Enzymes Of Ascorbate-glutathione Cycle Research Articles

Ascorbate-glutathione cycle in wheat and rice seedlings under anoxia and subsequent reaeration.

The most important part of the plant antioxidant system is the ascorbate-glutathione cycle (AGC), the activity of which is observed upon exposure to a range of stressors, including lack of O2, and oxidative stress occurring immediately after the restoration of oxygen access, hereafter termed reaeration or post-anoxia. The operation of the AGC (enzymes and low-molecular components) in wheat (Triticum aestivum, cv. Leningradka, non-resistant to hypoxia) and rice (Oryza sativa, cv. Liman, resistant) seedlings after 24 h anoxia and 1 h or 24 h reaeration was studied. Significant accumulation of oxidized forms of ascorbate and glutathione was revealed in the non-resistant plant (wheat) after 24 h of anoxia and reaeration, indicating the development of oxidative stress. In the resistant plant (rice), reduced forms of these antioxidants prevailed both in normoxia and under stress, which may indicate their intensive reduction. In wheat, the activities of ascorbate peroxidase and dehydroascorbate reductase in shoots, and monodehydroascorbate reductase and glutathione reductase in roots decreased under anoxia and reaeration. The activity of antioxidant enzymes was maintained in rice under lack of oxygen (ascorbate peroxidase, glutathione reductase) and increased during post-anoxia (AGC reductases). Anoxia stimulated accumulation of mRNA of the organellar ascorbate peroxidase genes OsAPX3, OsAPX5 in shoots, and OsAPX3-5 and OsAPX7 in roots. At post-anoxia, the contribution of the OsAPX1 and OsAPX2 genes encoding the cytosolic forms of the enzyme increased in the whole plant, and so did that of the OsAPX8 gene for the plastid form of the enzyme. The accumulation of mRNA of the genes OsMDAR2 and OsMDAR4 encoding peroxisomal and cytosolic monodehydroascorbate reductase as well as the OsGR2 and OsGR3 for cytosolic and organellar glutathione reductase was activated during reaeration in shoots and roots. In most cases, O2 deficiency activated the genes encoding the peroxisomal, plastid, and mitochondrial forms of the enzymes, and upon reaeration, an enhanced activity of the genes encoding the cytoplasmic forms was observed. Taken together, the inactivation of AGC enzymes was revealed in wheat seedlings during anoxia and subsequent reaeration, which disrupted the effective operation of the cycle and triggered the accumulation of oxidized forms of ascorbate and glutathione. In rice, anoxia led to the maintenance of the activity of AGC enzymes, and reaeration stimulated it, including at the level of gene expression, which ensured the effective operation of AGC.

Synergistic effects of exogenous glutathione and calcium on ascorbate-glutathione cycle and glutathione-associated enzymes upregulation under lead stress in Brassica napus L.

Heavy metals (HMs) such as lead (Pb) pose a significant threat to global food security due to their adverse effect on the health of crop plants. Calcium (Ca) and Glutathione (GSH) are signaling molecules to scavenge free radicals in HM-stressed plants. In this study, GSH and Ca's role is examined in supporting canola seedlings against Pb toxicity. In a pot experiment, the administration of Glutathione (GSH, 0 and 100µM) and/or calcium (CaCl2, 0 and 500µM) in canola seedlings was examined under lead stress (0 and 100µM of Pb(NO3)2. Compared with the control samples, Pb treatment increased MDA and H2O2 values by 61 and 53%, respectively, indicative of oxidative burst. However, using a combination of GSH and Ca lowered oxidative stress in Pb-stressed plants by an approximately twofold reduction in MDA and H2O2 content. Total PC content increased by 78% in Pb-stressed plants, suggesting that these chelating peptides diminish the damaging effects of Pb. Interestingly, further boosts in total PC levels were recorded in Pb-stressed plants treated with GSH and Ca concurrently. The addition of exogenous GSH and Ca to Pb-stressed canola plants limited Pb uptake and translocation and improved ascorbate-glutathione cycle performance. Moreover, compared to their separate usage, the co-treatment of exogenous GSH and Ca strengthened the GSH pool by increasing the activities of enzymes involved in GSH metabolism. The findings demonstrate that exogenous GSH and Ca modulate GSH synthesis, metabolism, and redox homeostasis synergistically to enhance resistance to oxidative stress generated by Pb.

