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Öğe Activation of Photorespiration Facilitates Drought Stress Tolerance in Lotus corniculatus(Springer, 2022) Unlusoy, Aybuke Guler; Yolcu, Seher; Bor, Melike; Ozdemir, Filiz; Turkan, IsmailPhotorespiration is the process that recycles 2-phosphoglycolate back to 3-phosphoglycerate resulting from the oxygenase activity of Rubisco. Recent studies proved the importance of photorespiration for plant survival under stress conditions, including drought stress. In the present study, physiological, biochemical and molecular responses of a moderately drought-tolerant plant Lotus corniculatus to PEG-mediated drought stress were examined. Growth, stomatal conductance (g(s)), maximum quantum yield of photosystem II (Fv/Fm), CO2 assimilation (A), electron transport (ETR) and transpiration rates (E) were decreased, whilst intercellular CO2 concentrations (Ci), non-photochemical quenching (NPQ) and photorespiration rates were increased in the drought stress-exposed plants. Activities and expression profiles of photorespiratory cycle enzymes correlated well with the increased photorespiration rates. In the line of our results, we conclude that the activation of photorespiration for recycling 2-phosphoglycolate (2PG) to chloroplast facilitated the maintenance of growth and drought stress tolerance in L. corniculatus. Accordingly, we can speculate that drought stress exerted by PEG20 (20% PEG6000) with an osmotic pressure of -0.73 MPa may be a threshold level for drought tolerance in L. corniculatus since the long-term effects of PEG20 on tolerance-related parameters (RGR, membrane integrity, leaf water status and photosynthesis) were more remarkable.Öğe Alternative electron sinks in chloroplasts and mitochondria of halophytes as a safety valve for controlling ROS production during salinity(Wiley, 2024) Demircan, Nil; Sonmez, Mustafa Cemre; Akyol, Turgut Yigit; Ozgur, Rengin; Turkan, Ismail; Dietz, Karl-Josef; Uzilday, BarisElectron flow through the electron transport chain (ETC) is essential for oxidative phosphorylation in mitochondria and photosynthesis in chloroplasts. Electron fluxes depend on environmental parameters, e.g., ionic and osmotic conditions and endogenous factors, and this may cause severe imbalances. Plants have evolved alternative sinks to balance the reductive load on the electron transport chains in order to avoid overreduction, generation of reactive oxygen species (ROS), and to cope with environmental stresses. These sinks act primarily as valves for electron drainage and secondarily as regulators of tolerance-related metabolism, utilizing the excess reductive energy. High salinity is an environmental stressor that stimulates the generation of ROS and oxidative stress, which affects growth and development by disrupting the redox homeostasis of plants. While glycophytic plants are sensitive to high salinity, halophytic plants tolerate, grow, and reproduce at high salinity. Various studies have examined the ETC systems of glycophytic plants, however, information about the state and regulation of ETCs in halophytes under non-saline and saline conditions is scarce. This review focuses on alternative electron sinks in chloroplasts and mitochondria of halophytic plants. In cases where information on halophytes is lacking, we examined the available knowledge on the relationship between alternative sinks and gradual salinity resilience of glycophytes. To this end, transcriptional responses of involved components of photosynthetic and respiratory ETCs were compared between the glycophyte Arabidopsis thaliana and the halophyte Schrenkiella parvula, and the time-courses of these transcripts were examined in A. thaliana. The observed regulatory patterns are discussed in the context of reactive molecular species formation in halophytes and glycophytes.