. coli cells expressing the cDNA. Genomic DNA blot analysis indicated the presence of a single copy of the gene, designated cysA, in the C. vulgaris genome. RNA blot hybridization indicated constitutive expression of cysA in cotyledons, hypocotyls and radicles of green and etiolated seedlings. These data suggested that this cDNA clone encodes CSase A the homolog of which in spinach is localized in the cytoplasm. The molecular phylogenetic tree of the amino acid sequences of CSaes from plants and bacteria suggested that there are three families in the CSase superfamily; the plant CSase A family, the plant CSase B family and the bacterial CSase family. The proteins in the plant CSase A family are the most conserved relative to the ancestral CSase protein.     

Correlations of Growth Rate and De-etiolation with Rate of Ent-Kaurene Biosynthesis in Pea (Pisum sativum L.)

Biosynthesis of the gibberellin precursor ent-kaurene-¹⁴C from mevalonic acid-2-¹⁴C was assayed in cell-free extracts of shoot tips of etiolated and light-grown Alaska (normal) and Progress No. 9 (dwarf) peas (Pisum sativum L.). During ontogeny of light-grown Alaska peas, kaurene-synthesizing activity increased from an undectectable level in 3-day-old epicotyls to a maximum in shoot tips of 9-day-old plants and remained relatively constant thereafter until postanthesis. The capacity for kaurene synthesis in extracts from shoot tips of 10-day-old etiolated Alaska seedlings increased approximately exponentially during the first 12 hr of de-etiolation in continuous high intensity white light and remained relatively constant during the succeeding 24 hr of irradiation. Extracts from light-grown Alaska (normal) shoot tips possessed greater capacity for kaurene synthesis than did extracts from light-grown Progress No. 9 (dwarf) shoot tips. Extracts from shoot tips of either light-grown cultivar displayed greater kaurene-synthesizing capacity than was observed in extracts from their dark-grown counterparts. It is concluded that gibberellin biosynthesis in pea shoot tips is subject to partial regulation by factors controlling the rate of biosynthesis of kaurene.     

In vitro antibacterial activities of methanol and aqueous leave extracts of selected medicinal plants against human pathogenic bacteria

People use medicinal plants as diet, and for treatment of infectious and noninfectious diseases and they use brief procedures like frying and cooking to do so. Medicinal plants; Moringa oleifera, Azadirachta indica, and Lepidium sativum which is believed to have active components that help to treat and manage various diseases were investigated for their antibacterial activities against Staphylococcus aureus, Salmonella Typhi, Streptococcus agalactiae and Shigella boydii. Solvent methanol and aqueous were used for extraction of crudes by means of maceration. Susceptibility testing was determined by using disc diffusion method and Minimum inhibitory concentration was determined by broth dilution method. Heat treated plant material activity against test pathogen was aimed to identify resistance capacity of plant material at different interval of time and temperature. All plant extracts under study was active against all tested pathogen after exposure to 45 °C for 30 min. The antibacterial activities of the non-heat-treated extracts of Azadirachta indica were relatively low; the results of this study show that extracts of Azadirachta indica have better residual antibacterial activities. Methanol extracts of all plant leaves showed highest activity as compared to the aqueous extracts. This is probably assigning the choice of extraction solvent for extracting desired active phytochemical from plants. Many of the people in the study area were illiterate and they did not have awareness about the ways use of medicinal plants. They use the medicinal plants by cooking and frying for different purposes. In the main, plant material can be affected as the temperature of treatment is increases with respect to various times of exposures.     

Effect of simulated gastrointestinal conditions and epithelial transport on extracts of green tea and sage

Few in vitro screening studies on the biological activities of plant extracts that are intended for oral administration consider the effect of the gastrointestinal system. This study investigated this aspect on extracts of Camellia sinensis (green tea) and Salvia officinalis (sage) using antimicrobial activity as a model for demonstration. Both the crude extracts and their products after exposure to simulated gastric fluid (SGF) as well as simulated intestinal fluid (SIF) were screened for antimicrobial activity. The chromatographic profiles of the crude plant extracts and their SGF as well as SIF products were recorded and compared qualitatively by means of high performance liquid chromatography coupled to mass spectrometry. The effect of epithelial transport on the crude plant extracts was determined by applying them to an in vitro intestinal epithelial model (Caco-2). The crude extracts for both plants exhibited reduced antimicrobial activity after exposure to SGF, while no antimicrobial activity was detected after exposure to SIF. These results suggested chemical modification or degradation of the antimicrobial compounds when exposed to gastrointestinal conditions. This was confirmed by a reduction of the peak areas on the LC–UV–MS chromatograms. From the chromatographic profiles obtained during the transport study, it is evident that some compounds in the crude plant extracts were either not transported across the cell monolayer or they were metabolised during passage through the cells. It can be deduced that the gastrointestinal environment and epithelial transport process can dramatically affect the chromatographic profiles and biological activity of orally ingested natural products.     

