Search

Alfalfa is a model plant defined as less sensitive than others to iron (Fe) deficiency. In the present work, some mechanisms induced in low Fe availability conditions were studied, including the effect of inoculation of alfalfa seeds with Pseudomonas putida. The effect of different Fe contents in the nutrient solution on the growth parameters was evaluated at 3 and 10 days, observing that low Fe conditions promoted biomass accumulation. Activation in the mechanisms of Fe acquisition, through acidification of the media and an increase in the ferric chelate reductase (FCR) activity, was observed in the absence of Fe at 10 days. The presence of P. putida KT2442 in the rhizosphere eliminated FCR activation through the excretion of siderophores. The effect of the siderophores on the modulation of FCR activity was demonstrated using a ppsD mutant strain, unable to segregate them, observing an activation of the activity similar to that observed in the absence of the bacteria. This, together with the demonstrated mechanisms to increase Fe availability, contributed to the conclusion that alfalfa can be used for recovery programmes of soils with low Fe availability. [ABSTRACT FROM PUBLISHER]

Measurements of leaf stomatal conductance, leaf CO2 assimilation rate, leaf chlorophyll fluorescence, and a previously published biochemical model have been used to evaluate the thermo-tolerance of the photosynthetic apparatus in two tomato genotypes ('Amalia' and 'Nagcarlang'). The study was carried out as two experiments. In Experiment 1, a brief (20 min) increase in leaf temperature to 35°C reduced the photosynthetic rate of 'Amalia' leaves grown at 25°C, but stimulated photosynthesis in 'Nagcarlang', due to an increase in the maximum rate of carboxylation of ribulose-1,5- bisphosphate-carboxylase/oxygenase (VCmax). The heat-sensitive step in 'Amalia' seemed to be the maximum rate of electron transport (Jmax). However, in Experiment 2, there was no significant difference between Jmax at 25°C and 35°C when plants had been acclimatised to these temperatures. [ABSTRACT FROM AUTHOR]

Purification and characterisation of pepper ( Capsicum annuum L) chloroplasts and chromoplasts isolated from commercial green, red and yellow mature fruits were undertaken. Induction of the synthesis of several antioxidants in organelles isolated from mature fruits was found. The ultrastructure of organelles and the presence and activity of SOD isozymes and enzymes involved in the ASC-GSH cycle, together with the non-enzymatic antioxidant content and some oxidative parameters, were analysed. It was found that lipids, rather than proteins, seem to be a target for oxidation in the chromoplasts. The ascorbate and glutathione contents were elicited during differentiation of chloroplasts into chromoplasts in both red and yellow fruits. The activity of SOD and of components of the ASC-GSH cycle was up-regulated, suggesting that these enzymes may play a role in the protection of plastids and could act as modulators of signal molecules such as O2˙− and H2O2 during fruit maturation. The presence of an Mn-SOD in chromoplasts isolated from yellow pepper fruits was also investigated in terms of structural and antioxidant differences between the two cultivars. [ABSTRACT FROM AUTHOR]

In the current state of climate change, we must assume that abiotic stresses act together under natural field conditions, these will increase in the coming years. Therefore, in this report we investigated how sugar metabolism was affected under simulated field conditions, where plants faced high ambient temperatures and a low-quality water irrigation. Our studies were carried out on fruits of two tomato recombinant lines, a tolerant and a sensitive one exposed to the combination of heat and salinity. Two ripening stages (mature green and red ripe fruits) were used in our analyzes, where the gene expression levels of the main biosynthetic genes and transporters, enzymatic activities and compounds related to the synthesis, accumulation, and degradation of sugars in plants were analyzed. The tolerant line showed highly significant differences in red ripe fruits in comparison to the sensitive one under the simulated field conditions (35°C + 60 mM NaCl), with an overexpression of the genes SlFBP, SlSPS, SlSUS3, and SlNi. These expression patterns correlated with a higher activity of the enzymes FBP, SPS, SUS3, AI, and G6PDH, which resulted in the accumulation of fructose, glucose and UDP-glucose. Our results showed the advantage of using tomato recombinant lines for rescuing important traits, such as the resistance to some abiotic stresses, and for the identification of important molecular and metabolic markers that could be used to determine fruit quality in green or red maturity stages under detrimental environmental field conditions., (© 2021 Scandinavian Plant Physiology Society.)

