Jasmonic Acid Improves Growth Performance of Soybean Under Nickel Toxicity By Regulating Nickel Uptake,Redox Balance,and Oxidative Stress Metabolism

Soil contamination with nickel (Ni) is a persistent threat to crop production worldwide. The present study examined the putative roles of jasmonic acid (JA) in improving Ni tolerance in soybean. Our findings showed that priming of soybean seeds with JA significantly improved the growth performance of soybean when grown under excessive Ni. The enhanced Ni tolerance of soybean prompted by JA could be ascribed to its ability to regulate Ni uptake and accumulation, and to decrease Ni-induced membrane damage as evidenced by reduced levels of reactive oxygen species (ROS), malondialdehyde, lipoxygenase activity, and electrolyte leakage in Ni-stressed plants. JA also boosted redox states and antioxidant capacity in Ni-stressed plants by maintaining increased levels of ascorbate and glutathione, and enhanced activities of ROS-detoxifying enzymes compared with Ni-stressed alone plants. Additionally, methylglyoxal detoxification system was significantly upregulated in JA-primed and “JA-primed?+?Ni-stressed” plants, indicating an alleviating effect of JA on Ni-induced methylglyoxal toxicity. Our results conclude that JA-mediated regulation of Ni uptake and accumulation, and enhanced ROS metabolism by activating antioxidant defense and glyoxalase systems contributed to improved performance of soybean under excessive Ni, thereby suggesting JA as an effective stress regulator in mitigating Ni toxicity in economically important soybean, and perhaps in other crops.

     

Glutathione-Mediated Alleviation of Chromium Toxicity in Rice Plants

A hydroponic experiment was conducted to determine the possible effect of exogenous glutathione (GSH) in alleviating chromium (Cr) stress through examining plant growth, chlorophyll contents, antioxidant enzyme activity, and lipid peroxidation in rice seedlings exposed to Cr toxicity. The results showed that plant growth and chlorophyll content were dramatically reduced when rice plants were exposed to 100 μM Cr. Addition of GSH in the culture solution obviously alleviated the reduction of plant growth and chlorophyll content. The activities of some antioxidant enzymes, including superoxide dismutase, catalase (CAT) and glutathione reductase in leaves, and CAT and glutathione peroxidase in roots showed obvious increase under Cr stress. Addition of GSH reduced malondialdehyde accumulation and increased the activities of these antioxidant enzymes in both leaves and roots, suggesting that GSH may enhance antioxidant capacity in Cr-stressed plants. Furthermore, exogenous GSH caused significant decrease of Cr uptake and root-to-shoot transport in the Cr-stressed rice plants. It can be assumed that GSH is involved in Cr compartmentalization in root cells.     

ANTIOXIDANT RESPONSES IN SCYTOSIPHON LOMENTARIA (PHAEOPHYCEAE) INHABITING COPPER‐ENRICHED COASTAL ENVIRONMENTS1

Scytosiphon lomentaria (Lingb.) Link. (Phaeophyceae) is one of the two dominant seaweeds in a coastal area of northern Chile affected by copper mine wastes, where the concentration of copper in water and algal tissues remains higher than in nonimpacted sites. Copper‐loaded plants develop oxidative stress, as demonstrated by the increased levels of reactive oxygen species and lipoperoxides. This stress was associated with 1) an enhanced activity of the antioxidant enzymes catalase, glutathione peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase and 2) an inhibition of the glutathione reductase activity. Furthermore, stressed plants showed a decrease in glutathione and phenolic compounds levels and an increase in total ascorbate. Reciprocal transplants revealed that plants rapidly adjusted their antioxidant system in response to the conditions of the receiving site. In individuals transplanted from the copper‐enriched environment to the control site, normal levels of lipoperoxides and antioxidant compounds were restored in 48 h and antioxidant enzymes recovered their basal activities in 96 h. Individuals transplanted from the control site to the copper‐enriched area adjusted their antioxidant compounds and antioxidant enzymes within 48 h and 96 h, respectively, and reached the functional status of the local plants. We conclude that S. lomentaria inhabiting the copper‐enriched area buffered oxidative stress by a simultaneous involvement of antioxidant enzymes and water‐soluble antioxidant compounds. These antioxidant responses were rapid and reversible, suggesting that copper resistance in S. lomentaria is a constitutive trait and that copper enrichment of the area did not result in a locally adapted copper‐tolerant ecotype.     