Phosphofructokinase activities in photosynthetic organisms : the occurrence of pyrophosphate-dependent 6-phosphofructokinase in plants and algae

A pyrophosphate-dependent phosphofructokinase (PPi-PFK) activity is detectable in extracts of a wide variety of primitive and advanced plants, the Charalean algae, and in the photosynthetic bacterium, Rhodospirillum rubrum. Angiosperms with extractable PPi-PFK activities 4- to 70-fold higher than the respective ATP-PFK activities tend to be succulent and to exhibit CAM. Even though PPi-PFK activity is not detected in crude extracts of some well known CAM plants, e.g. plants in the Crassulaceae, gel filtration of the extract and/or inclusion of the PPi-PFK activator, fructose 2,6-bisphosphate, in the assay reveals that a PPi-PFK activity is present in these species. Fructose 2,6-bisphosphate likewise activates PPi-PFK activities in extracts of C₃ and C₄ plants. C₃ and C₄ plant PPi-PFK activities are roughly equivalent to ATP-PFK activities in the same species. PPi-PFK activity is also detected in some bryophytes, lower vascular plants, ferns, and gymnosperms. The Charophytes, advanced algae presumed to be similar to species ancestral to vascular plants, exhibit at least 4-fold higher PPi-PFK than ATP-PFK activities. R. rubrum also exhibits a much higher PPi-PFK activity than ATP-PFK activity. These data indicate that PPi-PFK may serve as an alternate enzyme to ATP-PFK in glycolysis in a wide range of photosynthetic organisms.     

Industrial Dye Decolorization by Laccases from Ligninolytic Fungi

White-rot fungi were studied for the decolorization of 23 industrial dyes. Laccase, manganese peroxidase, lignin peroxidase, and aryl alcohol oxidase activities were determined in crude extracts from solid-state cultures of 16 different fungal strains grown on whole oats. All Pleurotus ostreatus strains exhibited high laccase and manganese peroxidase activity, but highest laccase volumetric activity was found in Trametes hispida. Solid-state culture on whole oats showed higher laccase and manganese peroxidase activities compared with growth in a complex liquid medium. Only laccase activity correlated with the decolorization activity of the crude extracts. Two laccase isoenzymes from Trametes hispida were purified, and their decolorization activity was characterized. Received: 26 May 1998 / Accepted: 7 August 1998     

Phytochrome radioimmunoassay

A phytochrome radioimmunoassay with a detection limit of about 2 nanograms has been developed. The radioimmunoassay does not suffer from the potential drawbacks of the commonly used spectral assay and requires less than 1 microliter of crude extract from dark-grown plants for quantitation of phytochrome. Measurement of phytochrome in crude extracts by radioimmunoassay gives values about 25% greater than those obtained by spectral assay. The amount of phytochrome detected in crude extracts of light-grown oats by radioimmunoassay is approximately 1% of that detected in comparable extracts from dark-grown oats. General interference by crude plant extracts with radioimmunoassays was also observed and corrected for.     

Evaluation of bioactive compounds,free radical scavenging and anticancer activities of bulb extracts of Boophone disticha from Eastern Cape Province,South Africa