In a changing environment, plants are able to acclimate to new conditions by regulating their metabolism through the antioxidant and redox systems involved in the stress response. Here, we studied a mitochondrial thioredoxin in wild-type (WT) Arabidopis thaliana and two Attrxo1 mutant lines grown in the absence or presence of 100 mM NaCl. Compared to WT plants, no evident phenotype was observed in the mutant plants under control condition, although they had higher number of stomata, loss of water, nitric oxide and carbonyl protein contents as well as higher activity of superoxide dismutase (SOD) and catalase enzymes than WT plants. Under salinity, the mutants presented lower water loss and higher stomatal closure, H 2 O 2 and lipid peroxidation levels accompanied by higher enzymatic activity of catalase and the different SOD isoenzymes compared to WT plants. These inductions may collaborate in the maintenance of plant integrity and growth observed under saline conditions, possibly as a way to compensate the lack of TRXo1. We discuss the potential of TRXo1 to influence the development of the whole plant under saline conditions, which have great value for the agronomy of plants growing under unfavorable environment., (© 2018 Scandinavian Plant Physiology Society.)

We present the first reported work that explores the potential of radiomics to predict patients who are at risk for developing immunotherapy-induced pneumonitis. Despite promising results with immunotherapies, immune-related adverse events (irAEs) are challenging. Although less common, pneumonitis is a potentially fatal irAE. Thus, early detection is critical for improving treatment outcomes; an urgent need to identify biomarkers that predict patients at risk for pneumonitis exists. Radiomics, an emerging field, is the automated extraction of high fidelity, high-dimensional imaging features from standard medical images and allows for comprehensive visualization and characterization of the tissue of interest and corresponding microenvironment. In this pilot study, we sought to determine whether radiomics has the potential to predict development of pneumonitis. We performed radiomic analyses using baseline chest computed tomography images of patients who did (N = 2) and did not (N = 30) develop immunotherapy-induced pneumonitis. We extracted 1860 radiomic features in each patient. Maximum relevance and minimum redundancy feature selection method, anomaly detection algorithm, and leave-one-out cross-validation identified radiomic features that were significantly different and predicted subsequent immunotherapy-induced pneumonitis (accuracy, 100% [p = 0.0033]). This study suggests that radiomic features can classify and predict those patients at baseline who will subsequently develop immunotherapy-induced pneumonitis, further enabling risk-stratification that will ultimately lead to better treatment outcomes.

The A-band of oxygen has been measured at low resolution at temperatures between 90 K and 373 K using the phase shift cavity ring down (PS-CRD) technique. For temperatures between 90 K and 295 K, the PS-CRD technique presented here involves an optical cavity attached to a cryostat. The static cell and mirrors of the optical cavity are all inside a vacuum chamber at the same temperature of the cryostat. The temperature of the cell can be changed between 77 K and 295 K. For temperatures above 295 K, a hollow glass cylindrical tube without windows has been inserted inside an optical cavity to measure the temperature of air flowing through the tube. The cavity consists of two highly reflective mirrors which are mounted parallel to each other and separated by a distance of 93 cm. In this experiment, air is passed through a heated tube. The temperature of the air flowing through the tube is determined by measuring the intensity of the oxygen absorption as a function of the wavenumber. The A-band of oxygen is measured between 298 K and 373 K, with several air flow rates. To obtain the temperature, the energy of the lower rotational state for seven selected rotational transitions is linearly fitted to a logarithmic function that contains the relative intensity of the rotational transition, the initial and final rotational quantum numbers, and the energy of the transition. Accuracy of the temperature measurement is determined by comparing the calculated temperature from the spectra with the temperature obtained from a calibrated thermocouple inserted at the center of the tube. This flowing air temperature sensor will be used to measure the temperatures of cooling air at the input (cold air) and output (hot air) after cooling the blades of a laboratory gas turbine. The results could contribute to improvements in turbine blade cooling design.

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 (Cys 174 ), but not the peroxidatic equivalent (Cys 52 ), in 2-Cys Prx. In contrast, GSSG was able to glutathionylate both peroxidatic (Cys 59 ) and resolving (Cys 84 ) 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.

