Purification of catalase from pea leaf peroxisomes: identification of five different isoforms

Pepper catalase: a broad analysis of its modulation during fruit ripening and by nitric oxide

Catalase is a major antioxidant enzyme located in plant peroxisomes that catalyzes the decomposition of H2O2. Based on our previous transcriptomic (RNA-Seq) and proteomic (iTRAQ) data at different stages of pepper (Capsicum annuum L.) fruit ripening and after exposure to nitric oxide (NO) enriched atmosphere, a broad analysis has allowed us to characterize the functioning of this enzyme. Three genes were identified, and their expression was differentially modulated during ripening and by NO gas treatment. A dissimilar behavior was observed in the protein expression of the encoded protein catalases (CaCat1-CaCat3). Total catalase activity was down-regulated by 50% in ripe (red) fruits concerning immature green fruits. This was corroborated by non-denaturing polyacrylamide gel electrophoresis, where only a single catalase isozyme was identified. In vitro analyses of the recombinant CaCat3 protein exposed to peroxynitrite (ONOO-) confirmed, by immunoblot assay, that catalase underwent a nitration process. Mass spectrometric analysis identified that Tyr348 and Tyr360 were nitrated by ONOO-, occurring near the active center of catalase. The data indicate the complex regulation at gene and protein levels of catalase during the ripening of pepper fruits, with activity significantly down-regulated in ripe fruits. Nitration seems to play a key role in this down-regulation, favoring an increase in H2O2 content during ripening. This pattern can be reversed by the exogenous NO application. While plant catalases are generally reported to be tetrameric, the analysis of the protein structure supports that pepper catalase has a favored quaternary homodimer nature. Taken together, data show that pepper catalase is down-regulated during fruit ripening, becoming a target of tyrosine nitration, which provokes its inhibition.

Analysis of Plant L-Cysteine Desulfhydrase (LCD) Isozymes by Non-denaturing Polyacrylamide Gel Electrophoresis

Hydrogen sulfide (H₂S) is a signaling molecule that achieves different regulatory functions in animal and plant cells. The cytosolic enzyme L-cysteine desulfhydrase (LCD; EC 4.4.1.28) catalyzes the conversion of cysteine (L-Cys) to pyruvate and ammonium with the concomitant generation of H₂S, this enzyme being considered one of the main sources of H₂S in higher plants. Using non-denaturing polyacrylamide gel electrophoresis (PAGE) in combination with a specific assay for LCD activity, the present protocol allows identifying diverse LCD isozymes present in different organs (roots, shoots, leaves, and fruits) and plant species including pea, garlic, Arabidopsis, and pepper.

Influence of Schumann Range Electromagnetic Fields on Components of Plant Redox Metabolism in Wheat and Peas

The Schumann Resonances (ScR) are Extremely Low Frequency (ELF) electromagnetic resonances in the Earth-ionosphere cavity excited by global lightning discharges. ScR are the part of electromagnetic field (EMF) of Earth. The influence of ScR on biological systems is still insufficiently understood. The purpose of the study is to characterize the possible role of the plant cell redox metabolism regulating system in the Schumann Resonances EMF perception. Activity of catalase and superoxide dismutase, their isoenzyme structure, content of malondialdehyde, composition of polar lipids in leaf extracts of wheat and pea plants treated with short-time (30 min) and long-time (18 days) ELF EMF with a frequency of 7.8 Hz, 14.3 Hz, 20.8 Hz have been investigated. Short-time exposure ELF EMF caused more pronounced bio effects than long-time exposure. Wheat catalase turned out to be the most sensitive parameter to magnetic fields. It is assumed that the change in the activity of wheat catalase after a short-term ELF EMF may be associated with the ability of this enzyme to perceive the action of a weak EMF through calcium calmodulin and/or cryptochromic signaling systems.

Reactive Oxygen Species, Antioxidant Responses and Implications from a Microbial Modulation Perspective

Simple Summary

Environmental conditions are subject to unprecedented changes due to recent progressive anthropogenic activities on our planet. Plants, as the frontline of food security, are susceptible to these changes, resulting in the generation of unavoidable byproducts of metabolism (ROS), which eventually affect their productivity. The response of plants to these unfavorable conditions is highly intricate and depends on several factors, among them are the species/genotype tolerance level, intensity, and duration of stress factors. Defensive mechanisms in plant systems, by nature, are concerned primarily with generating enzymatic and non-enzymatic antioxidants. In addition to this, plant-microbe interactions have been found to improve immune systems in plants suffering from drought and salinity stress.

Abstract

Plants are exposed to various environmental stresses in their lifespan that threaten their survival. Reactive oxygen species (ROS), the byproducts of aerobic metabolism, are essential signalling molecules in regulating multiple plant developmental processes as well as in reinforcing plant tolerance to biotic and abiotic stimuli. However, intensified environmental challenges such as salinity, drought, UV irradiation, and heavy metals usually interfere with natural ROS metabolism and homeostasis, thus aggravating ROS generation excessively and ultimately resulting in oxidative stress. Cellular damage is confined to the degradation of biomolecular structures, including carbohydrates, proteins, lipids, pigments, and DNA. The nature of the double-edged function of ROS as a secondary messenger or harmful oxidant has been attributed to the degree of existing balance between cellular ROS production and ROS removal machinery. The activities of enzyme-based antioxidants, catalase (CAT, EC 1.11.1.6), monodehydroascorbate reductase (MDHAR, E.C.1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and guaiacol peroxidase (GPX, EC 1.11.1.7); and non-enzyme based antioxidant molecules, ascorbate (AA), glutathione (GSH), carotenoids, α-tocopherol, prolines, flavonoids, and phenolics, are indeed parts of the defensive strategies developed by plants to scavenge excess ROS and to maintain cellular redox homeostasis during oxidative stress. This review briefly summarises current knowledge on enzymatic and non-enzymatic antioxidant machinery in plants. Moreover, additional information about the beneficial impact of the microbiome on countering abiotic/biotic stresses in association with roots and plant tissues has also been provided.

Nitric Oxide (NO) Scaffolds the Peroxisomal Protein-Protein Interaction Network in Higher Plants

The peroxisome is a single-membrane subcellular compartment present in almost all eukaryotic cells from simple protists and fungi to complex organisms such as higher plants and animals. Historically, the name of the peroxisome came from a subcellular structure that contained high levels of hydrogen peroxide (H2O2) and the antioxidant enzyme catalase, which indicated that this organelle had basically an oxidative metabolism. During the last 20 years, it has been shown that plant peroxisomes also contain nitric oxide (NO), a radical molecule than leads to a family of derived molecules designated as reactive nitrogen species (RNS). These reactive species can mediate post-translational modifications (PTMs) of proteins, such as S-nitrosation and tyrosine nitration, thus affecting their function. This review aims to provide a comprehensive overview of how NO could affect peroxisomal metabolism and its internal protein-protein interactions (PPIs). Remarkably, many of the identified NO-target proteins in plant peroxisomes are involved in the metabolism of reactive oxygen species (ROS), either in its generation or its scavenging. Therefore, it is proposed that NO is a molecule with signaling properties with the capacity to modulate the peroxisomal protein-protein network and consequently the peroxisomal functions, especially under adverse environmental conditions.

