Leaf responses to iron nutrition and low cadmium in peanut: anatomical properties in relation to gas exchange

Aims

This study evaluated how iron nutrition affect leaf anatomical and photosynthetic responses to low cadmium and its accumulation in peanut plants.

Methods

Seedlings were treated with Cd (0 and 0.2 μM CdCl₂) and Fe (0, 10, 25, 50 or 100 μM EDTA-Na₂Fe) in hydroponic culture.

Results

Cadmium accumulation is highest in Fe-deficient plants, and dramatically decreased with increasing Fe supply. The biomass, gas exchange, and reflectance indices were highest at 25 μM Fe²⁺ treatments, indicating the concentration is favorable for the growth of peanut plants. Both Fe deficiency and Cd exposure impair photosynthesis and reduce reflectance indices. However, they show different effects on leaf anatomical traits. Fe deficiency induces more and smaller stomata in the leaf surface, but does not affect the inner structure. Low Cd results in a thicker lamina with smaller stomata, thicker palisade and spongy tissues, and lower palisade to spongy thickness ratio. The stomatal length and length/width ratio in the upper epidermis, spongy tissue thickness, and palisade to spongy thickness ratio were closely correlated with net photosynthetic rate, stomatal conductance, and transpiration rate.

Conclusions

Cd accumulation rather than Fe deficiency alters leaf anatomy that may increase water use efficiency but inhibit photosynthesis.     

A novel malic enzyme gene, <Emphasis Type="Italic">Mime2</Emphasis>, from <Emphasis Type="Italic">Mortierella isabellina</Emphasis> M6-22 contributes to lipid accumulation

Objective

This study was aimed at cloning and characterizing a novel malic enzyme (ME) gene of Mortierella isabellina M6-22 and identifying its relation with lipid accumulation.

Methods

Mime2 was cloned from strain M6-22. Plasmid pET32aMIME2 was constructed to express ME of MIME2 in Escherichia coli BL21. After purification, the optimal pH and temperature of MIME2, as well as K_m and V_max for NADP⁺ were determined. The effects of EDTA or metal ions (Mn²⁺, Mg²⁺, Co²⁺, Cu²⁺, Ca²⁺, or Zn²⁺) on the enzymatic activity of MIME2 were evaluated. Besides, plasmid pRHMIME2 was created to express MIME2 in Rhodosporidium kratochvilovae YM25235, and its cell lipid content was measured by the acid-heating method. The optimal pH and temperature of MIME2 are 5.8 and 30 °C, respectively.

Results

The act ivity of MIME2 was significantly increased by Mg²⁺, Ca²⁺, or Mn²⁺ at 0.5 mM but inhibited by Cu²⁺ or Zn²⁺ (p?<?0.05). The optimal enzymatic activity of MIME2 is 177.46 U/mg, and the K_m and V_max for NADP⁺ are 0.703 mM and 156.25 μg/min, respectively. Besides, Mime2 transformation significantly increased the cell lipid content in strain YM25235 (3.15?±?0.24 vs. 2.17?±?0.31 g/L, p?<?0.01).

Conclusions

The novel ME gene Mime2 isolated from strain M6-22 contributes to lipid accumulation in strain YM25235.

     

Zn2+ and l-isoleucine induce the expressions of porcine β-defensins in IPEC-J2 cells

The β-defensins, expressed in epithelial cells of multiple tissues including intestine, play a critical role in the mammalian innate immunity. However, it is little known about the role of functional nutrients in the regulation of porcine β-defensins’ expressions in intestinal epithelial cells. The present study was conducted to determine the hypothesis that zinc and l-isoleucine regulate the expressions of porcine β-defensins in IPEC-J2 cells. Cells were cultured in DMEM/F12 medium containing supplemental 0–500 μg/mL l-isoleucine or 0–500 μmol/mL zinc sulfate that was used to increase the concentration of Zn²⁺ in the medium. At 12 h after the treatment by the appropriate concentrations of l-isoleucine or Zn²⁺, the mRNA and protein expressions of porcine β-defensin 1, 2 and 3 were increased (P < 0.05), and reached their maximum after treatment with 25 or 100 μmol/mL zinc sulfate and 25 or 50 μg/mL isoleucine (P < 0.05). These results suggested that both Zn²⁺ and l-isoleucine could induce β-defensins’ expressions in porcine intestinal epithelial cells.     

