Improvement of antioxidant activity of chitosan by chemical treatment and ionizing radiation

Modification of chitosan (CS) to N-maleoylchitosan (NMCS), N-phthaloylchitosan (NPhCS) and sulfonated-chitosan (SCS) was done using maleic anhydride, phthalic anhydride and chlorosulfonic acid, respectively followed by exposing them to γ-rays at different doses. The molecular weights and structural changes of irradiated chitosan derivatives were determined by GPC, FT-IR and UV-vis spectrophotometer. The molecular weights decreased with increasing irradiation dose. Results revealed that the main polysaccharide structure remained after irradiation. To investigate the enhancement of antioxidant activity of chitosan and its derivatives of different molecular weights, radical mediated lipid peroxidation inhibition, scavenging effect of DPPH radicals, reducing power and ferrous ion chelating activity assays were used. Chitosan derivatives with different molecular weights exhibit antioxidant activity. The lower the molecular weights of chitosan and its derivatives, the higher the antioxidant activity. NMCS possessed high scavenging effect on DPPH radicals compared with NPhCS, SCS and ascorbic acid. The irradiated chitosan and its derivatives could be used as natural antioxidants.     

Comparison in antioxidant action between α-chitosan and β-chitosan at a wide range of molecular weight and chitosan concentration

Antioxidant activity in α- and β-chitosan at a wide range of molecular weight (Mw) and chitosan concentration (CS) was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, reducing ability, chelating ability, and hydroxyl radical scavenging activity. The form of chitosan (FC) had significant (P <0.05) effect on all measurements except DPPH radical scavenging activity, and antioxidant activity was dependent on Mw and CS. High Mw (280–300 kDa) of β-chitosan had extremely lower half maximal effective concentrations (EC₅₀) than α-chitosan in DPPH radical scavenging activity and reducing ability. The 22–30 kDa of α- and β-chitosan showed significantly (P <0.05) higher activities in DPPH radical scavenging, reducing ability, and hydroxyl radical scavenging than samples at other Mw, while chelating ability was the highest in 4–5 kDa chitosan. CS had significant effect on all measurements and the effect was related to Mw. The antioxidant activity of 280–300 kDa chitosan was affected by coil-overlap concentrations (C¹) in the CS range of 4–10 mg/mL, forming entanglements. Reducing ability and hydroxyl radical scavenging activity were more predominant action in antioxidant activity of chitosan as shown by the lower EC₅₀ values than those in other antioxidant measurements.     

Grafting of <Emphasis Type="Italic">Cucumis sativus</Emphasis> onto <Emphasis Type="Italic">Cucurbita ficifolia</Emphasis> leads to improved plant growth,increased light utilization and reduced accumulation of reactive oxygen species in chilled plants

The effects of chilling at 14 and 7°C on plant growth, CO₂ assimilation, light allocation, photosynthetic electron flux and antioxidant metabolism were examined in cucumber (Cucumis sativus L. cv. Jinyan No. 4, CS) plants with figleaf gourd (Cucurbita ficifolia Bouché, CF) and cucumber as rootstocks, respectively. Growth inhibition by chilling at 7°C was characterized by irreversible inhibition of CO₂ assimilation in grafted plants with cucumber as rootstock and scion (CS/CS) but this effect was significantly alleviated by grafting onto CF roots (CS/CF). Chilled CS/CF plants exhibited a higher photosynthetic activity and lower proportion of energy dissipation than chilled CS/CS plants. Chilling resulted in a greater decrease in the electron flux in photosystem (PS) II (J _PSII) than the rate of energy dissipation either via light-dependent (J _NPQ) or via constitutive thermal dissipation and fluorescence (J _f,D) in CS/CS plants. In parallel with the reduction in J _PSII, electron flux to oxygenation (J _o) and carboxylation by Rubisco (J _c) all decreased significantly whilst alternative electron flux in PS II (J _a) increased, especially in CS/CS plants. Moreover, CS/CF plants exhibited higher activity of antioxidant enzymes, lower antioxidant content and less membrane peroxidation relative to CS/CS plants after chilling.     