Combined effect of trehalose and spermidine to alleviate zinc toxicity in Vigna radiata.

Zinc toxicity is affecting the growth and yield of major crops plants throughout globe by reducing key metabolic processes. In this backdrop, experiments were conducted to evaluate the influence of exogenous supplementation of trehalose (500 µM Treh) and spermidine (500 µM Spd) in alleviating the damaging effects of zinc toxicity (100 µM ZnSO4) in Vigna radiata. Growth, chlorophyll and photosynthesis were reduced due to Zn toxicity; however, exogenous supplementation of trehalose and spermidine not only increased the parameters but also alleviated the decline to considerable levels. Toxicity of zinc increased H2O2, lipid peroxidation and electrolyte leakage by 100.43%, 84.53% and 134.64%, respectively, and application of trehalose and spermidine a reduction of 29.32%, 39.09% and 44.91%, respectively, over the zinc-treated plants. Application of trehalose and spermidine increased the activity of nitrate reductase and the content of nitrogen concomitant with alleviation of the decline caused due to zinc toxicity. The activity of antioxidant system enzymes superoxide dismutase, catalase and the enzymes of ascorbate-glutathione cycle was significantly enhanced due to trehalose and spermidine application. Proline, glycine betaine and activity of γ-glutamyl kinase increased maximally by 281.84%, 126.21% and 181.08%, respectively, in plants treated with zinc + trehalose + spermidine over control. Significant enhancement in the content of total phenols and flavonoids was observed due to the treatment of trehalose and spermidine individually as well as combinedly. Application of trehalose and spermidine reduced the content of methylglyoxal by up-regulating the activity of glyoxylase cycle enzymes. In addition under zinc toxicity conditions, the content of zinc declined in trehalose- and spermidine-treated plants.

Seed Priming with the Selenium Nanoparticles Maintains the Redox Status in the Water Stressed Tomato Plants by Modulating the Antioxidant Defense Enzymes.

In the present research, selenium nanoparticles (SeNPs) were tested for their use as seed priming agents under field trials on tomatoes (Solanum lycopersicum L.) for their efficacy in conferring drought tolerance. Four different seed priming regimes of SeNPs were created, comprising 25, 50, 75, and 100 ppm, along with a control treatment of 0 ppm. Seeds were planted in split plots under two irrigation regimes comprising water and water stress. The results suggest that seed priming with SeNPs can improve tomato crop performance under drought stress. Plants grown with 75 ppm SeNPs-primed seeds had lower hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels by 39.3% and 28.9%, respectively. Seed priming with 75 ppm SeNPs further increased the superoxide dismutase (SOD) and catalase (CAT) functions by 34.9 and 25.4%, respectively. The same treatment increased the total carotenoids content by 13.5%, α-tocopherols content by 22.8%, total flavonoids content by 25.2%, total anthocyanins content by 19.6%, ascorbic acid content by 26.4%, reduced glutathione (GSH) content by 14.8%, and oxidized glutathione (GSSG) content by 13.12%. Furthermore, seed priming with SeNPs upregulated the functions of enzymes of ascorbate glutathione cycle. Seed priming with SeNPs is a smart application to sustain tomato production in arid lands.

Over-Expression of Dehydroascorbate Reductase Improves Salt Tolerance, Environmental Adaptability and Productivity in Oryza sativa.