Biochemical characterization of NADP+-dependent isocitrate dehydrogenase from Microcystis aeruginosa PCC7806

Microcystis aeruginosa is the key symptom of water eutrophication and produces persistent microcystins. Our special attention was paid to the isocitrate dehydrogenase (IDH) of M. aeruginosa (MaIDH) because it plays important roles in energy and biosynthesis metabolisms and its catalytic product 2-oxoglutarate provides the carbon skeleton for ammonium assimilation and also constitutes a signaling molecule of nitrogen starvation in cyanobacteria. Sequence alignment showed that MaIDH shared significant sequence identity with IDHs from other cyanobacteria (>80 %) and other bacteria (>45 %). The subunit molecular weight of MaIDH was determined to be 52.6 kDa by filtration chromatography, suggesting MaIDH is a typical homodimer. The purified recombinant MaIDH was completely NADP⁺-dependent and no NAD⁺-linked activity was detectable. The K _m values for NADP⁺ were 32.24 and 71.71 μM with Mg²⁺ and Mn²⁺ as a sole divalent cation, and DL-isocitrate linked K _m values were 32.56 μM (Mg²⁺) and 124.3 μM (Mn²⁺), respectively. As compared with Mn²⁺, MaIDH showed about 2.5-times and 4-times higher affinities (1/K _m) to NADP⁺ and dl-isocitrate with Mg²⁺. The optimum activity of MaIDH was found at pH 7.5, and its optimum temperature was 45 °C (Mn²⁺) and 50 °C (Mg²⁺). Heat-inactivation studies showed that heat treatment for 20 min at 45 °C caused a 50 % loss of enzyme activity. MaIDH was completely divalent cation dependent as other typical dimeric IDHs and Mn²⁺ was its best activator. Our study is expected to give a better understanding of primary metabolic enzymes in M. aeruginosa. This would provide useful basic information for the research of controlling the blue-green algae blooms through biological techniques.     

The effect of sodium bicarbonate on plant performance and iron acquisition system of FA-5 (Forner-Alcaide 5) citrus seedlings

This work studies the effect of bicarbonate on plant performance and the iron acquisition system of Forner-Alcaide 5 (FA-5) seedlings, a citrus genotype known for its tolerance to calcareous soils. Plants were irrigated for 6 weeks with or without 10 mM NaHCO₃. Treatment significantly decreased shoot growth, photosynthetic levels and iron concentration in shoots and roots. o,o-⁵⁷FeEDDHA experiments indicated that ⁵⁷Fe uptake by roots was inhibited in treated plants. Moreover, those seedlings accumulated more ⁵⁷Fe in roots, and enhanced mRNA accumulation of ferric reductase genes FRO1 and FRO2 and FC-R activity in roots. H⁺-ATPase activity and HA1 gene expression were also increased, while HA2 was not affected. In addition, expression of the iron transporter gene IRT1 was increased, while IRT2 was not significantly affected. Finally, according to PEPC enzymatic activity, PEPC1 gene expression was higher in treated roots. In conclusion, it appears that bicarbonate prevents medium acidification by roots, thus reducing Fe²⁺ uptake. Accordingly, Fe deficiency enhanced the expression of some genes related with the Fe acquisition system (IRT1, FRO1, FRO2, HA1 and PEPC1) and the activity of the corresponding enzymes, which appear to constitute an adaptive mechanism of FA-5 in these soils.     

In Vitro Antifungal Activity of Micafungin and Caspofungin Against Dermatophytes Isolated from China

Aims

The aims of this study are to investigate the in vitro activities of micafungin and caspofungin that are two new echinocandin antifungal drugs against clinically isolated dermatophytes in China and to define MEC (minimal effective concentration) as the reading endpoints of this study in accordance with (Clinical and laboratory Standards Institute) CLSI M38-A2 reference.