Time-dependent changes of the physiological status of Bromus inermis Leyss. seeds from chronic low-level radiation exposure areas

The seed progeny of smooth brome (Bromus inermis Leyss.) were evaluated over a year for their viability, mutation rate, resistance to radiation and antioxidant status in response to chronic radiation exposure. Bromus inermis is found in the Eastern Ural Radioactive Trace (EURT) area and the background territories (surrounding territories that are used as controls as they only have natural background radiation). The absorbed doses by smooth brome from the EURT area were 1.5–18.5 times higher compared to background locations for parent plants and 1.1–11.6 times higher for the seed embryos. There are predictable and asynchronous changes in the survival of shoots and root growth rate between background populations and chronically irradiated samples. The provocative dose of 250 Gy is more damaging in the winter months, than in the summer and autumn. The frequency of anomalies in shoots varied in different months, with the biggest rate of mutation recorded in physiologically harsher period (autumn–winter). There is no correlation between resulting survival rate of shoots and their resistance to radiation. The intense activity of the antioxidant systems (estimated by the content of low molecular weight antioxidants) allowed faster growth of the shoots and reduced the number of abnormalities seen in development.     

Antioxidant and antimicrobial potential of two extracts from Capparis spinosa L. and Rumex nervosus and molecular docking investigation of selected major compounds

The present study examined the phytochemical composition, antioxidant, antimicrobial properties, and molecular docking of different solvents extracts (methanol and water) of two medicinal plants, namely, Capparis spinosa L (CS) and Rumex nervosus (RN). Phytochemical analysis showed that total phenol, flavonoids, alkaloids, and vitamin C were significantly (P ≤ 0.05) higher in the methanolic extract of both plants than in other solvents. However, tannin content was significantly (P ≤ 0.05) high in the water extract for both plants. Chloroform and acetone extracts were significantly lower in phytochemicals than other solvents, therefore excluded in this study. GC–MS analysis showed one dominant compound in CS (isopropyl isothiocyanate) and two in RN (pyrogallol and palmitic acid). The antioxidant methods applied (DPPH, ABTS, β-Carotene/linoleic acid assay, and reducing the power) showed that the methanolic extract of CS exerted higher activity in methanolic extract but lower than that of BHA standard. The methanolic extract of both plants inhibited the bacterial pathogens when a minimum inhibitory concentration (MIC) method was applied, compared to water extract with RN-methanolic extract had a lower inhibition concentration than CS-methanolic extract. The molecular interactions study revealed that the palmitic acid and pyrogallol interacted with the receptors' active site. This work concluded that CS and RN showed a remarkable antioxidant and antibacterial effect with the high antimicrobial activity of RN extract.     

一氧化氮对UV-B辐射增强条件下燕麦幼苗氧化损伤的缓解作用

以燕麦品种“定燕2号”和“晋燕14号”为研究材料,研究紫外线B（ultraviolet rays-B, UV-B）辐射增强条件下,一氧化氮（nitric oxide, NO）供体硝普钠（sodium nitroprusside, SNP）对燕麦幼苗活性氧含量、膜脂过氧化和抗氧化物质含量的影响。结果表明：NO能够降低UV-B辐射增强条件下“定燕2号”和“晋燕14号”的超氧阴离子（superoxide radical, O₂^·-）产生速率、羟自由基（hydroxyl free radical, OH^·）、过氧化氢（hydrogen peroxide, H₂O₂）和丙二醛（malondialdehyde, MDA）含量。UV-B辐射时间为6 h,施加SNP时,“定燕2号”的超氧化物歧化酶（superoxide dismutase, SOD）活性和过氧化物酶（peroxidase, POD）活性、“晋燕14号”的SOD活性高于其他处理组;UV-B辐射时间为3 h,施加SNP时,“定燕2号”、“晋燕14号”的抗坏血酸过氧化物酶（ascorbate peroxidase, APX）活性显著高于0 h、12 h处理组。UV-B辐射时间为6 h,“定燕2号”的脱氢抗坏血酸（dehydroascorbic acid, DHA）含量显著高于其他处理组;而UV-B辐射时间为0 h,“晋燕14号”的DHA 含量显著高于其他处理组。NO对UV-B辐射增强下“定燕2号”和“晋燕14号”抗氧化性影响的综合测评均为：3 h>6 h>12 h>0 h。本研究结果为NO在燕麦育种、抗氧化机制等提供理论依据。     

Antioxidant activity of the simulated gastro-intestinal digestion hydrolysate of two edible Nigerian marine molluscs: Tympanatonus fuscatus var radula (L.) and Pachymelania aurita (M.)