Öğe Carnitine modulates antioxidative defense in ABI2 mutant under salt stress(Springer, 2024) Gokce, Azime; Cetinel, Askim Hediye Sekmen; Turkan, IsmailCarnitine, a ubiquitous compound in living organisms, fulfills diverse roles in energy metabolism, stress resilience, and detoxification. Its antioxidant and osmolyte traits offer relief to stressed plants. Antagonizing abscisic acid (ABA), carnitine influences ABA-responsive genes. Our study, using Arabidopsis thaliana wild-type Ler. (Landsberg erecta) and ABA-insensitive abi2-1 mutants, explored carnitine's impact on antioxidative responses and ABI2's role in salt-induced carnitine metabolism. The application of 5 mu M carnitine has alleviated the decrease in RWC, shoot weight, and rosette diameter WT plants caused by 80 mM salt stress for 4 days. Carnitine reduced cell membrane damage and salinity effects, evidenced by decreased lipid peroxidation and H2O2. In contrast, the impaired ABI2 of abi2-1, due to deficient phosphatase activity, further exacerbated the inhibitory effect of carnitine on the enzymes of the ascorbate-glutathione cycle, consequently reducing stress mitigation. While abi2-1 mutants exhibited unchanged superoxide dismutase (SOD) activity, they demonstrated increased catalase and peroxidase activity following carnitine treatment under salt stress compared to WT plants. Conversely, wild-type WT plants treated with carnitine exhibited elevated total glutathione content under salt stress, a response not observed in abi2-1 mutants under carnitine treatment. These results underscore the crucial role of ABI2-dependent ABA signaling in regulating plant carnitine metabolism.Öğe Changes in redox regulation during transition from C-3 to single cell C-4 photosynthesis in Bienertia sinuspersici(Elsevier Gmbh, 2018) Uzilday, Baris; Ozgur, Rengin; Yalcinkaya, Tolga; Turkan, Ismail; Sekmen, A. HediyeBienertia sinuspersici performs single cell C-4 photosynthesis without Kranz anatomy. Peripheral and central cytoplasmic compartments in a single chlorenchyma cell act as mesophyll cells and bundle sheath cells. Development of this specialized mechanism is gradual during plant development. Young leaves perform C-3 photosynthesis, while mature leaves have complete C-4 cycle. The aim of this work was to investigate changes in redox regulation and antioxidant defence during transition from C-3 to single cell C-4 photosynthesis in B. sinuspersici leaves. First, we confirmed gradual development of C-4 with protein blot and qRT-PCR analysis of C-4 enzymes. After this activities and isoenzymes of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and H2O2 and TBARS and glutathione pool and redox status (GSH/GSSG) were determined in young, developing and mature leaves during transition from C-3 to single cell C-4 photosynthesis. Activities of SOD, APX and POX decrease, while GR and DHAR were increased. However, most striking results were the changes in isoenzyme patterns of SOD, CAT and GR which were gradual through transition to C-4 photosynthesis.Öğe Changes in the alternative electron sinks and antioxidant defence in chloroplasts of the extreme halophyte Eutrema parvulum (Thellungiella parvula) under salinity(Oxford Univ Press, 2015) Uzilday, Baris; Ozgur, Rengin; Sekmen, A. Hediye; Yildiztugay, Evren; Turkan, IsmailBackground and Aims Eutrema parvulum (synonym, Thellungiella parvula) is an extreme halophyte that thrives in high salt concentrations (100-150 mM) and is closely related to Arabidopsis thaliana. The main aim of this study was to determine how E. parvulum uses reactive oxygen species (ROS) production, antioxidant systems and redox regulation of the electron transport system in chloroplasts to tolerate salinity. Methods Plants of E. parvulum were grown for 30 d and then treated with either 50, 200 or 300 mM NaCl. Physiological parameters including growth and water relationships were measured. Activities of antioxidant enzymes were determined in whole leaves and chloroplasts. In addition, expressions of chloroplastic redox components such as ferrodoxin thioredoxin reductases (FTR), NADPH thioredoxin reductases (NTRC), thioredoxins (TRXs) and peroxiredoxins (PRXs), as well as genes encoding enzymes of the water-water cycle and proline biosynthesis were measured. Key Results Salt treatment affected water relationships negatively and the accumulation of