Glutathione Status and Protein Synthesis during Drought and Subsequent Rehydration in Tortula ruralis

Glutathione status and its relationship to protein synthesis during water deficit and subsequent rehydration have been examined in the drought-tolerant moss, Tortula ruralis. During slow drying there is a small decrease in total glutathione but the percentage of oxidized glutathione (GSSG) increases. During rapid drying there is little change in total glutathione but a small increase in GSSG. On rehydration of slowly dried moss, GSSG rapidly declines to normal level. But when rapidly dried moss is rehydrated, there is an immediate, sharp increase in GSSG as a percentage of total glutathione. After 2 hours of rehydration GSSG starts declining and reaches a normal level in about 6 hours. When an increasing degree of steady state water deficit is imposed on the moss tissue with polyethylene glycol 6000, there is a progressive decrease in protein synthesis but an increase in oxidized glutathione. When 5 millimolar GSSG is supplied exogenously during rehydration of rapidly dried or slowly dried moss, protein synthesis is strongly inhibited. In vitro protein synthesis supported by moss mRNA is also inhibited by more than 85% by 150 micromolar GSSG. The role of glutathione status in water deficit-induced inhibition of protein synthesis is discussed.     

Effect of cadmium on antioxidative enzymes,glutathione content,and glutathionylation in tall fescue

The aim of this work was to assess the effect of different Cd2+concentrations on some antioxidant enzymes in Festuca arundinacea. Increased activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione S-transferase, and glutathione reductase were ascertained in response to low Cd²⁺ concentrations (0–20 μM), whereas the enzyme activities were less increased or decreased at a higher Cd²⁺ dosage (50 μM) and a longer exposure. The content of reduced glutathione (GSH) decreased significantly with increasing Cd²⁺ concentrations, whereas the content of oxidized glutathione (GSSG) increased proportionally to the amount of Cd²⁺ applied. Further experiments, performed by incubating the enzyme extracts with oxidized glutathione, evidenced that the addition of GSSG to the incubation mixtures caused significant decreases of some enzymatic activities. Finally, the effect of glutathione S-transferase, FaGST I, extracted from fescue seedlings and purified till homogeneity, on these enzyme activities was investigated. It was found that FaGST I enhanced the decreased enzymatic activities caused by GSSG.     

Arsenite treatment induces oxidative stress,upregulates antioxidant system,and causes phytochelatin synthesis in rice seedlings

The effects of arsenite treatment on generation of reactive oxygen species, induction of oxidative stress, response of antioxidative system, and synthesis of phytochelatins were investigated in two indica rice (Oryza sativa L.) cvs. Malviya-36 and Pant-12 grown in sand cultures for a period of 5–20 days. Arsenite (As₂O₃; 25 and 50 μM) treatment resulted in increased formation of superoxide anion (O₂^.−), elevated levels of H₂O₂ and thiobarbituric acid reactive substances, showing enhanced lipid peroxidation. An enhanced level of ascorbate (AA) and glutathione (GSH) was observed irrespective of the variation in the level of dehydroascorbate (DHA) and oxidized glutathione (GSSG) which in turn influenced redox ratios AA/DHA and GSH/GSSG. With progressive arsenite treatment, synthesis of total acid soluble thiols and phytochelatins (PC) increased in the seedlings. Among antioxidative enzymes, the activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), total ascorbate peroxidase (APX, EC 1.11.1.11), chloroplastic ascorbate peroxidase, guaiacol peroxidase (EC 1.11.1.7), monodehydroascorbate reductase (EC 1.6.5.4), and glutathione reductase (EC 1.6.4.2) increased in arsenite treated seedlings, while dehyroascorbate reductase (EC 1.8.5.1) activity declined initially during 5–10 days and increased thereafter. Results suggest that arsenite treatment causes oxidative stress in rice seedlings, increases the levels of many enzymatic and non-enzymatic antioxidants, and induces synthesis of thiols and PCs, which may serve as important components in mitigating arsenite-induced oxidative damage.     

