Antioxidative response of <Emphasis Type="Italic">Hordeum maritimum</Emphasis> L<Emphasis Type="Italic">.</Emphasis> to potassium deficiency

The objective of the present study was to determine the influence of potassium deprivation on the halophyte species Hordeum maritimum grown in hydroponics for 2 weeks. Treatments were with potassium (+K) or without potassium (−K). Growth, water status, mineral nutrition, parameters of oxidative stress [malondialdehyde (MDA), carbonyl groups (C=O), and hydrogen peroxide concentration (H₂O₂) contents], antioxidant enzyme activities [superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate peroxidase (MDHAR, EC 1.6.5.4), dehydroascorbate peroxidase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.6.4.2)], and antioxidant molecules [ascorbate (ASC), and glutathione (GSH)] were determined. Results showed that the growth of vegetative organs decreased owing to potassium deficiency with roots (−36%) more affected than shoots (−12%). Water status was only diminished in roots (reduction of 24%). Potassium deprivation decreased potassium concentration in both organs, this decrease was more pronounced in roots (−81%) than in shoots (−55%). In contrast to carbonyl groups, MDA content increased owing to potassium deprivation. Except for CAT activity that remained unaffected; SOD, GPX, APX, GR, MDHAR, and DHAR activities were significantly increased. H₂O₂ concentration was negatively correlated with the activities of enzymes and the accumulation of non-enzymatic antioxidants implicated in its detoxification. In conclusion, a cooperative process between the antioxidant systems is important for the tolerance of H. maritimum to potassium deficiency.     

Mediated catalysis of <Emphasis Type="Italic">Paracoccus pantotrophus</Emphasis> cytochrome <Emphasis Type="Italic">c</Emphasis> peroxidase by <Emphasis Type="Italic">P. pantotrophus</Emphasis> pseudoazurin: kinetics of intermolecular electron transfer

This work reports the direct electrochemistry of Paracoccus pantotrophus pseudoazurin and the mediated catalysis of cytochrome c peroxidase from the same organism. The voltammetric behaviour was examined at a gold membrane electrode, and the studies were performed in the presence of calcium to enable the peroxidase activation. A formal reduction potential, E ⁰′, of 230 ± 5 mV was determined for pseudoazurin at pH 7.0. Its voltammetric signal presented a pH dependence, defined by pK values of 6.5 and 10.5 in the oxidised state and 7.2 in the reduced state, and was constant up to 1 M NaCl. This small copper protein was shown to be competent as an electron donor to cytochrome c peroxidase and the kinetics of intermolecular electron transfer was analysed. A second-order rate constant of 1.4 ± 0.2 × 10⁵ M⁻¹ s⁻¹ was determined at 0 M NaCl. This parameter has a maximum at 0.3 M NaCl and is pH-independent between pH 5 and 9.     

Towards the mechanisms involved in the antioxidant action of Mn<Superscript>III</Superscript> [<Emphasis Type="Italic">meso</Emphasis>-tetrakis(4-<Emphasis Type="Italic">N</Emphasis>-methyl pyridinium) porphyrin] in mitochondria

Aerobic organisms are afforded with an antioxidant enzymatic apparatus that more recently has been recognized to include cytochrome c, as it is able to prevent hydrogen peroxide generation by returning electrons from the superoxide ion back to the respiratory chain. The present study investigated the glutathione peroxidase (GPx), superoxide dismutase (SOD) and cytochrome c-like antioxidant activities of para Mn(III)TMPyP in isolated rat liver mitochondria (RLM) and mitoplasts. In RLM, Mn^IIITMPyP decreased the lipid-peroxide content associated with glutathione (GSH) depletion consistent with the use of GSH as a reducing agent for high valence states of Mn^IIITMPyP. SOD and cytochrome c antioxidant activities were also investigated. Mn^IITMPyP was able to reduce ferric cytochrome c, indicating the potential to remove a superoxide ion by returning electrons back to the respiratory chain. In antimicyn A-poisoned mitoplasts, Mn^IIITMPyP efficiently decreased the EPR signal of DMPO-OH adduct concomitant with GSH depletion. The present results are consistent with SOD and GPx activities for Mn^IIITMPyP and do not exclude cytochrome c-like activity. However, considering that para Mn^IIITMPyP more efficiently reduces, rather than oxidizes, superoxide ion; electron transfer from the Mn^IITMPyP to the respiratory chain might not significantly contribute to the superoxide ion removal, since most of Mn^IITMPyP is expected to be produced at the expense of NADPH/GSH oxidation. The present results suggest GPx-like activity to be the principal antioxidant mechanism of Mn^IIITMPyP, whose efficiency is dependent on the NADPH/GSH content in cells.     