proline was increased by salinity. E. parvulum was able to tolerate 300 mM NaCl over long periods, as evidenced by H2O2 content and lipid peroxidation. While Ca2+ and K+ concentrations were decreased by salinity, Na+ and Cl-concentrations increased. Efficient induction of activities and expressions of water-water cycle enzymes might prevent accumulation of excess ROS in chloroplasts and therefore protect the photosynthetic machinery in E. parvulum. The redox homeostasis in chloroplasts might be achieved by efficient induction of expressions of redox regulatory enzymes such as FTR, NTRC, TRXs and PRXs under salinity. Conclusions E. parvulum was able to adapt to osmotic stress by an efficient osmotic adjustment mechanism involving proline and was able to regulate its ion homeostasis. In addition, efficient induction of water-water cycle enzymes and other redox regulatory components such as TRXs and PRXs in chloroplasts were able to protect the chloroplasts from salinity-induced oxidative stress.Öğe Combined effects of salt stress and cucurbit downy mildew (Pseudoperospora cubensis Berk. and Curt. Rostov.) infection on growth, physiological traits and antioxidant activity in cucumber (Cucumis sativus L.) seedlings(Academic Press Ltd- Elsevier Science Ltd, 2013) Nostar, Ozge; Ozdemir, Filiz; Bor, Melike; Turkan, Ismail; Tosun, NecipAbiotic and biotic stresses both decrease quality and quantity of cultivated plants. We compared responses of Cucumis sativus L. cvs Sardes and Beith alpha which were treated with 50 or 100 mM NaCl and/or infected by Pseudoperospora cubensis Berk. and Curt. Rostov.. Both cultivars were affected remarkably when fungus infection was combined with salt stress however; cv Sardes was found out to be relatively tolerant with sustainable growth performance, better leaf water status and lower lipid peroxidation levels under this condition. This relative tolerance could be related to the fine tuning of the activities of the antioxidative enzymes and proline levels. (C) 2013 Elsevier Ltd. All rights reserved.Öğe Contribution of Gamma amino butyric acid (GABA) to salt stress responses of Nicotiana sylvestris CMSII mutant and wild type plants(Elsevier Gmbh, 2012) Akcay, Nese; Bor, Melike; Karabudak, Tugba; Ozdemir, Filiz; Turkan, IsmailPlants accumulate high levels of Gamma amino butyric acid (GABA) in response to different environmental stresses and GABA metabolism has different functions such as osmotic and pH regulation, bypass of tricarboxylic acid cycle, and C:N balance. The cytoplasmic male sterile (CMS) II mutant of Nicotiana sylvestris has a deletion in the mitochondrial gene nad7 which encodes the NAD7 subunit of complex I which causes increased leaf respiration, impaired photosynthesis, slower growth and increased amino acid levels. In this study we aimed to elucidate the role of GABA and GABA metabolism in different genotypes of the same plant system under salt stress (100 mM NaCl) in short (24h) and long (7, 14 and 21 days) terms. We have investigated the differences in leaf fresh and dry weights, relative water content, photosynthetic efficiency (F-v/F-m), glutamate dehydrogenase (GDH. EC 1.4.1.4) and glutamate decarboxylase (GAD, EC 4.1.1.15) enzyme activities, GABA content and GAD gene expression profiles. GDH activity showed variations in CMSII and wild type (WT) plants in the first 24 h. GAD gene expression profiles were in good agreement with the GAD enzyme activity levels in CMSII and WT plants after 24 h. In long-term salinity, GAD activities increased in \NT but, decreased in CMSII. GABA accumulation in WT and CMSII plants in short and long term was induced by salt stress. Variations in GDH and GAD activities in relation to GABA levels were discussed and GABA metabolism has been proposed to be involved in better performance of CMSII plants under long term salinity. (C) 2011 Elsevier GmbH. All rights reserved.