Changes in ascorbate, glutathione, and related enzyme activities during thidiazuron-induced bud break of apple

The changes of ascorbic acid, dehydroascorbic acid, and glutathione content and related enzyme activities were studied in apple buds during dormancy and thidiazuron-induced bud break. An increase in ascorbic acid, reduced form of glutathione (GSH), total glutathione, total non-protein thiol (NPSH) and non-glutathione thiol (RSH) occurred as a result of induction by thidiazuron during bud break, whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased during the same period. Thidiazuron also enhanced the ratio of GSH/GSSG, and activities of ascorbate free radical reductase (AFR; EC 1.6.5.4), ascorbate peroxidase (EC 1.11.1.11). dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2). The ascorbic acid content and the activities of AFR, ascorbate peroxidase, and DHAR peaked when buds were in the side green or green tip stage just prior to the start of rapid expansion, and declined thereafter. The GSH, NPSH, RSH, ratio of GSH/GSSG, and activities of GR increased steadily during bud development.     

Protein Synthesis during Rehydration of Rapidly Dried Tortula ruralis: Evidence for Oxidation Injury

Rapidly dried Tortula ruralis, a drought-tolerant moss, is known to synthesize proteins on rehydration at a much lower rate than the slowly dried moss. The reasons for this low rate of protein synthesis are unclear. We have found that during rehydration of rapidly dried moss, there is a negative correlation between the rate of protein synthesis and the tissue levels of oxidized glutathione (GSSG) and lipid peroxidation. When rapidly dried moss, which is known to show extensive solute leakage, is rehydrated in the presence of 100 millimolar K⁺, 5 millimolar Mg²⁺, 1 millimolar ATP, and 1 millimolar GTP, either separately or together, there is no stimulation of protein synthesis. When it is hydrated in the presence of either 5 millimolar glucose-6-phosphate or 0.1 millimolar NADPH, protein synthesis is stimulated but the stimulation is transitory. A second addition of either of these two chemicals causes a second transient stimulation of protein synthesis. A transitory decrease in the rate of GSSG accumulation is observed during rehydration in the presence of glucose-6-phosphate or NADPH. Both glucose-6-phosphate and NADPH are known to reverse GSSG-induced inhibition of protein synthesis in rabbit reticulocyte lysate. Results of the present study suggest that the rate of protein synthesis during rehydration of rapidly dried moss is not limited by the availability of ions or energy sources. Since exogenously applied GSSG has been shown to inhibit in vivo and in vitro protein synthesis and since it is known to accumulate during rehydration of rapidly dried, but not slowly dried, moss, it is suggested that the low rate of protein synthesis during rehydration of the rapidly dried moss is, at least in part, due to endogenous GSSG.     

Magnesium deficiency and high light intensity enhance activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase in bean leaves

The influence of varied Mg supply (10-1000 micromolar) and light intensity (100-580 microeinsteins per square meter per second) on the concentrations of ascorbate (AsA) and nonprotein SH-compounds and the activities of superoxide dismutase (SOD; EC 1.15.11) and the H₂O₂ scavenging enzymes, AsA peroxidase (EC 1.11.1.7), dehydroascorbate reductase (EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2) were studied in bean (Phaseolus vulgaris L.) leaves over a 13-day period. The concentrations of AsA and SH-compounds and the activities of SOD and H₂O₂ scavenging enzymes increased with light intensity, in particular in Mg-deficient leaves. Over the 12-day period of growth for a given light intensity, the concentrations of AsA and SH-compounds and the activities of these enzymes remained more or less constant in Mg-sufficient leaves. In contrast, in Mg-deficient leaves, a progressive increase was recorded, particularly in concentrations of AsA and activities of AsA peroxidase and glutathione reductase, whereas the activities of guaiacol peroxidase and catalase were only slightly enhanced. Partial shading of Mg-deficient leaf blades for 4 days prevented chlorosis, and the activities of the O₂^.− and H₂O₂ scavenging enzymes remained at a low level. The results demonstrate the role of both light intensity and Mg nutritional status on the regulation of O₂^.− and H₂O₂ scavenging enzymes in chloroplasts.     