A Strobilurin Fungicide Relieves Bipolaris oryzae‐Induced Oxidative Stress in Rice

Although strobilurins are one of the most effective and broad spectrum classes of systemic fungicides, they may also increase plant stress tolerance by modulating the activity of antioxidant enzymes. To address this issue, the effect of azoxystrobin (Az) on the activity of antioxidant enzymes and on the concentrations of antioxidant metabolites and oxidative stress‐related compounds was studied in rice plants (cv. Metica‐1) either inoculated or not with Bipolaris oryzae, the causal agent of brown spot (BS). The Az minimally affected the enzyme activities, but consistently increased the glutathione reduced (GSH) concentrations in the noninoculated plants. The activities of superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione peroxidase, glutathione reductase and glutathione‐S‐transferase were increased upon B. oryzae infection, but such increases were greatly limited in the Az‐sprayed plants. Catalase activity decreased in the inoculated plants compared to the noninoculated plants regardless of fungicide treatment. The GSH concentration increased in response to the B. oryzae infection, and the Az‐sprayed plants sustained higher levels of GSH at advanced stages of fungal infection than did the nonsprayed plants. The inoculated plants exhibited an extensive oxidative stress as evidenced by higher concentrations of hydrogen peroxide and malondialdehyde compared to the noninoculated plants, but lower and later increases were recorded in the Az‐sprayed plants than in the nonsprayed plants. Therefore, Az greatly reduces B. oryzae‐induced oxidative stress by limiting BS development rather than by activating antioxidant enzymes. The GSH, however, seems to be Az‐modulated, and this may partially explain the constrained oxidative stress observed in the Az‐sprayed plants.     

Different responses of tobacco antioxidant enzymes to light and chilling stress

The effect of elevated light treatment (25 degrees C, PPFD 360 mumol m-2 sec-1) or chilling temperatures combined with elevated light (5 degrees C, PPFD 360 mumol m-2 sec-1) on the activity of six antioxidant enzymes, guaiacol peroxidases, and glutathione peroxidase (GPx, EC 1.11.1.9) protein accumulation were studied in tobacco Nicotiana tabacum cv. Petit Havana SR1. Both treatments caused no photooxidative damage, but chilling caused a transient wilting. The light treatment increased the activities of ascorbate peroxidase (APx, EC 1.11.1.11) and guaiacol peroxidases while catalase (EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2) were unchanged. In contrast, chilling treatment did not increase any of the antioxidant enzyme activities, but decreased catalase and to a lesser extent DHAR activities. Glutathione peroxidase protein levels increased sporadically under light treatment and constantly under chilling. Both chilling and light stress caused induction of glutathione synthesis and accumulation of oxidised glutathione, although the predominant part of the glutathione pool remained in the reduced form. Antioxidant enzymes from the chilling treated plants were measured at both 25 degrees C and 5 degrees C. Measurements at 5 degrees C revealed a 3-fold reduction in catalase activity, compared with that measured at 25 degrees C, indicating that the overall reduction in catalase after four days of chilling was approximately 10-fold. The overall reduction in activity for the other antioxidant enzymes after four days of chilling was 2-fold for GR and APx, 1.5-fold for MDHAR, 3.5-fold for DHAR. The activity of SOD was the same at 25 and 5 degrees C. These results indicate that catalase and DHAR are most strongly affected by the chilling treatment and may be the rate-limiting factor of the antioxidant system at low temperatures.     

Role of calcium in AMF-mediated alleviation of the adverse impacts of cadmium stress in Bassia indica [Wight] A.J. Scott

The aim of this study was to evaluate cadmium stress induced changes in the growth, lipid peroxidation and antioxidant activity of Bassia indica associated with arbuscular mycorrhizal fungi (AMF) and their amelioration by calcium application. Cadmium stress can cause alterations in the physiological and biochemical processes in plants. A calcium application combined with an AMF treatment resulted in the reduction of lipid peroxidation and the production of hydrogen peroxide, thereby mediating the mitigation of cadmium induced oxidative stress. The activity of antioxidant enzymes increased with cadmium application, whereas AMF inoculation combined with a calcium application further enhanced their activity. An increase in the content of non-enzymatic antioxidants such as ascorbate, reduced glutathione (GSH), oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO) in AMF-inoculated and calcium-treated plants further suggests their role in strengthening the antioxidant defense system that results in maintained growth. The application of calcium combined with the AMF treatment caused a significant reduction in lipid peroxidation and in the production of hydrogen peroxide, thereby mediating the mitigation of the cadmium induced oxidative stress. Increased proline accumulation was clearly evident in stressed plants, and the calcium application as well as the AMF inoculation further induced proline synthesis, thereby providing efficient protection against cadmium stress by increasing the maintenance of the systemic resistance criteria.     