Methods

Minimal effective concentrations (MECs) of micafungin and caspofungin for 82 dermatophyte strains were determined according to CLSI (formerly NCCLS) M38-A2 broth microdilution methods.

Results

(1) The MEC_90s of micafungin for Trichophyton violaceum and Trichophyton tonsurans were 0.25 μg/mL, and for Microsporum canis and Trichophyton verrucosum were 0.06 μg/mL. The MEC_90s for Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum gypseum and Epidermophyton floccosum were 0.03 μg/mL. (2) The MEC_90s of caspofungin for T. rubrum, T. violaceum and T. tonsurans were 1 μg/mL, and for T. mentagrophytes, M. canis, M. gypseum, E. floccosum and T. verrucosum were 0.5 μg/mL. (3) Compared with caspofungin, micafungin demonstrated lower MEC value to dermatophytes (P < 0.05).

Conclusions

Micafungin has stronger in vitro antifungal activity than caspofungin.     

Elevated CO2 improves root growth and cadmium accumulation in the hyperaccumulator Sedum alfredii

Aims

This study examined the effect of elevated CO₂ on plant growth, root morphology and Cd accumulation in S. alfredii, and assessed the possibility of using elevated CO₂ as fertilizer to enhance phytoremediation efficiency of Cd-contaminated soil by S. alfredii.

Methods

Both soil pot culture and hydroponic experiments were carried out to characterize plant biomass, root morphological parameters, and cadmium uptake in S. alfredii grown under ambient (350 μL L^?1) or elevated (800 μL L^?1) CO₂.

Results

Elevated CO₂ prompted the growth of S. alfredii, shoot and root biomass were increased by 24.6–36.7% and 35.0–52.1%, respectively, as compared with plants grown in ambient CO₂. After 10 days growth in medium containing 50 μM Cd under elevated CO₂, the development of lateral roots and root hairs were stimulated, additionally, root length, surface area, root volume and tip number were increased significantly, especially for the finest diameter roots. The total Cd uptake per pot was significantly greater under elevated CO₂ than under ambient CO₂. After 60 d growth, Cd phytoextraction efficiency was increased significantly in the elevated CO₂ treatment.

Conclusions

Results suggested that the use of elevated CO₂ may be a useful way to improve phytoremediation efficiency of Cd-contaminated soil by S. alfredii.     

Hyperfine interactions and electron distribution in FeIIFeI and FeIFeI models for the active site of the [FeFe] hydrogenases: Mössbauer spectroscopy studies of low-spin FeI

Mössbauer studies of [{μ-S(CH₂C(CH₃)₂CH₂S}(μ-CO)Fe^IIFe^I(PMe₃)₂(CO)₃]PF₆ (1 _OX ), a model complex for the oxidized state of the [FeFe] hydrogenases, and the parent Fe^IFe^I derivative are reported. The paramagnetic 1 _OX is part of a series featuring a dimethylpropanedithiolate bridge, introducing steric hindrance with profound impact on the electronic structure of the diiron complex. Well-resolved spectra of 1 _OX allow determination of the magnetic hyperfine couplings for the low-spin distal Fe^I ( $ {\text{Fe}}^{\text{I}} _{\text{ D}} $ Fe D I ) site, A _x,y,z  = [?24 (6), ?12 (2), 20 (2)] MHz, and the detection of significant internal fields (approximately 2.3 T) at the low-spin ferrous site, confirmed by density functional theory (DFT) calculations. Mössbauer spectra of 1 _OX show nonequivalent sites and no evidence of delocalization up to 200 K. Insight from the experimental hyperfine tensors of the Fe^I site is used in correlation with DFT to reveal the spatial distribution of metal orbitals. The Fe–Fe bond in [Fe₂{μ-S(CH₂C(CH₃)₂CH₂S}(PMe₃)₂(CO)₄] (1) involving two $ d_{{z^{2} }} $ d z 2 -type orbitals is crucial in keeping the structure intact in the presence of strain. On oxidation, the distal iron site is not restricted by the Fe–Fe bond, and thus the more stable isomer results from inversion of the square pyramid, rotating the $ d_{{z^{2} }} $ d z 2 orbital of $ {\text{Fe}}^{\text{I}} _{\text{ D}} $ Fe D I . DFT calculations imply that the Mössbauer properties can be traced to this $ d_{{z^{2} }} $ d z 2 orbital. The structure of the magnetic hyperfine coupling tensor, A, of the low-spin Fe^I in 1 _OX is discussed in the context of the known A tensors for the oxidized states of the [FeFe] hydrogenases.     

