POX Activity Research Articles

Ripening and storage conditions of Chétoui and Arbequina olives: Part II. Effect on olive endogenous enzymes and virgin olive oil secoiridoid profile determined by high resolution mass spectrometry

Several factors affect virgin olive oil (VOO) phenolic profile. The aim of this study was to monitor olive hydrolytic (β-glucosidase) and oxidative (peroxydase, POX, and polyphenoloxydase, PPO) enzymes during olive ripening and storage and to determine their capacity to shape VOO phenolic profile. To this end, olives from the cultivars Chétoui and Arbequina were stored at 4°C or 25°C for 4weeks and their enzymatic activities and oil phenolic profiles were compared to those of ripening olives. We observed different trends in enzymes activities according to cultivar and storage temperature. Secoiridoid compounds, determined by high resolution mass spectrometry (HRMS), and their deacetoxylated, oxygenated, and deacetoxy-oxygenated derivatives were identified and their contents differed between the cultivars according to olive ripening degree and storage conditions. These differences could be due to β-glucosidase, POX and PPO activities changes during olive ripening and storage. Results also show that oxidised phenolic compounds could be a marker of VOO ‘‘freshness”.

Exogenous Melatonin Improves Antioxidant Defense in Cucumber Seeds (Cucumis sativus L.) Germinated under Chilling Stress.

The relationship between exogenous melatonin applied into cucumber seeds during osmopriming and modifications of their antioxidant defense was studied. Accumulation of hydrogen peroxide, antioxidant enzyme activities and glutathione pool were investigated in embryonic axes isolated from the control, osmoprimed, and osmoprimed with melatonin seeds. Germinating cucumber seeds are very sensitive to chilling. Temperature 10°C causes oxidative stress in young seedlings. Seed pre-treatment with melatonin seemed to limit H2O2 accumulation during germination under optimal condition as well as during chilling stress and recovery period. Melatonin affected superoxide dismutase (SOD) activity and its isoforms during stress and recovery period but did not influence CAT and POX activities. Thus it is possible that in cucumber this indoleamine could act mostly as a direct H2O2 scavenger, but superoxide anion combat via SOD stimulation. The GSH/GSSG ratio is considered as an indirect determinant of oxidative stress. When the cells are exposed to oxidative stress GSSG is accumulated and the ratio of GSH to GSSG decreases. In our research pre-sowing melatonin application into the cucumber seeds caused high beneficial value of GSH/GSSG ratio that could be helpful for stress countering. Glutathione reductase (GSSG-R) activity in the axes isolated from these seeds was two fold higher than in those isolated from the control and from the osmoprimed without melatonin ones. Additional isoforms of GSSG-R in melatonin treated seeds were also observed. It explains high and effective GSH pool restoration in the seeds pre-treated with melatonin. We confirmed that melatonin could protect cucumber seeds and young seedlings against oxidative stress directly and indirectly detoxifying ROS, thereby plants grown better even in harmful environmental conditions. This work is the first that investigated on plant in vivo model and documented melatonin influence on redox state during seed germination. This way we try to fill lack of information about melatonin-regulated pathways involved in antioxidant strategy of plant defense.

Antioxidant Defense Mechanisms in Pseudomonas aeruginosa: Role of Iron-Cofactored Superoxide Dismutase in Response to UV-C Radiations.

The role of SOD gene in response to UV-C radiations was studied in Pseudomonas aeruginosa. Firstly, our results showed that the inactivation of sodM and/or sodB genes decreases the resistance of P. aeruginosa after exposure to UV-C rays. Furthermore, our results showed that SOD activity is dose dependant in all strains. However, significant increase in SOD activity was only shown at UV-C exposure time of 5min in sodB mutant. At an elevated dose equivalent to 30min of exposure, significant increase in SOD activity was observed in sodM. Catalase activities showed significant decrease in WT and in sodB mutant after an exposure time of 30min. CAT enzyme was present at higher levels than SOD, reflecting that alternate enzymes such as POX, is poorly associated with CAT activity, and an increase in POX activity is related to increase in stress tolerance. The overall results showed that sodB gene has an important protective role against UV-C radiations in P. aeruginosa, compared to SodM isoform.