Öğe Day and Night Fluctuations in GABA Biosynthesis Contribute to Drought Responses in Nicotiana tabacum L(Taylor & Francis Inc, 2021) Pelvan, Alpay; Bor, Melike; Yolcu, Seher; Ozdemir, Filiz; Turkan, IsmailWhen synchronized with the light/dark cycle the circadian rhythm is termed a diurnal rhythm and this organizes an organism's daily life cycle in relation to the metabolic shifts during the day/night cycles. This is a complex task, particularly under stress conditions. Accurate maintenance of the diurnal rhythm becomes an issue under environmental extremes, such as drought due to the impairment of metabolism, redox balance, and structural integrity. In plants, the non-proteinogenic amino acid GABA accumulates to high levels in response to several stress factors but this is not always dependent on the activation of its biosynthesis. Here we propose a regulatory role to GABA during the diurnal rhythm in plants which is similar to its function in animals where it adjusts the circadian rhythm. Here we investigated whether GABA-biosynthesis was affected by drought stress during the diurnal cycle. For this, we took samples from leaves of N. tabacum plants subjected to PEG-mediated drought stress (-0.73 MPa) during the day and night cycle during a 24 hour period. Glutamate, GABA, and proline contents, along with GDH, GAD enzyme activities and transcript profiles were analyzed. Overall, we conclude that the oscillations in GABA biosynthesis during day and night cycle have an impact on drought stress responses which needs to be elucidated by further analysis.Öğe Deploying root microbiome of halophytes to improve salinity tolerance of crops(Springer, 2020) Akyol, Turgut Yigit; Sato, Shusei; Turkan, IsmailSalinization of the soils is one of the most prominent problems threatening global food security. Root microbiome engineering using biofertilizers provides a sustainable way to increase agricultural productivity. Halophytes, which are extremely salt-tolerant plants, can tolerate up to 1300 mM NaCl. Members of the halophytic root microbiome now provide a promising solution to meet the increased demand in the agricultural output. Here, we explore the members of this microbiome and explain the plant growth-promoting functions of them. We discuss the manipulation of the root microbiome with synthetic microbial communities including keystone microorganisms of the halophytic root microbiome. Importantly, we provide a simple method in R software to find these putative keystone taxa using network analysis. We believe this strategy will provide a valuable tool for future studies performing the combined investigation of the root bacteria and fungi of halophytes.Öğe Different antioxidant defense responses to salt stress during germination and vegetative stages of endemic halophyte Gypsophila oblanceolata Bark.(Pergamon-Elsevier Science Ltd, 2012) Sekmen, Askim Hediye; Turkan, Ismail; Tanyolac, Zehra Ozgecan; Ozfidan, Ceyda; Dinc, AhmetSalinity is a major limiting factor to agricultural productivity. To ensure future productivity of the agricultural regions and achieve a selection of genetically transformed salt-tolerant plants, there is a need to select and characterize salt-tolerant plants. Gypsophila oblanceolata Bark. is a Turkish endemic and endangered halophyte occurring in salt marshes/hydromorphic soils. The aim of this experiment was to determine the responses of G. oblanceolata to salt stress during germination and vegetative growth. Therefore, effects of salinity (0, 50,100, 150, 300 mM NaCl) on germination and changes in the activities of antioxidant enzymes/isoenzymes (SOD. CAT and PDX) during germination under stress and recovery after stress were determined. Moreover, during vegetative growth (60 d old plants), changes in physiological parameters, ion concentrations, proline (Pro) content, lipid peroxidation (MDA), H2O2 content, NADPH oxidase activity and, antioxidant enzyme/isoenzyme system (superoxide dismutase (SOD), catalase (CAT), peroxidase (PDX), ascorbate peroxidase (APX), glutathione reductase (GR)) were also investigated. Salt stress decreased both the germination percentage and rate. Few seeds germinated at 100 mM NaCl. Exposure to high concentrations of NaCl did not permanently inhibit germination. Salinity (50 mM NaCl) caused a decrease in activities of SOD, CAT