Abiotic stress induces reactive oxygen species (ROS) generation in plants, and high ROS levels can cause partial or severe oxidative damage to cellular components that regulate the redox status. Here, we developed salt-tolerant transgenic rice plants that overexpressed the dehydroascorbate reductase gene (OsDHAR1) under the control of a stress-inducible sweet potato promoter (SWPA2). OsDHAR1-expressing transgenic plants exhibited improved environmental adaptability compared to wild-type plants, owing to enhanced ascorbate levels, redox homeostasis, photosynthetic ability, and membrane stability through cross-activation of ascorbate-glutathione cycle enzymes under paddy-field conditions, which enhanced various agronomic traits, including root development, panicle number, spikelet number per panicle, and total grain yield. dhar2-knockdown plants were susceptible to salt stress, and owing to poor seed maturation, exhibited reduced biomass (root growth) and grain yield under paddy field conditions. Microarray revealed that transgenic plants highly expressed genes associated with cell growth, plant growth, leaf senescence, root development, ROS and heavy metal detoxification systems, lipid metabolism, isoflavone and ascorbate recycling, and photosynthesis. We identified the genetic source of functional genomics-based molecular breeding in crop plants and provided new insights into the physiological processes underlying environmental adaptability, which will enable improvement of stress tolerance and crop species productivity in response to climate change.

Salicylic acid alleviates chromium (VI) toxicity by restricting its uptake, improving photosynthesis and augmenting antioxidant defense in Solanum lycopersicum L

Contamination of agricultural soil by chromium (Cr) is a serious menace to environmental safety and global food security. Although potential of salicylic acid (SA) in mitigating heavy metal (HM) toxicity in plants is well recognized, detailed physiological mechanisms behind such beneficial effects under Cr-stress in tomato (Solanum lycopersicum L.) plant are far from being completely unravelled. The present study evaluated the efficacy of exogenously applied SA, in alleviating Cr-mediated alterations on photosynthesis and antioxidant defense in tomato exposed to three different concentrations of Cr(VI) [0, 50, and 100mg Cr(VI) kg-1 soil]. Exposure of tomato plants to Cr resulted in increased Cr-accumulation and oxidative damage, as signposted by high Cr concentration in root as well as shoot, augmented malondialdehyde (MDA) and superoxides levels, and inhibition in enzymes of ascorbate-glutathione (AsA-GSH) cycle. Furthermore, a significant (P ≤ 0.05) reduction in photosynthetic pigments and gas exchange parameters was also evident in Cr-stressed tomato plants. Findings of the present study showed that exogenous application of 0.5mM SA not only promoted plant growth subjected to Cr, but also restored Cr-mediated disturbances in plant physiology. A significant (P ≤ 0.05) decrease in Cr acquisition and translocation as evidenced by improved growth and photosynthesis in SA-treated plants was observed. Additionally, exogenous SA application by virtue of its positive effect on efficient antioxidant system ameliorated the Cr-mediated oxidative stress in tomato plants as signposted by lower MDA and superoxide levels and improved AsA-GSH cycle. Overall, current study advocates the potential of exogenous SA application in amelioration of Cr-mediated physiological disturbances in tomato plant.

Salicylic acid underpins silicon in ameliorating chromium toxicity in rice by modulating antioxidant defense, ion homeostasis and cellular ultrastructure

Chromium (Cr) phytotoxicity affirmed the need of mitigation strategies to remediate polluted soils and restricts its accumulation in the food chains. Salicylic acid (SA) and silicon (Si) play pivotal roles in stimulating the plant performance and stress resilience. So far, their interactive effects against Cr-phytotoxicities are less known. Thus, we evaluated the beneficial roles of alone or/and combine applications of SA and Si in mitigating the toxic effects of Cr in the leaves and roots of rice (Oryza sativa) seedlings. Results indicated that SA (10 μM) and/or Si (5 μM) markedly retrieved the Cr (100 μM) induced toxicities by minimizing the Cr-accretion in both leaves and roots, enhancing the performance of light harvesting pigments (total chlorophylls and carotenoids), water retention and accumulation of osmolytes (water-soluble protein and total soluble sugars) and ultimately improved the growth and biomass. Additionally, SA and/or Si maintained the ionic balance by enhancing the nutrients transport, upregulated the ascorbate-glutathione (AsA-GSH) cycle enzymes, minimized the extra accumulation of reactive oxygen species (ROS) (H2O2 and O2•‒), malondialdehyde (MDA), recovered the membrane stability and damages in cellular ultrastructure in Cr-stressed rice plants. Overall findings suggested that SA underpins Si in mitigating the Cr-induced phytotoxicities on the above-reported parameters and combined applications of SA and Si were more effective than alone treatments. The uptake or cellular accumulation of Cr, osmoprotectants level and antioxidant defense system against oxidative stress can be considered as key toxicity biomarkers for the safe cultivation of rice in Cr-contaminated soils.