Characterization on TaMPK14, an MAPK family gene of wheat, in modulating N-starvation response through regulating N uptake and ROS homeostasis

Wheat MAPK gene TaMPK14 is N starvation response and is crucial in modulating plant low-N stress tolerance. Improving plant N use efficiency (NUE) contributes largely to the sustainable crop production worldwide. In this study, TaMPK14, a mitogen-activated protein kinase (MAPK) family gene in T. aestivum, was characterized for the role in mediating N starvation response. TaMPK14 harbors conserved domain/motifs specified by the plant MAPK proteins. In vitro assay for kinase activity of TaMPK14 validated its phosphorylation nature. TaMPK14 transcripts were upregulated in both roots and leaves under low-N treatment; moreover, the expression levels induced by N starvation were gradually restored following the N recovery progression. These results suggested transcriptional response of TaMPK14 upon the low-N stress. Compared with wild type (WT), the TaMPK14 overexpressing lines in N. tabacum displayed improved growth and N accumulation traits under deficient-N treatment, which indicated the crucial roles of the MAPK gene in mediating N starvation response. Additionally, the lines treated by N starvation were shown to be improved on cellular ROS homeostasis, displaying higher antioxidant enzymes (AE) activities and less ROS accumulative amount than WT. The transcripts of nitrate transporter gene NtNRT2.1 and those of AE genes NtSOD1, NtCAT1;2, and NtPOD4 were significantly upregulated in N-deprived TaMPK14 lines; overexpression of them conferred plants enhanced N uptake capacity and AE activities, respectively. Moreover, RNA-seq datasets generated from N-deprived transgenic lines contained numerous differential genes involving modulating various biological process, cellular component, and molecular function. Together, our investigation suggested that TaMPK14 improves plant N starvation response through transcriptional regulation of distinct NRT and AE genes as well as modulation of associated biological processes.

Plant catalases as NO and H2S targets

Catalase is a powerful antioxidant metalloenzyme located in peroxisomes which also plays a central role in signaling processes under physiological and adverse situations. Whereas animals contain a single catalase gene, in plants this enzyme is encoded by a multigene family providing multiple isoenzymes whose number varies depending on the species, and their expression is regulated according to their tissue/organ distribution and the environmental conditions. This enzyme can be modulated by reactive oxygen and nitrogen species (ROS/RNS) as well as by hydrogen sulfide (H2S). Catalase is the major protein undergoing Tyr-nitration [post-translational modification (PTM) promoted by RNS] during fruit ripening, but the enzyme from diverse sources is also susceptible to undergo other activity-modifying PTMs. Data on S-nitrosation and persulfidation of catalase from different plant origins are given and compared here with results from obese children where S-nitrosation of catalase occurs. The cysteine residues prone to be S-nitrosated in catalase from plants and from bovine liver have been identified. These evidences assign to peroxisomes a crucial statement in the signaling crossroads among relevant molecules (NO and H2S), since catalase is allocated in these organelles. This review depicts a scenario where the regulation of catalase through PTMs, especially S-nitrosation and persulfidation, is highlighted.

Sweet Pepper (Capsicum annuum L.) Fruits Contain an Atypical Peroxisomal Catalase That is Modulated by Reactive Oxygen and Nitrogen Species

During the ripening of sweet pepper (Capsicum annuum L.) fruits, in a genetically controlled scenario, enormous metabolic changes occur that affect the physiology of most cell compartments. Peroxisomal catalase gene expression decreases after pepper fruit ripening, while the enzyme is also susceptible to undergo post-translational modifications (nitration, S-nitrosation, and oxidation) promoted by reactive oxygen and nitrogen species (ROS/RNS). Unlike most plant catalases, the pepper fruit enzyme acts as a homodimer, with an atypical native molecular mass of 125 to 135 kDa and an isoelectric point of 7.4, which is higher than that of most plant catalases. These data suggest that ROS/RNS could be essential to modulate the role of catalase in maintaining basic cellular peroxisomal functions during pepper fruit ripening when nitro-oxidative stress occurs. Using catalase from bovine liver as a model and biotin-switch labeling, in-gel trypsin digestion, and nanoliquid chromatography coupled with mass spectrometry, it was found that Cys377 from the bovine enzyme could potentially undergo S-nitrosation. To our knowledge, this is the first report of a cysteine residue from catalase that can be post-translationally modified by S-nitrosation, which makes it especially important to find the target points where the enzyme can be modulated under either physiological or adverse conditions.

Plant peroxisomes at the crossroad of NO and H2 O2 metabolism

Plant peroxisomes are subcellular compartments involved in many biochemical pathways during the life cycle of a plant but also in the mechanism of response against adverse environmental conditions. These organelles have an active nitro-oxidative metabolism under physiological conditions but this could be exacerbated under stress situations. Furthermore, peroxisomes have the capacity to proliferate and also undergo biochemical adaptations depending on the surrounding cellular status. An important characteristic of peroxisomes is that they have a dynamic metabolism of reactive nitrogen and oxygen species (RNS and ROS) which generates two key molecules, nitric oxide (NO) and hydrogen peroxide (H₂ O₂ ). These molecules can exert signaling functions by means of post-translational modifications that affect the functionality of target molecules like proteins, peptides or fatty acids. This review provides an overview of the endogenous metabolism of ROS and RNS in peroxisomes with special emphasis on polyamine and uric acid metabolism as well as the possibility that these organelles could be a source of signal molecules involved in the functional interconnection with other subcellular compartments.

Nitrate- and nitric oxide-induced plant growth in pea seedlings is linked to antioxidative metabolism and the ABA/GA balance

This study looks at the effects of potassium nitrate (KNO3) and sodium nitroprusside (SNP), a nitric oxide (NO)-donor, on the development, antioxidant defences and on the abscisic acid (ABA) and gibberellin (GA) levels in pea seedlings. Results show that 10 mM KNO3 and 50 μM SNP stimulate seedling fresh weight (FW), although this effect is not reverted by the action of 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a NO-scavenger. The KNO3 treatment increased peroxidase (POX) and ascorbate oxidase (AOX) activities. SNP, on the other hand, reduced monodehydroascorbate reductase (MDHAR) activity and produced a significant increase in superoxide dismutase (SOD), POX and AOX activities. The "KNO3 plus cPTIO" treatment increased ascorbate peroxidase (APX), MDHAR, glutathione reductase (GR) and SOD activities, but POX activity decreased in relation to the KNO3 treatment. The "SNP plus cPTIO" treatment increased APX and MDHAR activities, whereas a huge decrease in POX activity occurred. Both the KNO3 and the SNP treatments increased reduced ascorbate (ASC) concentrations, which reached control values in the presence of cPTIO. All treatments increased the dehydroascorbate (DHA) level in pea seedlings, leading to a decrease in the redox state of ascorbate. In the "KNO3 plus cPTIO" treatment, an increase in the redox state of ascorbate was observed. Glutathione contents, however, were higher in the presence of SNP than in the presence of KNO3. In addition, KNO3 produced an accumulation of oxidised glutathione (GSSG), especially in the presence of cPTIO, leading to a decrease in the redox state of glutathione. The effect of SNP on reduced glutathione (GSH) levels was reverted by cPTIO, suggesting that NO has a direct effect on GSH biosynthesis or turnover. Both the KNO3 and SNP treatments produced an increase in GA4 and a decrease in ABA concentrations, and this effect was reverted in the presence of the NO-scavenger. Globally, the results suggest a relationship between antioxidant metabolism and the ABA/GA balance during early seedling growth in pea. The results also suggest a role for KNO3 and NO in the modulation of GA4 and ABA levels and antioxidant metabolism in pea seedlings. Furthermore, this effect correlated with an increase in the biomass of the pea seedlings.