Ability of lupine seeds to germinate and to tolerate desiccation as related to changes in free radical level and antioxidants in freshly harvested seeds

Seeds of yellow lupine (Lupinus luteus L. cv. Juno) were collected throughout their development on the mother plant to determine whether the ability to germinate and to tolerate desiccation is related to the level of free radicals and the changes in the redox state of ascorbate and glutathione as well as the activities of antioxidative enzymes. Electron paramagnetic resonance (EPR)-based analyses showed that development of lupine seed was accompanied by generation of free radicals with g₁ and g₂ values of 2.0049 ± 0.0004 and 2.0029 ± 0.0003, respectively. Free radical level increased significantly 25 DAF and decreased thereafter. The amount of hydrogen peroxide was high in fresh immature seeds and decreased during maturation drying. Ascorbate accumulated in lupine embryos during early seed filling stage whereas glutathione content increased during late seed filling phase. During maturation drying the redox state of both ascorbate and glutathione pools shifted towards the oxidized forms. While superoxide dismutase (SOD, EC 1.15.1.1), and ascorbate peroxidase (APX, EC 1.11.1.11) activities remained high at the early seed filling stage the activities of both dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) and that of catalase (CAT, EC 1.11.1.6) increased before seeds reached physiological maturity and decreased thereafter. The changes of isoform patterns of antioxidative enzymes were observed during seed maturation. Immature lupine seeds tested immediately after harvest acquired the ability to germinate when less than half-filled and reached high tolerance to desiccation just after physiological maturity. The physiological implications of the changes in antioxidative machinery for the acquisition of desiccation tolerance and seeds germinability are discussed.     

Effects of ambient oxygen and of fixed nitrogen on concentrations of glutathione, ascrobate, and associated enzymes in soybean root nodules

Soybean (Glycine max [L.] Merr.) root nodules contain the enzymes of the ascorbate-glutathione cycle for defense against activated forms of oxygen. Nodulated roots of hydroponically grown soybean plants were exposed to atmospheres containing 2, 21, 50, or alternating 21 and 50 kilopascals of O₂. The activities of ascorbate (ASC) peroxidase, monodehydroascorbate (MDHA) reductase, dehydroascorbate (DHA) reductase, and glutathione (GSSG) reductase were higher in nodules exposed to high pO₂. Nodule contents of ascorbate and reduced glutathione were also greater in the high pO₂ treatments. Treatment of nodulated plants with fixed nitrogen (urea) led to concomitant decreases in acetylene reduction activity, in leghemoglobin content, and in activities of ASC peroxidase, DHA reductase, and GSSG reductase. Activity of MDHA reductase and glutathione concentrations in nodules were not affected by treatment with urea. The enzymes of the ascorbate-glutathione cycle were also detected in uninfected soybean roots, although at levels substantially below those in nodules. These observations indicate that the ascorbate-glutathione cycle can adjust to varying physiological conditions in nodules and that there is a key link between N₂ fixation and defenses against activated forms of oxygen.     

Effect of zinc nutritional status on activities of superoxide radical and hydrogen peroxide scavenging enzymes in bean leaves

The effect of varied zinc (Zn) supply on the activities of superoxide dismutase (SOD), ascorbate (AsA) peroxidase, glutathione (GSSG) reductase, catalase and guaiacol peroxidase was studied in leaves of bean (Phaseolus vulgaris) plants grown for 15 days in nutrient solution. Zinc deficiency severely decreased plant growth and the leaf concentrations of soluble protein and chlorophyll. Resupply of Zn to deficient plants for up to 72h restored protein concentrations more rapidly than chlorophyll and plant growth. With the exception of guaiacol peroxidase, the activities of all enzymes were significantly decreased by Zn deficiency, in particular GSSG reductase and SOD. Within 72h of resupplying Zn to deficient plants, the enzyme activities reached the level of the Zn sufficient plants. The results indicate severe impairment in the ability of Zn-deficient leaves to enzymically scavenge O₂ ^- and H₂O₂. Consequences and reasons of this impairment are discussed in terms of photooxidation of chloroplast pigments and inhibition of the biosynthesis of the related scavenger enzyme proteins.     