Reactive oxygen species (ROS) are continually generated as a consequence of the normal metabolism in aerobic organisms. Accumulation and release of ROS into cell take place in response to a wide variety of adverse environmental conditions including salt, temperature, cold stresses and pathogen attack, among others. In plants, peroxidases class III, NADPH oxidase (NOX) locates in cell wall and plasma membrane, respectively, may be mainly enzymatic systems involving ROS generation. It is well documented that ROS play a dual role into cells, acting as important signal transduction molecules and as toxic molecules with strong oxidant power, however some aspects related to its function during plant-pathogen interactions remain unclear. This review focuses on the principal enzymatic systems involving ROS generation addressing the role of ROS as signal molecules during plant-pathogen interactions. We described how the chloroplasts, mitochondria and peroxisomes perceive the external stimuli as pathogen invasion, and trigger resistance response using ROS as signal molecule., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

Background and Aims: Reactive oxygen species (ROS), especially hydrogen peroxide, play a critical role in the regulation of plant development and in the induction of plant defence responses during stress adaptation, as well as in plant cell death. The antioxidant system is responsible for controlling ROS levels in these processes but redox homeostasis is also a key factor in plant cell metabolism under normal and stress situations. Thioredoxins (Trxs) are ubiquitous small proteins found in different cell compartments, including mitochondria and nuclei (Trxo1), and are involved in the regulation of target proteins through reduction of disulphide bonds, although their role under oxidative stress has been less well studied. This study describes over-expression of a Trxo1 for the first time, using a cell-culture model subjected to an oxidative treatment provoked by H2O2., Methods: Control and over-expressing PsTrxo1 tobacco (Nicotiana tabacum) BY-2 cells were treated with 35 mm H2O2 and the effects were analysed by studying the growth dynamics of the cultures together with oxidative stress parameters, as well as several components of the antioxidant systems involved in the metabolism of H2O2. Analysis of different hallmarks of programmed cell death was also carried out., Key Results: Over-expression of PsTrxo1 caused significant differences in the response of TBY-2 cells to high concentrations of H2O2, namely higher and maintained viability in over-expressing cells, whilst the control line presented a severe decrease in viability and marked indications of oxidative stress, with generalized cell death after 3 d of treatment. In over-expressing cells, an increase in catalase activity, decreases in H2O2 and nitric oxide contents and maintenance of the glutathione redox state were observed., Conclusions: A decreased content of endogenous H2O2 may be responsible in part for the delayed cell death found in over-expressing cells, in which changes in oxidative parameters and antioxidants were less extended after the oxidative treatment. It is concluded that PsTrxo1 transformation protects TBY-2 cells from exogenous H2O2, thus increasing their viability via a process in which not only antioxidants but also Trxo1 seem to be involved., (© The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Pepper fruits in green and red maturation stages were selected to study the protein pattern modified by oxidation measuring carbonylated proteins in isolated mitochondria, together with the accumulation of superoxide radical and hydrogen peroxide in the fruits. MALDI-TOF/TOF analysis identified as carbonylated proteins in both green and red fruits, formate dehydrogenase, NAD-dependent isocitrate dehydrogenase, porin, and defensin, pointing to a common regulation by carbonylation of these proteins independently of the maturation stage. However, other proteins such as glycine dehydrogenase P subunit and phosphate transporter were identified as targets of carbonylation only in green fruits, whereas aconitase, ATPase β subunit, prohibitin, orfB protein, and cytochrome C oxidase, were identified only in red fruits. In general, the results suggest that carbonylation of mitochondrial proteins is a PTM that drives the complex ripening process, probably establishing the accumulation and functionality of some mitochondrial proteins in the nonclimacteric pepper fruit., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Peroxiredoxins (Prxs) have emerged as important factors linking reactive oxygen species (ROS) metabolism to redox-dependent signaling events. Together with ROS, nitric oxide (NO) is a free radical product of the cell metabolism that is essential in the signal transduction. S-Nitrosylation is emerging as a fundamental protein modification for the transduction of NO bioactivity. Using recombinant pea mitochondrial PsPrxII F (PrxII F), the effect of S-nitrosoglutathione (GSNO) and sodium nitroprusside dehydrate (SNP), which are known to mediate protein S-nitrosylation processes, was studied. S-Nitrosylation of the PrxII F was demonstrated using the biotin switch method and LC ESI-QTOF tandem MS analysis. S-nitrosylated PrxII F decreased its peroxidase activity and acquired a new transnitrosylase activity, preventing the thermal aggregation of citrate synthase (CS). For the first time, we demonstrate the dual function for PrxII F as peroxidase and transnitrosylase. This switch was accompanied by a conformational change of the protein that could favor the protein-protein interaction CS-PrxII F. The observed in vivo S-nitrosylation of PrxII F could probably function as a protective mechanism under oxidative and nitrosative stress, such as occurs under salinity. We conclude that we are dealing with a novel regulatory mechanism for this protein by NO., Biological Significance: S-Nitrosylation is a post-translational modification that is increasingly viewed as fundamental for the signal transduction role of NO in plants. This study demonstrates that S-nitrosylation of the mitochondrial peroxiredoxin PrxII F induces a conformational change in the protein and provokes a reduction in its peroxidase activity, while acquiring a novel function as transnitrosylase. The implication of this mechanism will increase our understanding of the role of posttranslational modifications in the protein function in plants under stress situations such as salinity, in which NO could act as signaling molecule., (Copyright © 2015 Elsevier B.V. All rights reserved.)