Reactive oxygen species metabolism and phenylpropanoid pathway involved in disease resistance against Penicillium expansum in apple fruit induced by ϵ-poly-l-lysine

BACKGROUND

Blue mould caused by Penicillium expansum comprises a notable disease of apple fruit during storage. ϵ-Poly-l-lysine (PL) consists of ϵ-amino and α-hydroxyl and has been used in food preservation. In the present study, apple fruits (cv. Fuji) were used to investigate the effects of PL dipping treatment, at different concentrations of PL, on the lesion diameter of fruit inoculated with P. expansum, aiming to screen the optimal concentration for controlling blue mould. The effects of PL at the optimal concentration on reactive oxygen species (ROS) metabolism and the phenylpropanoid pathway were also investigated.

RESULTS

The results indicated that 25, 50, 100 and 200 µL L^-1 PL treatment significantly decreased the lesion diameter in apple fruit inoculated with P. expansum and the smallest lesion diameter was determined for 50 µL L^-1 PL-treated fruits. The results also indicated that 50 µL L^-1 PL treatment increased the hydrogen peroxide content and the activities of enzymes involved in ROS metabolism, including superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and peroxidase in apple fruit. The activity of phenylalanine ammonia-lyase and the contents of lignin, total phenolic compounds and flavonoids were also enhanced by PL treatment.

CONCLUSION

The disease resistance to P. expansum in apple fruits enhanced by PL treatment is related to activating ROS metabolism and the phenylpropanoid pathway and the accumulation of antifungal compounds. © 2018 Society of Chemical Industry.

Nitro-oxidative metabolism during fruit ripening

Pepper (Capsicum annuum L.) and tomato (Solanum lycopersicum L.), which belong to the Solanaceae family, are among the most cultivated and consumed fleshy fruits worldwide and constitute excellent sources of many essential nutrients, such as vitamins A, C, and E, calcium, and carotenoids. While fruit ripening is a highly regulated and complex process, tomato and pepper have been classified as climacteric and non-climacteric fruits, respectively. These fruits differ greatly in shape, color composition, flavor, and several other features which undergo drastic changes during the ripening process. Such ripening-related metabolic and developmental changes require extensive alterations in many cellular and biochemical processes, which ultimately leads to fully ripe fruits with nutritional and organoleptic features that are attractive to both natural dispersers and human consumers. Recent data show that reactive oxygen and nitrogen species (ROS/RNS) are involved in fruit ripening, during which molecules, such as hydrogen peroxide (H2O2), NADPH, nitric oxide (NO), peroxynitrite (ONOO-), and S-nitrosothiols (SNOs), interact to regulate protein functions through post-translational modifications. In light of these recent discoveries, this review provides an update on the nitro-oxidative metabolism during the ripening of two of the most economically important fruits, discusses the signaling roles played by ROS/RNS in controlling this complex physiological process, and highlights the potential biotechnological applications of these substances to promote further improvements in fruit ripening regulation and nutritional quality. In addition, we suggest that the term 'nitro-oxidative eustress' with regard to fruit ripening would be more appropriate than nitro-oxidative stress, which ultimately favors the consolidation of the plant species.

TabHLH1, a bHLH-type transcription factor gene in wheat, improves plant tolerance to Pi and N deprivation via regulation of nutrient transporter gene transcription and ROS homeostasis

Basic helix-loop-helix (bHLH) transcription factors (TFs) comprise a large TF family and act as crucial regulators in various biological processes in plants. Here, we report the functional characterization of TabHLH1, a bHLH TF member in wheat (Triticum aestivum). TabHLH1 shares conserved bHLH domain and targets to nucleus with transactivation activity. Upon Pi and N deprivation, the expression of TabHLH1 was up-regulated in roots and leaves, showing a pattern to be gradually increased within 23-h treatment regimes. The lines with overexpression of TabHLH1 exhibited drastically improved tolerance to Pi and N deprivation, showing larger plant phenotype, more biomass, higher concentration and more accumulation of P and N than wild type (WT) upon the Pi- and N-starvation stresses. NtPT1 and NtNRT2.2, the genes encoding phosphate transporter (PT) and nitrate transporter (NRT) in tobacco, respectively, showed up-regulated expression in TabHLH1-overexpressing plants; knockdown expression of them led to deteriorated growth feature, lowered biomass, and decreased nutrient accumulation of plants under Pi- and N-deficient conditions. Compared with WT, the TabHLH1-overexpressing plants also showed lowered reactive oxygen species (ROS) accumulation and improved antioxidant enzyme (AE) activities, such as those of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). NtSOD1, NtCAT1, and NtPOD1;6 that encode SOD, CAT, and POD, respectively, were up-regulated in TabHLH1-overexpressing plants. Further knockdown of these AE gene expression caused reduced antioxidant enzymatic activities, indicative of their crucial roles in mediating cellular ROS homeostasis in Pi- and N-starvation conditions. Together, TabHLH1 plays an important role in mediating adaptation to the Pi- and N-starvation stresses through transcriptional regulation of a set of genes encoding PT, NRT and AEs that mediate the taken up of Pi and N and the cellular homeostasis of ROS initiated by the nutrient stresses.

Wheat mitogen-activated protein kinase gene TaMPK4 improves plant tolerance to multiple stresses through modifying root growth, ROS metabolism, and nutrient acquisitions

KEY MESSAGE

Wheat MAPK member TaMPK4 responds to abiotic stresses of Pi and N deprivations and high salinity and is crucial in regulating plant tolerance to aforementioned stresses. Mitogen-activated protein kinase (MAPK) cascades are important signal transduction modules in regulating plant responses to various environmental stresses. In this study, a wheat MAPK member referred to TaMPK4 was characterized for its roles in mediating plant tolerance to diverse stresses. TaMPK4 shares conserved domains generally identified in plant MAPKs and possesses in vitro kinase activity. Under stresses of Pi and N deprivations and high salinity, TaMPK4 was strongly upregulated and its expressions were restored upon recovery treatments from above stresses. Sense- and antisense-expressing TaMPK4 in tobacco significantly modified plant growth under the stress conditions and dramatically modified the root architecture through transcriptional regulation of the auxin transport-associated genes NtPIN3 and NtPIN9, whose downregulated expressions dramatically reduced the root growth. Compared with wild type (WT), the antioxidant enzymatic activities under the stress conditions, P accumulation under P deprivation, and N amount under N deficiency were altered dramatically in the transgenic plants, showing higher in the TaMPK4-overexpressing and lower in the TaMPK4-knockout plants, which were in concordance with the modified expressions of a set of antioxidant enzyme genes (NtPOD2;1, NtPOD9, NtSOD2, NtFeSOD, and NtCAT), two phosphate transporter genes (NtPT and NtPT2), and two nitrate transporter genes (NtNRT1.1-s and NtNRT1.1-t), respectively. Downregulated expression of above genes in tobacco largely reduced the plant growth, and Pi and N acquisitions under the stress conditions. TaMPK4 also involved regulations of plant K(+) and osmolyte contents under high salinity. Thus, TaMPK4 is functional in regulating plant tolerance to diverse stresses through modifying various biological processes.