Effect of Isoproterenol Administration on Rat Heart Glutathione Status

The intraperitoneal administration of 3, 10 and 80 mg/Kg isoproterenol produced in the cardiac muscle a dose dependent increase of GSH content and a slight elevation of GSSG content. In addition, the treatment with the catecholamine at the doses of 3 and 10 mg/Kg produced a slight decrease of the mixed glutathione disulfides level, whilst at the dose of 80 mg/Kg, this effect was more pronounced. These changes were not accompanied by modifications of the activities of the enzymes glutathione peroxidase, glutathione reductase and glutathione S-transferase.     

Influence of estrogen on glutathione levels and glutathione-metabolizing enzymes in uteri and R3230AC mammary tumors of rats

The glutathione content and the activities of several enzymes in its metabolism, glutathione reductase, glutathione peroxidase and γ-glutamyl transpeptidase, were assayed in uteri obtained from estrogen-treated rats and in R3230AC mammary adenocarcinomas obtained from ovariectomized, intact and estrogen-treated hosts. Normal mammary glands, obtained 10–12 days post-partum, were also examined for these parameters.A daily pharmacological dose of 0.4 μg of estradiol-17β induced a maximal increase in uterine weight and in reduced glutathione (GSH); higher doses of estrogen did not significantly increase either of these parameters. Levels of oxidized glutathione (GSSG) were comparable in both estrogen-treated and untreated rats. The time course of the estrogen-induced uterotrophic response was associated with increases in glutathione reductase, glutathione peroxidase and γ-glutamyl transpeptidase activities with the increased GSH level preceding the increase in uterine weight. Compared to neoplasms from intact or ovariectomized animals, tumors from estrogen-treated hosts exhibited significant decreases in levels of GSSG and GSH, as well as in glutathione reductase and glutathione peroxidase activities, but demonstrated a significant elevation of γ-glutamyl transpeptidase activity. Normal glands from lactating rats had decreased GSH levels, lower activities of glutathione reductase and glutathione peroxidase, but elevated γ-glutamyl transpeptidase activity versus tumors from intact rats. Tumors from estrogen-treated rats more closely resembled mammary glands during lactation. The divergent growth responses elicited by estrogen in the uterus and mammary tumor are correlated with the observed changes in GSH levels and enzymes involved in glutathione metabolism.     

Parameters related to oxygen free radicals in erythrocytes,plasma and epidermis of the hairless rat

The following parameters related to oxygen free radicals (OFR) were determined in erythrocytes and the epidermis of hairless rats: catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), reduced (GSH) and oxidized (GSSG) glutathione, glutathione S-transferase (GST), superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS). GSH, GSSG and TBARS were also analyzed in plasma. In erythrocytes, the Pearson correlation coefficients (r) were significant (p < 0.001) between glutathione and other parameters as follows: GSH correlated negatively with GSSG (r = -0.665) and TBARS (r = -0.669); GSSG correlated positively with SOD (r = 0.709) and TBARS (r = 0.752). Plasma GSSG correlated negatively with erythrocytic thermostable GST activity (r = -0.608; p=0.001) and with erythrocytic total GST activity (r = -0.677; p < 0.001). In epidermis (p < 0.001 in all cases), GSH content correlated with GSSG (r = 0.682) and with GPx (r = 0.663); GSSG correlated with GPx (r = 0.731) and with GR (r = 0.794). By multiple linear regression analysis some predictor variables (R(2)) were found: in erythrocytes, thermostable GST was predicted by total GST activity and GSSG, GSSG content was predicted by GSH and by the GSH/GSSG ratio and GPx activity was predicted by GST, CAT and SOD activities; in epidermis, GSSG was predicted by GR and SOD activities and GR was predicted by GSSG, TBARS and GPx. It is concluded that the hairless rat is a good model for studying OFR-related parameters simultaneously in blood and skin, and that it may provide valuable information about other animals under oxidative stress.     

