Antioxidative response of <Emphasis Type="Italic">Hordeum maritimum</Emphasis> L<Emphasis Type="Italic">.</Emphasis> to potassium deficiency

The objective of the present study was to determine the influence of potassium deprivation on the halophyte species Hordeum maritimum grown in hydroponics for 2 weeks. Treatments were with potassium (+K) or without potassium (−K). Growth, water status, mineral nutrition, parameters of oxidative stress [malondialdehyde (MDA), carbonyl groups (C=O), and hydrogen peroxide concentration (H₂O₂) contents], antioxidant enzyme activities [superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate peroxidase (MDHAR, EC 1.6.5.4), dehydroascorbate peroxidase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.6.4.2)], and antioxidant molecules [ascorbate (ASC), and glutathione (GSH)] were determined. Results showed that the growth of vegetative organs decreased owing to potassium deficiency with roots (−36%) more affected than shoots (−12%). Water status was only diminished in roots (reduction of 24%). Potassium deprivation decreased potassium concentration in both organs, this decrease was more pronounced in roots (−81%) than in shoots (−55%). In contrast to carbonyl groups, MDA content increased owing to potassium deprivation. Except for CAT activity that remained unaffected; SOD, GPX, APX, GR, MDHAR, and DHAR activities were significantly increased. H₂O₂ concentration was negatively correlated with the activities of enzymes and the accumulation of non-enzymatic antioxidants implicated in its detoxification. In conclusion, a cooperative process between the antioxidant systems is important for the tolerance of H. maritimum to potassium deficiency.     

Phytochelatin synthesis and response of antioxidants during cadmium stress in Bacopa monnieri L.

The phytotoxicity imposed by cadmium (Cd) and its detoxifying responses of Bacopa monnieri L. have been investigated. Effect on biomass, photosynthetic pigments and protein level were evaluated as gross effect, while lipid peroxidation and electrolyte leakage reflected oxidative stress. Induction of phytochelatins and enzymatic and non-enzymatic antioxidants were monitored as plants primary and secondary metal detoxifying responses, respectively. Plants accumulated substantial amount of Cd in different plant parts (root, stem and leaf), the maximum being in roots (9240.11 microg g(-1) dw after 7 d at 100 microM). Cadmium induced oxidative stress, which was indicated by increase in lipid peroxidation and electrical conductivity with increase in metal concentration and exposure duration. Photosynthetic pigments showed progressive decline while protein showed slight increase at lower concentrations. Enzymes viz., superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (GPX, EC 1.11.1.7) ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) showed stimulation except catalase (CAT, EC 1.11.1.6) which showed declining trend. Initially, an enhanced level of cysteine, glutathione and non-protein thiols was observed, which depleted with increase in exposure concentration and duration. Phytochelatins induced significantly at 10 microM Cd in roots and at 50 microM Cd in leaves. The phytochelatins decreased in roots at 50 microM Cd, which may be correlated with reduced level of GSH, probably due to reduced GR activity, which exerted increased oxidative stress as also evident by the phenotypic changes in the plant like browning of roots and slight yellowing of leaves. Thus, besides synthesis of phytochelatins, availability of GSH and concerted activity of GR seem to play a central role for Bacopa plants to combat oxidative stress caused by metal and to detoxify it. Plants ability to accumulate and tolerate high amount of Cd through enhanced level of PCs and various antioxidants suggest it to be a suitable candidate for phytoremediation.     

Increased antioxidative capacity in maize calli during and after oxidative stress induced by a long lead treatment

Maize (Zea mays L., cv. Samodek) callus cultures were exposed for long period (22 months) to lead (0.5 mM lead chloride) and lead content, oxidative damage and antioxidative response were evaluated at different steps. Inductively coupled plasma (ICP) emission spectroscopy analysis showed that lead entered the cells and it accumulated, but its internal concentration was maintained 10-fold less than the external one. Increase of both polyamine and lipid peroxide content indicated that cells underwent a stress condition due to an oxidative attack, counteracted by an increase of antioxidative defence enzyme activities, ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2). After 10 months, from the start of the lead treatment, a stock of calli was transferred for 6 months in a lead-deprived medium and then re-exposed to lead for a further 6 months. Analysis indicated that lead-deprived calli maintained high levels of APX and GR activities, suggesting that, over the experimental time–course, cells with high APX and GR activity were selected and allowed to enrich the cultures. These cultures, after a new lead treatment, showed a lower oxidative damage compared to continuously lead-treated calli.     