S-nitrosylation is emerging as a key post-translational protein modification for the transduction of NO as a signaling molecule in plants. This data article supports the research article entitled "Functional and structural changes in plant mitochondrial PrxII F caused by NO" [1]. To identify the Cys residues of the recombinant PrxII F modified after the treatment with S-nitrosylating agents we performed the LC ESI-QTOF tandem MS and MALDI peptide mass fingerprinting analysis. Change in A 650 nm was monitored to estimate the thermal aggregation of citrate synthase in the presence S-nitrosylated PrxII F. The effect of the temperature on the oligomerization pattern and aggregation of PrxII F was analysed by SDS-PAGE and changes in absorbance at 650 nm, respectively.

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.

Together with reactive oxygen species, nitric oxide is an essential part of the signal transduction induced by stress conditions. In this work we study the pattern of S-nitrosylated proteins from mitochondria of pea plants subjected to 150mM NaCl for 5 and 14days. A differential pattern of target proteins was found during plant development and salt stress, with a minor number of S-nitrosylated proteins at 14 days specifically some key enzymes related to respiration and photorespiration. At this time of stress, only ATP synthase β subunit, peroxiredoxin and Hsp90 were S-nitrosylated and no changes in protein levels were observed, although the activity of PrxII F may be reduced by S-nitrosylation. The NADH/NAD(+) ratio was also high at 14days but not the NADPH/NADP(+). An enhancement in NO measured by fluorimetry and confocal microscopy was observed in leaves, being part of the NO localized in mitochondria. An increase in mitochondrial GSNOR activity was produced in response to short and long-term NaCl treatment, where a higher number of nitrated proteins were also observed. The results indicated that posttranslational modifications seem to modulate respiratory and photorespiratory pathways, as well as some antioxidant enzymes, through differential S-nitrosylation/denitrosylation in control conditions and under salt stress., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Nitric oxide (NO) has emerged as an important signaling molecule in plants, but little is known about the effects of reactive nitrogen species in plant mitochondria. In this study, the effects of DETA-NONOate, a pure NO slow generator, and of SIN-1 (3-morpholinosydnonimine), a peroxynitrite producer, on the activities of respiratory pathways, enzymatic and non-enzymatic antioxidants have been investigated in isolated mitochondria from pea leaves. No significant changes in lipid peroxidation, protein oxidation or in ascorbate and glutathione redox state were observed after DETA-NONOate treatments whereas cytochrome pathway (CP) respiration was reversibly inhibited and alternative pathway (AP) respiration showed little inhibition. On the other hand, NO did not affect neither activities of Mn superoxide dismutase (Mn-SOD) nor enzymes involved in the ascorbate and glutathione regeneration in mitochondria except for ascorbate peroxidase (APX), which was reversely inhibited depending on ascorbate concentration. Finally, SIN-1 treatment of mitochondria produced a decrease in CP respiration, an increase in protein oxidation and strongly inhibited APX activity (90%), with glutathione reductase and dehydroascorbate reductase (DHAR) being moderately inhibited (30 and 20%, respectively). This treatment did not affect monodehydroascorbate reductase (MDHAR) and Mn-SOD activities. Results showed that mitochondrial nitrosative stress was not necessarily accompanied by oxidative stress. We suggest that NO-resistant AP and mitochondrial APX may be important components of the H(2) O(2) -signaling pathways under nitrosative stress induced by NO in this organelle. Also, MDHAR and DHAR, via ascorbate regeneration, could constitute an essential antioxidant defense together with Mn-SOD, against NO and ONOO(-) stress in plant mitochondria., (Copyright © Physiologia Plantarum 2012.)