Changes in antioxidative enzymes in cucumber cotyledons during natural senescence: comparison with those during dark-induced senescence

Changes in 7 antioxidative enzymes in naturally senescent cotyledons of cucumber ( Cucumis sativus ) were investigated. The activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (EC 1.11.1.6), dehydroascorbate reductase (EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2) gradually decreased during the progression of senescence, while those of ascorbate peroxidase (APX; EC 1.11.1.11) and guaiacol peroxidase (GPX; EC 1.11.1.7) gradually increased. The activity of monodehydroascorbate reductase (MDAR; EC 1.6.5.4) was not significantly changed. Western blot analysis showed that the protein level of mitochondrial SOD gradually declined. The protein level of catalase transiently decreased and then increased in the later stages of senescence, despite the decrease in its activity. The overall behavior was markedly different from that found in cotyledons of artificially senescing seedlings transferred into darkness; the activities of SOD, catalase, APX, GPX and GR gradually increased.     

Evaluation of radical scavenging system in two microalgae in response to interactive stresses of UV-B radiation and nitrogen starvation

The effects of UV-B radiation and/or deprivation of nitrogen stresses on growth rate, some antioxidant compounds, and activities of some antioxidant enzymes, superoxide dismutase (SOD; EC1.15.1.1), ascorbate peroxidase (APx; EC1.11.1.11), guaiacol peroxidase (GUPx; EC1.11.1.7) and glutathione reductase (GR, EC 1.6.4.2), as well as the levels of total glutathione pool, UV-B absorbing pigments, malondialdehyde (MDA) and H₂O₂ concentrations were studied in Spirulina platensis and Dunaliella salina. Less damage was observed in response to the combined UV-B and nitrogen deprivation as shown by growth rate and photosynthetic pigments especially in Dunaliella salina. A significant increase in flavonoids and phenolics under dual stress was observed. Conversely, a great reduction in malondialdehyde (MDA) and H₂O₂ concentrations were recorded under the combined stress compared to the effect of each stress. Furthermore, a significant increase in GSH/GSSG ratio toward the control was recorded in response to combined stresses, whereas a significant reduction in this ratio was observed in both microalgae in response to each stress. Increased activities of antioxidant enzymes were recorded under UV-B and nitrogen deprivation stresses.     

Erythrocyte antioxidants in aging and dementia

Age of patients and oxidative stress in brain cells may contribute to pathogenesis of Alzheimer’s disease (AD). Erythrocytes (red blood cells, RBC) are considered as passive “reporter cells” for the oxidative status of the whole body and remain poorly investigated in AD. The aim of this study was to assess whether the antioxidant status of RBC changes in aging and AD. Blood was taken from AD and non-Alzheimer’s dementia patients, aged-matched and younger controls. The antioxidant status of RBC was evaluated in each person participated in the study by measuring levels of H₂O₂, organic hydroperoxides, glutathione (GSH) and glutathione disulfide (GSSG), activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione S-transferase, and glucose-6-phosphate dehydrogenase. In both aging and dementia, oxidative stress in RBC was shown to increase as evidenced by elevated concentrations of H₂O₂, organic hydroperoxides, decreased GSH/GSSG ratio, and decreased glutathione S-transferase activity. Decreased glutathione peroxidase activity in RBC may be considered as a new peripheral marker for Alzheimer’s disease while changes of other parameters of oxidative stress reflect age-related events.     

Properties and physiological function of a glutathione reductase purified from spinach leaves by affinity chromatography