<Emphasis Type="Italic">In vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis> antioxidant effects of three Veronica species

The aim of the present study was to examine the antioxidant activity of three Veronica species (Plantaginaceae). The antioxidant potential of various extracts obtained from aerial flowering parts was evaluated by DPPH-free (1,1-diphenyl-2-picrylhydrazyl-free) radical scavenging activity and ferric-reducing antioxidant power assays. Considerable antioxidant activity was observed in the plant samples (FRAP values ranged from 0.97 to 4.85 mmol Fe²⁺/g, and DPPH IC₅₀ values from 12.58 to 66.34 μg/ml); however, these levels were lower than the activity of the control compound butylated hydroxytoluene (BHT) (FRAP: 10.58 mmol Fe²⁺/g; DPPH IC₅₀: 9.57 μg/ml). Also, the in vivo antioxidant effects were evaluated in several hepatic antioxidant systems in rats (activities of glutathione peroxidase, glutathione reductase, peroxidase, catalase, xanthine oxidase, glutathione content and level of thiobarbituric acid reactive substances) after treatment with different Veronica extracts, or in combination with carbon tetrachloride (CCl₄). Pretreatment with 100 mg/kg b.w. of Veronica extracts inhibited CCl₄-induced liver injury by decreasing TBA-RS level, increasing GSH content, and bringing the activities of CAT and Px to control levels. The present study suggests that the extracts analyzed could protect the liver cells from CCl₄-induced liver damage by their antioxidative effect on hepatocytes.     

Physiological function of soluble cytochrome <Emphasis Type="Italic">c</Emphasis>-552 from alkaliphilic <Emphasis Type="Italic">Pseudomonas alcaliphila</Emphasis> AL15-21<Superscript>T</Superscript>

It has been found that the alkaliphilic Gram-negative bacterium Pseudomonas alcaliphila AL15-21^T produces a larger amount of soluble c-type cytochromes at pH 10.0 under air-limited condition than at pH 7.0 under high aeration. Cytochrome c-552 was confirmed as the major c-type cytochrome among three soluble c-type cytochromes in the strain. To understand the physiological function of cytochrome c-552, a P. alcaliphila AL15-21^T cytochrome c-552 gene deletion mutant without a marker gene was constructed by electrotransformation adjusted in this study for the strain. The maximum specific growth rate and maximum cell turbidity of cells grown at pHs 7.0 and 10.0 under the high-aeration condition did not differ significantly between the wild-type and cytochrome c-552 deletion mutant strains. In the mutant grown at pH 10.0 under low-aeration condition, marked decreases in the maximum specific growth rate (40%) and maximum cell turbidity (25%) compared with the wild type were observed. On the other hand, the oxygen consumption rates of cell suspensions of the mutant obtained by the growth at pH 10 under low-aeration condition were slightly higher than that of the wild type. Considering the high electron-retaining ability of cytochrome c-552, the above observations could be accounted for by cytochrome c-552 acting as an electron sink in the periplasmic space. This may facilitate terminal oxidation in the respiratory system at high pH under air-limited conditions.     

Fecundity and feeding of <Emphasis Type="Italic">Galerucella calmariensis</Emphasis> and <Emphasis Type="Italic">G. pusilla</Emphasis> on <Emphasis Type="Italic">Lythrum salicaria</Emphasis>

