Total Ascorbate Peroxidase Activity Research Articles

Effect of various abiotic stressors on some biochemical indices of Lepidium sativum plants

In this study, the regulation of ascorbate peroxidase (APX) specific activity, anthocyanin, carotenoid, hydrogen peroxide, lipid peroxidation, and protein levels in cress leaves in response to different abiotic stresses were investigated. The total APX specific activity was significantly elevated after 9 days of drought treatment, short-term (2 h) exposure to 10, 100 and 370 µE of light, long-term exposure (at least 6 days) to 100 mM NaCl versus the specific APX activity in the controls. Furthermore, a significant change in total APX activity was detected in response to treatment with different temperatures; this change was an early response to 4 °C and 30 °C for a maximum of 4 h, while short-term exposure to 35 °C did not change total APX activity. The results of the present study revealed that plants have a wide range of mechanisms to cope with different stresses that possibly involve morphological changes. The results indicated that Lepidium sativum plants launch common protective pathways only under drought, salinity and high light stresses, while other protective mechanisms/strategies could be responsible for increasing the plants tolerance towards temperature and low light. Future studies will investigate changes in the photosynthetic quantum yield and specific target metabolites, proteins, and nonenzymatic antioxidants.

Overexpression of a cytosolic ascorbate peroxidase from Panax ginseng enhanced salt tolerance in Arabidopsis thaliana

Ascorbate peroxidase (APX) plays an essential role in the antioxidant defense mechanism in the plant, serving in the ascorbate–glutathione cycle for the cellular H2O2 metabolism process. As the perennial plant, Panax ginseng Meyer encounters a lot of unfavorable growth conditions, and among them soil salinity significantly decreases the yield. Two APX genes from Panax ginseng were isolated and designated as PgAPX1 and PgAPX2, which are most similar with previously characterized cytosolic APX of Daucus carota and Spuriopimpinella brachycarpa, as revealed by sequence analysis of their deduced amino acid sequences. PgAPXs transcripts are most abundant in leaf tissue, whereas PgAPX1 expression level was higher compared to PgAPX2. Consistent with higher PgAPX1 expression during salt stress in ginseng, PgAPX1-overexpressing Arabidopsis lines (PgAPX1ox) increased the germination rate and root length compared with wild-type (WT) under 200 mM NaCl stress treatment. Furthermore, higher chlorophyll content, relative water content, total APX activity, proline content, and lower H2O2 accumulation were shown in PgAPX1ox plants compared to WT under 200 mM NaCl stress condition. Transcription analysis showed that PgAPX1oxArabidopsis lines were more salt-tolerant by upregulating the ion homeostasis mechanism.

Excess boron responsive regulations of antioxidative mechanism at physio-biochemical and molecular levels in Arabidopsis thaliana

This work was aimed to evaluate the effect of boron (B) toxicity on oxidative damage level, non-enzymatic antioxidant accumulation such as anthocyanin, flavonoid and proline and expression levels of antioxidant enzymes including superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) and their respective activities as well as expression levels of miR398 and miR408 in Arabidopsis thaliana. Plants were germinated and grown on MS medium containing 1 mM B (1B) and 3 mM B (3B) for 14 d. Toxic B led to a decrease of photosynthetic pigments and an increase in accumulation of total soluble and insoluble sugars in accordance with phenotypically viewed chlorosis of seedlings through increasing level of B concentration. Along with these inhibitions, a corresponding increase in contents of flavonoid, anthocyanin and proline occurred that provoked oxidative stress tolerance. 3B caused a remarkable increase in total SOD activity whereas the activities of APX, GR and CAT remained unchanged as verified by expected increase in H2O2 content. In contrast to GR, the coincidence was found between the expressions of SOD and APX genes and their respective activities. 1B induced mir398 expression, whereas 3B did not cause any significant change in expression of mir408 and mir398. Expression levels of GR genes were coordinately regulated with DHAR2 expression. Moreover, the changes in expression level of MDAR2 was in accordance with changes in APX6 expression and total APX activity, indicating fine-tuned regulation of ascorbate-glutathione cycle which might trigger antioxidative responses against B toxicity in Arabidopsis thaliana.