Reduced chilling tolerance in elongating cucumber seedling radicles is related to their reduced antioxidant enzyme and DPPH-radical scavenging activity

Cucumber seedling radicles become more chilling sensitive as they elongate. Chilling seedlings with radicles 20 mm long for 48 h at 2.5°C inhibited subsequent growth by 36%, while it reduced the growth of 70 mm-long radicles by 63%. Although the growth rate of non-chilled cucumber radicles at 25°C is constant from 20 to 80 mm, tissue viability [i.e. reduction of TTC (2,3,5-triphenyltetrazolium chloride) to formazan] and DPPH ( α,α -diphenyl- β -picrylhydrazyl) radical scavenging activity of apical tissue declines as radicles elongate from 20 to 80 mm in length. TTC reduction, DPPH-radical scavenging activity and protein content of apical tissue were higher in 20 than in 70 mm radicles immediately after chilling and after an additional 48 h of growth at 25°C. Catalase (CAT; EC 1.11.1.6) and ascorbate peroxidase (APX; EC 1.11.1.11) activity was higher in the apical tissue of 20 than in 70 mm radicles before chilling. Immediately after chilling and after an additional 48 h at 25°C, superoxide dismutase (SOD; EC 1.15.1.1), glutathione reductase (GR; EC 1.6.4.2), and guaiacol peroxidase (GPX; EC 1.11.1.7) activity increased more rapidly in 70 mm radicles than in 20 mm radicles (SOD, GR, and GPX activity in 70 mm radicles was 1.5-, 1.9- and 8.6-fold higher, respectively, than in 20 mm radicles). However, APX and CAT activity in 20 mm radicles were always higher than in 70 mm radicles. Growth after chilling enhanced the activity of all antioxidant enzymes compared to that found in non-chilled tissue; however, CAT activity in 70 mm radicles did not recover to levels found in non-chilled tissue. Higher levels of CAT, APX and DPPH-radical scavenging activity are correlated with higher chilling tolerance of 20 mm-long cucumber radicles compared to 70 mm-long radicles.     

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.     

Changes of antioxidants and GSH-associated enzymes in isoproturon-treated maize

The recommended field dose (RFD) of isoproturon induced significant accumulations of H₂O₂ in the leaves of 10-d-old maize seedlings throughout the following 20 d; the accumulation increased with time and also with herbicide dose. Meanwhile, low doses significantly increased ascorbic acid, glutathione and thiols while high doses caused diminutions. Superoxide dismutase (SOD; EC 1.15.1.1) activity was significantly enhanced up to the 12th d whereas ascorbate peroxidase (APX; EC 1.11.1.7) activity was significantly reduced after the fourth d onwards. Catalase (CAT; EC 1.11.1.6) and guaiacol peroxidase (GPX; EC 1.11.1.7) activities were similarly increased during the first 4 d but decreased from the 12th and the eighth d, respectively. Low doses increased SOD and GPX activities but high doses led to diminutions whereas CAT and APX were reduced by all doses. The activities of γ-glutamyl-cysteine synthethase (γ-GCS; EC 6.3.2.2) and glutathione synthethase (GSS; EC 6.3.2.3) were enhanced for 4 d; high doses caused general reductions. Isoproturon significantly reduced activities of glutathione S-transferase (GST; EC 2.5.1.18) isoforms [GST_(CDNB), GST_(ALA), or GST_(MET)] after the fourth d, however, it had no effect on GST_(ATR). Similar reductions in activities of glutathione peroxidase (GSPX; EC 1.15.1.1) and glutathione reductase (GR; EC 1.6.4.2) were detected up to the 16th and the 12th d, respectively. The activities of GST isoforms, GSPX and GR were reduced by high doses. These changes seemed to be related and might point to an oxidative stress state that exacerbated with prolonged time and/or increased isoproturon dose.     