Fructans, ascorbate peroxidase, and hydrogen peroxide in ryegrass exposed to ozone under contrasting meteorological conditions

Ozone (O3) is the most abundant tropospheric oxidant as well as an important component of photochemical pollution. Once inside the plant, ozone can produce reactive oxygen species that change the antioxidative pool and the carbohydrate metabolism. The current study aimed to analyze whether the contents and the composition of the fructan, the ascorbate peroxidase activity, and the H2O2 accumulation were changed in Lolium multiflorum ssp. italicum cv. Lema plants as response to short-term exposure to ozone and/or to different meteorological conditions, in two contrasting seasons (winter and summer). Results showed that higher solar radiation tends to decrease fructose content and, along with temperature, increases the ascorbate peroxidase (APX) activity. Such activity and levels of fructans practically did not vary during the time the experiment was being done, but APX daylight variation was modified by the ozone. Thus, the higher levels of this pollutant decreased the APX activity and increased fructose content, as well as changed the size of the fructan chains. Hydrogen peroxide (H2O2) accumulation was higher in plants that were fumigated with ozone when compared to the control, and it decreased throughout the day. As a conclusion, fructan contents increased when the APX activity decreased. It suggested that fructans could also help the defense system when there is a reduction on the APX activity in the plant.

Influence of UV radiation on chlorophyll, and antioxidant enzymes of wetland plants in different types of constructed wetland

A surface- and vertical subsurface-flow-constructed wetland were designed to study the response of chlorophyll and antioxidant enzymes to elevated UV radiation in three types of wetland plants (Canna indica, Phragmites austrail, and Typha augustifolia). Results showed that (1) chlorophyll content of C. indica, P. austrail, and T. augustifolia in the constructed wetland was significantly lower where UV radiation was increased by 10 and 20 % above ambient solar level than in treatment with ambient solar UV radiation (p < 0.05). (2) The malondialdehyde (MDA) content, guaiacol peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities of wetland plants increased with elevated UV radiation intensity. (3) The increased rate of MDA, SOD, POD, and CAT activities of C. indica, P. australis, and T. angustifolia by elevated UV radiation of 10 % was higher in vertical subsurface-flow-constructed wetland than in surface-flow-constructed wetland. The sensitivity of MDA, SOD, POD, and CAT activities of C. indica, P. austrail, and T. augustifolia to the elevated UV radiation was lower in surface-flow-constructed wetland than in the vertical subsurface-flow-constructed wetland, which was related to a reduction in UV radiation intensity through the dissolved organic carbon and suspended matter in the water. C. indica had the highest SOD and POD activities, which implied it is more sensitive to enhanced UV radiation. Therefore, different wetland plants had different antioxidant enzymes by elevated UV radiation, which were more sensitive in vertical subsurface-flow-constructed wetland than in surface-flow-constructed wetland.

Root antioxidant responses of two Pisum sativum cultivars to direct and induced Fe deficiency

The contribution of antioxidant defence systems in different tolerance to direct and bicarbonate-induced Fe deficiency was evaluated in two pea cultivars (Kelvedon, tolerant and Lincoln, susceptible). Fe deficiency enhanced lipid peroxidation and H2 O2 concentration in roots of both cultivars, particularly in the sensitive one grown under bicarbonate supply. The results obtained on antioxidant activities (SOD, CAT, POD) suggest that H2 O2 accumulation could be due to an overproduction of this ROS and, at the same time, to a poor capacity to detoxify it. Moreover, under bicarbonate supply the activity of POD isoforms was reduced only in the sensitive cultivar, while in the tolerant one a new isoform was detected, suggesting that POD activity might be an important contributor to pea tolerance to Fe deficiency. The presence of bicarbonate also resulted in stimulation of GR, MDHAR and DHAR activities, part of the ASC-GSH pathway, which was higher in the tolerant cultivar than in the sensitive one. Overall, while in the absence of Fe only slight differences were reported between the two cultivars, the adaptation of Kelvedon to the presence of bicarbonate seems to be related to its greater ability to enhance the antioxidant response at the root level.

Overexpression of VP, a vacuolar H+-pyrophosphatase gene in wheat (Triticum aestivum L.), improves tobacco plant growth under Pi and N deprivation, high salinity, and drought

Establishing crop cultivars with strong tolerance to P and N deprivation, high salinity, and drought is an effective way to improve crop yield and promote sustainable agriculture worldwide. A vacuolar H+-pyrophosphatase (V-H+-PPase) gene in wheat (TaVP) was functionally characterized in this study. TaVP cDNA is 2586-bp long and encodes a 775-amino-acid polypeptide that contains 10 conserved membrane-spanning domains. Transcription of TaVP was upregulated by inorganic phosphate (Pi) and N deprivation, high salinity, and drought. Transgene analysis revealed that TaVP overexpression improved plant growth under normal conditions and specifically under Pi and N deprivation stresses, high salinity, and drought. The improvement of growth of the transgenic plants was found to be closely related to elevated V-H+-PPase activities in their tonoplasts and enlarged root systems, which possibly resulted from elevated expression of auxin transport-associated genes. TaVP-overexpressing plants showed high dry mass, photosynthetic efficiencies, antioxidant enzyme activities, and P, N, and soluble carbohydrate concentrations under various growth conditions, particularly under the stress conditions. The transcription of phosphate and nitrate transporter genes was not altered in TaVP-overexpressing plants compared with the wild type, suggesting that high P and N concentrations regulated by TaVP were caused by increased root absorption area instead of alteration of Pi and NO3- acquisition kinetics. TaVP is important in the tolerance of multiple stresses and can serve as a useful genetic resource to improve plant P- and N-use efficiencies and to increase tolerance to high salinity and drought.

Ultrasonic vibration seeds showed improved resistance to cadmium and lead in wheat seedling

Heavy metals have long-term adverse impacts on the health of soil ecosystems and even exhibit hazardous influences on human health. Literatures have shown that heavy metals could result in the reduction of crops growth and development and finally result in crops production decline. To determine whether or not ultrasonic vibration alleviate damage induced by cadmium and lead in crops, the wheat seeds, which is one of the most important agriculture crops in China and other countries in the world, were exposed to 10 min ultrasonic vibration and then the toxicological effects were investigated. Wheat seeds were soaked for 3 h with water and then the seeds were placed in clean beaker with some water, the beaker were placed in ultrasonic apparatus to vibrate (model, KQ-200VDV; frequency, 45 KHz; power, 160 W). Pretreatment seeds of 80 were sown in dishes (Ø 15 cm). After seeds emergence, the seedlings were thinned to 60 per dish. The dishes with seedlings were placed in a growth chamber maintained at 25 °C, 70% relative humidity and 380 μmol mol(-1) CO2 under dark condition. A 400 μmol m(-2) s(-1) photosynthetically active radiation was provided for 8 h (dark for 16 h) after the seed germination. When the seedlings were 2 days old, the seedlings were subjected to cadmium and lead for 4 days and then some selective biochemical and physiological parameters were measured. (1) Although each doses of ultrasonic vibration could improve seed germination, enhance biosynthesis of protein and chlorophyll and seedlings growth, the optimum dosage of ultrasonic vibration was 10 min. (2) Compared with the controls, cadmium and lead stress led to significant increase in the concentrations of malondialdehyde (MDA) and O(-2) and in the conductivity of electrolyte leakage, but the activities of catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), the glutathione concentration, and the shoot weight were decreased by Cd and Pb stress. In the case of the seeds exposed to ultrasonic vibration and the seedlings followed by cadmium lead stress, the concentrations of MDA and O(-2), and the conductivity of electrolyte leakage were significantly lower than those in cadmium and lead stress; the activities of CAT, SOD, and GR and the shoot weight were significantly higher (except for glutathione (GSH) concentration) than those in cadmium and lead stress seedlings. The membrane is responsible for the selective inflow and outflow of molecules, ions, and water, and is a dynamic structure that performs a variety of functions. Cellular membrane systems play an important role in the compartmentalization of cells and maintaining intercellular homeostasis. Abiotic and biotic stress can induce functional impairments to the cellular membrane systems through triggering an increased formation of reactive oxygen species (ROS), such as superoxide (O2 (-)), hydrogen peroxide (H2O2), and hydroxyl radicals. There are several pathways that can be utilized to eliminate ROS in plants, e.g., CAT, SOD, and GR and GSH, etc. compared with controls, cadmium, and lead enhanced the concentrations of ROS; decreased the SOD, CAT, and GR activities; the GSH concentration, and the seedling growth. In the case of ultrasonic pretreatment followed by cadmium and lead stresses, the activities of CAT, SOD, and GR were significant higher, and the conductivity of electrolyte leakage and the concentrations of MDA and O2 (-) were significant lower than that of those subjected by cadmium and lead stress. This phenomenon demonstrated ultrasonic pretreatment can help plant eliminate the ROS by enhance the activities of antioxidant enzymes. These results suggested that ultrasonic vibration can alleviate the toxicological effect induced by heavy mental.