The multifunctional nature of antioxidant peptides makes them more attractive candidates as dietary ingredients in health maintenance. Therefore, food protein-derived antioxidant peptides are continuously investigated. This study investigated the in vitro antioxidant properties of hydrolysate and ultrafiltered peptide fractions of Pachymelania aurita and Tympanatonus fuscatus var radula-two commonly consumed marine molluscs known as periwinkles in southern Nigeria. Simulated gastrointestinal digestion (SGID) of soluble proteins of T. fuscatus and P. aurita was carried out using pepsin, trypsin and chymotrypsin, and the SGID hydrolysates were fractionated using a 3 kDa membrane filter. The hydrolysates and their fractions were investigated for anti-lipid peroxidation, hydroxyl radical scavenging activity (HRSA), ferric reducing antioxidant property (FRAP) and metal chelation activity, and they demonstrated clear antioxidant properties in all the assay models used. Low molecular weight fractions of the hydrolysates demonstrated more potent antioxidant activity than higher molecular weight fractions. This is profound in the metal chelation assay, where low molecular weight peptide fractions, T ≤ 3 kDa and P ≤ 3 kDa (IC₅₀ values of 8.10 ± 0.011 and 5.56 ± 0.50 µg/ml respectively) had activity that is similar to that of EDTA (11.84 ± 0.89 µg/ml). Similar activity effects were observed in other assays where there was about 3-fold higher activity in low molecular weight fractions. These results demonstrate the presence of antioxidant peptide(s) in the protein hydrolysates of the periwinkles.     

Increased level of superoxide dismutase (SOD) activity in larvae of Chironomus ramosus (Diptera: Chironomidae) subjected to ionizing radiation

A battery of enzymes from the eukaryotic antioxidant defense system was measured in salivary gland and in whole body extract of fourth instar larvae of Chironomus ramosus with an objective of finding any clue for the dipteran insect's capacity to tolerate heavy doses of ionizing radiation. Levels of activity of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GSH-Px) were quantified in 30 days old larvae exposed to LD₂₀ dose of gamma radiation. Compared to controls, activity of Cu,Zn-SOD increased 3 to 4 fold and catalase 2 fold in response to ionizing radiation stress, while activities of GR and GSH-Px enzymes were decreased. Among the other SOD isoenzymes, our results showed comparable levels of Mn-SOD and Cu,Zn-SOD activity in control and irradiated groups of larvae. The increase in levels of the Cu,Zn-SOD isoenzyme was also confirmed by Western blot and zymography supported by densitometric quantification. No evidence of Fe-SOD was found in C. ramosus larvae. These findings could help to explain the persistence of natural populations of Chironomus in radioactively contaminated regions.     

Effects of different UV radiation on photoprotective pigments and antioxidant activity of the hot‐spring cyanobacterium Leptolyngbya cf. fragilis

UV‐induced synthesis/accumulation of photoprotective pigments and antioxidant activity were investigated in the hot‐spring cyanobacterium Leptolyngbya cf. fragilis. The results indicated that UV radiation may induce biosynthesis of carotenoids, allophycocyanin, phycoerythrin, and scytonemin while phycocyanin degrades in response to longtime UV radiation. Moreover, pigment composition of L. cf. fragilis was significantly altered with increasing UV radiation times, probably due to destruction and resynthesis of accessory pigments as an adaptation strategy to UV stress. The in vitro antioxidant analysis of different extracts of UV treated cyanobacteria exhibited concentration‐dependent antioxidant activity. Ethyl acetate extract of 72 h UV treatment showed maximum total antioxidant activity (IC50 = 71.73 ± 5.3 μg mL^?1) followed by ethyl acetate control (non‐UV irradiated) extract (IC50 = 109.43 ± 2.76 μg mL^?1). This is the first report for the UV‐induced synthesis of photoprotective pigments and their antioxidant activity in L. cf. fragilis.     