Effect of Si on the Antioxidative Defense of Young Maize Roots Under NaCl Stress

Salinity stress usually causes a serious yield reduction in crop production. Silicon (Si) has been reported to be able to alleviate stress damage, but the mechanism is still unclear. The aim of this work was to study the effect of exogenous silicon (Si) on the young maize plants welfare. For that the activities of major antioxidant enzymes (superoxide dismutase, SOD; peroxidases, POX; ascorbate peroxidase, APX) and on the lipid peroxidation (content of malondialdehyde, MDA) were investigated in the roots of salt-stressed maize (Zea mays L.). Two maize hybrids (Novania and Almansa) contrasting in their response to NaCl were tested. Four treatments with three replicates were monitored: control (without Si and NaCl), 2.5 mM Si, 150 mM NaCl, 150 mM NaCl and 2.5 mM Si. Maize roots were harvested 10 days after the treatment. MDA, ascorbate content and enzyme activities were assayed spectrophotometrically. The isoenzyme pattern of the antioxidant enzymes was detected by native PAGE. Compared with the plants treated with salt alone, added Si significantly increased MDA content in hybrid Almansa, while in Novania no increase was observed. The addition of Si significantly enhanced the activities of SOD in salt–stressed plants in both hybrids. The activities of POX and APX in salt stressed roots were significantly increased in Almansa hybrid in the presence of Si. The isoenzyme pattern followed changes in the activity of SOD; however in POX and APX such a tendency was not registered. The changes of the intensity and in the case of POX also the number of bands were detected. From these results we conclude, that Si addition fortified enzymatic antioxidative response operates in roots of young maize plants by a still unknown mechanism. The approval effect of Si is evident in the case of the SOD detoxifying system regardless of the hybrid, and for the POX family in the more sensitive maize hybrid Almansa. The presented outputs point out that silicon may protect plant tissues from oxidative damage under salt stress. Since the alleviative effect seems to be hybrid-specific, silicon alleviation of salt stress is probably not a universal feature in general and should be carefully considered between plants and/or hybrids.

Alleviation of the adverse effects of salinity stress using trehalose in two rice varieties

A possible survival strategy of plants under effects of salinity is to use some compounds that could help plants to alleviate salt stress effect. The effect of exogenously application of trehalose as seed soaking prior to irrigation with different salinity levels (0, 30 and 60mM NaCl) to rice (Oriza sativa L.) varieties (Giza 177 and Giza 178) was investigated. Salinity stress decreased photosynthetic pigments and total carbohydrate, concomitantly with increasing total soluble sugars content, trehalose and proline content for both rice varieties. The activities of SOD, CAT and POX were increased with increasing salinity level. Soaking rice seeds with 25mM of trehalose (Tre) could alleviate the harmful effects of salinity stress. Moreover, a higher solute concentration contributing to osmotic adjustment and the higher antioxidant enzymes activity were observed in shoots of salinity treated Giza 178 than those of Giza 177.

Effects of juglone and lawsone on oxidative stress in maize coleoptile cells treated with IAA.

Naphthoquinones are secondary metabolites widely distributed in nature and produced by bacteria, fungi and higher plants. Their biological activity may result from induction of oxidative stress, caused by redox cycling or direct interaction with cellular macromolecules, in which quinones act as electrophiles. The redox homeostasis is known as one of factors involved in auxin-mediated plant growth regulation. To date, however, little is known about the crosstalk between reactive oxygen species (ROS) produced by quinones and the plant growth hormone auxin (IAA). In this study, redox cycling properties of two naphthoquinones, juglone (5-hydroxy-1,4-naphthoquinone) and lawsone (2-hydroxy-1,4-naphthoquinone), were compared in experiments performed on maize coleoptile segments incubated with or without the addition of IAA. It was found that lawsone was much more effective than juglone in increasing both H2O2 production and the activity of antioxidative enzymes (SOD, POX and CAT) in coleoptile cells, regardless of the presence of IAA. An increase in the activity of Cu/Zn-SOD isoenzymes induced by both naphthoquinones suggests that juglone- and lawsone-generated H2O2 was primarily produced in the cytosolic and cell wall spaces. The cell potential to neutralize hydrogen peroxide, determined by POX and CAT activity, pointed to activity of catalase as the main enzymatic mechanism responsible for degradation of H2O2 Therefore, we assumed that generation of H2O2, induced more efficiently by LW than JG, was the major factor accounting for differences in the toxicity of naphthoquinones in maize coleoptiles. The role of auxin in the process appeared negligible. Moreover, the results suggested that oxidative stress imposed by JG and LW was one of mechanisms of allelopathic action of the studied quinones in plants.