Ascorbate peroxidase from Jatropha curcas enhances salt tolerance in transgenic Arabidopsis.

Ascorbate peroxidase (APX) plays a central role in the ascorbate-glutathione cycle and is a key enzyme in cellular H2O2 me-tabolism. It includes a family of isoenzymes with different character-istics, which are identified in many higher plants. In the present study, we isolated the APX gene from Jatropha curcas L, which is similar with other previously characterized APXs as revealed by alignment and phylogenetic analysis of its deduced amino acid sequence. Real-time qPCR analysis showed that the expression level of JcAPX transcript significantly increased under NaCl stress. Subsequently, to elucidate the contribution of JcAPX to the protection against salt-induced oxi-dative stress, the expression construct p35S: JcAPX was created and transformed into Arabidopsis and transcribed. Under 150-mM NaCl stress, compared with wild type (WT), the overexpression of JcAPX in Arabidopsis increased the germination rate, the number of leaves, and the rosette area. In addition, the transgenic plants had longer roots, higher total chlorophyll content, higher total APX activity, and lower H2O2 content than the WT under NaCl stress conditions. These results suggested that higher APX activity in transgenic lines increases the salt tolerance by enhancing scavenging capacity for reactive oxygen spe-cies under NaCl stress conditions.

Alleviation of ultraviolet-C-induced oxidative damage through overexpression of cytosolic ascorbate peroxidase

Experiments were conducted to investigate the relationship between ultraviolet (UV) C-induced oxidative damage and the activity of ascorbate peroxidase (APX), using transgenic tobacco (Nicotiana tabacum L. cv. Petit Havana) plants overexpressing cytosolic APX gene (apx1). Transgenic plants having 2.3 fold higher total APX activity, as compared to the wild type plants, showed normal morphological characters. Exposure of 70-day-old plants to fixed intensity UV-C radiation caused an increase in the malondialdehyde (MDA) content in wild type as well as transgenic plants. However, the wild type plants showed significantly higher (p < 0.05) lipid peroxidation as compared to the transgenic plants. Higher proline accumulation was recorded in transgenic plants as compared to the wild type plants, after 24 hours of UV-C exposure. Although the ascorbate content decreased continuously with increasing exposure to UV-C radiation, yet the wild type plants exhibited higher ascorbate levels than the transgenic plants. A marked difference in H2O2 content, between the wild type and transgenic plants, was consistently observed up to 20 hours of UV-C exposure. A direct correlation of ascorbate, MDA and H2O2 levels was recorded with the extent of oxidative stress, signifying that these could be used as potential bio-marker molecules for oxidative stress. The results clearly demonstrate that overexpression of cytosolic APX can protect tobacco plants from UV-C-induced oxidative damage.

Oligo-Carrageenans Stimulate Growth by Enhancing Photosynthesis, Basal Metabolism, and Cell Cycle in Tobacco Plants (var. Burley)

Leaves of tobacco plants var. Burley were sprayed with water (control) or with oligo-carrageenans kappa2 (K), lambda (L), and iota (I) at 1 mg ml−1, once a week, four times in total, and cultivated for 4 months without treatment. Plants treated with K, L, and I showed an increase in leaf biomass of 1.9, 1.8, and 2.5 times, respectively, despite that cellular size was similar in control and treated plants. In addition, net photosynthesis, efficiency of photosystem II and the level of chlorophyll a and b increased in plants treated with oligo-carrageenans. Moreover, the activity of ribulose 1,5-biphosphate carboxylase/oxygenase (rubisco) increased in treated plants, mainly with oligo-carrageenan I, whereas its content did not change compared to control plants. The activity of several NAD(P)H-synthesizing enzymes involved in basal metabolism increased in treated plants, mainly with oligo-carrageenan I. Furthermore, the relative level of transcripts encoding the cell cycle regulatory cyclins A and D and CDKs A and B increased in treated plants, mainly with oligo-carrageenan I. In addition, the amount of ascorbate (ASC) and the activity of ascorbate peroxidase (AP) increased in treated plants, mainly with oligo-carrageenan I, whereas the level of glutathione remained unchanged. Interestingly, the increases in total ascorbate and AP activity linearly correlated with the increase in leaf biomass. Thus, oligo-carrageenans enhanced photosynthesis, basal metabolism, and cell cycle as well as ASC levels and AP activity which may explain, at least in part, the stimulation of plant growth.