and PDX during germination. However, after stress, the activities of all enzymes were increased in recovered-plants. During vegetative growth, increased activities of SOD, CAT and APX in 50 and 100 mM NaCl treated-plants may help to avoid oxidative damage in G. oblanceolata. However, at higher doses, induced stimulation of the CAT, PDX and GR was not sufficient to cope with the enhanced ROS production and MDA level. From the results obtained in present study, it can be suggested that G. oblanceolata is a moderately salt-tolerant species. Differential responses of antioxidant enzymes to salt stress during germination and vegetative growth suggested different antioxidant metabolism in G. oblanceolata. (C) 2011 Elsevier B.V. All rights reserved.Öğe Differential regulation of reactive oxygen species in dimorphic chloroplasts of single cell C-4 plant Bienertia sinuspersici during drought and salt stress(Frontiers Media Sa, 2023) Uzilday, Baris; Ozgur, Rengin; Yalcinkaya, Tolga; Sonmez, Mustafa Cemre; Turkan, IsmailSingle cell C-4 (SCC4) plants, discovered around two decades ago, are promising materials for efforts for genetic engineering of C-4 photosynthesis into C-3 crops. Unlike C-4 plants with Kranz anatomy, they exhibit a fully functional C-4 photosynthesis in just a single cell and do not require mesophyll and bundle sheath cell spatial separation. Bienertia sinuspersici is one such SCC4 plant, with NAD-malic enzyme (NAD-ME) subtype C-4 photosynthesis. Its chlorenchyma cell consist of two compartments, peripheral compartment (PC), analogous to mesophyll cell, and central compartment (CC), analogous to bundle sheath cell. Since oxidative stress creates an important constraint for plants under salinity and drought, we comparatively examined the response of enzymatic antioxidant system, H2O2 and TBARS contents, peroxiredoxin Q, NADPH thioredoxin reductase C, and plastid terminal oxidase protein levels of PC chloroplasts (PCC) and CC chloroplasts (CCC). Except for protein levels, these parameters were also examined on the whole leaf level, as well as catalase and NADPH oxidase activities, water status and growth parameters, and levels of C-4 photosynthesis related transcripts. Many C-4 photosynthesis related transcript levels were elevated, especially under drought. Activities of dehydroascorbate reductase and especially peroxidase were elevated under drought in both compartments (CCC and PCC). Even though decreases of antioxidant enzyme activities were more prevalent in PCC, and the examined redox regulating protein levels, especially of peroxiredoxin Q, were elevated in CCC under both stresses, PCC was less damaged by either stress. These suggest PCC is more tolerant and has other means of preventing or alleviating oxidative damage.Öğe Differential responses of the scavenging systems for reactive oxygen species (ROS) and reactive carbonyl species (RCS) to UV-B irradiation in Arabidopsis thaliana and its high altitude perennial relative Arabis alpina(Springernature, 2021) Ozgur, Rengin; Uzilday, Baris; Yalcinkaya, Tolga; Akyol, Turgut Yigit; Yildirim, Hasan; Turkan, IsmailThe present work aimed to compare antioxidant response and lipid peroxide detoxification capacity of an arctic-alpine species Arabis alpina to its close relative model species Arabidopsis thaliana under acute short duration (3 h and 6 h) UV-B stress (4.6 and 8.2 W/m(2)). After 3 and 6 h exposure to UV-B, A. alpina showed lower lipid peroxidation and H2O2 accumulation when compared to A. thaliana. Moreover, F-v/F-m value of A. thaliana dropped to 0.70, while A. alpina dropped to 0.75 indicating better protection of PSII in this species. For elucidation of the antioxidant response, activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR) and dehydroascorbate reductase (DHAR) were measured. SOD induction with 6 h of UV-B was more prominent in A. alpina. Also, A. alpina had higher chloroplastic FeSOD activity when compared to A. thaliana. APX activity was also significantly induced in A. alpina, while its activity decreased at 3 h or did not change at 6 h in A. thaliana. A. alpina was able to maintain constant CAT activity, but drastic decreases were observed in A. thaliana at both time points. Moreover, A. alpina was able to maintain or induce aldehyde dehydrogenase (ALDH), alkenal reductases (AERs) and glutathione-S-transferases (GST) activity, while an opposite trend was observed in A. thaliana. These findings indicate that A. alpina was able to maintain/induce its antioxidant defence and lipid peroxide detoxification conferring better protection against UV-B.