Antioxidative responses and proline level in leaves and roots of pea plants subjected to nickel stress

The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione S-transferase (GST) as well as proline content were studied in leaves and roots of 14 day-old pea plants treated with NiSO₄ (10, 100, 200 μm) for 1, 3, 6 and 9 days. Exposure of pea plants to nickel (Ni) resulted in the decrease in CuZnSOD as well as total SOD activities in both leaves and roots. The activity of APX in leaves of plants treated with 100 and 200 μm Ni increased following the 3rd day after metal application, while in roots at the end of the experiment the activity of this enzyme was significantly reduced. In both organs CAT activity generally did not change in response to Ni treatment. The activity of GST in plants exposed to high concentrations of Ni increased, more markedly in roots. In both leaves and roots after Ni application accumulation of free proline was observed, but in the case of leaves concentration of this amino acid increased earlier and to a greater extent than in roots. The results indicate that stimulation of GST activity and accumulation of proline in the tissues rather than antioxidative enzymes are involved in response of pea plants to Ni stress.     

Age-related peculiarities of antioxidant system functioning in the blood of ostriches

The intensity of lipid peroxidation, activity of some enzymes antioxidant system - superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-S-transferase, amount of recovered glutathione and ceruloplasmin in the blood serum of ostriches in a period from 6- to 60-month age were first investigated. The increase of concentration of lipid peroxidation products is accompanied by the decline of amount of general lipids in the ostriches blood. Every life cycle period of ostriches is characterized by the indexes of functioning of the antioxidant system and intensity of accumulation intermediate lipid peroxidation products inherent in it. The pubescence period and intensive oviposition are characterized by the increase of products lipid peroxidation concentration and decrease of antioxidant enzymes activity, which can testify to the exhaustion of protective possibilities of enzymatic link of antioxidant defence.     

Water stress-induced abscisic acid accumulation triggers the increased generation of reactive oxygen species and up-regulates the activities of antioxidant enzymes in maize leaves

The interrelationship among water-stress-induced abscisic acid (ABA) accumulation, the generation of reactive oxygen species (ROS), and the activities of several antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) was investigated in leaves of detached maize (Zea mays L.) plants exposed to -0.7 MPa water stress induced by polyethylene glycol (PEG 6000). Time-course analyses of ABA content, the production of ROS, and the activities of antioxidant enzymes in water-stressed leaves showed that a significant increase in the content of ABA preceded that of ROS, which was followed by a marked increase in the activities of these antioxidant enzymes. Pretreatment with an ABA biosynthesis inhibitor, tungstate, significantly suppressed the accumulation of ABA, and also reduced the increased generation of ROS and the up-regulation of these antioxidant enzymes in water-stressed leaves. A mild oxidative stress induced by paraquat, which generates O(2)(-) and then H(2)O(2), resulted in a significant enhancement in the activities of antioxidant enzymes in non-water-stressed leaves. Pretreatment with some ROS scavengers, such as Tiron and dimethylthiourea (DMTU), and an inhibitor of NAD(P)H oxidase, diphenyleneiodonium (DPI), almost completely arrested the increase in ROS and the activities of these antioxidant enzymes induced by water stress or ABA treatment. These data suggest that water stress-induced ABA accumulation triggers the increased generation of ROS, which, in turn, leads to the up-regulation of the antioxidant defence system.     

Involvement of plasma-membrane NADPH oxidase in abscisic acid- and water stress-induced antioxidant defense in leaves of maize seedlings

The roles of the plasma-membrane (PM) NADPH oxidase in abscisic acid (ABA)- and water stress-induced antioxidant defense were investigated in leaves of maize ( Zea mays L.) seedlings. Treatment by exogenous ABA (100 micro M ABA) or osmotic stress (-0.7 MPa induced by polyethylene glycol) significantly increased the activity of the PM NADPH oxidase, the production of leaf O(2)(-), the activities of several antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase), and the contents of antioxidant metabolites (ascorbate and reduced glutathione). Pretreatment with three different inhibitors of NADPH oxidase (diphenylene iodonium, imidazole and pyridine) or an inhibitor of ABA biosynthesis (tungstate) reduced the increase in the activity of the PM NADPH oxidase and the production of leaf O(2)(-), and the capacity of antioxidant defense systems mediated by ABA. The inhibitory effects above caused by tungstate were reversed by exogenous ABA. These data indicate that NADPH oxidase is involved in the ABA-induced production of active oxygen species (AOS), and our results depict a minimal chain of events initiated by water stress-induced ABA accumulation, which then triggers the production of AOS by membrane-bound NADPH oxidase, resulting in the induction of antioxidant defense systems against oxidative damage in plants.     