Functional and physical molecular size of the chicken hepatic lectin determined by radiation inactivation and sedimentation equilibrium analysis

Radiation inactivation and sedimentation equilibrium analysis were used to determine the functional and physical size of the chicken hepatic membrane receptor that binds N-acetylglucosamine-terminated glycoproteins. Purified plasma membranes from chicken liver were irradiated with high energy electrons and assayed for 125I-agalactoorosomucoid binding. Increasing the dose of ionizing radiation resulted in a monoexponential decay in binding activity due to a progressive loss of binding sites. The molecular mass of the chicken lectin, determined in situ by target analysis, was 69,000 +/- 9,000 Da. When the same irradiated membranes were solubilized in Brij 58 and assayed, the binding protein exhibited a target size of 62,000 +/- 4,000 Da; in Triton X-100, the functional size of the receptor was 85,000 +/- 10,000 Da. Sedimentation equilibrium measurements of the purified binding protein yielded a lower limit molecular weight of 79,000 +/- 7,000. However, the solubilized lectin was detected as a heterogeneous population of oligomers with molecular weights as high as 450,000. Addition of calcium or calcium plus N-acetylglucosamine decreased the higher molecular weight species, but the lower limit molecular weights remained invariant. Similar results were determined when the chicken lectin was solubilized in Brij 58, C12E9, or 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonic acid (CHAPS). Results from the present study suggest that in the plasma membrane, the functional species of the chicken hepatic lectin exists as a trimer. However, in detergent solution, the purified receptor forms a heterogeneous population of irreversible oligomers that exhibit binding activity proportional to size.     

Aromatic amino acid oxidation products as antioxidants

The accumulation of UV photolysis products of amino acids tyrosine and tryptophan, which possess antioxidant activity, has been studied by the method of luminol-dependent chemiluminescence. The amount of antioxidant products was judged by the value of the total antioxidant potential of a UV-irradiated solution, the measure of which was the distance between the peaks of the chemiluminescence curve in the system 2,2′-azo-bis(2-amidinopropane) hydrochloride + luminol with a UV-irradiated and an unirradiated sample (induction period, τ _i ). Simultaneously, the absorption and fluorescence spectra of unirradiared and UV-irradiated amino acid solutions were recorded. It was shown that exposure of a tryptophan solution to radiation led to accumulation of a fluorescent product N-formyl kynurenine (λ_em = 325 nm, λ_max = 440 nm), and the curve of its accumulation was similar to the growth of antioxidant potential. When a tyrosine solution was irradiated, the main fluorescent product was dityrosine (λ_em = 310 nm, λ_max = 415 nm). Nevertheless, the dose dependences of the formation of dityrosine and the total antioxidant potential were completely different. It was found that another product of tyrosine UV photolysis, dihydroxyphenylalanine, possessed pronounced antioxidant activity. It was concluded that the main antioxidant produced under UV irradiation of tryptophan is formyl kynurenine, and under irradiation of tyrosine it is dihydroxyphenylalanine.     

Cytogenetic and oxidative alterations after exposure of cultured human whole blood cells to lithium metaborate dehydrate

Boron compounds have an ability of supporting antioxidant properties in human and animal tissues. Lithium metaborate dihydrate (LiBO₂·2H₂O; LMD) is commonly used in nonlinear optic materials, cellular phones and pagers. But, there are limited data on the genotoxic and antioxidant effects of LMD in cultured human whole blood cells. The aim of this study was to evaluate for the genotoxicity and antioxidant/oxidant activity of LMD on human whole blood lymphocytes (n = 5). LMD was applied at various concentrations (0–1,280 µg/ml) to cultured blood samples. Antioxidant/oxidant activity was evaluated by measuring the total oxidant status (TOS) and total antioxidant capacity levels. Micronuclei and chromosomal aberration tests were used in genotoxicity studies. Our results clearly revealed that all tested concentrations of LMD were found to be non-genotoxic when compared to that of the control group. In addition, LMD exhibited antioxidant activities at low concentrations. In addition the TOS levels were not changed at all concentrations of LMD. Consequently, our results clearly demonstrated that LMD is non-genotoxic and it has an important antioxidant potential in vitro.     