Salt stress affects mitotic activity and modulates antioxidant systems in onion roots

This study was aimed to explore the effect of short-term salt stress and recovery on cytology and the activity of antioxidant enzyme in roots of onion (Allium cepa L.) plant. Roots of A. cepa were treated with different concentrations of NaCl (0, 50, 100, 150, 200 mM), and cytological and physiological indicators in the root of plant were measured in different processing time. With the increase of NaCl concentrations and processing time, mitotic activity and relative division rate (RDR) were reduced. However, during recovery, mitotic activity and RDR were restored but their values were less than control values. Salt stress caused an increase while in recovery experiments there was a slight reduction in chromosomal aberrations. A significant increase in SOD and POX activities except in 200 mM occurred after 18 h of stress which was still higher than control in recovered plants. CAT activity showed 53.90 % decrease after 18 h of salt stress and also a significant decrease was observed after 24 h post stress. The results suggest that at high salt stress up to 150 mM, the roots of A. cepa are capable to rapidly activate antioxidant defence system to resist the salt-induced oxidative stress, but could not control the cytogenetical activities. The results also suggest that the recovery is possible at physiological and cytogenetical level by retaining chromosomal and DNA integrity.

Does methyl jasmonate modify the oxidative stress response in Phaseolus coccineus treated with Cu?

The contribution of methyl jasmonate (MJ) as a signal molecule able to take part in the defense mechanism against copper (Cu)-imposed oxidative stress was studied in the leaves and roots of runner bean (Phaseolus coccineus) plants. Roots of plants cultivated hydroponically were preincubated in MJ (10µM) for 1h or 24h and subsequently exposed to Cu (50µM) for 5h (short-term experiment) or 5 days (long-term experiment). Enzymatic (activity of superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; guaiacol peroxidase, POX) and non-enzymatic (accumulation of malondialdehyde, MDA; homoglutathione, hGSH; proline; anthocyanins; low molecular weight organic acids, LMWOAs) responses were determined in the leaves and roots. The antioxidative defense mechanism was significantly activated after Cu supplementation. In most cases, activities of ROS (reactive oxygen species) scavenging enzymes like SOD, CAT, APX, POX, as well as MDA, hGSH and proline concentrations increased following Cu exposure. MJ showed a time-dependent effect on antioxidative enzymes activity. In the short-term experiment, MJ elevated CAT, APX and POX activities in the roots, and POX activity in the leaves of non-Cu-treated plants. In the long-term experiment, MJ not only decreased POX and partially CAT activity in the roots, but also increased the MDA level and partially CAT activity in the leaves of the control plants. In Cu-treated plants, MJ reduced APX, but elevated POX activity in the leaves after 5-h exposure. After 5-day-Cu treatment, MJ inhibited POX activity in the leaves and mainly reduced SOD and CAT activities in the roots. Moreover, in the long-term experiment, MJ reduced tartrate and pyruvate in the leaves of Cu-stressed plants, but mostly elevated tartrate and malate in the roots comparing with Cu alone treatment. MJ alone and under Cu excess did not alter accumulation of MDA, hGSH and proline comparing with Cu alone, but partially elevated anthocyanin concentration. The results indicated that MJ was both partially potent in modifying the antioxidative enzymes activity and metabolites accumulation in non-stress and Cu-stress conditions.