Activity of enzymatic antioxidant defense systems in chilled and heat shocked cucumber seedling radicles

Chilling whole cucumber seedlings that had 10‐mm long radicles for 4 days at 2.5°C significantly inhibited subsequent radicle growth both by increasing the time it took the seedlings to recover from chilling and attain a linear rate of radicle growth, and by decreasing the subsequent rate of linear growth. Exposing cucumber seedlings to 45°C for up to 20 min had no effect on subsequent radicle growth, while longer exposures produced reductions in growth. A heat shock at 45°C for 10 min induced the optimal protection to 4 days of chilling at 2.5°C by reducing chilling inhibition from 60 to 42%. Two hours after being chilled, heat shocked or heat shocked and then chilled, there was no difference in protein content of the apical 1 cm of the seedling radicle among these treatments and the non‐heat shocked, non‐chilled control. Two days after treatment, the protein content was still similar in tissue that had been heat shocked or heat shocked and chilled, while it was significantly reduced in tissue that had been chilled. In general, 2 h after treatment, the activity of the 5 antioxidant enzymes examined in this study [superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (GPX; EC 1.11.1.7) and glutathione reductase (GR; EC 1.6.4.2)] were reduced by chilling and unaffected or increased by heat shock. When heat shock was followed by chilling, there was a consistent effect of the heat shock treatment on preventing the loss of enzyme activity following chilling. This protective effect of the heat shock treatment was even more pronounced after 2 days of recovery at 25°C for SOD, CAT and APX. In contrast, the activity of GR and GPX was substantially higher in chilled tissue than in tissue that had been heat shocked before being chilled. Elevated levels of GR and GPX therefore appear to be correlated with the development of chilling injury, while elevated levels of SOD, CAT and APX appear to be correlated with the development of heat shock‐induced chilling tolerance.     

Comparative study on calli from two reed ecotypes under heat stress

The different physiological responses to heat stress in calli from two ecotypes of common reed (Phragmites communis Trin.) plants (dune reed (DR) and swamp reed (SR)) were studied. The relative water content, the relative growth rate, cell viability, membrane permeability (MP), H₂O₂ content, MDA content, proline level, and the activities of enzymes, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), and lipoxygenase (LOX) were assayed. Results showed that under heat stress, DR callus could maintain the higher relative growth rate and cell viability than SR callus, while H₂O₂ content, MDA content, and MP in SR callus increased more than in DR callus. The activities of antioxidant enzymes, such as SOD, CAT, POD, APX, and GR in two calli were enhanced by high temperature. However, antioxidant enzymes in DR callus showed the higher thermal stability than those in SR callus. LOX activity increased more in SR callus than in DR callus under heat stress. High temperature markedly elevated proline content in DR callus whereas had no effect on that in SR callus. Taken together, DR callus is more thermotolerant than SR callus, which might be due to the higher activity of antioxidant enzymes and proline level compared with SR callus under heat stress.     

抗氧化系统参与循环干旱锻炼提高烟草植株抗旱性的形成

对漂浮育苗的烟草幼苗进行控水-半萎焉-复水-恢复的循环干旱锻炼。结果表明,这种干旱锻炼能显著提高烟草叶片抗氧化剂谷胱甘肽（GSH）、抗坏血酸（AsA）的含量、还原型抗氧化剂在总抗氧化剂中的比例和抗氧化酶包括超氧化物歧化酶（SOD）、抗坏血酸过氧化物酶（APX）、过氧化氢酶（CAT）、愈创木酚过氧化物酶（GPX）、谷胱甘肽还原酶（GR）的活性,降低丙二醛（MDA）的含量。当烟草植株遭受后续的干旱胁迫时,与未锻炼的对照相比,干旱锻炼过的烟草植株能保持较高的GSH和AsA含量、还原型抗氧化剂在总抗氧化剂中的比例和抗氧化酶（SOD、APx、CAT、GPX和GR）活性,以及较低的MDA含量,表明这种循环干旱锻炼提高了细胞抗氧化能力,有助于缓解烟草植株由干旱引起的氧化胁迫及其所导致的伤害,最终提高其抗旱性。这些结果表明。抗氧化系统参与了循环干旱锻炼提高烟草植株抗旱性的形成过程。     