Physiological responses to water deficiency in bread wheat (Triticum aestivum L.) lines with genetically different leaf pubescence.

Studying the relationship between leaf pubescence and drought resistance is important for assessing Triticum aestivum L. genetic resources. The aim of the work was to assess resistance of common wheat genotypes with different composition and allelic state of genes that determine the leaf pubescence phenotype. We compared the drought resistance wheat variety Saratovskaya 29 (S29) with densely pubescent leaves, carrying the dominant alleles of the Hl1 and Hl3 genes, and two near isogenic lines, i: S29 hl1, hl3 and i: S29 Hl2aesp, with the introgression of the additional pubescence gene from diploid species Aegilops speltoides. Under controlled conditions of the climatic chamber, the photosynthetic pigments content, the activity of ascorbate-glutathione cycle enzymes and also the parameters of chlorophyll fluorescence used to assess the physiological state of the plants photosynthetic apparatus were studied in the leaves of S29 and the lines. Tolerance was evaluated using the comprehensive index D, calculated on the basis of the studied physiological characteristics. The recessive state of pubescence genes, as well as the introduction of the additional Hl2aesp gene, led to a 6-fold decrease in D. Under the water deficit influence, the fluorescence parameters profile changed in the lines, and the viability index decreased compared with S29. Under drought, the activity of ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase in the line i: S29 hl1, hl3 decreased 1.9, 3.3 and 2.3 times, in the line i: S29 Hl2aesp it decreased 1.8, 3.6 and 1.8 times respectively, compared with S29. In a hydroponic greenhouse, line productivity was studied. Compared with S29, the thousand grains mass in the line i: S29 hl1, hl3 under water deficit was reduced. The productivity of the line i: S29 Hl2aesp was significantly reduced regardless of water supply conditions in comparison with S29. Presumably, the revealed effects are associated with violations of cross-regulatory interactions between the proteins of the trichome formation network and transcription factors that regulate plant growth and stress response.

Effect of fungicide pretreatment on lipid peroxidation, antioxidant enzyme systems and proline accumulation in tomato (Lycopersiconesculentum Mill.) leaves under high temperature stress

The aim of the present study was to determine the effect of high temperature stress (HT) and to evaluate the protective role of fungicide pretreatment against HT stress in tomato leaves. The oxidative stress was triggered under HT stress through an increase in the content of malondialdehyde (MDA) and hydrogen peroxide (H2O2). Also, it caused a decline in photosynthetic pigments and enhanced the proline in tomato. However, the activities of catalase (CAT; EC 1.11.1.6), peroxidase (POX; EC 1.11.1.7), and glutathione S-transferase (GST; EC.2.5.1.18), as well as ascorbate-glutathione cycle enzymes (APX, EC 1.11.1.11, DHAR, EC 1.8.5.1, MDHAR EC 1.6.5.4, GR; EC 1.6.4.2) were found to be increased after heat treatment. In addition, the transcript level of LeCAT1, LeAPX1, LeAPX6, LecGR, LeDHAR genes was up-regulated under HT stress. Foliar pretreatment of fungicide improved the physiological process that decrease H2O2 and MDA content, enhance pigment content, increase proline accumulation and CAT, POX, and GST activity, as well as LeCAT1 and LeGST2 transcript levels compared to nonpretreated leaves under control temperature. When tomato leaves exposed to high temperature stress, fungicide pretreatment accelerated the antioxidant enzyme system by enhancing activities and gene expression levels of CAT, POX, GST, and ascorbate-glutathione enzyme, resulting in the decrement of MDA and H2O2 contents. Further, the protective effect of fungicide pretreatment improved the efficiency of the photosynthetic pigment under HT stress. Consequently, the study was to indicate the evidence for the ability of potential use of fungicide as a protective agent against HT stress in tomato.