Influence of arsenic stress on growth, physiological activities and artemisinin production in two varieties of Artemisia (Artemisia annua) differing in artemisinin yield

Artemisinin, extracted from the leaves of Artemisia annua L., has been recognized as an effective and safe remedy against malaria. A pot experiment was conducted according to randomized block design using five replicates to screen the A. annua L. varieties, namely 'CIM-Arogya' and 'Jeevan Raksha' under arsenic stress. Four concentrations of arsenic [0 (control), 15, 30 and 45 mg kg-1 soil] were applied to the soil. Measurements for growth characteristics, physiological attributes, biochemical parameters, yield and quality attributes were carried out at pre-flowering [90 days after planting (DAP)] and flowering (120 DAP) stages. The variety 'Jeevan Raksha' was more adversely affected by arsenic stress than the 'CIM-Arogya', suggesting that the 'CIM-Arogya' was more arsenic tolerant than the 'Jeevan Raksha'. The highest arsenic concentration (45 mg kg-1 soil) proved most toxic dose as compared to other arsenic doses applied. It reduced the rate of photosynthesis and leaf-chlorophyll content significantly both at 90 and 120 DAP. The activities of CAT, POX and APX were also rapidly stimulated due to the highest concentration of arsenic at both the growth stages. Noticeably, all applied doses of arsenic significantly increased the production of artemisinin in the leaves. As compared to control, 'CIM-Arogya' contained the maximum artemisinin content under the highest arsenic stress, increasing the artemisinin content by 38.0 and 42.6% at 90 and 120 DAP, respectively; while, 'Jeevan Raksha' showed an increase in artemisinin content by 32.6 and 35.7% at the respective dates of sampling. At the highest arsenic stress, the yield of artemisinin was increased by 42.9 and 45.7% in 'CIM-Arogya' and by 37.5 and 40.5% in 'Jeevan Raksha'. Generation rate of H2O2 increased consistently when arsenic was applied irrespective of the varieties used, indicating the role of H2O2 in artemisinin biosynthesis in A. annua L.

Seed priming improves seed germination and reduces oxidative stress in black cumin (Nigella sativa) in presence of cadmium

Seed priming is a technique which is potentially able to promote rapid and more uniform seed germination and plant growth. In order to study the effects of seed priming treatments on some physiological and biochemical parameters, black cumin seeds were subjected to hormopriming and halopriming. The results indicated that germination percentage and rate were not impressed by cadmium. Radicle length was reduced more than plumule length and was expressed as the sensitivity index. Hormopriming (100mg/L of salicylic acid) improved the germination, radicle elongation and dry weight (30.74, 42, and 31.57%, respectively) in compared with the control under cadmium stress (30mgL-1). The maximum plumule elongation and plumule dry weight were related to the seeds primed with KNO3 about 48.61 and 25%, respectively. Increase in cadmium concentration until 30mg/L increased electrical conductivity, malondialdehyde (MDA) and proline content for the all priming treatments and unprimed seeds, although in primed seeds was lower than that unprimed seeds. In highest cadmium concentration (30mg/L), POX activity significantly increased in SA, KNO3 and KCl treatments about 56.25, 50 and 40.62% as compared with control, respectively. The reduction in soluble protein was observed in unprimed and primed seedlings with SA, KNO3 and KCl under highest cadmium concentration. In conclusion, the seed priming with SA due to improve germination performance of black cumin in different Cd levels can enhance tolerance of seedlings to toxic metals stress in the irrigation water.

Aloe Vera Gel and Honey‐Based Edible Coatings Combined with Chemical Dip as a Safe Means for Quality Maintenance and Shelf Life Extension of Fresh‐Cut Papaya

AbstractThe functionality of Aloe vera gel and honey (10% v/v) for quality improvement of fresh‐cut papaya was evaluated individually as well as in combination with chemical dip containing calcium chloride (2% w/v), ascorbic acid (AA) (1% w/v) and vanillin (8 mM). The changes in the physicochemical attributes such as pH, titratable acidity, total soluble solids, weight loss percentage, AA, total phenolic content (TPC), browning index, browning enzymes (polyphenol oxidase [PPO] and peroxidase [POX]) and microbial load of fresh‐cut papaya were evaluated during their storage at 4 ± 1C. It has been observed that A. vera gel and 10% honey in combination with chemical dip have a preventive role toward quality maintenance of fresh‐cut papaya as indicated by retention of TPC and AA, reduced microbial load and relatively low PPO and POX activity during storage period of 12 days at 4C.Practical ApplicationsAloe vera gel and honey have been widely used in food industries due to their antioxidant and antimicrobial activities. Most recently, their uses have been expanded for quality enhancement of horticultural commodities as these are found to be safe for food applications. From the present study, it is evident that these selected edible coatings derived from natural sources could maintain the quality of fresh‐cut fruit like papaya and also satisfy the consumer's need for safe food. Thus, the studied work has the practical applications in fresh‐cut industries.