Copper affects the enzymes of the ascorbate-glutathione cycle and its related metabolites in the roots of Phaseolus vulgaris

The involvement of the ascorbate-glutathione cycle in the defence against Cu-induced oxidative stress was studied in the roots of Phaseolus vulgaris L. cv. Limburgse vroege. All the enzymes of this cycle [ascorbate peroxidase (APOD), EC 1.11.1.11; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; dehydroascorbate reductase (DHAR), EC 1.8.5.1; glutathione reductase (GR), EC 1.6.4.2] were increased, and the total ascorbate and glutathione pools rose after a 15 μ M root Cu treatment. In the first hours after the start of the experiment, the accumulation of dehydroascorbate (DHA), formed as a result of a Cu-mediated direct oxidation of ascorbate (AA), was limited by a non-enzymatic reduction using glutathione (GSH) as the reductant. At 24 h, the enzyme capacities of both DHAR and GR were increased to maintain the redox status of the AA and GSH pools. After 72 h of Cu application, the DHAR capacity was inhibited and MDHAR was responsible for maintaining the AA pool in its reduced form. Although the GR capacity was enhanced after 72 h in the treated plants, the GSSG/GSH ratio was increased. This could be due to direct participation of GSH in the detoxification of Cu through reduction and complexation.     

UV-B induced changes in antioxidant enzymes and their isoforms in cucumber (Cucumis sativus L.) cotyledons

To assess the role of antioxidant defense system on exposure to ultra-violet-B (UV-B) radiation, the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPX), as well as the level of antioxidants ascorbic acid (AA) and alpha-tocopherol were monitored in cucumber (Cucumis sativus L. var long green) cotyledons. UV-B enhanced the activity of antioxidant enzymes as well as AA content, but decreased the level of alpha-tocopherol. Significant increase was observed in the activities of SOD and GPX. Analysis of isoforms of antioxidant enzymes by native-PAGE and activity staining revealed three isoforms of GPX in unexposed dark-grown cotyledons (control), and their intensity was enhanced by UV-B exposure. In addition, four new isoforms of GPX were observed in cotyledons after UV-B exposure. Although no new isoforms were observed for the other antioxidant enzymes, the activities of their existing isoforms were enhanced by UV-B.     

Effects of cadmium and copper on peroxidase, NADH oxidase and IAA oxidase activities in cell wall, soluble and microsomal membrane fractions of pea roots

Twelve-day-old seedlings of pea (Pisum sativum L.) that were treated for 4 days by 20 and 100 micromol/l Cd(NO3)2 or CuSO4 showed a growth reduction in all organs. From root protein extracts, the activities of guaiacol peroxidase (GPX; EC 1.11.1.7), ascorbate peroxidase (APX; EC 1.11.1.11), coniferyl alcohol peroxidase (CAPX), NADH oxidase, and indole-3-acetic acid (IAA) oxidase were measured in covalently--and ionically--[symbol: see text] bound cell wall, soluble, and microsomal membrane fractions. With the exception of 20 micromol/l Cu, metal treatments enhanced GPX activity in all fractions. Only IAA oxidase activity was metal-elevated in the covalently bound cell wall fraction, while the ionic one showed Cd stimulation for all assayed enzymic activities. These effects were not entirely observed in Cu-treated plants, since APX and IAA oxidase activities were only enhanced in this fraction. However, soluble extract showed stimulation of APX activity, while in the microsomal fraction metal exposure also increased the activities of CAPX and NADH oxidase. Differential responses of root cell fractions to the presence of cadmium and copper ions are discussed in regard to the contribution of their enzymic capacities in antioxidant, lignification, and auxin degradation pathways. Comparisons between metals and dose effects are also underlined.     