Effect of the chelation of metal cation on the antioxidant activity of chondroitin sulfates

The antioxidant potencies of chondroitin sulfates (CSs) from shark cartilage, salmon cartilage, bovine trachea, and porcine intestinal mucosa were compared by three representative methods for the measurement of the antioxidant activity; DPPH radical scavenging activity, superoxide radical scavenging activity, and hydroxyl radical scavenging activity. CSs from salmon cartilage and bovine trachea showed higher potency in comparison with CSs from shark cartilage and porcine intestinal mucosa. Next, CS from salmon cartilage chelating with Ca²⁺, Mg²⁺, Mn²⁺, or Zn²⁺ were prepared, and their antioxidant potencies were compared. CS chelating with Ca²⁺ or Mg²⁺ ions showed rather decreased DPPH radical scavenging activity in comparison with CS of H⁺ form. In contrast, CS chelating with Ca²⁺ or Mg²⁺ ion showed remarkably enhanced superoxide radical scavenging activity than CS of H⁺ or Na⁺ form. Moreover, CS chelating with divalent metal ions, Ca²⁺, Mg²⁺, Mn²⁺, or Zn²⁺, showed noticeably higher hydroxyl radical scavenging activity than CS of H⁺ or Na⁺ form. The present results revealed that the scavenging activities of, at least, superoxide radical and hydroxyl radical were enhanced by the chelation with divalent metal ions.     

Baseline Data from a Belgium-Wide Survey of Campylobacter Species Contamination in Chicken Meat Preparations and Considerations for a Reliable Monitoring Program

From February to November 2007, chicken meat preparations (n = 656) were sampled at 11 processing companies across Belgium. All samples were tested for Campylobacter by enrichment culture and by direct plating according to standard methods. Almost half (48.02%) of the samples were positive for Campylobacter spp. The mean Campylobacter count was 1.68 log₁₀ CFU/g with a standard deviation of ± 0.64 log₁₀ CFU/g. The study revealed a statistically significant variation in Campylobacter contamination levels between companies; processors with a wider frequency distribution range of Campylobacter counts provided chicken meat preparations with higher Campylobacter incidences and concentrations. There was no significant difference between the counts of Campylobacter spp. in various preparation types. However, the Campylobacter counts and incidences in chicken wings were the highest and portioned-form products (legs, wings, and breasts) showed a higher probability of being Campylobacter positive compared to minced-form products (sausages, burgers, and minced meat). The proportion of Campylobacter-positive samples was significantly higher in July than in other months. Recovery of Campylobacter spp. recovery by direct plating was higher (41.0%) compared to detection after enrichment (24.2%). Statistical modeling of the survey data showed that the likelihood of obtaining a positive result by enrichment culture increases with an increase in the Campylobacter concentration in the sample. In the present study, we provide the first enumeration data on Campylobacter contamination in Belgian chicken meat preparations and address proposals for improving Campylobacter monitoring programs.     

Antioxidant and free radical scavenging properties of N-acetylcysteine amide (NACA) and comparison with N-acetylcysteine (NAC)

The antioxidant potential of N-acetylcysteine amide (NACA), also known as AD4, was assessed by employing different in vitro assays. These included reducing power, free radical scavenging capacities, peroxidation inhibiting activity through linoleic acid emulsion system and metal chelating capacity, as compared to NAC and three widely used antioxidants, α-tocopherol, ascorbic acid and butylated hydroxytoluene (BHT). Of the antioxidant properties that were investigated, NACA was shown to possess higher 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging ability and reducing power than NAC, at all the concentrations, whereas the scavenging ability of H₂O₂ differed with concentration. While NACA had greater H₂O₂ scavenging capacity at the highest concentration, NAC was better than NACA at lower concentrations. NAC and NACA had a 60% and 55% higher ability to prevent β-carotene bleaching, respectively, as compared to control. The chelating activity of NACA was more than 50% that of the metal chelating capacity of EDTA and four and nine times that of BHT and α-tocopherol, respectively. When compared to NACA and NAC; α-tocopherol had higher DPPH scavenging abilities and BHT and α-tocopherol had better β-carotene bleaching power. These findings provide evidence that the novel antioxidant, NACA, has indeed enhanced the antioxidant properties of NAC.     