Influence of exogenous jasmonic acid on the functioning of a defense system of potato seedlings (<i>Solanum tuberosum</i> L.) grown on artificial ion exchange substrate and infected with potato virus X

The content of reactive oxygen species, the activities of ascorbate-glutathione cycle enzymes, the content of low molecular weight antioxidants: ascorbate and glutathione, the activity of phenolic peroxidase, the content of water-soluble phenols and the expression level of the hypersensitive response marker gene (HSR) and PR protein genes (Chit, Glu and TLP) in potato seedlings grown on an ion-exchange substrate in the presence of jasmonic acid at a concentration of 10 -8 and 10 -6 M and infected with potato virus X were studied. Accumulation of reactive oxygen species, an increase in the content of reduced ascorbate and an intensive consumption of reduced glutathione upon action of jasmonic acid, as well as a sharp increase in the expression of HSR, Chit, Glu, and TLP genes in the leaves of potato seedlings grown on a substrate with the addition of 10 -6 M jasmonic acid before infection were shown. In control plants, the expression of the HSR and TLP genes increased only after infection with potato virus X.

Role of Ascorbate and Ascorbate–Glutathione Cycle for Photosynthetic Protection in Selected Indigenous Rice Landraces Under Drought Stress

From precise drought tolerance screening of local rice landraces of Koraput, six rice landraces were identified as superior drought tolerant capacity in our earlier study. However, little information is available on their physiological response of redox regulation and photochemical activity under drought stress. The present work evaluates their redox regulations driven by ascorbate–glutathione cycle and photochemical activity of photosystem II under simulated drought stress by polyethylene glycol 6000. Leaf chlorophyll content, electron transport rate and effective quantum yield of PSII were significantly higher in studied indigenous rice genotypes in comparison with susceptible check variety under drought condition. Further, greater quantities of ascorbate and elevated levels of ascorbate–glutathione cycle enzyme activities were observed under drought treatment in studied indigenous rice genotypes in compared with susceptible IR64. The findings suggested that maintenance of better photochemical activity in studied rice genotypes under water-deficit condition may be due to improved redox regulation of ascorbate and efficient ascorbate regeneration pathways. This study thus shows a new light into drought stress response of indigenous rice of Koraput with global implications.

Local and Systemic Changes in Photosynthetic Parameters and Antioxidant Activity in Cucumber Challenged with Pseudomonas syringae pv lachrymans.

We studied changes in gas exchange, photochemical activity and the antioxidant system in cucumber leaves locally infected with Pseudomonas syringae pv lachrymans and in uninfected systemic ones. Infection-induced declined net photosynthesis rate and the related changes in transpiration rate, the intracellular CO2 concentration, and prolonged reduction in maximal PSII quantum yield (Fv/Fm), accompanied by an increase in non-photochemical quenching (NPQ), were observed only in the infected leaves, along with full disease symptom development. Infection severely affected the ROS/redox homeostasis at the cellular level and in chloroplasts. Superoxide dismutase, ascorbate, and tocopherol were preferentially induced at the early stage of pathogenesis, whereas catalase, glutathione, and the ascorbate–glutathione cycle enzymes were activated later. Systemic leaves retained their net photosynthesis rate and the changes in the antioxidant system were partly like those in the infected leaves, although they occurred later and were less intense. Re-balancing of ascorbate and glutathione in systemic leaves generated a specific redox signature in chloroplasts. We suggest that it could be a regulatory element playing a role in integrating photosynthesis and redox regulation of stress, aimed at increasing the defense capacity and maintaining the growth of the infected plant.

Nitrate reductase is required for salicylic acid-induced water stress tolerance of pepper by upraising the AsA-GSH pathway and glyoxalase system.