A two [4Fe-4S]-cluster-containing ferredoxin as an alternative electron donor for 2-hydroxyglutaryl-CoA dehydratase from<Emphasis Type="Italic"> Acidaminococcus fermentans</Emphasis>

The key step in the fermentation of glutamate by Acidaminococcus fermentans is a reversible syn-elimination of water from (R)-2-hydroxyglutaryl-CoA to (E)-glutaconyl-CoA catalyzed by 2-hydroxyglutaryl-CoA dehydratase, a two-component enzyme system. The actual dehydration is mediated by component D, which contains 1.0 [4Fe-4S]²⁺ cluster, 1.0 reduced riboflavin-5′-phosphate and about 0.1 molybdenum (VI) per heterodimer. The enzyme has to be activated by the extremely oxygen-sensitive [4Fe-4S]^1+/2+-cluster-containing homodimeric component A, which generates Mo(V) by an ATP/Mg²⁺-induced one-electron transfer. Previous experiments established that the hydroquinone state of a flavodoxin (m=14.6 kDa) isolated from A. fermentans served as one-electron donor of component A, whereby the blue semiquinone is formed. Here we describe the isolation and characterization of an alternative electron donor from the same organism, a two [4Fe-4S]^1+/2+-cluster-containing ferredoxin (m=5.6 kDa) closely related to that from Clostridium acidiurici. The protein was purified to homogeneity and almost completely sequenced; the magnetically interacting [4Fe-4S] clusters were characterized by EPR and Mössbauer spectroscopy. The redox potentials of the ferredoxin were determined as ?405 mV and ?340 mV. Growth experiments with A. fermentans in the presence of different iron concentrations in the medium (7–45 μM) showed that flavodoxin is the dominant electron donor protein under iron-limiting conditions. Its concentration continuously decreased from 3.5 μmol/g protein at 7 μM Fe to 0.02 μmol/g at 45 μM Fe. In contrast, the concentration of ferredoxin increased stepwise from about 0.2 μmol/g at 7–13 μM Fe to 1.1±0.1 μmol/g at 17–45 μM Fe.     

Reducing basal salicylic acid enhances Arabidopsis tolerance to lead or cadmium

Aims

Phytoremediation is an emerging strategy for the removal of heavy metal contaminants. However, one of the prerequisite is to understand adequately plant resistant mechanisms. The present study was performed to assess the role of endogenous SA in plant response to Pb or Cd using wild-type (wt) Arabidopsis and its SA-accumulating mutant snc1, SA-reducing transgenic line nahG, SA signal-blocking npr1-1, and snc1/nahG (i.e. expression of nahG in snc1 plant) with a comparable level of SA to the wt.

Methods

Plants were grown hydroponically in controlled conditions. For heavy metal exposure, Pb²⁺ or Cd²⁺ at final concentrations of 50 μM, 100 μM, and 150 μM, respectively, was added to the culture solution. Unless otherwise indicated, samples were harvested after 7 d of exposure, and used for analyses.

Results

Compared to the wt level, the high endogenous SA significantly potentiated Pb- and Cd-induced plant growth retardation, whereas SA deficiency decreased the growth inhibition, and SA signaling blockage also had some protective effect. The expression of nahG in snc1 plant mitigated effectively the growth inhibition. The SA-related mechanism was involved in redox homeostasis, photosynthetic process, and soluble matter accumulation.