Curcumin and its synthetic analogue dimethoxycurcumin differentially modulates antioxidant status of normal human peripheral blood mononuclear cells

Curcumin is a polyphenol derived from the herb Curcuma longa, which has been extensively studied in terms of its antitumour, antioxidant, and chemopreventive activity as well as various other effects. In the present work we compared curcumin with its synthetic analogue dimethoxycurcumin (dimc) in terms of its antioxidant enzyme-modulating effects in human peripheral blood mononuclear cells (PBMC). We found that these compounds modulate antioxidant enzymes differentially. Both curcumin and dimethoxycurcumin effected a decrease in lipid peroxidation status in PBMC, however, curcumin had better activity in this regard. An increase in the activity of catalase was seen in the case of curcumin-treated PBMC, whereas dimc increased catalase activity significantly to almost twofold level. Real time-polymerase chain reaction (RT-PCR) analysis revealed significant up-regulation of catalase at mRNA level post treatment with curcumin as well as dimc, however, dimc had better activity in this regard. Glutathione reductase (GR) activity and reduced glutathione levels increased in the case of peripheral blood mononuclear cells (PBMC) treated with curcumin, however, the trend was reversed with dimethoxycurcumin where, both glutathione reductase activity and reduced glutathione levels were significantly reduced. RT-PCR analysis of glutathione reductase mRNA levels showed decrease in mRNA levels post treatment with dimethoxycurcumin (dimc) further corroborating GR enzyme assay results, however, we could not obtain significant result post curcumin treatment. NFkB reporter assay and western blot analysis of nuclear as well as cytosolic fractions of NFkB revealed that curcumin inhibits NFkB activation whereas inhibition was much less with dimc. It has been reported that curcumin and dimc exerts differential cytotoxicity in normal and tumour cells and the reason for this had been attributed to the differential uptake of these compounds by normal cells and tumour cells. Based on our results we propose that differential modulation of antioxidant enzymes via NFkB pathway could be the reason behind differential cytotoxicity of dimc as well as curcumin in normal cells and tumour cells in addition to differential uptake of these compounds as reported previously.     

Ascorbic acid improves the tolerance of wheat plants to lead toxicity

Among the heavy metals (HMs), lead (Pb) is considered as a toxic HM which adversely affects growth and development of crop plants. The present experiment was aimed to investigate the potential role of ascorbic acid (ASC) in the reversal of Pb-inhibited nitrogen and sulfur assimilation enzymes activity and activity of photosynthesis enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and growth response in wheat plants. Wheat seedlings were subjected to 0 mM (control) and 0.2 mM and 0.6 mM of ASC with and without 2 mM of Pb. Plants treated with Pb exhibited the following reduced growth characteristics (root length, shoot length, root fresh weight (FW), shoot FW, root dry weight (DW) and shoot DW). A decrease was also observed in the activity of Rubisco and ATP sulfurylase (ATP-S), relative water content (RWC), accumulation of total chlorophyll (Total Chl) and content of nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg)] in Pb-treated plants. However, an increase in Chl degradation and in the activity of O-acetylserine(thiol)lyase (OAS-TL) and accumulation of cysteine (Cys), malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) was observed in plants under Pb stress. On the contrary, exogenous application of ASC mitigated the Pb-toxicity-induced oxidative damage by enhancing the activities of antioxidant enzymes, such as superoxide dismutase, catalase and glutathione reductase. Improved activity of antioxidant enzymes suppressed the formation of MDA and H₂O₂, which was reflected in the form of improved growth characteristics. Moreover, ASC induced improvement in plants defense systems by reduced Chl degradation and improved the content of essential nutrients (N, P, K, Ca and Mg) and Cys, RWC and the activity of Rubisco, ATP-S, NR and OAS-TL.     