Boophone disticha (B. disticha) is a bulbous tropical and subtropical flowering plant widespread in Africa, which is frequently used to treat several human ailments. Until the present, there is no scientific validation on the biological activity of this plant from the Eastern Cape Province of South Africa and as a result, this study aimed to assess the bioactive compounds, free radicals scavenging and anticancer potentials of crude bulb extracts (chloroform, acetone, and ethanol) of Boophone disticha obtained from this geographical location. Standard biochemical techniques and Gas-chromatography mass spectrometry (GCMS) analysis were used to pinpoint the bioactive compounds in the crude extracts sequel to their antioxidant potentials against radicals such as 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), hydrogen peroxide and nitric oxide as well as their ferric ion reducing power. In addition, their cytotoxicity effects against Human cervix adenocarcinoma (HeLa) cells were assessed as an in vitro model for anticancer. The phytochemical evaluation of the crude extracts showed the presence of phenolics, flavonoids, and alkaloids. GCMS profiles confirmed the presence of some bioactive compounds in the crude extracts of B. disticha that could be responsible for their biological activities. The plant extracts possessed considerable antioxidant activity and exhibited dose-dependent radicals’ inhibition from all assays carried out. Furthermore, the cytotoxicity effects against HeLa cells recorded inhibition concentration (IC₅₀) of 1.5, 1.6, and 1.9 µg/mL for acetone, chloroform, and ethanolic extracts of B. disticha, respectively. Findings from the present study suggest that B. disticha could be a good prospective source of antioxidant and anticancer agents. Therefore, further research on the isolation and purification of compounds from these extracts are indispensable.     

Pharmacological properties and preliminary phytochemical analysis of Pseudocaryopteris foetida (D.Don) P.D. Cantino leaves

Medicinal plants have significant contribution in pharmaceutical industries being producers of compounds utilized as precursors for drug development. A plant of Lamiaceae family; Pseudocaryopteris foetida had not been investigated for its biomedical potential. Current research was aimed to investigate phytochemical analysis, cytotoxic potential and antioxidant activity of crude methanolic extract and fractions of Pseudocaryopteris foetida (leaves). The preliminary phytochemical analysis of crude methanolic extracts and fractions of Pseudocaryopteris foetida revealed that plant is rich in phenolic and flavonoid classes of secondary metabolites while presence of tannin was observed only in crude methanolic extract. The cytotoxicity was determined using brine shrimp lethality test. Different concentrations (25, 50, 100, 150, 200 and 250 µg/mL) of crude methanolic extract and fractions exhibited dose dependent cytotoxicity. However, The LD₅₀ for all the extracts was more than 200 µg/mL indicating weak cytotoxic potential of Pseudocaryopteris foetida. The antioxidant capabilities of crude methanolic extract and fraction of Pseudocaryopteris foetida were analyzed by in vitro bio assays including DPPH, ABTS, Reducing power and phosphomolybdate antioxidant assays using ascorbic acid as standard. The crude methanolic extract showed IC₅₀ (256.38 ± 0.6 and 314.95 ± 1.1 µg/mL) for DPPH and ABTS respectively, while total antioxidant capacity was calculated as 55.79 ± 0.5 µg/mL for crude methanolic extract of Pseudocaryopteris foetida while ascorbic acid indicated total antioxidant capacity of 71.89 ± 2.3 µg/mL. Study concluded that leaves of Pseudocaryopteris foetida were the rich source of antioxidant phytochemicals. Based on preliminary investigations further research should be focused to isolate bioactive phytochemicals as leading source of clinical medicines in future.     

The DNA Repair Protein XRCC1 Functions in the Plant DNA Demethylation Pathway by Stimulating Cytosine Methylation (5-meC) Excision,Gap Tailoring,and DNA Ligation

DNA methylation patterns are the dynamic outcome of antagonist methylation and demethylation mechanisms, but the latter are still poorly understood. Active DNA demethylation in plants is mediated by a family of DNA glycosylases typified by Arabidopsis ROS1 (repressor of silencing 1). ROS1 and its homologs remove 5-methylcytosine and incise the sugar backbone at the abasic site, thus initiating a base excision repair pathway that finally inserts an unmethylated cytosine. The DNA 3′-phosphatase ZDP processes some of the incision products generated by ROS1, allowing subsequent DNA polymerization and ligation steps. In this work, we examined the possible role of plant XRCC1 (x-ray cross-complementing group protein 1) in DNA demethylation. We found that XRCC1 interacts in vitro with ROS1 and ZDP and stimulates the enzymatic activity of both proteins. Furthermore, extracts from xrcc1 mutant plants exhibit a reduced capacity to complete DNA demethylation initiated by ROS1. An anti-XRCC1 antibody inhibits removal of the blocking 3′-phosphate in the single-nucleotide gap generated during demethylation and reduces the capacity of Arabidopsis cell extracts to ligate a nicked DNA intermediate. Our results suggest that XRCC1 is a component of plant base excision repair and functions at several stages during active DNA demethylation in Arabidopsis.     