Pepper (Capsicum annuum L.) fruits are highly appreciated by producers and consumers for their economical and nutritional value. Four different cultivars of coloured peppers in immature and mature stages were harvested throughout the spring and examined for their content of phenolic compounds, ascorbic acid and total antioxidant capacity (TAA) as well as for lipid peroxidation and carbonyl proteins as index of oxidative stress. Ripening and harvest period influenced the antioxidants and the development of oxidative processes in the cultivars differently: lipid peroxidation increased in mature peppers except in one cultivar (Y1075), while no changes in protein oxidation or in TAA were produced, except in Y1075 in which both parameters increased. Each cultivar presented differences in antioxidant compounds depending on the harvest period, but we could recommend May as the optimal if all cultivars have to be harvested at the same time, when levels of ascorbate, phenols and TAA were not decreased, fresh weight and proteins were elevated, and levels of oxidation were not as high as in June (except for Y1075). A previous study of the response of each cultivar to different environmental conditions results essential to establish a good program of selection of cultivars with high quality and productivity.

Mitochondria play an essential role in reactive oxygen species (ROS) signal transduction in plants. Redox regulation is an essential feature of mitochondrial function, with thioredoxin (Trx), involved in disulphide/dithiol interchange, playing a prominent role. To explore the participation of mitochondrial PsTrxo1, Mn-superoxide dismutase (Mn-SOD), peroxiredoxin (PsPrxII F), and alternative oxidase (AOX) under salt stress, their transcriptional and protein levels were analysed in pea plants growing under 150 mM NaCl for a short and a long period. The activities of mitochondrial Mn-SOD and Trx together with the in vivo activities of the alternative pathway (AP) and the cytochrome pathway (CP) were also determined, combined with the characterization of the plant physiological status as well as the mitochondrial oxidative indicators. The analysis of protein and mRNA levels and activities revealed the importance of the post-transcriptional and post-translational regulation of these proteins in the response to salt stress. Increases in AOX protein amount correlated with increases in AP capacity, whereas in vivo AP activity was maintained under salt stress. Similarly, Mn-SOD activity was also maintained. Under all the stress treatments, photosynthesis, stomatal conductance, and CP activity were decreased although the oxidative stress in leaves was only moderate. However, an increase in lipid peroxidation and protein oxidation was found in mitochondria isolated from leaves under the short-term salinity conditions. In addition, an increase in mitochondrial Trx activity was produced in response to the long-term NaCl treatment. The results support a role for PsTrxo1 as a component of the defence system induced by NaCl in pea mitochondria, providing the cell with a mechanism by which it can respond to changing environment protecting mitochondria from oxidative stress together with Mn-SOD, AOX, and PrxII F.

The effects of an oligogalacturonic acid (OGA) pool on root length of intact alfalfa seedlings (Medicago sativa L.), on extracellular pH and on both extracellular and intracellular O₂⁻ dynamics were examined in this study. Lower OGA concentrations (25, 50 and 75 μg mL⁻¹)promoted root length, but 50 μg mL⁻¹ had a stronger effect in promoting growth, while the higher OGA concentration (100 μg mL⁻¹)had no significant effect. Extracellular alkalinization was tested only at concentrations higher than 50 μg mL⁻¹ OGA, showing that the response is determined not only by the specific size of OGA, but also by the concentration of OGA. The promoting effect of OGA on root growth at 25, 50 and 75 μg mL⁻¹ OGA concentrations in alfalfa root appeared to be unrelated to extracellular alkalinization. A possible explanation could be the induction of an O₂⁻ burst at non-toxic levels, which could drive directly or indirectly several processes associated with root elongation in 25, 50 and 75 μg mL⁻¹ OGA-treated seedlings. Analyses using confocal microscopy showed that the increase in the O₂⁻ generation, mainly in the epidermal cells, induced by 50 μg mL⁻¹ OGA could be related to the promoting effect on root growth. The combination of OGA with DPI allowed us to demonstrate that there are different O₂⁻-generating sources in the epidermal cells of the meristematic zone, likely NADPH oxidase and oxidases or oxido-reductase enzymes, insensitive to DPI, that maintain detectable O₂⁻ accumulation at 60 and 120 min of treatment. These results suggest that OGA induce an oxidative burst by several O₂⁻-generating sources in the active growth zones., (Copyright © 2010 Elsevier GmbH. All rights reserved.)