Exogenous proline and glycinebetaine increase NaCl-induced ascorbate-glutathione cycle enzyme activities, and proline improves salt tolerance more than glycinebetaine in tobacco Bright Yellow-2 suspension-cultured cells

Up-regulation of the antioxidant system provides protection against NaCl-induced oxidative damage in plants. Antioxidants and activity of enzymes involved in the ascorbate-glutathione (ASC-GSH) cycle in tobacco Bright Yellow-2 (BY-2) were investigated to assess the antioxidant protection offered by exogenous proline and glycinebetaine (betaine from now on) against salt stress using cells grown in suspension culture. Reduced ascorbate (ASC) was detected in BY-2 cells but dehydroascorbate (DHA) was not. Large quantities of a reduced form of glutathione (GSH) and smaller quantities of an oxidized form of glutathione (GSSG) were detected in BY-2 cells. Salt stress significantly reduced the contents of ASC and GSH as well as activities of ASC-GSH cycle enzymes such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Exogenous proline or betaine increased the activities of all enzymes except MDHAR involved in NaCl-induced ASC-GSH cycle. Levels of ASC and GSH in BY-2 cells under salt stress were lower in the presence of proline or betaine than in the absence of proline or betaine whereas there was no difference in redox status. Proline proved more effective than betaine in maintaining the activity of enzymes involved in NaCl-induced ASC-GSH cycle. Neither proline nor betaine had any direct protective effect on NaCl-induced enzyme activity involved in the antioxidant system; however, both improved salt tolerance by increasing enzyme activity. The present study, together with our earlier findings [Hoque MA, Okuma E, Banu MNA, Nakamura Y, Shimoishi Y, Murata Y. Exogenous proline mitigates the detrimental effects of salt stress more than exogenous betaine by increasing antioxidant enzyme activities. J Plant Physiol 2006;164:553-61.], suggests that proline offered greater protection against salt stress than betaine did because proline was more effective in increasing the activity of enzymes involved in the antioxidant system.     

Transgenic tobacco plants overexpressing glyoxalase enzymes resist an increase in methylglyoxal and maintain higher reduced glutathione levels under salinity stress

The mechanism behind enhanced salt tolerance conferred by the overexpression of glyoxalase pathway enzymes was studied in transgenic vis-à-vis wild-type (WT) plants. We have recently documented that salinity stress induces higher level accumulation of methylglyoxal (MG), a potent cytotoxin and primary substrate for glyoxalase pathway, in various plant species [Yadav, S.K., Singla-Pareek, S.L., Ray, M., Reddy, M.K. and Sopory, S.K. (2005) MG levels in plants under salinity stress are dependent on glyoxalase I and glutathione. Biochem. Biophys. Res. Commun. 337, 61-67]. The transgenic tobacco plants overexpressing glyoxalase pathway enzymes, resist an increase in the level of MG that increased to over 70% in WT plants under salinity stress. These plants showed enhanced basal activity of various glutathione related antioxidative enzymes that increased further upon salinity stress. These plants suffered minimal salinity stress induced oxidative damage measured in terms of the lipid peroxidation. The reduced glutathione (GSH) content was high in these transgenic plants and also maintained a higher reduced to oxidized glutathione (GSH:GSSG) ratio under salinity. Manipulation of glutathione ratio by exogenous application of GSSG retarded the growth of non-transgenic plants whereas transgenic plants sustained their growth. These results suggest that resisting an increase in MG together with maintaining higher reduced glutathione levels can be efficiently achieved by the overexpression of glyoxalase pathway enzymes towards developing salinity stress tolerant plants.     

Effect of salinity and different nitrogen sources on the activity of antioxidant enzymes and indole alkaloid content in Catharanthus roseus seedlings

The activities of antioxidant enzymes viz. glutathione reductase, GR; superoxide dismutase, SOD; peroxidase, POD; catalase, CAT and glutathione-S-transferase, GST and alkaloid accumulation were investigated in leaf pairs (apical, middle, basal) and in roots of Catharanthus roseus seedlings under the conditions of different nitrogen sources (20 mM KNO(3) and 2 mM NH(4)Cl) and salinity, in the absence (non-saline control) and in the presence of 100 mM NaCl in the nutrient solution. Salinity caused a reduction in plant biomass. The biomass production of ammonium-fed plants was lower than that of nitrate-fed plants. The antioxidant enzymes exhibited higher activity in saline-treated plants. Changes in antioxidant enzyme activity caused by different nitrogen sources differed in all leaf pairs, as well as in roots of C. roseus. Ammonium-fed plants showed higher CAT, GR and GST activity in leaf pairs as well as in roots, while POD and SOD activity were higher in nitrate-fed plants. Higher peroxidase activity concomitant with the increased accumulation of alkaloid was found in all leaf pairs, as well as in roots of C. roseus of NO(3)(-) fed plants as compared to NH(4)(+) fed plants.     