Rootstocks improve cucumber photosynthesis through nitrogen metabolism regulation under salt stress

We examined the growth, photosynthetic parameters, initial and total ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, the relative expression of rbcL, rbcS, and rca gene, and nitrogen metabolism of cucumber (Cucumis sativus L. cv. Jinchun No.2, CS) plants grafted onto figleaf gourd (Cucurbita ficifolia Bouché, CF) and pumpkin (Cucurbita moschata Duch. cv. Chaojiquanwang, CM) rootstocks. Growth inhibition under salt stress (90 mM NaCl) was characterized by the irreversible inhibition of CO₂ assimilation in the cucumber plants grafted onto cucumber rootstocks (CS/CS). In contrast, this effect was significantly alleviated by grafting the cucumber plants onto the CF and CM roots (CS/CF, CS/CM). Under NaCl stress, the CS/CF and CS/CM plants exhibited higher photosynthetic activity, higher initial and total Rubisco activity, and higher Rubisco-related gene expression than the CS/CS plants. Salinity resulted in a lesser increase in nitrate content and decrease in free amino acid content in the CS/CF and the CS/CM plants compared with the CS/CS plants. Accordingly, the activity of nitrate reductase, glutamine synthetase, and glutamate synthase decreased significantly, especially in the CS/CS plants. These results suggest that grafting cucumber plants onto salt-tolerant rootstocks enhances Rubisco activity and the expression of Rubisco-related genes by effectively accelerating nitrate transformation into amino acids under NaCl stress, thereby improving the photosynthetic performance of cucumber leaves.     

Effect of UV-B radiation on the growth and antioxidant enzymes of Antarctic sea ice microalgae <Emphasis Type="Italic">Chlamydomonas</Emphasis> sp. ICE-L

The effect of ultraviolet-B (UV-B) radiation on Antarctic phytoplankton has become an attractive ecological issue as a result of annual springtime ozone depletion. The effects of UV-B radiation on the growth and antioxidant enzymes were investigated using Antarctic sea ice microalgae Chlamydomonas sp. ICE-L as the material in this study. The results demonstrated that UV-B radiation could notably inhibit the growth, especially at high UV-B radiation intensity (70 μW cm⁻²). Malondialdehyde and O₂ ^·− content in ICE-L increased rapidly in early days (1–3 days) exposed to UV-B radiation enhancement, then decreased rapidly. In the stress of UV-B radiation enhancement, the superoxide dismutase, peroxidase and Catalase activities of 1–4 days in ICE-L were obviously higher than those in the control, and their activities became higher at high UV-B radiation intensity (70 μW cm⁻²). These enzymes activity of 7 days would kept stable at low UV-B radiation intensity (35 μW cm⁻²), but kept high level at high UV-B radiation intensity (70 μW cm⁻²). However, the ascorbate peroxidase activity in ICE-L kept stable under the stress of UV-B radiation enhancement. The above experimental results indicated that the antioxidant enzyme system played an important role in the adaptation of Antarctic ice microalgae under the UV-B radiation change of Antarctic ecosystems.     

The effect of gold and silver nanoparticles,chitosan and their combinations on bacterial biofilms of food-borne pathogens

Abstract

The antimicrobial activity of gold and silver nanoparticles (AuNPs, AgNPs), chitosan (CS) and their combinations was established by determining the minimum inhibitory concentration for planktonic (MICPC₈₀) and biofilm growth (MICBC₈₀), for biofilm formation (MICBF₈₀), metabolic activity (MICBM₈₀) and reduction (MICBR₈₀), and for the metabolic activity of preformed biofilm (MICMPB₈₀). Biofilms were quantified in microtitre plates by crystal violet staining and metabolic activity was evaluated by the MTT assay. Chitosan effectively suppressed biofilm formation (0.31–5?mg ml^?1) in all the tested strains, except Salmonella enterica Infantis (0.16–2.5?mg ml^?1) where CS and its combination with AgNPs induced biofilm formation. Nanoparticles inhibited biofilm growth only when the highest concentrations were used. Even though AuNPs, AgNPs and CS were not able to remove biofilm mass, they reduced its metabolic activity by at least 80%. The combinations of nanoparticles with CS did not show any significant positive synergistic effect on the tested target properties.     