Glutathione reductase (EC 1.6.4.2) was purified from spinach (Spinacia oleracea L.) leaves by affinity chromatography on ADP-Sepharose. The purified enzyme has a specific activity of 246 enzyme units/mg protein and is homogeneous by the criterion of polyacrylamide gel electrophoresis on native and SDS-gels. The enzyme has a molecular weight of 145,000 and consists of two subunits of similar size. The pH optimum of spinach glutathione reductase is 8.5–9.0, which is related to the function it performs in the chloroplast stroma. It is specific for oxidised glutathione (GSSG) but shows a low activity with NADH as electron donor. The pH optimum for NADH-dependent GSSG reduction is lower than that for NADPH-dependent reduction. The enzyme has a low affinity for reduced glutathione (GSH) and for NADP⁺, but GSH-dependent NADP⁺ reduction is stimulated by addition of dithiothreitol. Spinach glutathione reductase is inhibited on incubation with reagents that react with thiol groups, or with heavymetal ions such as Zn²⁺. GSSG protects the enzyme against inhibition but NADPH does not. Pre-incubation of the enzyme with NADPH decreases its activity, so kinetic studies were performed in which the reaction was initiated by adding NADPH or enzyme. The Km for GSSG was approximately 200 M and that for NADPH was about 3 M. NADP⁺ inhibited the enzyme, assayed in the direction of GSSG reduction, competitively with respect to NADPH and non-competitively with respect to GSSG. In contrast, GSH inhibited non-competitively with respect to both NADPH and GSSG. Illuminated chloroplasts, or chloroplasts kept in the dark, contain equal activities of glutathione reductase. The kinetic properties of the enzyme (listed above) suggest that GSH/GSSG ratios in chloroplasts will be very high under both light and dark conditions. This prediction was confirmed experimentally. GSH or GSSG play no part in the light-induced activation of chloroplast fructose diphosphatase or NADP⁺-glyceraldehyde-3-phosphate dehydrogenase. We suggest that GSH helps to stabilise chloroplast enzymes and may also play a role in removing H₂O₂. Glucose-6-phosphate dehydrogenase activity may be required in chloroplasts in the dark in order to provide NADPH for glutathione reductase.Abbreviations GSH reduced form of the tripeptide glutathione - GSSG oxidised form of glutathione     

Effect of 24-epibrassinolide on growth, protein content and antioxidative defense system of Brassica juncea L. subjected to cobalt ion toxicity

Brassica juncea L. plants were subjected to cobalt (Co) ion (0, 5?×?10^?4, 10^?3, 1.5?×?10^?3 and 2?×?10^?3?M) toxicity and were sprayed with different concentrations of 24-epibrassinolide (24-EBL) (0, 10^?10, 10^?8 and 10^?6?M) at 15-day stage after sowing. They were sampled at 30 and 60?days after sowing and analyzed for growth parameters in terms of shoot length and number of leaves. Thereafter, leaves were excised and content of proteins and the activities of antioxidative enzymes (superoxide dismutase (SOD) (EC 1.15.1.1) catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APOX) (EC 1.11.1.11), guaiacol peroxidase (POD) (EC 1.11.1.7) glutathione reductase (GR) (EC 1.6.4.2), monodehydroascorbate reductase (MDHAR) (EC 1.1.5.4) and dehydroascorbate reductase (DHAR) (EC 1.8.5.1)) were analyzed. The plants exposed to cobalt ion exhibited a significant decline in growth in terms of shoot length and number of leaves. However, foliar spray treatment with 24-EBL was able to alleviate the stress generated by cobalt ion and significantly improved the above parameters. The activities of antioxidative enzymes (SOD, CAT, POD, GR, APOX, MDHAR and DHAR) and protein content were also regulated considerably in leaves of plants treated with 24-EBL alone, 10^?8?M concentration being the most effective. The activities of antioxidative enzymes also increased in leaves of B. juncea plants by the application of cobalt ion to soil and consequently sprayed with 24-EBL. Similarly, the protein content was also regulated in leaves of B. juncea plants treated with 24-EBL as compared to untreated control plants, thereby revealing stress-protective properties of 24-EBL.     