Fecundity and feeding of two introduced sibling biological control species, Galerucella calmariensis and G. pusilla (Coleoptera: Chrysomelidae) on purple loosestrife, Lythrum salicaria L. (Lythraceae) were compared at constant temperatures of 12.5, 15, 20, 25, and 27.5 °C. Larval feeding was also carried out at 30 °C, but at this temperature, larvae developed only to the L2 stage and none pupated. Thus, data for this temperature were not used in the analysis. There were significant species × temperature interactions in fecundity. Of the two species, Galerucella pusilla laid more eggs. Although egg production of both species was lowest at 12.5 °C and increased to 20 °C, at higher temperatures, the two species reacted differently. From 25 to 27.5 °C, egg production decreased for G. pusilla, but G. calmariensis fecundity peaked at 27.5 °C. Significant temperature × species × life-stage interactions were also observed in feeding. For each species, the amount of feeding varied with temperature and stage of development. Galerucella pusilla adults consumed more foliage at 15, 20, and 27.5 °C. However, at 12.5 °C G. calmariensis adults fed more than G. pusilla. G. pusilla larvae consumed an average of 25% less foliage than G. calmariensis. The lower larval consumption of G. pusilla suggests that when food is limited, G. pusilla larvae may have a higher survival rate because of its ability to complete larval development with less food and produce more progeny due to its greater fecundity. When food is not limited neither species would have a competitive advantage and both species could coexist temporally and spatially. However, since G. calmariensis larvae consumed more leaf material, the larval stage of this species would have a greater impact on purple loosestrife than G. pusilla.     

Activities of photosystem II and antioxidant enzymes in chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L<Emphasis Type="Italic">.</Emphasis>) cultivars exposed to chilling temperatures

This study was carried out to determine the effect of chilling on both cold-acclimated and non-acclimated chickpea (Cicer arietinum L.) cultivars (Gökçe and Can?tez 87). Chickpea seedlings grown in soil culture for 12 days were subjected to chilling temperatures (2 and 4°C for 12 days) after maintaining in cold-acclimation (10°C, 7 days) or non-acclimation (25°C, 7 days) periods. The lowest values of growth parameters were obtained with cold-acclimated plants, whereas non-acclimated plants exhibited the lowest water content values, especially at 2°C. There was no effect of cold-acclimation period on chlorophyll fluorescence parameters. Plants subjected to chilling temperatures after cold-acclimation were more tolerant with respect to chlorophyll fluorescence parameters, and Gökçe had better photosystem II (PSII) photochemical activity. In the chilling treatments, total chlorophyll (a + b) content reduced, especially at 2°C, while anthocyanin and flavonoid contents increased to a greater extent in Gökçe and carotenoid content of the cultivars did not change. Malondialdehyde (MDA) content was higher for Can?tez 87, mostly at 2°C, while proline accumulation was greater for Gökçe. The cold-acclimation period led to a remarkable increase in antioxidant enzyme activities of both cultivars. The superoxide dismutase (SOD) activity was much higher in Gökçe for both chilling temperatures and the ascorbate peroxidase (APX) activity increased only in the cold-acclimated 4°C treatments. Similarly, with APX activity, the glutathione reductase (GR) and peroxidase (POD) activities of cultivars were higher in cold-acclimated plants at both the chilling temperatures, mostly in Gökçe. The results of this study indicate that cold-acclimation increased the cultivars ability to withstand the chilling temperatures. The lower MDA content and higher antioxidant and photochemical activities in Gökçe indicated an enhanced chilling tolerance capacity of this cultivar to protect the plant from oxidative damage.     

Electron transfer in <Emphasis Type="Italic">Paracoccus denitrificans</Emphasis> with the modified <Emphasis Type="Italic">fbc</Emphasis> operon

Membrane fragments of two mutant strains of Paracoccus denitrificans genetically modified in the bc ₁ complex have been studied for comparison of enzymic activities of succinate-cytochrome-c reductase and its components, viz. succinate dehydrogenase (Complex II) and ubiquinol-cytochrome-c reductase (Complex III) and their response to changes in concentration of succinate, cytochrome c, ionic strength, pH, temperature and sensitivity to antimycin A. The mutants synthesized and assembled the b and c hemes in the ratio characteristic for the wild type strain. The mutant strain M 71 expressing the truncated copy of cytochrome c ₁ (devoid of a stretch of 150 mainly acidic amino acids) was less sensitive to increasing concentration of cytochrome c and changes in ionic strength of the medium, but maintained the original affinity to succinate and sensitivity to antimycin A. The mutant strain M 36 with an overexpressed bc ₁ content showed the highest response to changes in ionic strength and physical parameters, exhibited the lowest turnover number values with succinate-cytochrome-c reductase, but positively affected the succinate dehydrogenase. In view of the interaction of the redox components in native membranes the functional analyses of separated Complexes II and III should be regarded with caution.     