溴化1-己基-3-甲基咪唑对斜生栅藻谷胱甘肽及其代谢酶的影响

研究了浓度为0、1、5、10、15、20 mg/L的新兴离子液体溴化1-己基-3-甲基咪唑([C6mim]Br)在24h、48h、72h和96h对斜生栅藻还原型谷胱甘肽（GSH）及其代谢酶-谷胱甘肽过氧化物酶（GPX）、谷胱甘肽转硫酶（GST）和谷胱甘肽还原酶（GR）的影响。结果表明：GSH含量在24h、48h和72h时,在最低处理浓度下不变,其他处理浓度下随胁迫浓度增加而降低,96h时则与对照无差异或较小;GPX和GST的活性在72h之前明显升高（最高浓度组的GST活性有波动）,96h时均降低至对照水平;GR活性在24h时,[C6mim]Br=1 mg/L时升高,之后降低,在48h增高至对照水平,72h时,[C6mim]Br≥10 mg/L的处理组高于对照水平,96h时,除最低处理组外,均降至对照水平以下。GR是GSH系统中的限速酶,GST则是该系统中活性和灵敏性最高的酶,可作为[C6mim]Br胁迫时的敏感的生物标志物。1 mg/L的[C6mim]Br可引起藻细胞的氧化胁迫,具有环境毒性。     

Exogenous Nitric Oxide (as Sodium Nitroprusside) Ameliorates Polyethylene Glycol-Induced Osmotic Stress in Hydroponically Grown Maize Roots

The present study was designed to examine whether exogenous sodium nitroprusside (SNP) supplementation has any ameliorating action against PEG-induced osmotic stress in Zea mays cv. FRB-73 roots. Twenty percent or 40 % polyethylene glycol (PEG6000; ?0.5 MPa and ?1.76 MPa, respectively) treatment alone or in combination with 150 and 300 μM SNP was applied to hydroponically grown maize roots for 72 h. Although only catalase (CAT) activity increased when maize roots were exposed to PEG-induced osmotic stress, induction of this antioxidant enzyme was inadequate to detoxify the extreme levels of reactive oxygen species, as evidenced by growth, water content, superoxide anion radical (O ₂ ^?? ), hydroxyl radical (OH^?) scavenging activity, and TBARS content. However, supplementation of PEG-exposed specimens with SNP significantly alleviated stress-induced damage through effective water management and enhancement of antioxidant defense markers including the enzymatic/non-enzymatic systems. Exogenously applied SNP under stress resulted in the up-regulation of glutathione peroxidase (GPX), glutathione S-transferase (GST), ascorbate peroxidase (APX), glutathione reductase (GR), total ascorbate, and glutathione contents involved in ascorbate–glutathione cycle. On the other hand, growth rate, osmotic potential, CAT, APX, GR, and GPX increased in maize roots exposed to both concentrations of SNP alone, but activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase decreased. Based on the above results, an exogenous supply of both 150 and 300 μM SNP to maize roots was protective for PEG-induced toxicity. The present study provides new insights into the mechanisms of SNP (NO donor) amelioration of PEG-induced osmotic stress damages in hydroponically grown maize roots.     

Combined action of antioxidant defense system and osmolytes in chilling shock-induced chilling tolerance in Jatropha curcas seedlings