Peach fruits were selected to study the protein pattern and antioxidant system as well as oxidative parameters such as superoxide radical and hydrogen peroxide accumulation, at two maturity stages, which were chosen for being suitable for the processing industry and fresh consumption. The proteins phosphoenolpyruvate carboxylase, sucrose synthase, and 1-aminocyclopropane-1-carboxylate oxidase, as well as the antioxidants glutathione synthetase and ascorbate peroxidase, appeared as new in the mature peach fruits. Activities of superoxide dismutase (SOD) and components of the ascorbate-glutathione cycle were also measured to explore their role in the two maturity stages studied. Changes in the SOD isoenzyme pattern and an increase in the activities of ascorbate peroxidase, monodehydroascorbate reductase, and glutathione reductase were observed in mature fruits, revealing an efficient system to cope with the oxidative process accompanying ripening.

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.

Seedlings of Lycopersicon esculentum Mill. var. Amalia were grown in a growth chamber under a photoperiod of 16 h light at 25 degrees C and 8 h dark at 20 degrees C. Five different treatments were applied to 30-day-old plants: Control treatment (plants maintained in the normal growth conditions throughout the experimental time), heat acclimation (plants exposed to 35 degrees C for 4 h in dark for 3 days), dark treatment (plants exposed to 25 degrees C for 4 h in dark for 3 days), heat acclimation plus heat shock (plants that previously received the heat acclimation treatment were exposed to 45 degrees C air temperature for 3 h in the light) and dark treatment plus heat shock (plants that previously received the dark treatment were exposed to 45 degrees C air temperature for 3 h in the light). Only the heat acclimation treatment increased the thermotolerance of the photosynthesis apparatus when the heat shock (45 degrees C) was imposed. In these plants, the CO(2) assimilation rate was not affected by heat shock and there was a slight and non-significant reduction in maximum carboxylation velocity of Rubisco (V(cmax)) and maximum electron transport rate contributing to Rubisco regeneration (J(max)). However, the plants exposed to dark treatment plus heat shock showed a significant reduction in the CO(2) assimilation rate and also in the values of V(cmax) and J(max). Chlorophyll fluorescence measurements showed increased thermotolerance in heat-acclimated plants. The values of maximum chlorophyll fluorescence (F(m)) were not modified by heat shock in these plants, while in the dark-treated plants that received the heat shock, the F(m) values were reduced, which provoked a significant reduction in the efficiency of photosystem II. A slight rise in the total superoxide dismutase (SOD) activity was found in the plants that had been subjected to both heat acclimation and heat shock, and this SOD activity was significantly higher than that found in the plants subjected to dark treatment plus heat shock. The activity of Fe-SOD isoenzymes was most enhanced in heat-acclimated plants but was unaltered in the plants that received the dark treatment. Total CuZn-SOD activity was reduced in all treatments. Darkness had an inhibitory effect on the Mn-SOD isoenzyme activity, which was compensated by the effect of a rise in air temperature to 35 degrees C. These results show that the heat tolerance of tomatoplants may be increased by the previous imposition of a moderately high temperature and could be related with the thermal stability in the photochemical reactions and a readjustment of V(cmax) and J(max). Some isoenzymes, such as the Fe-SODs, may also play a role in the development of heat-shock tolerance through heat acclimation. In fact, the pattern found for these isoenzymes in heat-acclimated Amalia plants was similar to that previously described in other heat-tolerant tomato genotypes.

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.

The functional activities of the photosynthetic apparatus of two tomato cultivars of different thermotolerance were investigated after a short period of high temperature treatment. Seedlings of two tomato genotypes, Lycopersicon esculentum var. Campbell-28 and the wild thermotolerant Nagcarlang, were grown under a photoperiod of 16h at 25 degrees C and dark period of 8h at 20 degrees C. At the fourth true leaf stage, a group of plants was exposed to heat stress of 45 degrees C for 2 h. The heat shock treatment caused important reductions of the net photosynthetic rate (Pn) of Campbell-28 plants due to non-stomatal components. These non-stomatal effects were not evident in Nagcarlang-treated plants. This reduction in the CO2 assimilation rate observed in Campbell-28 was generated by affections in the Calvin cycle and also in the PSII functioning. No changes in these parameters were observed in the thermotolerant genotype after the stress. Injury to the plasma membrane because of the heat stress was evident only in the Campbell-28 genotype. Heat led to a sun-type adaptation response of the photosynthesis pigment apparatus for the Nagcarlang genotype, but not for Campbell-28, and thus an increase in chlorophyll a/b ratio and a decrease in chlorophyll/carotenoid ratio were shown in Nagcarlang stressed plants.