Temperature responses of photosynthesis and respiration in <Emphasis Type="Italic">Populus</Emphasis><Emphasis Type="Italic">balsamifera</Emphasis> L.: acclimation versus adaptation

To examine the role of acclimation versus adaptation on the temperature responses of CO₂ assimilation, we measured dark respiration (R _n) and the CO₂ response of net photosynthesis (A) in Populus balsamifera collected from warm and cool habitats and grown at warm and cool temperatures. R _n and the rate of photosynthetic electron transport (J) are significantly higher in plants grown at 19 versus 27°C; R _n is not affected by the native thermal habitat. By contrast, both the maximum capacity of rubisco (V _cmax) and A are relatively insensitive to growth temperature, but both parameters are slightly higher in plants from cool habitats. A is limited by rubisco capacity from 17–37°C regardless of growth temperature, and there is little evidence for an electron-transport limitation. Stomatal conductance (g _s) is higher in warm-grown plants, but declines with increasing measurement temperature from 17 to 37°C, regardless of growth temperature. The mesophyll conductance (g _m) is relatively temperature insensitive below 25°C, but g _m declines at 37°C in cool-grown plants. Plants acclimated to cool temperatures have increased R _n/A, but this response does not differ between warm- and cool-adapted populations. Primary carbon metabolism clearly acclimates to growth temperature in P. balsamifera, but the ecotypic differences in A suggest that global warming scenarios might affect populations at the northern and southern edges of the boreal forest in different ways.     

Characterization of recombinant fructose-1,6-bisphosphate aldolase from <Emphasis Type="Italic">Methylococcus capsulatus</Emphasis> Bath

The gene fba from the thermotolerant obligate methanotroph Methylococcus capsulatus Bath was cloned and expressed in Escherichia coli BL21(DE3). The fructose-1,6-bisphosphate aldolase (FBA) carrying six His on the C-end was purified by affinity metal chelating chromatography. The Mc. capsulatus FBA is a hexameric enzyme (240 kDa) that is activated by Co²⁺ and inhibited by EDTA. The enzyme displays low K _m to fructose-1,6-bisphosphate (FBP) and higher K _m to the substrates of aldol condensation, dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. The FBA also catalyzes sedoheptulose-1,7-bisphosphate cleavage. The presence of Co²⁺ in the reaction mixture changes the kinetics of FBP hydrolysis and is accompanied by inhibition of the reaction by 2 mM FBP. Phylogenetically, the Mc. capsulatus enzyme belongs to the type B of class II FBAs showing high identity of translated amino acid sequence with FBAs from autotrophic bacteria. The role of the FBA in metabolism of Mc. capsulatus Bath, which realizes simultaneously three C₁ assimilating pathways (the ribulose monophosphate, the ribulose bisphosphate, and the serine cycles), is discussed.     

Transgenic cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.) seedlings expressing a tobacco glutathione <Emphasis Type="Italic">S</Emphasis>-transferase fail to provide improved stress tolerance

Transgenic cotton (Gossypium hirsutum L.) lines expressing the tobacco glutathione S-transferase (GST) Nt107 were evaluated for tolerance to chilling, salinity, and herbicides, antioxidant enzyme activity, antioxidant compound levels, and lipid peroxidation. Although transgenic seedlings exhibited ten-fold and five-fold higher GST activity under normal and salt-stress conditions, respectively, germinating seedlings did not show improved tolerance to salinity, chilling conditions, or herbicides. Glutathione peroxidase (GPX) activity in transgenic seedlings was 30% to 60% higher under normal conditions, but was not different than GPX activity in wild-type seedlings under salt-stress conditions. Glutathione reductase, superoxide dismutase, ascorbate peroxidase, and monodehydroascorbate reductase activities were not increased in transgenic seedlings under salt-stress conditions, while dehydroascorbate reductase activity was decreased in transgenic seedlings under salt-stress conditions. Transgenic seedlings had 50% more oxidized glutathione when exposed to salt stress. Ascorbate levels were not increased in transgenic seedlings under salt-stress conditions. Malondialdehyde content in transgenic seedlings was nearly double that of wild-type seedlings under normal conditions and did not increase under salt-stress conditions. These results show that expression of Nt107 in cotton does not provide adequate protection against oxidative stress and suggests that the endogenous antioxidant system in cotton may be disrupted by the expression of the tobacco GST.     