Liver injury and its molecular mechanisms in mice caused by exposure to cerium chloride

Cerium has been demonstrated to damage liver of mice, but very little is known about the molecular mechanisms underlying the mouse liver apoptosis. In order to understand the liver injury induced by intragastric administration of cerium chloride (CeCl3) for 60 consecutive days, the hepatocyte ultrasrtucture, various oxidative stress parameters, and the stress-related gene expression levels were investigated for the mouse liver. The results demonstrated that CeCl3 had an obvious accumulation in the mouse liver, leading to a classical laddering cleavage of DNA and hepatocyte apoptosis. CeCl3 significantly promoted the accumulation of reactive oxygen species and inhibited the stress-related gene expression of superoxide dismutase, catalase, glutathione peroxidase, metallothionein, heat-shock protein 70, glutathione-S-transferase, P53, and transferring, and it effectively activated the cytochrome p450 1A. It implied that CeCl3 resulted in apoptosis and alteration of expression levels of the genes related with metal detoxification/metabolism regulation and radical scavenging action in mice.

Microwave pretreatment can enhance tolerance of wheat seedlings to CdCl2 stress

In order to determine the role of microwave in cadmium stress tolerance of wheat (Triticum aestivum L.), seeds were exposed to microwave radiation for 0, 5, 10 and 15 s (wavelength 125 mm, power density 126 mW cm(-2), 2450 MHz), and when the seedlings were 7 d old (with one fully expanded leaves), they were treated with 150 μM CdCl(2) solution for 10 d. Changes in a number of physiological and biochemical characteristics were measured and used as indicators of the protective capacity of microwave radiation in this experiment. Our results showed that 150 μM CdCl(2) treatment reduced plant height, root length, dry weight, AsA and GSH concentration and the activities of SOD, POD, CAT and APX, enhanced the concentration of MDA, H(2)O(2) and the production rate of O(2)- when compared with the control. However, seeds with microwave pretreatment 5 or 10 s conferred tolerance to cadmium stress in wheat seedlings by decreasing the concentration of MDA and H(2)O(2), the production rate of O(2)- and increasing the activities of SOD, POD, CAT, APX and AsA and GSH concentration. Therefore, antioxidative enzymes and antioxidative compounds may participate in tolerance of wheat seedlings to cadmium stress. The results also showed that the microwave radiation had a positive physiological effect on the growth and development of cadmium stressed seedlings. This is the first investigation reporting the use of microwave pretreatment to enhance cadmium stress tolerance of wheat.

Neutron irradiation affects the expression of genes involved in the response to auxin, senescence and oxidative stress in Arabidopsis

We report, in Arabidopsis thaliana plants, the effect of neutron irradiation on the transcription of a set of genes belonging to different physiological groups: auxin action, senescence, oxidative stress, and some aspects of photosynthesis. The results indicated that, in the wild-types, the effect on the ARF1, ARF2, and 19 genes was of down-regulation, whereas of the tested AUX/IAA only AUX/IAA7 showed up-regulation. Different results were obtained as regards the irradiation of the auxin transport mutants aux1 and eir1, because in these cases the ARF genes were up-regulated, whereas AUX/IAA7 was down-regulated in eir1. On the other hand, the senescence activated genes SAG12 and SAG13, and those connected to oxidative stress were up-regulated in the wild-type, but down-regulated in aux1. The gene CAB1, connected to photosynthesis, was also down-regulated in the wild-type, but up-regulated in aux1. Gene expression recovered in many cases almost to the initial condition in a time lapse of 24 hours, even though some effect persisted for a longer time. In particular, the state of juvenility of arf2 was extended by irradiation, whereas, in all the other cases, senescence was accelerated. The research indicates that through mutant selection or genetic engineering a true possibility exists of producing organism more suitable for life in space.

ROS resistance in Pisum sativum cv. Alaska: the involvement of nucleoside diphosphate kinase in oxidative stress responses via the regulation of antioxidants

This study investigated the reactive oxygen species (ROS) tolerance mechanism of a paraquat-resistant Pisum sativum line (R3-1) compared with the wild type (WT). Physiological and biochemical analyses showed significant differences in the phenotypes, such as delayed leaf and floral development, superior branching, and greater biomass and yields in the R3-1 line, as well as an increased level of antioxidant pigments and a lower rate of cellular lipid peroxidation in the resistant R3-1. Additionally, the phosphorylation of crude proteins showed distinguishable differences in band mobility and intensity between the R3-1 and WT plants. cDNA cloning and sequence analysis of NDPKs, which were candidate phosphorylated proteins, revealed that two of the deduced amino acids in NDPK2 (IL12L and Glu205Lys) and one in NDPK3 (P45S) were mutated in R3-1. Using glutathione S-transferase-NDPK fusion constructs, we found that the precursor recombinant R3-1 NDPK2 showed an increased level of activity and autophosphorylation in R3-1 plants compared to WT plants. Native PAGE analysis of the crude proteins revealed that NDPK and catalase (CAT) activity co-existed in the same area of the gel. In a yeast two-hybrid assay, the N-terminal region of NDPK2 showed an interaction with the full-length CAT1 protein. Furthermore, we found that WT showed a decreased level of CAT activity compared with R3-1 under illumination and/or on media containing ROS-releasing reagents. Taken together, these results suggest that there is a strong interaction between NDPK2 and CAT1 in R3-1 plants, which possibly plays a vital role in the antioxidant defense against ROS.

H2O2 in plant peroxisomes: an in vivo analysis uncovers a Ca(2+)-dependent scavenging system

Oxidative stress is a major challenge for all cells living in an oxygen-based world. Among reactive oxygen species, H2O2, is a well known toxic molecule and, nowadays, considered a specific component of several signalling pathways. In order to gain insight into the roles played by H2O2 in plant cells, it is necessary to have a reliable, specific and non-invasive methodology for its in vivo detection. Hence, the genetically encoded H2O2 sensor HyPer was expressed in plant cells in different subcellular compartments such as cytoplasm and peroxisomes. Moreover, with the use of the new green fluorescent protein (GFP)-based Cameleon Ca2+ indicator, D3cpv-KVK-SKL, targeted to peroxisomes, we demonstrated that the induction of cytoplasmic Ca2+ increase is followed by Ca2+ rise in the peroxisomal lumen. The analyses of HyPer fluorescence ratios were performed in leaf peroxisomes of tobacco and pre- and post-bolting Arabidopsis plants. These analyses allowed us to demonstrate that an intraperoxisomal Ca2+ rise in vivo stimulates catalase activity, increasing peroxisomal H2O2 scavenging efficiency.