Glutathione peroxidase, glutathione reductase, glutathione S-transferase, and gamma-glutamyltranspeptidase activities in the human early pregnancy placenta

GSH peroxidase, GSSG reductase, GSH S-transferase, and gamma-glutamyltranspeptidase activities were measured in the supernatant of 13 human early pregnancy placenta homogenates. From measurements of GSH peroxidase activity with both H2O2 and cumene hydroperoxide as second substrate it was deduced that immature placenta contains only the Se-dependent form. All the specimens investigated exhibited GSSG reductase and gamma-glutamyltranspeptidase activities. GSH S-transferase activity was noted only using 1-chloro-2,4-dinitrobenzene as electrophilic substrate, while no detectable activity was found with 1,2-dichloro-4-nitrobenzene, 1,2-epoxy-3-(p-nitrophenoxy) propane, and p-nitrobenzylchloride. It is concluded that human placenta is equipped, from early pregnancy, with the enzymatic systems which are involved in GSH-mediated cellular detoxication and in preserving the integrity of the sulfhydryl status of the cells.     

Exogenous salicylic acid regulates reactive oxygen species metabolism and ascorbate–glutathione cycle in <Emphasis Type="Italic">Nitraria tangutorum</Emphasis> Bobr. under salinity stress

The effect of 0.5–1.5 mM salicylic acid (SA) on modulating reactive oxygen species metabolism and ascorbate–glutathione cycle in NaCl-stressed Nitraria tangutorum seedlings was investigated. The individual plant fresh weight (PFW) and plant dry weight (PDW) significantly increased under 100 mM NaCl while remained unchanged or decreased under 200–400 mM NaCl compared to the control. Superoxide anion (O ₂ ^·? ), hydrogen peroxide (H₂O₂), thiobarbituric acid reactive substances (TBARS), reduced ascorbate (AsA), dehydroascorbate (DHA), reduced glutathione (GSH) and oxidized glutathione (GSSG) increased whereas the ratios of AsA/DHA and GSH/GSSG decreased under varied NaCl treatments. Ascorbate peroxidase (APX) and glutathione reductase (GR) activities were enhanced while dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities remained unvaried under 100–400 mM NaCl stresses. In addition, exogenous SA further increased PFW, PDW and root/shoot ratio. SA effectively diminished O ₂ ^·? accumulation. H₂O₂ and TBARS decreased under 0.5 and 1.0 mM SA treatments compared to those without SA. 0.5 mM of SA increased while 1.0 and 1.5 mM SA decreased APX activities. DHAR activities were elevated by 0.5 and 1.0 mM SA but not by 1.5 mM SA. MDHAR and GR activities kept constant or significantly increased at varying SA concentrations. Under SA treatments, AsA and GSH contents further increased, DHA and GSSG levels remained unaltered, while the decreases in AsA/DHA and GSH/GSSG ratios were inhibited. The above results demonstrated that the enhanced tolerance of N. tangutorum seedlings conferred by SA could be attributed mainly to the elevated GR and DHAR activities as well as the increased AsA/DHA and GSH/GSSG ratios.     

Redox regulation and storage processes during maturation in kernels of Triticum durum

Metabolic changes during the development and maturation of Triticum durum Desf. (L.) kernels were studied, with particular emphasis on changes in the redox state of ascorbate and glutathione, as well as in the activities of the enzymes responsible for the recycling of their oxidized forms (ascorbic free radical reductase, EC 1.6.5.4; dehydroascorbate reductase, EC 1.8.5.1; glutathione reductase, EC 1.6.4.2) and for detoxification or utilization of hydrogen peroxide (ascorbate peroxidase, EC 1.11.1.11; catalase, EC 1.11.1.6). In parallel with this analysis, the production and storage of reserve compounds was studied, in particular, soluble carbohydrates (mono- di-saccharides and fructans) and the transition from sulphydryl groups to disulphide bridges into proteins. The results indicate that both the activities of the ascorbate and glutathione redox enzymes and that of catalase are high before the start of drying maturation, after which they decrease. Moreover, analysis of the redox state of ascorbate and glutathione pairs and the sulphydryl to disulphide transition into proteins suggests that these three parameters are tightly related during kernel maturation, thus confirming the involvement of the two redox pairs in protein maturation as well as in protection against reactive oxygen species. The physiological implications of the changes in cellular redox state and in soluble carbohydrates for the acquisition of desiccation tolerance and reaching the resting phase in orthodox seeds are also discussed.