Optimal methods for evaluating antimicrobial activities from plant extracts

The search for antimicrobial agents from plants has been a growing interest in the last few decades. However, results generated from many of these studies cannot be directly compared due to the absence of standardization in particular antimicrobial methods employed. The need for established methods with consistent results for the evaluation of antimicrobial activities from plant extracts has been proposed by many researchers. Nevertheless, there are still many studies reported in the literature describing different methodologies. The aim of this study was to find optimal methods to give consistent quantitative antimicrobial results for studying plant extracts. Three different agar-based assays (pour plate disc diffusion (PPDD), streak plate disc diffusion (SPDD) and well-in agar (WA)) and one broth-based (turbidometric (TB)) assay were used in this study. Extracts from two plant species (Duabanga grandiflora and Acalypha wilkesiana) were tested on two bacterial species, namely Escherichia coli and Staphylococcus aureus. Amongst the agar-based assays, PPDD produced the most reproducible results. TB was able to show the inhibitory effects of the test samples on the growth kinetic of the bacteria including plant extracts with low polarity. We propose that both agar- (i.e PPDD) and broth-based assays should be employed when assessing the antimicrobial activity of plant crude extracts.     

In vitro antioxidant,antimicrobial and antiproliferative studies of four different extracts of Orthosiphon stamineus,Gynura procumbens and Ficus deltoidea

BackgroundMedicinal plants are important source of drugs with pharmacological activities. Therefore, there is always rising demands to discover more therapeutic agents from various species. Orthosiphon stamineus, Gynura procumbens and Ficus deltoidea are high valued medicinal plants of Malaysia contain rich source of phenolic and flavonoid compounds. The aims of the present study were to evaluate anti-oxidant, antimicrobial and anti-proliferative effects on A549, HePG2 and MCF7 cell lines of four different extracts of Orthosiphon stamineus, Gynura procumbens and Ficus deltoidea.MethodologyThe leaves of all selected plants were extracted with methanol, chloroform, ethyl acetate and butanol separately with simple cold maceration. Antioxidant activity of all crude extracts were quantitatively measured against DPPH and Ferric Reducing Assay. Antimicrobial evaluation was done by Microdilution and MTT assay and antipoliferative activity of all extracts of selected plant were evaluated against A549, HePG2 and MCF7 cell lines.ResultsResults showed that methanol extract exhibited highest percentage free radical scavenging activity of almost all extracts of selected plants. Antimicrobials results showed chloroform and methanol extracts of O. stamineus extract were the two most active extracts against resistant MRSA but not S. aureus. Only methanol extract of G. procumbens showed antimicrobial activity against the tested pathogens. Chloroform and methanol extracts of F. deltoidea elicited antimicrobial activity against S. aureus but not MRSA. Antiproliferative activity against three tested cell lines results showed that ethyl acetate extract of O. stamineus showed good effect whereas methanol extract of F. deltoidea and G. procumbens exhibited good antiproliferative activity.ConclusionsThe results of the present investigation demonstrated significant variations in the antioxidant, antimicrobial and antiproliferative effects of different solvent extracts. These data could be helpful in isolation of pure potent compounds with good biological activities from the extracts of plants.     

Evaluation of antioxidant properties of medical plants using microbial test systems

The antioxidant activities of extracts from leaves of the medicinal plants growing in Siberia were examined. Total antioxidant activity was determined using in vitro methods including DPPH (2,2-diphenyl-1-picrylhydrazyl radical) free radical scavenging assay, chelating capacity assay with ferrozine, evaluation of capacity to protect plasmid DNA against oxidative damage, measurement of H₂O₂ production, and measurement of total flavonoid and tannin content as well. Using in vivo experiments, we also evaluated capacities of the plant extracts to protect bacteria Escherichia coli against bacteriostatic and bactericidal effects of H₂O₂, and influence of the plant extracts on expression of antioxidant gene katG, encoding catalase. The extracts from Chamerion angustifolium, Filipendula vulgaris and Pyrola rotundifolia indicated the highest levels of antioxidant activity both in vivo and in vitro. Our data suggest that the extracts of the tested plants may provide antioxidant effects on bacteria simultaneously through different pathways, including direct radical scavenging, iron chelation and induction of genes encoding antioxidant enzymes.