Glutathionylation of Pea Chloroplast 2-Cys Prx and Mitochondrial Prx IIF Affects Their Structure and Peroxidase Activity and Sulfiredoxin Deglutathionylates Only the 2-Cys Prx

Together with thioredoxins (Trxs), plant peroxiredoxins (Prxs), and sulfiredoxins (Srxs) are involved in antioxidant defense and redox signaling, while their regulation by post-translational modifications (PTMs) is increasingly regarded as a key component for the transduction of the bioactivity of reactive oxygen and nitrogen species. Among these PTMs, S-glutathionylation is considered a protective mechanism against overoxidation, it also modulates protein activity and allows signaling. This study explores the glutathionylation of recombinant chloroplastic 2-Cys Prx and mitochondrial Prx IIF from Pisum sativum. Glutathionylation of the decameric form of 2-Cys Prx produced a change in the elution volume after FPLC chromatography and converted it to its dimeric glutathionylated form, while Prx IIF in its reduced dimeric form was glutathionylated without changing its oligomeric state. Mass spectrometry demonstrated that oxidized glutathione (GSSG) can glutathionylate resolving cysteine (Cys174), but not the peroxidatic equivalent (Cys52), in 2-Cys Prx. In contrast, GSSG was able to glutathionylate both peroxidatic (Cys59) and resolving (Cys84) cysteine in Prx IIF. Glutathionylation was seen to be dependent on the GSH/GSSG ratio, although the exact effect on the 2-Cys Prx and Prx IIF proteins differed. However, the glutathionylation provoked a similar decrease in the peroxidase activity of both peroxiredoxins. Despite growing evidence of the importance of post-translational modifications, little is known about the enzymatic systems that specifically regulate the reversal of this modification. In the present work, sulfiredoxin from P. sativum was seen to be able to deglutathionylate pea 2-Cys Prx but not pea Prx IIF. Redox changes during plant development and the response to stress influence glutathionylation/deglutathionylation processes, which may represent an important event through the modulation of peroxiredoxin and sulfiredoxin proteins.This research was supported by MICINN, Spain (BFU2014-52452-P co-financed by FEDER) and Seneca Foundation, Murcia, Spain (Excellence Group 19876/GERM/15).Peer reviewedPeer Reviewe

Major As species, lipid peroxidation and protein carbonylation in rice plants exposed to increasing As(V) concentrations

Arsenic (As) uptake by plants is mainly carried out as arsenate (As(V)), whose chemical analogy with phosphate is largely responsible for its elevated toxicity. Arsenate is known to stimulate reactive oxygen species (ROS) formation in plants that provoke oxidative stress. This manuscript reports the results of a hydroponics study using rice (Oryza sativa L.) seedlings as a test plant, where the effects of increasing arsenate concentrations (0–10 mg L−1) on both lipid and protein oxidation, as well as As accumulation and speciation in plant roots and shoots were examined. Plant yield was negatively affected by increasing As concentration. Accumulation in plant roots was higher than in shoots at low arsenate doses (0.5–2.5 mg L−1), while root to shoot transport was drastically enhanced at the highest doses (5 and 10 mg L−1). Moreover, As(V) was the dominating species in the shoots and As(III) in the roots. Rice leaves in the 10 mg As L−1 treatment showed the highest lipid peroxidation damage (malondialdehyde concentration), whilst protein oxidation was not remarkably influenced by As dose. Lipid peroxidation seems to be therefore conditioned by As accumulation in rice plants, particularly by the presence of high As(V) concentrations in the aerial part of the plants as a consequence of unregulated translocation from roots to shoots above a threshold concentration (1.25–2.5 mg L−1) in the growing media. These results provide relevant information regarding As(V) toxic concentrations for rice plants, highlight the importance of major As species analysis in plant tissues regarding As toxicity and contribute to better understand plants response to elevated As concentrations in the growing media.This work was supported by Fundación Séneca (Murcia Region) through the projects 19460/PI/14 and 19876/GERM/15-Excellence Project,and the Intramural-CSIC project 201840E107Peer reviewe