A trial was conducted to evaluate whether nitrate reductase (NR) participates in salicylic acid (SA)-improved water stress (WS) tolerance in pepper (Capsicum annuum L.) plants. Before starting WS treatment, 0.5 mM SA was applied to half of the well-watered (WW) plants as well as to WS-plants as a foliar spray once a day for a week. The soil water holding capacity was maintained at 40 and 80% of the full water storing capacity for WS and and well-watered (WW) plants, respectively. Water stress caused substantial decreases in total plant dry weight, Fv /Fm , chlorophyll a and b, relative water content, leaf water potential (ΨI) by 53, 37, 49, 21, 36 and 33%, respectively relative to control, but significant increases in malondialdehyde (MDA), hydrogen peroxide (H2 O2 ), electrolyte leakage (EL), methylglyoxal (MG), proline, key antioxidant enzymes' activities, NO and NR activity. The SA reduced oxidative stress, but improved antioxidant defence system, ascorbate-glutathione (AsA-GSH) cycle enzymes, glyoxalase system-related enzymes, glyoxalase I (Gly I) and glyoxalase II (Gly II), plant growth, photosynthetic traits, NO, NR and proline. SA-induced WS tolerance was further improved by supplementation of sodium nitroprusside (SNP), a donor of NO. NR inhibitor, sodium tungstate (ST) was applied in conjunction with SA and SA + SNP to the WW and WS-plants to assess whether NR contributes to SA-improved WS tolerance. ST abolished the beneficial effects of SA by reducing NO and NR activity in WS-pepper, but the application of SNP along with SA + ST reversed negative effects of ST, showing that NO and NR are jointly needed for SA-induced WS tolerance of pepper plants.

Effects of salt stress on antioxidant and ascorbate glutathione cycle enzyme activities in Pokkali rice varieties – Vytilla 1-9

The enzymatic and non-enzymatic antioxidant levels in the released salt tolerant Pokkali, (vytilla, VTL 1-9) varieties were studied under different NaCl concentrations (0-150 mM NaCl). The specific activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate-glutathione cycle enzymes and non-enzymatic antioxidants like superoxide (O2-), hydrogen peroxide (H2O2), malondialdehyde (MDA), glutathione (GSH) and ascorbic acid (AsA) was determined in plants exposed to salt stress. IR-28 was used as positive control and the VTL varieties were used as negative control. The H2O2 and superoxide (O2-) contents were higher in IR-28 at all the applied concentrations of NaCl. The VTL varieties without salt treatment did not evoke any response substantiating the role of salt priming in antioxidant signalling. The MDA contents were higher in the positive and negative control. MDA content was reduced in the NaCl treated VTL varieties. In the positive and negative control varieties, the quantity of ascorbate and glutathione contents were lesser and upregulated in salt treated VTL varieties. Highest H2O2 content was observed in 150 mM NaCl treatment. The H2O2 contents decreased with the increase in all concentrations of NaCl and lowest H2O2 contents was observed in VTL-1 and highest in VTL-2 and VTL-8 treated with 150 mM NaCl. Superoxide contents varied in all the nine varieties depending on the salt concentration. The SOD levels in all the varieties showed a positive correlation with the superoxide and H2O2 content. Lesser quantities of SOD, CAT and the ascorbate - glutathione cycle enzymes were expressed in the positive and negative control. The increased NaCl concentration (25-150 mM) upregulated antioxidant and ascorbate-glutathione cycle enzymes in the VTL varieties. The APX activity was lower in the control and salt treated plants. The GR activity increased linearly in all the varieties with respect to salt concentrations. The MDHAR and DHAR activities showed marginally linear increase, with all concentrations of NaCl. The APX activity was similar or lower to MDHAR activity while DHAR activity was similar to MDHAR activity. The results of the present study reveals the higher levels of enzymatic and non-enzymatic antioxidants under salt stress reflect the salt tolerance potential of pokkali varieties mediated by the up regulation of ROS scavenging enzymes.