Overexpression of Rat Neurons Nitric Oxide Synthase in Rice Enhances Drought and Salt Tolerance.

Nitric oxide (NO) has been shown to play an important role in the plant response to biotic and abiotic stresses in Arabidopsis mutants with lower or higher levels of endogenous NO. The exogenous application of NO donors or scavengers has also suggested an important role for NO in plant defense against environmental stress. In this study, rice plants under drought and high salinity conditions showed increased nitric oxide synthase (NOS) activity and NO levels. Overexpression of rat neuronal NO synthase (nNOS) in rice increased both NOS activity and NO accumulation, resulting in improved tolerance of the transgenic plants to both drought and salt stresses. nNOS-overexpressing plants exhibited stronger water-holding capability, higher proline accumulation, less lipid peroxidation and reduced electrolyte leakage under drought and salt conditions than wild rice. Moreover, nNOS-overexpressing plants accumulated less H2O2, due to the observed up-regulation of OsCATA, OsCATB and OsPOX1. In agreement, the activities of CAT and POX were higher in transgenic rice than wild type. Additionally, the expression of six tested stress-responsive genes including OsDREB2A, OsDREB2B, OsSNAC1, OsSNAC2, OsLEA3 and OsRD29A, in nNOS-overexpressing plants was higher than that in the wild type under drought and high salinity conditions. Taken together, our results suggest that nNOS overexpression suppresses the stress-enhanced electrolyte leakage, lipid peroxidation and H2O2 accumulation, and promotes proline accumulation and the expression of stress-responsive genes under stress conditions, thereby promoting increased tolerance to drought and salt stresses.

Physiological and Biochemical Changes During Heat Stress Induced Browning of Detached Backhousia myrtifolia (Cinnamon Myrtle) Tissues

Postharvest discolouration is found in leaf and floral tissues of Backhousia myrtifolia (Cinnamon myrtle). Towards discerning the biochemical mechanisms, heat-induced browning was investigated. Differential browning behaviour was observed for green versus yellowed leaves. Initial pre-treatment chlorophyll contents (Chl a and b) and chlorophyll fluorescence (CF) were measured for both coloured leaves. After heat treatment, both, coloured leaf and floral tissue, were analysed for electrolyte leakage (EL), malondialdehyde (MDA) content, polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL) enzyme activities, total phenolic content, diphenylpicryl-hydrazyl (DPPH) antioxidant activity and surface colour. They were also rated for their browning score (BS). Low chlorophyll fluorescence ratios (F v /F m values) of 0.68 for both leaf types suggested that this sub-tropical plant species experienced cold stress during winter period in which the study was conducted. Compared to detached green leaves, detached yellowed leaves showed more browning after heat treatment. Yellowed leaves had significantly greater EL levels, higher pre-treatment PPO and POX activities, and greater pre- and post-treatment PAL activities than green leaves. PPO, POD and PAL enzymes are typically involved in browning mechanisms in plant tissues. Their higher levels in yellowed leaves at least partly accounted for their greater browning than for green leaves.

Influence of trinexapac-ethyl in improving drought resistance of wheatgrass and tall fescue