Reactive oxygen species homeostasis and circadian rhythms in plants

Elucidation of the molecular mechanisms by which plants sense and respond to environmental stimuli that influence their growth and yield is a prerequisite for understanding the adaptation of plants to climate change. Plants are sessile organisms and one important factor for their successful acclimation is the temporal coordination of the 24 h daily cycles and the stress response. The crosstalk between second messengers, such as Ca2+, reactive oxygen species (ROS), and hormones is a fundamental aspect in plant adaptation and survival under environmental stresses. In this sense, the circadian clock, in conjunction with Ca2+- and hormone-signalling pathways, appears to act as an important mechanism controlling plant adaptation to stress. The relationship between the circadian clock and ROS-generating and ROS-scavenging mechanisms is still not fully understood, especially at the post-transcriptional level and in stress situations in which ROS levels increase and changes in cell redox state occur. In this review, we summarize the information regarding the relationship between the circadian clock and the ROS homeostasis network. We pay special attention not only to the transcriptional regulation of ROS-generating and ROS-scavenging enzymes, but also to the few studies that have been performed at the biochemical level and those conducted under stress conditions.This work was supported by the Ministry of Science and Innovation (Spain) (‘Ramón y Cajal’ Fellowship awarded to MCM and MINECO/FEDER [BFU2017-86585-P] grant), the Séneca Foundation (Murcia, Spain) (Excellence Project [19876/GERM/15]), and the Ramón Areces Foundation (Spain

Response of antioxidative enzymes to plum pox virus in two apricot cultivars Authors

Recent evidence has indicated that activated oxygen species (AOS) may function as molecular signals in the induction of defence genes. In the present work, the response of antioxidative enzymes to the plum pox virus (PPV) was examined in two apricot (Prunus armeniaca L.) cultivars, which behaved differently against PPV infection. In the inoculated resistant cultivar (Goldrich), a decrease in catalase (CAT) as well as an increase in total superoxide dismutase (SOD) and dehydroascorbate reductase (DHAR) activities were observed. Ascorbate peroxidase (APX), glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR) did not change significantly in relation to non-inoculated (control) plants. In the susceptible cultivar (Real Fino), inoculation with PPV brought about a decrease in CAT, SOD and GR, whereas a rise in APX, MDHAR and DHAR activities was found in comparison to non-inoculated (control) plants. Apricot leaves contain only CuZn-SOD isozymes, which responded differently to PPV depending on the cultivar. Goldrich leaves contained 6 SODs and both SOD 1 and SOD 2 increased in the inoculated plants. In leaves from Real Fino, 5 SODs were detected and only SOD 5 was increased in inoculated plants. The different behaviour of SODs (H2O2-generating enzymes) and APX (an H2O2-remover enzyme) in both cultivars suggests an important role for H2O2 in the response to PPV of the resistant cultivar, in which no change in APX activity was observed. This result also points to further studies in order to determine if an alternative H2O2-scavenging mechanism takes place in the resistant apricot cultivar exposed to PPV. On the other hand, the ability of the inoculated resistant cultivar to induce SOD 1 and SOD 2 as well as the important increase of DHAR seems to suggest a relationship between these activities and resistance to PPV. This is the first report about the effect of PPV infection on the antioxidative enzymes of apricot plants. It opens the way for the further studies, which are necessary for a better understanding of the role of antioxidative processes in viral infection by PPV in apricot plants.Peer reviewe

Effect of salt stress on the superoxide dismutase activity in leaves of citrus limonum in different rootstock-scion combinations

5 pages, 2 tables, 1 figure.The effect of salinity on leaf superoxide dismutase (SOD) activity of lemon trees of different rootstock-scion combinations was studied. In leaves from Citrus limonum cv.Verna scions on Citrus macrophylla and C. reticulata rootstocks, salinity treatment clearly caused a significant depression in both Fe-SOD and Mn-SOD activities and an increase in Cu,Zn-SOD activity. However, in leaves from Citrus limonum on Citrus aurantium rootstook, the reduction observed in the activity values of Fe-SODs and Mn-SODs was not statistically significant. Salt stress also produced a decrease in the content of soluble proteins and chlorophylls. However, this drop was greater in C. limonum leaves on C. macrophylla than for other combinations.Peer reviewe