Physiological and biochemical changes in wheat cultivars under salt stress as affected by foliar boron application

In this study, interactive effects of salt stress (150 mM NaCl) and foliar boron (H3BO3; 30 µM) application was studied in two wheat (Triticum aestivum L.) genotypes (Momtchil and Pamukova-97). Chlorophyll a and total chlorophyll content in Momtchil were not affected by salinity, foliar boron and salinity+foliar boron application while chlorophyll b content was increased by foliar boron and salinity+foliar boron application as compared to relative controls, probably due to higher total carotenoid and free proline level. In Pamukova-97, however, foliar boron and salinity+foliar boron application led to the reduced photosynthetic pigment content because of the absence of such a protective mechanism. Antioxidant enzymes of ascorbate-glutathione cycle and superoxide dismutase was not induced by all applications and both remarkable H2O2 accumulation and membrane damage was determined in the leaves of wheat cultivars, as demonstrated by higher MDA content in leaves. As a result, it may be concluded that expected ameliorative effect of foliar boron application did not occur in salt-affected wheat cultivars used in this study.

Effects of exogenous melatonin and glutathione on zinc toxicity in safflower (Carthamus tinctorius L.) seedlings.

The phytotoxicity caused by 500μM ZnSO4.7H2O and its detoxifying by co-application of 100μM of MT melatonin (MT) and glutathione (GSH) in 6-week-old safflower plants have been investigated. Reduced biomass production and total chlorophyll content on the one hand and increased content of hydrogen peroxide (H2O2), malondialdehyde (MDA) with increase in lipoxygenase activity, on the other hand, showed Zn- induced oxidative damage in safflower seedlings. When MT, GSH and especially MT+GSH exogenously were applied to Zn-stressed seedlings, the content of H2O2, MDA and the activity of lipoxygenase considerably decreased. In Zn- treated seedlings, the application of these signaling molecules led to a considerable increment in ascorbate (ASC), GSH and phytochelatin (PC) contents along with the induction of activity of antioxidant enzymes including ascorbate-glutathione cycle enzymes when compared with the plants stressed with Zn only. In Zn-stressed safflower seedlings treated with MT, GSH and MT+GSH, decreased activity of enzymes involved in glyoxalase system may be associated with the role of MT and GSH in reducing Zn uptake and reducing Zn-induced toxicity and subsequently, lower plant's defense responses. The data showed that the effects of MT and GSH, in particular, the combination of these two molecules in reducing Zn uptake and diminishing its accumulation in the shoots of safflower seedlings, and also the participation of MT and GSH on increasing plant ability to tolerate high amount of Zn through stimulation of various antioxidant defense systems suggest them as suitable candidates to better the survival of safflower in soils contaminated with Zn excess.

Effects of 1-methylcyclopropene on ascorbate-glutathione cycle enzyme activities of postharvest Dendrobium ‘Khao Sanan’

Effects of 1-methylcyclopropene on ascorbate-glutathione cycle enzyme activities of postharvest <i>Dendrobium</i> ‘Khao Sanan’

Catalase, superoxide dismutase and ascorbate-glutathione cycle enzymes confer drought tolerance of Amaranthus tricolor

The study was performed to explore physiological, non-enzymatic and enzymatic detoxification pathways of reactive oxygen species (ROS) in tolerance of Amaranthus tricolor under drought stress. The tolerant genotype VA13 exhibited lower reduction in growth, photosynthetic pigments, relative water content (RWC) and negligible increment in electrolyte leakage (EL), lower increment in proline, guaiacol peroxidase (GPOX) activity compared to sensitive genotype VA15. This genotype also had higher catalase (CAT), superoxide dismutase (SOD), remarkable and dramatic increment in ascorbate-glutathione content, ascorbate-glutathione redox and ascorbate-glutathione cycle enzymes activity compared to sensitive genotype VA15. The negligible increment of ascorbate-glutathione content, ascorbate-glutathione redox and ascorbate-glutathione cycle enzymes activities and dramatic increment in malondialdehyde (MDA), hydrogen peroxide (H2O2) and EL were observed in the sensitive genotype VA15. SOD contributed superoxide radical dismutation and CAT contributed H2O2 detoxification in both sensitive and tolerant varieties, however, these had a great contribution in the tolerant variety. Conversely, proline and GPOX accumulation were higher in the sensitive variety compared to the tolerant variety. Increase in ascorbate-glutathione cycle enzymes activities, CAT, ascorbate-glutathione content, SOD, and ascorbate-glutathione redox clearly evident that CAT, ascorbate-glutathione cycle and SOD played a significant activity in ROS detoxification of tolerant A. tricolor variety.