Effect of elevated CO2, temperature and limited water supply on antioxidant status during regrowth of nodulated alfalfa

Atmospheric CO₂ is a major contributor to the greenhouse effect and is one of the main inducers of climate change. Previous studies with nodulated alfalfa plants have shown that elevated CO₂ increased the growth of plants grown under well‐watered or limited water supply conditions. The beneficial effects of atmospheric CO₂ enrichment included higher photosynthetic rates, growth and water‐use efficiency and an increase in the root/shoot ratio. However, at the moment, we do not have information on the possible implications of the beneficial effect of elevated CO₂ as it may relate to a higher capacity of the violaxanthin–antheraxanthin–zeaxanthin (VAZ) cycle, the dissipation of excess radiation as heat and the effect on photooxidation, and to an improved leaf antioxidant system (Halliwell–Asada cycle). The aim of the present study was to determine the effects of the interaction between CO₂ (ambient, around 350 vs 700 μmol mol⁻¹), temperature (ambient vs ambient + 4°C) and water availability (well irrigated vs partially irrigated) on the leaf antioxidant status of nodulated alfalfa during regrowth. Parameters measured in this study included relative growth rate (RGR), H₂O₂ content, oxidative damage [measured as thiobarbituric acid‐reacting substances (TBARS)], leaf pigment composition (chlorophylls and xanthophylls), ascorbate (ASA) and glutathione pool levels and antioxidant enzymes. Our results revealed that during alfalfa regrowth, the effects of elevated CO₂, limited water supply, temperature and their interactions on growth were not related to significant or general changes in leaf antioxidant capacity, H₂O₂ accumulation or oxidative stress (TBARS concentrations). The beneficial effects of CO₂ enrichment in well‐watered and limited water‐subjected plants were not associated with an increase in the capacity of alfalfa leaves to dissipate excess radiation as heat through the VAZ cycle or with an increase in the antioxidant capacity, measured in terms of Halliwell–Asada cycle enzymes and antioxidant compounds. Furthermore, elevated CO₂ did not affect RGRs during the last 15 days of regrowth and reduced the activity of several antioxidant enzymes (catalase, superoxide dismutase and glutathione reductase and ASA peroxidase in limited water‐subjected plants), suggesting a lower basal rate of oxygen activation and H₂O₂ formation, leading to a relaxation of the antioxidant system.     

Role of Burkholderia cepacia CS8 in Cd-stress alleviation and phytoremediation by Catharanthus roseus

The current study was performed to assess the effect of Burkholderia cepacia CS8 on the phytoremediation of cadmium (Cd) by Catharanthus roseus grown in Cd-contaminated soil. The plants cultivated in Cd amended soil showed reduced growth, dry mass, gas-exchange capacity, and chlorophyll contents. Furthermore, the plants exhibited elevated levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) under Cd stress. The bacterized plants showed higher shoot length, root length; fresh and dry weight. The improved stress tolerance in inoculated plants was attributed to the reduced quantity of MDA and H₂O₂, enhanced synthesis of protein, proline, phenols, flavonoids, and improved activity of antioxidant enzymes including peroxidase, superoxide dismutase, ascorbate peroxidase, and catalase. Similarly, the 1-aminocyclopropane-1-carboxylate deaminase activity, phosphate solubilization, auxin, and siderophore production capability of B. cepacia CS8 improved growth and stress alleviation in treated plants. The bacterial inoculation enhanced the amount of water extractable Cd from soil. Furthermore, the inoculated plants showed higher bioconcentration factor and translocation factor. The current study exhibits that B. cepacia CS8 improves stress alleviation and phytoextraction potential of C. roseus plants growing under Cd stress.