The ascorbate peroxidase regulated by H2O2 and ethylene is involved in cotton fiber cell elongation by modulating ROS homeostasis

Ascorbate peroxidase (APX) is a reactive oxygen species (ROSs) scavenging enzyme involved in regulation of intracellular ROS levels by reduction of H2O2 to water using ascorbate as an electron donor. In New Phytologist (2007) 175: 462-471, we identified a cotton cytosolic APX1 (GhAPX1) that was significantly accumulated during the fast fiber-cell elongation period, through a proteomics approach. Both the transcript levels of GhAPX1 and the total APX activity were highly induced in response to in vitro applied H2O2 or ethylene. Further analysis showed that ethylene promoted H2O2 production 1 day after it was included in the culture medium, suggesting that H2O2 induced cell elongation processes may be placed downstream of the ethylene signal transduction pathway. In this addendum, quantitative real-time RT-PCR showed that only cytosolic APX1, not other cotton APX genes including a second cytosolic APX2, a glyoxysomal and a stromal APXs, was upregulated during fiber cell elongating. Exogenous H2O2 was found to induce ethylene production if wild-type cotton ovules were cultured for a longer period of time, implying that there was a feedback regulatory mechanism from H2O2 to ethylene biosynthesis in modulating cotton fiber development.

Ectopic expression of Mn-SOD in Lycopersicon esculentum leads to enhanced tolerance to salt and oxidative stress

Production of reactive oxygen species (ROS) is associated with a number of physiological disorders in plants. Superoxide dismutase (SOD) catalyzes the breakdown of Superoxide (O2-) into O2 and H2O2 and provides the first line of defense against the toxic effects of elevated levels of ROS. The effect of increased expression of Mn Superoxide dismutase (Mn-SOD) on salt stress tolerance was studied using transformed tomato (Lycopersicon esculentum cv. Zhongshu No. 5) plants. Northern blots confirmed expression of the heterologous Mn-SOD in transgenic plants. Strong Mn-SOD enzyme activity was detected by native PAGE in transformed plants. Transgenic plants showed resistance to the superoxide-generating herbicide methyl viologen (MV, 10-4 M). The total SOD activity was one and one half- to two-fold higher, and APX (ascorbate peroxidase) activity was six to seven fold higher in transgenic, than in wild-type (WT) plant under MV stress. Germination of transgenic tomato seeds at a NaCl concentration of 150 mM was greater than wild-type seeds. When exposed to salt stress, roots of transgenic plants were less stunted and leaf injury was lower than that observed in WT plants. Also, the total APX activity of transgenic plants was 4 to 5 fold higher than that of WT under NaCl (200 mM) stress.

A cotton ascorbate peroxidase is involved in hydrogen peroxide homeostasis during fibre cell development