Peroxidase activity of cytochrome <Emphasis Type="Italic">bd</Emphasis> from <Emphasis Type="Italic">Escherichia coli</Emphasis>

Cytochrome bd from Escherichia coli is able to oxidize such substrates as guaiacol, ferrocene, benzohydroquinone, and potassium ferrocyanide through the peroxidase mechanism, while none of these donors is oxidized in the oxidase reaction (i.e. in the reaction that involves molecular oxygen as the electron acceptor). Peroxidation of guaiacol has been studied in detail. The dependence of the rate of the reaction on the concentration of the enzyme and substrates as well as the effect of various inhibitors of the oxidase reaction on the peroxidase activity have been tested. The dependence of the guaiacol-peroxidase activity on the H₂O₂ concentration is linear up to the concentration of 8 mM. At higher concentrations of H₂O₂, inactivation of the enzyme is observed. Guaiacol markedly protects the enzyme from inactivation induced by peroxide. The peroxidase activity of cytochrome bd increases with increasing guaiacol concentration, reaching saturation in the range from 0.5 to 2.5 mM, but then starts falling. Such inhibitors of the ubiquinol-oxidase activity of cytochrome bd as cyanide, pentachlorophenol, and 2-n-heptyl 4-hydroxyquinoline-N-oxide also suppress its guaiacol-peroxidase activity; in contrast, zinc ions have no influence on the enzyme-catalyzed peroxidation of guaiacol. These data suggest that guaiacol interacts with the enzyme in the center of ubiquinol binding and donates electrons into the di-heme center of oxygen reduction via heme b ₅₅₈, and H₂O₂ is reduced by heme d. Although the peroxidase activity of cytochrome bd from E. coli is low compared to peroxidases, it might be of physiological significance for the bacterium itself and plays a pathophysiological role for humans and animals.     

Cytochrome <Emphasis Type="Italic">c</Emphasis> signalosome in mitochondria

Cytochrome c delicately tilts the balance between cell life (respiration) and cell death (apoptosis). Whereas cell life is governed by transient electron transfer interactions of cytochrome c inside the mitochondria, the cytoplasmic adducts of cytochrome c that lead to cell death are amazingly stable. Interestingly, the contacts of cytochrome c with its counterparts shift from the area surrounding the heme crevice for the redox complexes to the opposite molecule side when the electron flow is not necessary. The cytochrome c signalosome shows a higher level of regulation by post-translational modifications—nitration and phosphorylation—of the hemeprotein. Understanding protein interfaces, as well as protein modifications, would puzzle the mitochondrial cytochrome c-controlled pathways out and enable the design of novel drugs to silence the action of pro-survival and pro-apoptotic partners of cytochrome c.     

Induction of phytochelatins and antioxidant defence system in <Emphasis Type="Italic">Brassica juncea</Emphasis> and <Emphasis Type="Italic">Vigna radiata</Emphasis> in response to chromium treatments

Growth performance, chromium (Cr) accumulation potential and induction of antioxidative defence system and phytochelatins (PCs) were studied in hydroponically grown Brassica juncea (Indian mustard) and Vigna radiata (mungbean) at various levels of Cr treatments (0, 50, 100, 200 μM Cr). B. juncea accumulated twofolds and threefolds higher Cr in root and shoot, respectively than in V. radiata. Compared to B. juncea, V. radiata was found to be particularly sensitive to Cr as observed by the severity and development of Cr toxicity symptoms and decreased growth. Induction of PC and enzymes of antioxidant defence system were monitored as plant’s primary and secondary metal detoxifying responses, respectively. There was induction of PC and enzymes of antioxidant defence system in both the plants. PCs were induced significantly in roots and shoot of both the plants at all the levels of Cr treatments. Significantly higher activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) were observed in shoot of B. juncea than V. radiata at all the levels of Cr treatments. Induction of PCs along with antioxidant defence system in response to Cr stress suggests the cumulative role of PCs and antioxidants in conferring tolerance against accumulated Cr in B. juncea, and thereby signifies the suitability of this plant as one of the potential remediators of Cr.     