Conclusions

These results suggest that Pb- or Cd-induced phytotoxicity in Arabidopsis was intensified by elevated endogenous SA, whereas ameliorated by reduced SA.     

Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

The effect of bicarbonate ion (HCO₃⁻) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10 mM HCO₃⁻ (−Fe+Bic and −Fe, respectively). After 21 d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO₃⁻ (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO₃⁻ upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H⁺-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15 d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO₃⁻ prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.     

Asymmetric effects of litter removal and litter addition on the structure and function of soil microbial communities in a managed pine forest

Aims

The effect of different MeJA doses applied prior to or simultaneously with toxic Al on biochemical and physiological properties of Vaccinium corymbosum cultivars with contrasting Al resistance was studied.

Methods

Legacy (Al-resistant) and Bluegold (Al-sensitive) plants were treated with and without toxic Al under controlled conditions: a) without Al and MeJA, b) 100 μM Al, c) 100 μM Al + 5 μM MeJA, d) 100 μM Al + 10 μM MeJA and e) 100 μM Al + 50 μM MeJA. MeJA was applied to leaves 24 h prior to or simultaneously with Al in nutrient solution. After 48 h, Al-concentration, lipid peroxidation (LP), H₂O₂, antioxidant activity, total phenols, total flavonoids, phenolic compounds and superoxide dismutase activity (SOD) of plant organs were analyzed.

Results

Al-concentrations increased with Al-treatment in both cultivars, being Al, LP and H₂O₂ concentrations reduced with low simultaneous MeJA application. Higher MeJA doses induced more oxidative damage than the lowest. Legacy increased mainly non-enzymatic compounds, whereas Bluegold increased SOD activity to counteract Al³⁺.

Conclusions

Low MeJA doses applied simultaneously with Al³⁺ increased Al-resistance in Legacy by increasing phenolic compounds, while Bluegold reduced oxidative damage through increment of SOD activity, suggesting a diminution of its Al-sensitivity. Higher MeJA doses could be potentially toxic. Studies are needed to determine the molecular mechanisms involved in the protective MeJA effect against Al-toxicity.

     

Biological nitrification inhibition (BNI) activity in sorghum and its characterization

Aims

The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI). Here, we aimed at the quantification and characterization of the BNI function in sorghum that includes inhibitor production, their chemical identity, functionality and factors regulating their release.

Methods

Sorghum was grown in solution culture and root exudate was collected using aerated NH₄Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided chromatographic fractionation was used to isolate biological nitrification inhibitors (BNIs). The chemical structure was analyzed using NMR and mass spectrometry; pH-stat systems were deployed to analyze the role of rhizosphere pH on BNIs release.

Results

Sorghum roots released two categories of BNIs: hydrophilic- and hydrophobic-BNIs. The release rates for hydrophilic- and hydrophobic- BNIs ranged from 10 to 25 ATU?g^?1 root dwt. d^?1. Addition of hydrophilic BNIs (10 ATU?g^?1 soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated are: sakuranetin (ED₈₀ 0.6 μM; isolated from hydrophilic-BNIs fraction) and sorgoleone (ED₈₀ 13.0 μM; isolated from hydrophobic-BNIs fraction), which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH ₄ ⁺ in the root environment and the stimulatory effect of NH ₄ ⁺ lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED₅₀ 0.2 μM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED₅₀ 100 μM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay.

Conclusions

There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.     

Purification, characterization and kinetic properties of extracellular l-asparaginase produced by Cladosporium sp.