Ecophysiological responses of winter wheat seedling to aerosol wet deposition of Xi'an area, China

Aerosol leads to 30% reduction in solar radiation reaching the earth's surface, and a similar reduction in crops yield for both wheat and rice. To determine the effect of aerosol wet deposition on crops, aerosol samples were collected in September, 2006 at Xi'an urban suburb (34 degrees 44'N, 109 degrees 49'E), and wheat seedlings were treated with aerosol of different concentrations in laboratory conditions. Changes in physiological and biochemical parameters of wheat seedlings were measured. In comparison with the control, the activities of superoxide dismudase (SOD) and catalase (CAT) and the concentration malondialdehyde (MDA) and oxidized glutathione (GSSG) of wheat seedlings increased progressively with increasing concentrations of added aerosol, while the opposite trend was seen for the activities of nitric oxide synthase (NOS), the concentrations of glutathione (GSH) and nitric oxide (NO), and the ratio of GSH/GSSG. When the seedlings were treated with the aerosol of 1 and 2 mg/L, the coleoptile elongation, shoot elongation and biomass accumulation were increased, the effect at treatment of 2 mg/L was most significant. However, aerosol treatments with rates of 3 and 4 mg/L resulted in a decrease in coleoptile elongation, shoot elongation and biomass accumulation in seedlings, and significant effect was for the treatment of 4 mg/L. Hence, lower concentrations of aerosol wet deposition were in favor of crops growth, but its higher concentrations could result in deleterious effects for crops and decreased crops growth.

Fine and coarse regulation of reactive oxygen species in the salt tolerant mutants of barnyard grass and their wild-type parents under salt stress

The growth of the wild-type and three salt tolerant mutants of barnyard grass (Echinochloa crusgalli L.) under salt stress was investigated in relation to oxidative stress and activities of the antioxidant enzymes superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), phenol peroxidase (POD: EC 1.11.1.7), glutathione reductase (GR: EC 1.8.1.7) and ascorbate peroxidase (APX: EC 1.11.1.1). The three mutants (fows B17, B19 and B21) grew significantly better than the wild-type under salt stress (200 mM NaCl) but some salt sensitive individuals were still detectable in the populations of the mutants though in smaller numbers compared with the wild-type. The salt sensitive plants had slower growth rates, higher rates of lipid peroxidation and higher levels of reactive oxygen species (ROS) in their leaves compared with the more tolerant plants from the same genotype. These sensitivity responses were maximized when the plants were grown under high light intensity suggesting that the chloroplast could be a main source of ROS under salt stress. However, the salt sensitivity did not correlate with reduced K(+)/Na(+) ratios or enhanced Na(+) uptake indicating that the sensitivity responses may be mainly because of accumulation of ROS rather than ion toxicity. SOD activities did not correlate to salt tolerance. Salt stress resulted in up to 10-fold increase in CAT activity in the sensitive plants but lower activities were found in the tolerant ones. In contrast, the activities of POD, APX and GR were down regulated in the sensitive plants compared with the tolerant ones. A correlation between plant growth, accumulation of ROS and differential modulation of antioxidant enzymes is discussed. We conclude that loss of activities of POD, APX and GR causes loss of fine regulation of ROS levels and hence the plants experience oxidative stress although they have high CAT activities.

Proteome of plant peroxisomes: new perspectives on the role of these organelles in cell biology

Peroxisomes are cell organelles bounded by a single membrane with a basically oxidative metabolism. Peroxisomes house catalase and H(2)O(2)-producing flavin-oxidases as the main protein constituents. However, since their discovery in early fifties, a number of new enzymes and metabolic pathways have been reported to be also confined to these organelles. Thus, the presence of exo- and endo-peptidases, superoxide dismutases, the enzymes of the plant ascorbate-glutathione cycle plus ascorbate and glutathione, several NADP-dehydrogenases, and also L-arginine-dependent nitric oxide synthase activity has evidenced the relevant role of these organelles in cell physiology. In recent years, the study of new functions of peroxisomes has become a field of intensive research in cell biology, and these organelles have been proposed to be a source of important signal molecules for different transduction pathways. In plants, peroxisomes participate in seed germination, leaf senescence, fruit maturation, response to abiotic and biotic stress, photomorphogenesis, biosynthesis of the plant hormones jasmonic acid and auxin, and in cell signaling by reactive oxygen and nitrogen species (ROS and RNS, respectively). In order to decipher the nature and specific role of the peroxisomal proteins in these processes, several approaches including in vivo and in vitro import assays and generation of mutants have been used. In the last decade, the development of genomics and the report of the first plant genomes provided plant biologists a powerful tool to assign to peroxisomes those proteins which harbored any of the two peroxisomal targeting signals (PTS, either PTS1 or PTS2) described so far. Unfortunately, those molecular approaches could not give any response to those proteins previously localized in plant peroxisomes by classical biochemical and cell biology methods that did not contain any PTS. However, more recently, proteomic studies of highly purified organelles have provided evidence of the presence in peroxisomes of new proteins not previously reported. Thus, the contribution of proteomic approaches to the biology of peroxisomes is essential, not only for elucidation of the mechanisms involved in the import of the PTS1- and PTS2-independent proteins, but also to the understanding of the role of these organelles in the cell physiology of plant growth and development.

Weak microwave can alleviate water deficit induced by osmotic stress in wheat seedlings

The aim of the investigation is to determine the effect of microwave pretreatment of wheat seeds on the resistance of seedlings to osmotic stress. Changes in biophysical, physiological and biochemical characters were measured. The results showed: (1) The magnetic field intensity and seeds temperature increased progressively with microwave pretreatments of 5, 10, 15, 20 s and 25 s compared with controls. Although each microwave pretreatment resulted in an increase in alpha-amylase activity and photon emission intensity, the increase of alpha-amylase activity and photon emission intensity was maximal at a microwave pretreatment of 10 s. (2) Osmotic stress induced by PEG treatment enhanced the concentration of malondialdehyde, while decreasing the activities of nitricoxide synthase, catalase, peroxidase, superoxide dismutase and the concentration of nitric oxide, ascorbic acid, glutathione in the seedlings compared with controls. However, compared to osmotic stress alone, in the seedlings treated with microwave irradiation plus osmotic stress the concentration of malondialdehyde decreased, while the activities of nitricoxide synthase, catalase, peroxidase, superoxide dismutase and the concentration of nitric oxide, ascorbic acid and glutathione increased. These results suggest that a suitable dose of microwave radiation can enhance the capability to eliminate free radicals induced by osmotic stress in wheat seedlings resulting in an increase in resistance to osmotic stress.