Cloning and Functional Characterization of a Novel Glutathione <Emphasis Type="Italic">S</Emphasis>-Transferase Gene from <Emphasis Type="Italic">Limonium bicolor</Emphasis>

Plant glutathione S-transferases (GSTs) are involved in protecting plants against both diverse biotic and abiotic stresses. In the present study, a novel GST gene (LbGST1) was cloned from Limonium bicolor (Bunge) Kuntze (Plumbaginaceae). To characterize its function in salt tolerance, tobacco lines transformed with LbGST1 were generated. Compared with wild-type (WT) tobacco, transgenic plants overexpressing LbGST1 exhibited both GST and glutathione peroxidase activities. Moreover, superoxide dismutase, peroxidase (POD), and catalase activities in transgenic plants were significantly higher than those in WT plants, particularly when grown under conditions of salt stress. Similarly, levels of proline in transgenic plants were also higher than those in WT plants grown under NaCl stress conditions. Whereas, Malondialdehyde contents in transgenic plants were lower than those in WT plants under NaCl conditions. Furthermore, Na⁺ content in transgenic plants was lower than that in WT plants under these stress conditions. Subcellular localization analysis revealed that the LbGST1 protein was localized in the nucleus. These results suggested that overexpression of LbGST1 gene can affect many physiological processes associated with plant salt tolerance. Therefore, we hypothesize that LbGST1 gene can mediate many physiological pathways that enhance stress resistance in plants.     

Cellular response of <Emphasis Type="Italic">Chlorella zofingiensis</Emphasis> to exogenous selenium

An investigation of the cellular response of the freshwater microalga Chlorella zofingiensis to exogenous selenium showed that Chlorella cells can tolerate sodium selenite up to a concentration of 100 mg l⁻¹. Cells grown in such a selenium-supplemented medium accumulated boiling-stable proteins in a concentration-dependant manner. Western blot analysis revealed that three of these boiling-stable proteins cross-reacted with anti-dehydrin antibody. Selenium was also found to exert an effect on antioxidative enzymes: superoxide dismutase (Fe-SOD and Mn-SOD isoforms) accumulated in response to selenium stress of 100 mg l⁻¹ sodium selenite, as did a new form of selenium-dependent glutathione peroxidase. Upon transfer of the cells to a selenium-free medium, the boiling-stable proteins, the superoxide dismutase isoforms and the selenium-dependent glutathione peroxidase were all down regulated. The accumulation of boiling-stable proteins and the increased activities of the antioxidant enzymes in selenium-treated Chlorella cells suggest that these compounds are probably involved in the mechanism(s) of selenium tolerance of this alga.     

Effect of temperature on the life history of <Emphasis Type="Italic">Eretmocerus</Emphasis> sp. nr. <Emphasis Type="Italic">furuhashii</Emphasis>, a parasitoid of <Emphasis Type="Italic">Bemisia tabaci</Emphasis>

Eretmocerus sp. nr. furuhashii (Hymenoptera: Aphelinidae) is an indigenous parasitoid of Bemisia tabaci (Gennadius)(Hemiptera: Aleyrodidae) from southern China; the effects of constant temperatures on the life history of E. sp. nr. furuhashii were examined in the laboratory. The developmental period ranged from 39.2 days at 20°C to 12.40 days at 32°C. A total of 263.4 degree-days were required to complete development with a lower developmental threshold temperature of 11.1°C. Of the eggs produced, 59.3% completed development at 20°C with completion increasing to 71.5% at 26°C. Adult female longevity was 10.8 days at 20°C and 5.2 days at 32°C while the mean daily offspring reproduced per female was highest at 29°C with 5.9 offspring. Adult oviposition peaked three days after emergence at 26, 29 and 32°C, and four days post-emergence at 20°C and 23°C. The total numbers of offspring produced per female ranged from 25.7 individuals at 32°C to 41.1 individuals at 20°C. The sex ratio had a female bias and ranged from 0.72 at 17°C to 0.51 at 35°C. The intrinsic rate of increase was 0.1727 at 29°C followed with 0.1606 at 32°C. Results indicated that E. sp. nr. furuhashii reaches its maximum biological potential at temperatures ranging from 26°C to 32°C.     