l-asparaginase from Cladosporium sp. grown on wheat bran by SSF was purified. Enzyme appeared to be a trimer with homodimer of 37 kDa and another 47 kDa amounting to total mass of 121 kDa as estimated by SDS-PAGE and 120 kDa on gel filtration column. The optimum temperature and pH of the enzyme were 30 °C and 6.3, respectively with Vmax of 4.44 μmol/mL/min and Km of 0.1 M. Substrate specificity studies indicated that, l-asparaginase has greater affinity towards l-asparagine with substrate hydrolysis efficiency (Vmax/Km ratio) eightfold higher than that of l-glutamine. l-asparaginase activity in presence of thiols studied showed decrease in Vmax and increase in Km, indicating nonessential mode of inactivation. Among the thiols tested, β-mercaptomethanol, exerted inhibitory effect, suggesting a critical role of disulphide linkages in maintaining a suitable conformation of the enzyme. Metal ions such as Ca²⁺, Co²⁺, Cu²⁺, Mg²⁺, Na⁺, K⁺ and Zn²⁺ significantly affected enzyme activity whereas presence of Fe³⁺, Pb²⁺ and KI stimulated the activity. Detergents studied also enhanced l-asparaginase activity. In-vitro half-life of purified l-asparaginase in mammalian blood serum was 93.69 h. The enzyme inhibited acrylamide formation in potato chips by 96 % making it a potential candidate for food industry to reduce acrylamide content in starchy fried food commodities.     

Characterization of a novel GH2 family α-l-arabinofuranosidase from hyperthermophilic bacterium Thermotoga thermarum

The 2,367-bp ORF of TtAFase from Thermotoga thermarum DSM 5069 encodes a calculated 90-kDa α-l-arabinofuranosidase (TtAFase), which does not belonging to any reported glycosyl hydrolase families α-l-arabinofuranosidases in the database and represents a novel one of glycosyl hydrolase family 2. The purified recombinant TtAFase produced in Escherichia coli BL21 (DE3) had optimum activity at pH 5.5 and at 80 °C. It was stable up to 80 °C and from pH 4.5–8.5. Kinetic experiments at 80 °C with p-nitrophenyl α-l-arabinofuranoside as a substrate gave a K _m of 0.77 mM, V _max of 2.3 μmol mg^?1 min^?1 and k _cat of 4.5 s^?1. The enzyme had no apparent requirement of metal ions for activity, and its activity was significantly inhibited by Cu²⁺ or Zn²⁺.     

Maintaining elevated Fe2+ concentration in solution culture for the development of a rapid and repeatable screening technique for iron toxicity tolerance in rice (Oryza sativa L.)

Background and aims

Iron toxicity decreases rice (Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes.

Methods

Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe²⁺ concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship.

Results

Optimized nutrient solution conditions were 300 mg L^?1 Fe supplied as Fe²⁺ at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained sufficient Fe²⁺ stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association (P?<?0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress.

Conclusion

This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity.     

Oxidation and reduction of sulfite contribute to susceptibility and detoxification of SO2 in Populus × canescens leaves

Key Message

The critical level for SO ₂ susceptibility of Populus × canescens is approximately 1.2 μL L ^?1 SO ₂ . Both sulfite oxidation and sulfite reduction and assimilation contribute to SO ₂ detoxification.

Abstract

In the present study, uptake, susceptibility and metabolism of SO₂ were analyzed in the deciduous tree species poplar (Populus × canescens). A particular focus was on the significance of sulfite oxidase (SO) for sulfite detoxification, as SO has been characterized as a safety valve for SO₂ detoxification in herbaceous plants. For this purpose, poplar plants were exposed to different levels of SO₂ (0.65, 0.8, 1.0, 1.2 μL L^?1) and were characterized by visible injuries and at the physiological level. Gas exchange parameters (stomatal conductance for water vapor, CO₂ assimilation, SO₂ uptake) of the shoots were compared with metabolite levels (sulfate, thiols) and enzyme activities [SO, adenosine 5′-phosphosulfate reductase (APR)] in expanding leaves (80–90 % expanded). The critical dosage of SO₂ that confers injury to the leaves was 1.2 μL L^?1 SO₂. The observed increase in sulfur containing compounds (sulfate and thiols) in the expanding leaves strongly correlated with total SO₂ uptake of the plant shoot, whereas SO₂ uptake rate was strongly correlated with stomatal conductance for water vapor. Furthermore, exposure to high concentration of SO₂ revealed channeling of sulfite through assimilatory sulfate reduction that contributes in addition to SO-mediated sulfite oxidation to sulfite detoxification in expanding leaves of this woody plant species.     