Various methods are available for improving drought resistance in turfgrasses. Several studies have reported the application of plant growth regulators as an effective method for reducing drought stress effects. A factorial experiment based on a randomized complete block design with three replications was performed in 2011 and 2012 to investigate the effects of the gibberellic acid (GA) inhibitors trinexapac-ethyl (TE) and drought stress on the physiological responses of wheatgrass (Agropyron desertorum) and tall fescue (Festuca arundinacea) to drought stress. The foliage of wheatgrass and tall fescue were sprayed with 1.95 ml L−1 TE at 0.113 % a.i. 14 days prior to and at the beginning of the drought stress. Both TE-treated and untreated plants were placed to well-watered and no water circumstances for 45 days in field conditions. Results indicated that drought stress reduced turf quality (color, density, and uniformity), relative water content (RWC), and total chlorophyll content, but increased proline content, electrolyte leakage (EL), malondialdehyde (MDA) and soluble sugar content (SSC) in both species. Superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and peroxidase (POD) activities in the two turfgrass species initially increased transiently, but declined subsequently. TE application increased SOD, APX, POX, and CAT activities, especially under drought stress conditions. Correlation analysis showed that there were significantly positive correlation between turf quality and RWC and negative correlation between turf quality and proline content, EL, MDA and SSC in both species. The use of TE seems to have enhanced resistance to drought stress in both species by improving proline, SSC and antioxidant activities.

Effects of salt stress on lipid peroxidation and antioxidative enzymes of alfalfa (Medicago sativa L.) cultivars

The effect of salt stress on enzyme activities of nine alfalfa cultivars at germination and seedling stage was studied. The activities of SOD, GR, POX and APOX were higher in salt tolerant and lower in salt sensitive cultivars. Results of the effect of salt stress on the SOD, GR, POX, APOX activities and MDA content may be used to select salt tolerance cultivars at the germination and seedling stages. SOD, GR, POX, APOX and MDA may play an important role in salt tolerant mechanisms in alfalfa. DOI: http://dx.doi.org/10.3329/bjb.v43i2.21672 Bangladesh J. Bot. 43(2): 191-196, 2014 (September)

Metabolic profiling and stress response of anaerobic and respiratory cultures of Lactobacillus plantarum C17 grown in a chemically defined medium

We investigated the effect of anaerobic (AN) and respiratory conditions (RS; oxygen, hemin and menaquinone) on the growth, enzymatic activities (POX, NOX, NPR), metabolic profile (1H-NMR spectroscopy), and response to oxidative (catalase, tolerance of H2O2) and heat stresses of Lactobacillus plantarum C17 (wild-type) and its natural oxidative stress-tolerant mutant C17-m58, using chemostat cultivation in a modified chemically defined medium (mCDM). Respiratory growth impaired biomass production and tolerance of heat stress in mCDM compared with cultivation in the complex Weissella medium broth (WMB). POX activity, oxygen consumption, and H2O2 tolerance were higher in respiratory cells and in C17-m58. Significant amounts of formate and acetate were found in AN cultures of wild-type and mutant strains, confirming the activation of an anaerobic pyruvate formate lyase–acetate kinase (PFL-ACK) pathway in L. plantarum. The presence of succinate supports the presence of an incomplete TCA cycle in this species. High concentrations of pyruvate were measured in RS supernatants, indicating reduced functionality of POX in vivo (35 °C) and the need to clarify the regulation and control of oxygen metabolism. Adipate was found in respiratory samples, likely because of lipid peroxidation, and its production by respiring lactic acid bacteria may be investigated and exploited for biotechnological uses.

Effect of biocontrol agent Bacillus subtilis and mycorrhizal fungus Glomus mosseae on growth, mineral nutrition, physiological changes and Essential Oil quality and quantity of Thymus daenensis Celak

In order to study the effects of biocontrol agent (Bacillus subtilis) and Arbuscular mycorrhizal (Glomus mosseae) on the plant growth, peroxidase (POX) and phenylalanine ammonia-lyase (PAL) activity, nutrient content, essential oil yield and root colonization of Thymus daenensis transplants, a randomized complete block design with three replications and four treatments was carried out at the Glasshouse, in 2011-2012. Treatments were included: 1- Glomus mosseae 2- Bacillus subtilis 3- co-inoculation of G. mosseae and B. subtilis and 4- no inoculated. Results showed that the Co-inoculation with G. mosseae and B. subtilis resulted 74% increase in shoot /root dry weight, increased dry herb yield by about 30% and stimulated essential oil yield by 14 % compared to uninoculated controls. The percent of root colonization in the plants inoculated with G. mosseae was more than 7 times higher compared to non-inoculated plants, but dual inoculation resulted in a 68 % reduction in root colonization compared to single inoculation with G. mosseae. The Zn content significantly increased about three times higher than the control plants after dual inoculation. All microbial inoculation treatments significantly increased the concentration of Thymol and carvacerol in T. daenensis plants with respect to the control plants. This study further revealed that the single inoculation with B. subtilis significantly enhanced PAL and pox activity compared to the other treatments. Our findings confirm that plants Co-inoculated with G. mosseae and B. subtilis during the nursery stage, can create a more synergistic effect that supports thyme (T. deneansis) quality and quantity yields in a sustainable cultivation

SacPox from the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius is a proficient lactonase.