Low-coverage massively parallel pyrosequencing of cDNAs enables proteomics in non-model species: comparison of a species-specific database generated by pyrosequencing with databases from related species for proteome analysis of pea chloroplast envelopes

Proteomics is a valuable tool for establishing and comparing the protein content of defined tissues, cell types, or subcellular structures. Its use in non-model species is currently limited because the identification of peptides critically depends on sequence databases. In this study, we explored the potential of a preliminary cDNA database for the non-model species Pisum sativum created by a small number of massively parallel pyrosequencing (MPSS) runs for its use in proteomics and compared it to comprehensive cDNA databases from Medicago truncatula and Arabidopsis thaliana created by Sanger sequencing. Each database was used to identify proteins from a pea leaf chloroplast envelope preparation. It is shown that the pea database identified more proteins with higher accuracy, although the sequence quality was low and the sequence contigs were short compared to databases from model species. Although the number of identified proteins in non-species-specific databases could potentially be increased by lowering the threshold for successful protein identifications, this strategy markedly increases the number of wrongly identified proteins. The identification rate with non-species-specific databases correlated with spectral abundance but not with the predicted membrane helix content, and strong conservation is necessary but not sufficient for protein identification with a non-species-specific database. It is concluded that massively parallel sequencing of cDNAs substantially increases the power of proteomics in non-model species.

Ultraviolet-B-induced oxidative stress and antioxidant defense system responses in ascorbate-deficient vtc1 mutants of Arabidopsis thaliana

Ultraviolet-B (UV-B) radiation has a negative impact on plant cells, and results in the generation of reactive oxygen species (ROS). In order to increase our understanding of the effects of UV-B on antioxidant processes, we investigated the response of an ascorbate-deficient Arabidopsis thaliana mutant vtc1 to short-term increased UV-B exposure. After UV-B supplementation, vtc1 mutants exhibited oxidative damage. Evidence for damage included an increase in H(2)O(2) content and the production of thiobarbituric acid reactive substances (TBARS); a decrease in chlorophyll content and chlorophyll fluorescence parameters were also reported. The vtc1 mutants had higher total glutathione than the wild type (WT) during the first day of UV-B treatment. We found reduced ratio of glutathione/total glutathione and increased ratio of dehydroascorbate/total ascorbate in the vtc1 mutants, compared to the WT plants. In addition, the enzymes responsible for ROS scavenging, including superoxide dismutase, catalase, and ascorbate peroxidase, had insufficient activity in the vtc1 mutants, compared to the WT plants. The same reduced activity in the vtc1 mutants was reported for the enzymes responsible for the regeneration of ascorbate and glutathione (including monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase). These results suggest that the ascorbate-deficient mutant vtc1 is more sensitive to supplementary UV-B treatment than WT plants and ascorbate can be considered an important antioxidant for UV-B radiation.

Differential expression and regulation of antioxidative enzymes by cadmium in pea plants

The long-term effects of 50 microM CdCl(2) on the enzymatic and non-enzymatic antioxidative defences of pea (Pisum sativum L.) plants was studied in terms of activity, protein content and transcripts levels. Cadmium caused a reduction of the total glutathione content (GSH+GSSG), with the reduced form of glutathione (GSH) being most affected. The content of ascorbic acid (ASC) was also decreased by the treatment. The transcript levels of catalase (CAT) and monodehydroascorbate reductase (MDHAR) showed a Cd-dependent increase, although CAT activity and its protein content were depressed, which suggests a posttranslational modification of this protein induced by cadmium. Glutathione reductase (GR), and ascorbate peroxidase (APX) did not change significantly, either in activity or accumulation of transcript. However, cadmium treatment provoked a strong reduction in mRNA, protein level and activity of CuZn-superoxide dismutase (SOD), being the most negatively affected antioxidative enzyme, and in less extent of Mn-SOD. Transcriptome analysis of the antioxidative enzymes in leaves of pea plants grown with cadmium and treated with some modulators of the signal transduction cascade suggested that at least Ca(2+) channels, phosphorylation/dephosphorylation processes, nitric oxide, cGMP, salicylic acid (SA) and H(2)O(2) were involved in some steps between the cadmium signal and transcript expression of CuZn-SOD, CAT and MDHAR. This indicated the existence of cross-talk between these elements and reactive oxygen species (ROS) metabolism during cadmium stress.

Inhibition of the catalase activity from Phaseolus vulgaris and Medicago sativa by sodium chloride

Changes in catalase activity during the development of the Rhizobium-legume symbiosis as well as its response in salinized plants of Phaseolus vulgaris and Medicago sativa, was studied. Besides, it was examined the behavior of the enzyme, isolated from leaves and root nodules, during in vitro incubation with NaCl doses. Nodule catalase activities of both legumes were assayed with several enzyme inhibitors and also purified. Leaf catalase activity of Phaseolus vulgaris and Medicago sativa decreased and increased respectively throughout the ontogeny, but root nodule catalase kept a high and stable value. This last result suggests that both legumes require the maintenance of high nodule catalase in nitrogen-fixing nodules. Under salt stress conditions leaf and nodule catalase activity decreased in both, grain and pasture legumes. Because catalase from leaf of Medicago sativa and nodules of Phaseolus vulgaris were relatively sensitive to NaCl during in vitro experiments, the detoxifying role of this enzyme for H(2)O(2) should be limited in such conditions. Both catalases, from determinate and indeterminate nodules, were affected neither by oxygen nor superoxide radicals but showed a strong (Phaseolus vulgaris) or partial (Medicago sativa) inhibition with dithiothreitol, dithionite and beta-mercaptoethanol. Besides, cyanide was the most potent inhibitor of nodule catalases. Finally, catalases partially purified by immobilized metal ion affinity chromatography migrated at 42 (Phaseolus vulgaris) and 46kDa (Medicago sativa) on SDS-PAGE, whereas native forms on sephacryl S-300 columns exhibited a molecular mass of 59 and 48kDa (Phaseolus vulgaris) and 88 and 53kDa (Medicago sativa).

Heme oxygenase up-regulation in ultraviolet-B irradiated soybean plants involves reactive oxygen species

Ultraviolet-B (UV-B) radiation has a negative impact on plant cells, and leads to the generation of reactive oxygen species (ROS). Heme oxygenase (HO, EC 1.14.99.3) plays a protective role against oxidative stress in mammals, but little is known about this issue in plants. Here, we report for the first time the response of HO in leaves of soybean (Glycine max L.) plants subjected to UV-B radiation. Under 7.5 and 15 kJ m(-2 )UV-B doses, HO, catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.11) activities were increased and the production of thiobarbituric acid reactive substances (TBARS) regain control values after 4 h of plant recuperation. Treatment with 30 kJ m(-2) UV-B provoked a decrease in these antioxidant enzyme activities. Immunoblot analysis showed a 4.3 and 3.7-fold increase in HO-1 protein expression after irradiation with 7.5 and 15 kJ m(-2), respectively. HO-1 transcript levels were enhanced (up to 77%) at these doses, as assessed by semi-quantitative RT-PCR. These data demonstrated that increased HO activity was associated with augmented protein expression and transcript levels. Plants pre-treated with the antioxidant ascorbic acid did not show the UV-B-induced up-regulation of HO-1 mRNA, but hydrogen peroxide treatment could mimic this reaction. Our results indicate that HO is up-regulated in a dose-depending manner as a mechanism of cell protection against oxidative damage and that such response occurred as a consequence of HO-1 mRNA enhancement involving ROS.