Dissecting the integrative antioxidant and redox systems in plant mitochondria. Effect of stress and S-nitrosylation

Mitochondrial respiration provides the energy needed to drive metabolic and transport processes in cells. Mitochondria are a significant site of reactive oxygen species (ROS) production in plant cells, and redox-system components obey fine regulation mechanisms that are essential in protecting the mitochondrial integrity. In addition to ROS, there are compelling indications that nitric oxide can be generated in this organelle by both reductive and oxidative pathways. ROS and reactive nitrogen species play a key role in signaling but they can also be deleterious via oxidation of macromolecules. The high production of ROS obligates mitochondria to be provided with a set of ROS scavenging mechanisms. The first line of mitochondrial antioxidants is composed of superoxide dismutase and the enzymes of the ascorbate-glutathione cycle, which are not only able to scavenge ROS but also to repair cell damage and possibly serve as redox sensors. The dithiol-disulfide exchanges form independent signaling nodes and act as antioxidant defense mechanisms as well as sensor proteins modulating redox signaling during development and stress adaptation. The presence of thioredoxin (Trx), peroxiredoxin (Prx) and sulfiredoxin (Srx) in the mitochondria has been recently reported. Cumulative results obtained from studies in salt stress models have demonstrated that these redox proteins play a significant role in the establishment of salt tolerance. The Trx/Prx/Srx system may be subjected to a fine regulated mechanism involving post-translational modifications, among which S-glutathionylation and S-nitrosylation seem to exhibit a critical role that is just beginning to be understood. This review summarizes our current knowledge in antioxidative systems in plant mitochondria, their interrelationships, mechanisms of compensation and some unresolved questions, with special focus on their response to abiotic stress.Peer reviewedPeer Reviewe

Response of Phragmites australis to increasing As(V) concentrations: Accumulation and speciation of As, and plant oxidative stress

The use of macrophytes has been proposed recently as a suitable option for the phytostabilization or rhizofiltration of soils or waters contaminated by trace elements. As one of the most representative species of this type of plant, common reed (Phragmites australis (Cav.) Trin. ex Steud.) has shown tolerance to high concentrations of potentially hazardous elements, as is the case of arsenic. However, a deeper knowledge of how these plants deal with this toxicity, including their oxidative response, is needed for the optimum utilization of this species in phytoremediation procedures. In fact, little is known about how common reed plants react to As toxicity or the tolerance limits and accumulation potential of this species. In this work, common reed plants were exposed to a range of As(V) mass concentrations (0.5–10 mg L) in a hydroponic experiment, and the performance of the plants (growth, photosynthetic pigments, and oxidative stress related parameters) was evaluated and related to the major As species present in the different parts of the plants. The plants did not show any apparent symptom of toxicity and no significant effects were found for any of the different plant parameters analyzed. Arsenic was mostly accumulated as As(III) in the roots of the plants, and almost no translocation to the aerial part of the plants was observed for any of the As species analyzed. Common reed has shown a high capacity for As accumulation in its roots with no signs of toxicity, despite small nutrient imbalances. Thus, it can be considered to be a good candidate for use in the rhizofiltration and phytostabilization of As contaminated waters and soils, respectively.This work was funded by the Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU), the Spanish Agencia Estatal de Investigación (AEI) and the European Regional Development Fund (FEDER Funds) through the projects RTI 2018-100819-BI00 and BFU 2017-86585-P and by the Fundación Séneca (Murcia, Spain) through the Excellence Project 19876/GERM/15. S. De Brasi-Velasco was supported by a FPI‐MINECO gran

Effect of oil refinery sludges on the growth and antioxidant system of alfalfa plants