BackgroundSacPox, an enzyme from the extremophilic crenarchaeal Sulfolobus acidocaldarius (Sac), was isolated by virtue of its phosphotriesterase (or paraoxonase; Pox) activity, i.e. its ability to hydrolyze the neurotoxic organophosphorus insecticides. Later on, SacPox was shown to belong to the Phosphotriesterase-Like Lactonase family that comprises natural lactonases, possibly involved in quorum sensing, and endowed with promiscuous, phosphotriesterase activity.ResultsHere, we present a comprehensive and broad enzymatic characterization of the natural lactonase and promiscuous organophosphorus hydrolase activities of SacPox, as well as a structural analysis using a model.ConclusionKinetic experiments show that SacPox is a proficient lactonase, including at room temperature. Moreover, we discuss the observed differences in substrate specificity between SacPox and its closest homologues SsoPox and SisLac together with the possible structural causes for these observations.

Thylakoid peroxidase activity responsible for oxidized chlorophyll accumulation during ripening of olive fruits (Olea europaea L.)

Type III peroxidase (EC 1.11.1.7) (POX) is the enzyme direct responsible of the 132 OH chlorophyll formation on oxidative catabolism of chlorophylls (chls). Despite the higher content of oxidized derivatives of chlorophylls (ox-chls) in fruits of the Arbequina variety compared to Hojiblanca, the evolution of total chlorophyll oxidative peroxidase activity (POX-chl) showed that this activity levels were higher in fruits of Hojiblanca compared with Arbequina variety. Subsequently, a deepened study on the subcellular distribution of POX-chl activity from mesocarp and epicarp cells of olive fruit of both varieties was made, finding that the POX-chl activity located in thylakoid fraction (the only fraction in direct contact with chls in vivo) was in Arbequina fruits higher than in Hojiblanca ones and involved more than 50% of the membranous POX-Chl activity. It has been demonstrated also that the evolution of the POX-chl activity in thylakoid membranes enriched fraction throughout the whole life cycle was parallel with the formation and accumulation of ox-chls in olive fruits. Data allowed to conclude that the formation of ox-chls during the chl catabolism is mediated by a POX-chl activity localized in thylakoid fraction and allow to hypothesize that the high percentage of POX activity found in the soluble cell fraction, estimated at 99.8%, may be involved in the loss of pigmentation by oxidation occurring during fruit processing for obtaining olive oil.

Flooding effects on soil phenol oxidase activity and phenol release during rice straw decomposition

AbstractPhenol oxidase (Pox) plays a key role in soil C cycle and its presence may affect soil C mineralization during crop residue decomposition. To examine soil dynamics and relationships between Pox, phenols, Fe2+, and C mineralization, we designed a 53‐d laboratory experiment conducted with and without rice straw addition and under non‐flooded and flooded conditions. The results demonstrate that rice straw can indeed decompose faster under flooded conditions. The addition of rice straw significantly increased soil Pox activity (up to 15‐fold), but only under flooded conditions. Rice straw application increased alkali extractable phenol (AEP) concentration by 129% at day 4. However, flooded conditions reduced soil AEP by 61% and 49% at day 53 with and without rice straw application, respectively. Phenol oxidase activity was positively correlated with dissolved organic C and Fe2+, while negatively related to AEP, which itself was positively correlated with C mineralization (i.e., CO2 emission rates). Also, all relationships between soil Pox, AEP, Fe2+, and C were stronger under flooded conditions. We therefore conclude that flooded conditions in paddy soil may promote straw decomposition as a result of the stimulation of Pox activity and phenol decomposition.