Exogenous silicon alters ascorbate-glutathione cycle in two salt-stressed indica rice cultivars (MTU 1010 and Nonabokra).

Silicon is widely available in soil and is known to mitigate both biotic and abiotic stress in plants. Very low doses of silicon are becoming increasingly essential in rice for biofortification and preventing water loss. Soil salinity is a matter of grave concern in various parts of the world, and silicon is a suitable candidate to mitigate salinity-induced stress of important plants in affected areas. The present study investigates the protective capability of exogenously applied silicon in ameliorating NaCl-induced toxicity in two rice (Oryza sativa L.) cultivars, the salt-sensitive MTU 1010, and salt-tolerant Nonabokra. Rice seedlings were treated with three doses of NaCl (25, 50, and 100mM), initially alone and subsequently in combination with 2mM sodium silicate (Na2SiO3, 9H2O). After 21days, these plants were examined to determine levels of reduced glutathione, ascorbic acid, cysteine, and activities of different enzymes involved in the ascorbate-glutathione cycle, viz., glutathione reductase (GR), ascorbate peroxidase (APX), glutathione peroxidase (GPx), and glutathione S-transferase (GST). Though ROS levels increased in both the cultivars with increasing NaCl concentrations, cv. MTU 1010 accumulated comparatively higher amounts. A differential response of NaCl-induced toxicity on the two cultivars was observed with respect to the various enzymatic and non-enzymatic antioxidants. APX and GST activities, as well as, cysteine contents, increased concomitantly with salt concentrations, whereas GR activity declined at increasing salt concentrations, in both cultivars. Activity of GPx increased in cv. Nonabokra but declined in cv. MTU 1010, under similar NaCl concentrations. Reduced glutathione (GSH) contents decreased in both cultivars, whereas ascorbate contents declined in only the sensitive cultivar. Application of silicon, along with NaCl, in the test seedlings of both the cultivars, reduced ROS accumulation and boosted antioxidant defense mechanism, through enhancing ascorbate and GSH levels, and activities of ascorbate-glutathione cycle enzymes as well. However, amelioration of salt-induced damages in the sensitive cv. MTU 1010 was more pronounced upon silicon administration, than the tolerant cv. Nonabokra. Thus, cv. MTU 1010 was found to be more responsive to applied silicon. Hence, this study was instrumental in realizing a successful strategy in silicon-mediated amelioration of salinity stress in plants.

Differential antioxidant enzyme activity inrapid-response glyphosate-resistant Ambrosia trifida.

The giant ragweed (Ambrosia trifida L.) rapid-response (RR) biotype exhibits a sacrificial form of glyphosate resistance whereby an oxidative burst in mature leaves results in foliage loss, while juvenile leaves remain uninjured. This work investigated the safening capacity of antioxidant enzymes in RR juvenile leaves following glyphosate treatment and examined cross tolerance to paraquat. Basal antioxidant enzyme activities were similar between glyphosate-susceptible (GS) and RR biotypes. Lipid peroxidation was first detected in RR mature leaves at 8 h after treatment (HAT) and by 32 HAT was 5.3 and 21.1 times greater than that in RR juvenile leaves and GS leaves, respectively. Preceding lipid peroxidation in the RR biotype at 2 and 4 HAT, the only increase in enzymatic activity was observed in ascorbate-glutathione cycle enzymes in RR juvenile leaves, particularly ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Sensitivity to paraquat was similar between biotypes. The RR biotype is not inherently more tolerant to oxidative stress. The difference in tissue damage between RR juvenile and mature leaves following glyphosate treatment is attributable at least partially to the transient increase in antioxidant enzyme expression in juvenile leaves (0-8 HAT), but may also be attributable to lower overall RR induction in juvenile leaves compared with mature leaves. © 2018 Society of Chemical Industry.