Low non-freezing temperature is one of the major environmental factors affecting growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas is considered as a sustainable energy plants with great potential for biodiesel production. In this study, chilling shock at 5 °C followed by recovery at 26 °C for 4 h significantly improved survival percentage of J. curcas seedlings under chilling stress at 1 °C. In addition, chilling shock could obviously enhance the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR), and the levels of antioxidants ascorbic acid (AsA) and glutathione (GSH), as well as the contents of osmolytes proline and betaine in leaves of seedlings of J. curcas compared with the control without chilling shock. During the process of recovery, GR activity, AsA, GSH, proline and betaine contents sequentially increased, whereas SOD, APX and CAT activities gradually decreased, but they markedly maintained higher activities than those of control. Under chilling stress, activities of SOD, APX, CAT, GR and GPX, and contents of AsA, GSH, proline and betaine, as well as the ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)] in the shocked and non-shock seedlings all dropped, but shocked seedlings sustained significantly higher antioxidant enzyme activity, antioxidant and osmolyte contents, as well as ratio of reduced antioxidants to total antioxidants from beginning to end compared with control. These results indicated that the chilling shock followed by recovery could improve chilling tolerance of seedlings in J. curcas, and antioxidant enzymes and osmolytes play important role in the acquisition of chilling tolerance.     

Nitric oxide modulates antioxidant defense and the methylglyoxal detoxification system and reduces salinity-induced damage of wheat seedlings

The present study investigates the possible regulatory role of exogenous nitric oxide (NO) in antioxidant defense and methylglyoxal (MG) detoxification systems of wheat seedlings exposed to salt stress (150 and 300 mM NaCl, 4 days). Seedlings were pre-treated for 24 h with 1 mM sodium nitroprusside, a NO donor, and then subjected to salt stress. The ascorbate (AsA) content decreased significantly with increased salt stress. The amount of reduced glutathione (GSH) and glutathione disulfide (GSSG) and the GSH/GSSG ratio increased with an increase in the level of salt stress. The glutathione S-transferase (GST) activity increased significantly with severe salt stress (300 mM). The ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT) and glutathione peroxidase (GPX) activities did not show significant changes in response to salt stress. The glutathione reductase (GR), glyoxalase I (Gly I), and glyoxalase II (Gly II) activities decreased upon the imposition of salt stress, especially at 300 mM NaCl, with a concomitant increase in the H₂O₂ and lipid peroxidation levels. Exogenous NO pre-treatment of the seedlings had little influence on the non-enzymatic and enzymatic components compared to the seedlings of the untreated control. Further investigation revealed that NO pre-treatment had a synergistic effect; that is, the pre-treatment increased the AsA and GSH content and the GSH/GSSG ratio, as well as the activities of MDHAR, DHAR, GR, GST, GPX, Gly I, and Gly II in most of the seedlings subjected to salt stress. These results suggest that the exogenous application of NO rendered the plants more tolerant to salinity-induced oxidative damage by enhancing their antioxidant defense and MG detoxification systems.     

Effect of pretreatment with hydrogen sulfide donor sodium hydrosulfide on heat tolerance in relation to antioxidant system in maize (Zea mays) seedlings

Hydrogen sulfide (H₂S) is a signal molecule that is involved in plant growth, development and the acquisition of stress tolerance including heat tolerance, but the mechanism of H₂S-induced heat tolerance is not completely clear. In present study, the effect of sodium hydrosulfide (NaHS), a H₂S donor, treatment on heat tolerance of maize seedlings in relation to antioxidant system was investigated. The results showed that NaHS treatment improved survival percentage of maize seedlings under heat stress in a concentration-dependent manner, indicating that H₂S treatment could improve heat tolerance of maize seedlings. To further study mechanism of NaHS-induced heat tolerance, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX) activities, and glutathione (GSH) and ascorbic acid (AsA) contents in maize seedlings were determined. The results showed that NaHS treatment increased the activities of CAT, GPX, SOD and GR, and GSH and AsA contents as well as the ratio of reduced antioxidants to total antioxidants [AsA/(AsA+DHA) and GSH/(GSH +GSSG)] in maize seedlings under normal culture conditions compared with the control. Under heat stress, antioxidant enzymes activities, antioxidants contents and the ratio of the reduced antioxidants to total antioxidants in control and treated seedlings all decreased, but NaHS-treated seedlings maintained higher antioxidant enzymes activities and antioxidants levels as well as the ratio of reduced antioxidants to total antioxidants. All of above-mentioned results suggested that NaHS treatment could improve heat tolerance of maize seedlings, and the acquisition of this heat tolerance may be relation to enhanced antioxidant system activity.     