Microdistribution of major to trace elements between roots of Halimione portulacoides and host sediments (Tagus estuary marsh,Portugal)

Aim

This study presents a micrometre-scale map of the elemental distribution within roots and surrounding sediment of Halimione portulacoides of a contaminated salt marsh in the Tagus estuary.

Methods

Microprobe particle induced X-ray emission analysis was performed in sediment slices containing roots with tubular rhizoconcretions attached to host sediments.

Results

Strong concentration gradients were found particularly in the inner part of rhizoconcretions adjacent to the root wall. Local enrichment was observed in sediment interstices with Fe precipitates and other associated elements. A maximum of 55 % of Fe was measured near the concretion–root interface, with a decrease to <5 % in the host sediment. Maximum concentrations of P (3 %), As (1,200 μg g^?1) and Zn (3,000 μg g^?1) were registered in concretions, one order of magnitude above the values of the host sediment. The elemental concentration profiles across roots showed that the epidermis was an efficient selective barrier to the entrance of elements. Fe and As were retained in the epidermis. The highest Cu and Zn concentrations were also observed in the epidermis. However, the concentrations of Mn, Cu and Zn increased in the inner root.

Conclusions

As and Fe were mostly retained in the concretion, whereas P, Mn, Cu and Zn were mobilised by the root.     

Characterization of a recombinant l-fucose isomerase from Caldicellulosiruptor saccharolyticus that isomerizes l-fucose, d-arabinose, d-altrose, and l-galactose

A recombinant l-fucose isomerase from Caldicellulosiruptor saccharolyticus was purified as a single 68 kDa band with an activity of 76 U mg^?1. The molecular mass of the native enzyme was 204 kDa as a trimer. The maximum activity for l-fucose isomerization was at pH 7 and 75°C in the presence of 1 mM Mn²⁺. Its half-life at 70°C was 6.1 h. For aldose substrates, the enzyme displayed activity in decreasing order for l-fucose, with a k _cat of 11,910 min^?1 and a K _m of 140 mM, d-arabinose, d-altrose, and l-galactose. These aldoses were converted to the ketoses l-fuculose, d-ribulose, d-psicose, and l-tagatose, respectively, with 24, 24, 85, 55% conversion yields after 3 h.     

Trypanocidal and cytotoxic evaluation of synthesized thiosemicarbazones as potential drug leads against sleeping sickness

Thiosemicarbazones have become one of the promising compounds as new clinical candidates due to their wide spectrum of pharmaceutical activities. The wide range of their biological activities depends generally on their related aldehyde or ketone groups. Here, we report the pharmacological activities of some thiosemicarbazones synthesized in this work. Benzophenone and derivatives were used with N(4)-phenyl-3-thiosemicarbazide to synthesize corresponding five thiosemicarbazones (1–5). Their structures were characterized by spectrometrical methods analysis IR, NMR ¹H & ¹³C and MS. The compounds were then screened in vitro for their antiparasitic activity and toxicity on Trypanosoma brucei brucei and Artemia salina Leach respectively. The selectivity index of each compound was also determined. Four thiosemicarbazones such as 4, 2, 3 and 1 reveal interesting trypanocidal activities with their half inhibitory concentration (IC₅₀) equal to 2.76, 2.83, 3.86 and 8.48 μM respectively, while compound 5 (IC₅₀ = 12.16 μM) showed a moderate anti-trypanosomal activity on parasite. In toxicity test, except compound 1, which showed a half lethal concentration LC₅₀ >281 μM, the others exerted toxic effect on larvae with LC₅₀ of 5.56, 13.62, 14.55 and 42.50 μM respectively for thiosemicarbazones 4, 5, 3 and 2. In agreement to their selectivity index, which is greater than 1 (SI >1), these compounds clearly displayed significant selective pharmaceutical activities on the parasite tested. The thiosemicarbazones 2–5 that displayed significant anti-trypanosomal and cytoxicity activities are suggested to have anti-neoplastic and anti-cancer activities.