Reactive oxygen species (ROS) play important roles in multiple physiological processes such as cellular signalling and stress responses, whereas, the hydrogen peroxide (H(2)O(2)) scavenging enzyme ascorbate peroxidase (APX) participates in the regulation of intracellular ROS levels. Here, a cotton (Gossypium hirsutum) cytosolic APX1 (GhAPX1) was identified to be highly accumulated during cotton fibre elongation by proteomic analysis. GhAPX1 cDNA contained an open reading frame of 753-bp encoding a protein of 250 amino acid residues. When GhAPX1 was expressed in Escherichia coli, the purified GhAPX1 was a dimer consisting of two identical subunits with a molecular mass of 28 kDa. GhAPX1 showed the highest substrate specificity for ascorbate. Quantitative real-time polymerase chain reaction (PCR) analyses showed that GhAPX1 was highly expressed in wild-type 5-d postanthesis fibres with much lower transcript levels in the fuzzless-lintless mutant ovules. Treating in vitro cultured wild-type cotton ovules with exogenous H(2)O(2) or ethylene induced the expression of GhAPX1 and hence increased total APX activity proportionally, followed by extended fibre cell elongation. These data suggest that GhAPX1 expression is upregulated in response to an increase in cellular H(2)O(2) and ethylene. GhAPX1 encodes a functional enzyme that is involved in hydrogen peroxide homeostasis during cotton fibre development.

Tolerance to low temperature and paraquat-mediated oxidative stress in two maize genotypes

Tolerance to low temperature and paraquat-mediated oxidative stress was investigated in two Zea mays genotypes, VA36 and A619, grown at 25/22°C and 16/14°C for 50 d after germination. VA36, the tolerant genotype, showed an enhanced resistance to paraquat as compared to A619, the sensitive genotype, when grown at low temperature. In VA36, superoxide dismutase and ascorbate peroxidase activities increased during growth at both 25/22°C or 16/14°C. In A619, superoxide dismutase activity was similar in plants grown at both 16/14°C or 25/22°C. Ascorbate peroxidase activity was always significantly lower in plants grown at low temperature than in plants grown at 25/22°C. The total ascorbate peroxidase activity was correlated with the cytosolic ascorbate peroxidase protein content in all but A619 plants grown at low temperature for 25 d. The isozyme pattern of SOD showed a higher abundance of MnSOD in VA36 than in A619 and of FeSOD in A619 compared to VA36. Growth at low temperature enhanced resistance to paraquat infiltration more in VA36 than in A619. SOD and APX activities were generally higher and more stable with the increase of paraquat concentration in VA36 than in A619. Damage indicated by Fv/Fm and ion leakage after paraquat infiltration were generally higher in plants grown at 25/22°C than at 16/14°C and higher in A619 than in VA36. However, no causal link is proved between the extent of damage and the increase of SOD and APX activities alone. It is suggested that tolerance to oxidative stress requires an integrated enhancement of the antioxidant system.

Tolerance to low temperature and paraquat-mediated oxidative stress in two maize genotypes

Tolerance to low temperature and paraquat-mediated oxidative stress was investigated in two Zea mays genotypes, VA36 and A619, grown at 25/22 degrees C and 16/14 degrees C for 50 d after germination. VA36, the tolerant genotype, showed an enhanced resistance to paraquat as compared to A619, the sensitive genotype, when grown at low temperature. In VA36, superoxide dismutase and ascorbate peroxidase activities increased during growth at both 25/22 degrees C or 16/14 degrees C. in A619, superoxide dismutase activity was similar in plants grown at both 16/14 degrees C or 25/22 degrees C. Ascorbate peroxidase activity was always significantly lower in plants grown at low temperature than in plants grown at 25/22 degrees C, The total ascorbate peroxidase activity was correlated with the cytosolic ascorbate peroxidase protein content in all but A619 plants grown at low temperature for 25 d. The isozyme pattern of SOD showed a higher abundance of MnSOD in VA36 than in A619 and of FeSOD in A619 compared to VA36. Growth at low temperature enhanced resistance to paraquat infiltration more in VA36 than in A619. SOD and APX activities were generally higher and more stable with the increase of paraquat concentration in VA36 than in A619. Damage indicated by F-v/F-m and ion leakage after paraquat infiltration were generally higher in plants grown at 25/22 degrees C than at 16/14 degrees C and higher in A619 than in VA36, However, no causal link is proved between the extent of damage and the increase of SOD and APX activities alone. It is suggested that tolerance to oxidative stress requires an integrated enhancement of the antioxidant system.