Oxidative stress is not related to the mode of action of herbicides that inhibit acetolactate synthase

Imazethapyr (IM) is an imidazolinone herbicide which inhibits the biosynthesis of branched chain amino acids, by blocking acetolactate synthase (ALS; EC 4.1.3.18), the first common enzyme of the pathway. To study new aspects of the mode of action of ALS-inhibiting herbicides, pea plants grown in hydroponic cultures were supplied with IM and were analysed with reference to the antioxidant system and oxidative markers. A slight lipid peroxidation was detected in leaves after IM treatment, but no changes were noted in electrolyte leakage or carbonyl content. The ascorbate pool of leaves was oxidized under IM treatment. The analysis of the antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT) and guaiacol peroxidase (GPX), showed that IM treatment only caused an enhancement of GPX activity in leaves. In roots, the herbicide caused a decrease in lipid peroxidation. The enhancement of the reduced glutathione content detected in IM-treated roots can be related to the detected increase of GR activity. The lack of more noticeable effects on antioxidant enzymatic activities could be explained by the inability of IM-treated plants to respond to oxidative stress with modifications in their protein synthesis. Our results suggest that oxidative stress is not related to the mode of action of ALS-inhibitors. The slight changes detected in the antioxidative status of treated plants are too secondary in time and intensity to be related to the lethality caused by ALS-inhibitors     

Changes in the antioxidative systems of Ocimum basilicum L. (cv. Fine) under different sodium salts

The effects of different sodium salts on some physiological parameters and antioxidant responses were investigated in a medicinal and aromatic plant, Ocimum basilicum L. (cultivar Fine). Plants were subjected to an equimolar concentration of Na₂SO₄ (25?mM) and NaCl (50?mM) for 15 and 30?days. Growth, oxidative stress parameters [electrolyte leakage, peroxidation, and hydrogen peroxide (H₂O₂) concentration], antioxidant enzyme activities [ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and peroxidases (POD, EC 1.11.1.7)], as well as antioxidant molecules [ascorbate and glutathione] were determined. The two salts affected leaf growth rates to the same extent, after 15 or 30?days of treatment, indicating a similar effect of Na₂SO₄ and NaCl salinity on growth, even if different (enzymatic and non-enzymatic) antioxidant mechanisms were involved in H₂O₂ detoxification. However, under both salts, the efficiency of the antioxidant metabolism seemed to be sufficient to avoid the deleterious effects of reactive oxygen species (ROS). Indeed, both ion leakage and peroxidation did not change under either Na₂SO₄ or NaCl salinity. As a whole, these data suggest that a cooperative process between the antioxidant systems is important for the tolerance of Ocimum basilicum L., cv. Fine to Na₂SO₄ and NaCl salinity.     

Exogenous treatment with salicylic acid leads to increased antioxidant capacity in leaves of barley plants exposed to paraquat

Our previous study suggests that salicylic acid mediates tolerance in barley plants to paraquat (Ananieva et al. 2002). To further define the role of SA in paraquat induced responses, we analysed the capacity of the antioxidative defence system by measuring the activities of several antioxidative enzymes: superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1), catalase (CAT, EC 1.11.1.6), and guaiacol peroxidase (POX, EC 1.11.1.7). Twelve-day-old barley seedlings were supplied with 500 micromol/L SA or 10 micromol/L Pq via the transpiration stream and kept in the dark for 24 h. Then they were exposed to 100 micromol m(-2) s(-1) PAR and samples were taken 6 h after the light exposure. Treatment of seedlings with 10 micromol/L Pq reduced the activity of APX and GR, did not affect the activity of POX and DHAR but caused over a 40% increase in the activity of CAT. Pre-treatment with 500 micromol/L SA for 24 h in the dark before Pq application increased the activities of the studied enzymes in both the chloroplasts (SOD activity) and the other compartments of the cell (POX, CAT activity). The effect of SA pre-treatment was highly expressed on DHAR and POX activity. The data suggest that SA antagonizes Pq effects, via elicitation of an antioxidative response in barley plants.