Potassium-induced alleviation of salinity stress in <Emphasis Type="Italic">Brassica campestris</Emphasis> L.

Salinity is an important abiotic factor that adversely affects major agricultural soils of the world and hence limits crop productivity. An optimum mineral-nutrient status of plants plays critical role in determining plant tolerance to various stresses. A pot experiment was conducted on mustard (Brassica campestris L.) to study the protective role of added potassium (K, 40 mg kg⁻¹ soil) against salinity-stress (0, 40 and 80 mM NaCl)-induced changes in plant growth, photosynthetic traits, ion accumulation, oxidative stress, enzymatic antioxidants and non-enzymatic antioxidants at 30 days after sowing. Increasing NaCl levels decreased the growth, photosynthetic traits and the leaf ascorbate and glutathione content but increased the leaf ion accumulation and oxidative stress, and the activity of antioxidant enzymes. In contrast, K-nutrition improved plant growth, photosynthetic traits, activity of antioxidant enzymes and the ascorbate and glutathione content, and reduced ion accumulation and oxidative stress traits in the leaves, more appreciably at 40 mM than at 80 mM NaCl. The study illustrates the physiological and biochemical basis of K-nutrition-induced NaCl tolerance in mustard as a means to achieving increased crop productivity in a sustainable way.     

Trichoderma harzianum enhances antioxidant defense of tomato seedlings and resistance to water deficit

Some plant-symbiotic strains of the genus Trichoderma colonize roots and induce profound changes in plant gene expression that lead to enhanced growth, especially under biotic and abiotic stresses. In this study, we tested the hypothesis that one of the protective mechanisms enhanced by T. harzianum T22 colonization is the antioxidant defense mechanism. Having established that strain T22 modulates the expression of the genes encoding antioxidant enzymes, the status of antioxidant defense of tomato seedlings in response to colonization by T22 and water deficit was investigated. Total ascorbate or glutathione levels were not affected by either stimuli, but under water deficit, antioxidant pools became more oxidized (lower ratios of reduced to oxidized forms), whereas colonized plants maintained redox state as high as or higher than unstressed and untreated plants. The enhanced redox state of colonized plants could be explained by their higher activity of ascorbate and glutathione-recycling enzymes, higher activity of superoxide dismutase, catalase, and ascorbate peroxidase, in both root and shoot throughout the experiment. Similar enzymes were induced in uncolonized plants in response to water-deficit stress but to a lower extent when compared with colonized plants. This orchestrated enhancement in activity of reactive oxygen species (ROS)-scavenging pathways in colonized plants in response to stress supports the hypothesis that enhanced resistance of colonized plants to water deficit is at least partly due to higher capacity to scavenge ROS and recycle oxidized ascorbate and glutathione, a mechanism that is expected to enhance tolerance to abiotic and biotic stresses.     

温度对梯棱羊肚菌抗氧化酶活及其基因表达的影响

大田栽培条件下,环境温度无法精确调控,温度胁迫是影响羊肚菌生长发育的重要因素。抗氧化酶和抗氧化活性物质是羊肚菌抵御逆境胁迫的重要因子。温度胁迫下,羊肚菌菌丝会通过增加相应酶活性来减少活性氧的积累,降低对细胞的损伤。作者研究了不同温度对梯棱羊肚菌菌丝生长、抗氧化酶（超氧化物歧化酶SOD、过氧化氢酶CAT、谷胱甘肽还原酶GR、谷胱甘肽过氧化物酶GPX）活性及其基因表达和抗氧化活性物质的影响,结果显示：在5-25℃的温度区间内,随着温度的增加,菌丝生长速度加快,菌丝的老化速度也加快;对抗氧化酶活性研究发现,SOD、GPX和GR在低温下活性更高,CAT在高温下活性更高;抗氧化活性物质含量会随温度升高而增加,如还原型抗坏血酸（AsA）和还原型谷胱甘肽（GSH）;温度越高,羊肚菌菌丝中H₂O₂、O^2-和丙二醛含量也随之增加。因此,在温度胁迫下,羊肚菌通过启动不同的抗氧化酶和抗氧化活性物质来减少活性氧含量,缓解菌丝损伤,本研究为探讨温度对羊肚菌种质质量的影响和栽培条件优化提供了基础数据支撑。     

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

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