Influence of Temperature on Virulence of Fungal Isolates of <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> and <Emphasis Type="Italic">Beauveria bassiana</Emphasis> to the Two-Spotted Spider Mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Twenty-three isolates of Metarhizium anisopliae (Metschnikoff) Sokorin and three isolates of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales: Clavicipitaceae) were assessed for their virulence against the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Based on the screening results, nine isolates of M. anisopliae and two isolates of B. bassiana were tested for their virulence against young adult (1- to 2-day-old) female T. urticae at constant temperatures of 20, 25, 30 and 35°C. At all temperatures tested, all the fungal isolates were pathogenic to T. urticae but mortality varied with isolates and temperatures. Fungal isolates were more virulent at 25, 30 and 35°C than at 20°C. The lethal time to 50% mortality (LT₅₀) and lethal time to 90% mortality (LT₉₀) values decreased with increased temperature. There were no significant differences in virulence between fungal isolates at 30 and 35°C; however, significant differences were observed at 20 and 25°C.     

Effect of salt stress on physiological and antioxidative responses in two species of <Emphasis Type="Italic">Salicornia</Emphasis> (<Emphasis Type="Italic">S. persica</Emphasis> and <Emphasis Type="Italic">S. europaea</Emphasis>)

The effects of salt stress on growth parameters, free proline content, ion accumulation, lipid peroxidation, and several antioxidative enzymes activities were investigated in S. persica and S. europaea. The seedlings were grown for 2 months in half-strength Hoagland solution and treated with different concentrations of NaCl (0, 85, 170, 340, and 510 mM) for 21 days. The fresh and dry weights of both species increased significantly at 85 and 170 mM NaCl and decreased at higher concentrations. Salinity increased proline content in both the species as compared to that of control. Sodium (Na⁺) content in roots and shoots increased, whereas K⁺ and P_i content in both organs decreased. At all NaCl concentrations, the total amounts of Na⁺ and K⁺ were higher in shoots than in roots. Malondialdehyde (MDA) content declined at moderate NaCl concentrations (85 and 170 mM) and increased at higher levels. With increased salinity, superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPX) activities also increased gradually in both species. In addition, it seems that GPX, CAT, and SOD activities play an essential protective role in the scavenging reactive oxygen species (ROS) in both species. Native polyacrylamide gel electrophoresis (PAGE) indicated different isoform profiles between S. persica and S. europaea concerning antioxidant enzymes. These results showed that S. persica exhibits a better protection mechanism against oxidative damage and it is more salt-tolerant than S. europaea possibly by maintaining and/or increasing growth parameters, ion accumulation, and antioxidant enzyme activities.     

The peroxidase activity of cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>6</Subscript><Emphasis Type="Italic">f</Emphasis> complex from spinach chloroplasts

The cytochrome b ₆ f (Cyt b ₆ f) complex, which functions as a plastoquinol-plastocyanin oxidoreductase and mediates the linear electron flow between photosystem II (PSII) and photosystem I (PSI) and the cyclic electron flow around PSI, was isolated from spinach (Spinacia oleracea L.) chloroplasts using n-octyl-β-D-glucopyranoside (β-OG). The preparation was also able to catalyze the peroxidase-like reaction in the presence of hydrogen peroxide (H₂O₂) and guaiacol. The optimal conditions for peroxidase activity of the preparation included: pH 3.6, ionic strength 0.1, and temperature 35°C. The apparent Michaelis constant (K _m) values for H₂O₂ and guaiacol were 50 mM and 2 mM, respectively. The bimolecular rate constant (k _obs) was about 26 M⁻¹ s⁻¹ and the turnover number (K _cat) was about 60 min⁻¹ (20 mM guaiacol, 100 mM sodium phosphate, pH 3.6, 25°C, [H₂O₂]<100mM). These parameters were similar to those of several other heme-containing proteins, such as myoglobin and Cyt c.