7 Pags.- 6 Tabl.- 1 Fig.The refining process in the petrochemical industry generates oil refinery sludges, a potentially contaminating waste product, with a high content of hydrocarbons and heavy metals. Faster degradation of hydrocarbons has been reported in vegetated soils than in non-vegetated soils, but the impact of these contaminants on the plants physiology and on their antioxidant system is not well known. In this study, the effect of the addition of petroleum sludge to soil on the physiological parameters, nutrient contents, and oxidative and antioxidant status in alfalfa was investigated. An inhibition of alfalfa growth and an induction of oxidative stress, as indicated by an increase in protein oxidation, were found. Also, the superoxide dismutase isoenzymes, peroxidase, and those enzymes involved in the ascorbate–glutathione cycle showed significant activity increases, parallel to an enhancement of total homoglutathione, allowing plants being tolerant to this situation. This information is necessary to establish successful and sustainable plant-based remediation strategies.The research was financially supported by SÉNECA Foundation (project 00570/PI/04 and M.C. Martí fellowship, co-financed with SREF and FSE), by the Spanish Ministry of Science and Innovation (project AGL2007-61948, co-financed with FEDER), and the Aragón Government (group A03).Peer reviewe

Combination of soil organic and inorganic amendments helps plants overcome trace element induced oxidative stress and allows phytostabilisation

Trace element (TE)-contaminated soils require the improvement of their physico-chemical properties in order to allow their restoration through phytostabilization technologies. This study aimed to determine the usefulness of oxidative stress related parameters to validate the suitability of two different combinations of organic (solid fraction of pig slurry) and inorganic (paper mill sludge or a commercial red mud derivative) amendments for the phytostabilization of an acidic (4.2) TE-contaminated mine soil from SE Spain. Two wild species (Silybum marianum and Piptatherum miliaceum) were greenhouse cultivated and the development of the plants, their ionome, and oxidative stress related parameters were determined. Both amendment combinations increased significantly soil pH (to 5–6) and soil/pore water total organic C and total N concentrations, allowing an adequate plant growth and development (plants did not grow in untreated soils). The combination of amendments significantly reduced metal availability and showed to be effective (specially the one including the red mud derivative) in limiting shoot TE concentrations, which were all within common ranges (exclusion based tolerance of these species). Both protein carbonylation and lipid peroxidation were significantly higher in S. marianum plants from phytostabilized soils than in those from non-contaminated soils, which confirms the oxidative stress these plants suffer despite their satisfactory growth in the treated soils. P. miliaceum plants showed no differences between phytostabilized and non-contaminated soils. Therefore, the combination of amendments and TE-tolerant autochthonous species would be a suitable option for the phytostabilisation of soils contaminated by mining activities, reducing TE solubility and allowing an adequate plant growth.This work was financed by the Spanish Ministry of Economy and Competitiveness (previously Science and Innovation) and EU FEDER Funds through the project CTM2013-48697-C2-1-R, and by Fundación Séneca (Murcia Region) through the projects 19460/PI/14 and 19876/GERM/15-Excellence Project.Peer reviewe

Changes in photosynthetic parameters and antioxidant activities following heat-shock treatment in tomato plants

Seedlings of two tomato genotypes, Lycopersicon esculentum Mill. var. Amalia and the wild thermotolerant type Nagcarlang, were grown under a photoperiod of 16 h light at 25°C and 8 h dark at 20°C. At the fourth true leaf stage, a group of plants were exposed to a heat-shock temperature of 45°C for 3 h, and measurements of chlorophyll fluorescence, gas-exchange characteristics, dark respiration and oxidative and antioxidative parameters were made after releasing the stress. The heat shock induced severe alterations in the photosynthesis of Amalia that seem to mitigate the damaging impact of high temperatures by lowering the leaf temperature and maintaining stomatal conductance and more efficient maintenance of antioxidant capacity, including ascorbate and glutathione levels. These effects were not evident in Nagcarlang. In Amalia plants, a larger increase in dark respiration also occurred in response to heat shock and the rates of the oxidative processes were higher than in Nagcarlang. This suggests that heat injury in Amalia may involve chlorophyll photooxidation mediated by activated oxygen species (AOS) and more severe alterations in the photosynthetic apparatus. All these changes could be related to the more dramatic effect of heat shock seen in Amalia than in Nagcarlang plants.Peer reviewe