The dehydrogenase-mediated recycling of NADPH is a key antioxidant system against salt-induced oxidative stress in olive plants

NADPH is an important molecule in the redox balance of the cell. In this paper, using olive tissue cultures as a model of the function of the NADPH-generating dehydrogenases in the mechanism of oxidative stress induced by severe salinity conditions was studied. When olive (Olea europaea) plants were grown with 200 mM NaCl, a 40% reduction in leaf fresh weight was produced. The content of non-enzymatic antioxidants such as ascorbate and glutathione was diminished between 20% to 39%, whereas the H2O2 content was increased threefold. In contrast, the analysis of the activity and protein contents of the main antioxidative enzymes showed a significant increase of catalase, superoxide dismutase and glutathione reductase. Overall, these changes strongly suggests that NaCl induces oxidative stress in olive plants. On the other hand, while the content of glucose-6-phosphate was increased almost eightfold in leaves of plants grown under salt stress, the content of NAD(P)H (reduced and oxided forms) did not show significant variations. Under salt stress conditions, the activity and protein contents of the main NADPH-recycling enzymes, glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (ICDH), malic enzyme (ME) and ferrodoxin-NADP reductase (FNR) showed an enhancement of 30-50%. In leaves of olive plants grown with 200 mM NaCl, analysis of G6PDH by immunocytochemistry and confocal laser scanning microscopy showed a general increase of this protein in epidermis, palisade and spongy mesophyll cells. These results indicate that in olive plants, salinity causes reactive oxygen species (ROS)-mediated oxidative stress, and plants respond to this situation by inducing different antioxidative enzymes, especially the NADPH-producing dehydrogenases in order to recycle NADPH necessary for the protection against oxidative damages. These NADP-dehydrogenases appear to be key antioxidative enzymes in olive plants under salt stress conditions.

Senescence-specific regulation of catalases in Arabidopsis thaliana (L.) Heynh

Oxygen free radicals are thought to play an essential role in senescence, especially those derived from peroxisomes. Therefore, the activities of different isoforms of the peroxisomal hydrogen peroxide (H2O2)-scavenging enzyme catalase (CAT) were analysed during senescence of Arabidopsis. CAT2 activity decreased with bolting time parallel with cytosolic ascorbate peroxidase 1 (APX1) activity before loss of chlorophyll could be measured. At the same time point, the H2O2 content increased. Subsequently, the stress-inducible CAT3 isoform was activated and APX1 activity was recovered, accompanied by a decline of the H2O2 content. In very late stages, low activities of the seed-specific CAT1 became detectable in leaves, but H2O2 increased again. Further analyses of CAT expression by promoter: beta-glucuronidase (GUS) fusions in transgenic plants revealed a vasculature-specific CAT3 expression, whereas CAT2 expression turned out to be specific for photosynthetic active tissues. CAT2 expression is down-regulated during leaf senescence, while CAT3 expression is induced with age and corresponds to an accumulation of H2O2 in the vascular bundles. CAT2 down-regulation on the transcriptional level appears as the initial step in creating the H2O2 peak during bolting time, while the decrease in APX1 activity might only be a secondary and amplifying effect.

Glutathione reductase from pea leaves: response to abiotic stress and characterization of the peroxisomal isozyme

The glutathione reductase (GR; EC 1.6.4.2) isozyme present in peroxisomes has been purified for the first time, and its unequivocal localization in these organelles, by immunogold electron microscopy, is reported. The enzyme was purified c. 21-fold with a specific activity of 9523 units mg(-1) protein, and a yield of 44 microg protein kg(-1) leaves was obtained. The subunit size of the peroxisomal GR was 56 kDa and the isoelectric point was 5.4. The enzyme was recognized by a polyclonal antibody raised against total GR from pea (Pisum sativum) leaves. The localization of GR in peroxisomes adds to chloroplasts and mitochondria where GR isozymes are also present, and suggests a multiple targeting of this enzyme to distinct cell compartments depending on the metabolism of each organelle under the plant growth conditions. The expression level of GR in several organs of pea plants and under different stress conditions was investigated. The possible role of peroxisomal GR under abiotic stress conditions, such as cadmium toxicity, high light, darkness, high temperature, wounding and low temperature, is discussed.

Effect of hydrogen peroxide on catalase gene expression, isoform activities and levels in leaves of potato sprayed with homobrassinolide and ultrastructural changes in mesophyll cells

The effect of hydrogen peroxide (H₂O₂) on catalase (CAT) isoform activities and amounts and on mRNA levels was studied in leaves from potato plants untreated and treated with homobrassinolide (HBR). Northern blot analysis revealed that 100 mm H₂O₂ supplied through the leaf petiole for 4 h did not induce CAT expression. In contrast, CAT1 and CAT2 responded differently to longer treatment, as CAT2 transcript levels increased markedly whereas CAT1 transcript levels remained unchanged. Western blot analysis showed disparity between the level of CAT1 transcript and CAT1 amount, which actually decreased after 28 h. CAT2 amount correlated well with transcript accumulation and CAT2 activity as visualised by zymogram analysis. H₂O₂ modified the relative importance of CAT isoforms. After 4 h, CAT1 was prevalent in untreated and H₂O₂-treated leaves. After 28 h, CAT2 was prevalent in H₂O₂-treated leaves; therefore, the quantified increase in total CAT activity in these leaves was due to the rise in CAT2. HBR pre-treatment increased CAT2 basal level not changing the pattern of CAT responses to H₂O₂, only lowering its amplitude. Even so, ultrastructural studies showed that HBR significantly reduced H₂O₂ negative effects on cellular sub-structures, allowing better recovery of affected structures and reducing the macroscopic injury symptoms on leaves, thus data point to a HBR protective role.

A protective association between catalase and isocitrate lyase in peroxisomes

Glyoxysomes are specialized peroxisomes in germinating seeds, which catalyze many reactions that convert fatty acids into carbohydrates thus generating H(2)O(2). They are characterized by the presence of catalase (CAT, E.C. 1.11.1.6) in their matrix which protects cells from oxidative stress. Here, we investigated the possibility that a protein can be protected from oxidative damage by its association with CAT. We purified peroxisomal CAT from germinating castor beans by ion exchange, gel filtration, and hydroxylapatite chromatography. Gel filtration of the matrix proteins, cross-linking, and co-immunoprecipitation studies indicate that CAT associates with a glyoxysomal matrix protein, isocitrate lyase (ICL, E.C. 4.1.3.1). In addition, we found that H(2)O(2) inactivates ICL and degrades its product, glyoxylate, when CAT is inactive. ICL and its product appear to be sensitive to oxidative damage; thus, association of CAT with ICL would afford protection from H(2)O(2).

Cadmium toxicity and oxidative metabolism of pea leaf peroxisomes

The effect of growing pea plants with 50 microM CdCl2 on the activated oxygen metabolism was studied at subcellular level in peroxisomes isolated from pea leaves. Cadmium treatment produced proliferation of peroxisomes as well as an increase in the content of H2O2 in peroxisomes from pea leaves, but in peroxisomal membranes no significant effect on the NADH-dependent O2*- production was observed. The rate of lipid peroxidation of membranes was slightly decreased in peroxisomes from Cd-treated plants. This could be due to the Cd-induced increase in the activity of some antioxidative enzymes involved in H2O2 removal, mainly ascorbate peroxidase and glutathione reductase, as well as the NADP-dependent dehydrogenases present in these organelles. The activity of xanthine oxidase did not experiment changes by Cd treatment and this suggests that O2*- production in the peroxisomal matrix is not involved in Cd toxicity. This was supported by the absence of changes in plants treated with Cd in the Mn-SOD activity, responsible for O2*- removal in the peroxisomal matrix. Results obtained indicate that toxic Cd levels induce imbalances in the activated oxygen metabolism of pea leaf peroxisomes, but its main effect is an enhancement of the H2O2 concentration of these organelles. Peroxisomes respond to Cd toxicity by increasing the activity of antioxidative enzymes involved in the ascorbate-glutathione cycle and the NADP-dependent dehydrogenases located in these organelles.