Öğe Effect of Coronatine on Antioxidant Enzyme Response of Chickpea Roots to Combination of PEG-Induced Osmotic Stress and Heat Stress(Springer, 2013) Ceylan, Hulya Arikan; Turkan, Ismail; Sekmen, Askim HediyeAbiotic stresses, such as high temperature and drought, are major limiting factors of crop production and growth. Coronatine (COR), a structural and functional analog of jasmonates, is suggested to have a role in abiotic stress tolerance. The aim of our study was to examine whether pretreatment with COR enhances the tolerance of chickpea (Cicer arietinum L. cv ICC 4958) roots to PEG-induced osmotic stress, heat stress, and their combination. Therefore, seedlings raised hydroponically in a growth chamber for 15 days were pretreated with or without COR at 0.01 mu M for 24 h and then exposed to 6 % PEG 6000-induced osmotic stress or heat (starting at 35 A degrees C and then gradually increased 1 A degrees C every 15 min and kept at 44 A degrees C for 1 h) stress for 3 days. After different treatment periods, the changes in relative growth rate (RGR); malondialdehyde (MDA), proline (Pro), and hydrogen peroxide (H2O2) contents; and the activities of antioxidant enzymes/isoenzymes in roots of chickpea seedlings with or without 0.01 mu M COR application were studied. RGR in roots was increased by COR application. Under all stress conditions, H2O2, MDA, and Pro levels increased sharply, but pretreatment with COR significantly reduced them. Moreover, COR increased the activities of H2O2 scavenger enzymes such as catalase (CAT) under heat stress, ascorbate peroxidase (POX) under PEG stress, and CAT and POX under combined stresses. Therefore, COR might alleviate adverse effects of PEG stress and heat stress and combined stresses on roots of chickpea by reduction of H2O2 production, enhancing or keeping the existent activity of antioxidant enzymes, thereby preventing membrane peroxidation.Öğe Effect of Coronatine on Antioxidant Enzyme Response of Chickpea Roots to Combination of PEG-Induced Osmotic Stress and Heat Stress(Springer, 2013) Ceylan, Hulya Arikan; Turkan, Ismail; Sekmen, Askim HediyeAbiotic stresses, such as high temperature and drought, are major limiting factors of crop production and growth. Coronatine (COR), a structural and functional analog of jasmonates, is suggested to have a role in abiotic stress tolerance. The aim of our study was to examine whether pretreatment with COR enhances the tolerance of chickpea (Cicer arietinum L. cv ICC 4958) roots to PEG-induced osmotic stress, heat stress, and their combination. Therefore, seedlings raised hydroponically in a growth chamber for 15 days were pretreated with or without COR at 0.01 mu M for 24 h and then exposed to 6 % PEG 6000-induced osmotic stress or heat (starting at 35 A degrees C and then gradually increased 1 A degrees C every 15 min and kept at 44 A degrees C for 1 h) stress for 3 days. After different treatment periods, the changes in relative growth rate (RGR); malondialdehyde (MDA), proline (Pro), and hydrogen peroxide (H2O2) contents; and the activities of antioxidant enzymes/isoenzymes in roots of chickpea seedlings with or without 0.01 mu M COR application were studied. RGR in roots was increased by COR application. Under all stress conditions, H2O2, MDA, and Pro levels increased sharply, but pretreatment with COR significantly reduced them. Moreover, COR increased the activities of H2O2 scavenger enzymes such as catalase (CAT) under heat stress, ascorbate peroxidase (POX) under PEG stress, and CAT and POX under combined stresses. Therefore, COR might alleviate adverse effects of PEG stress and heat stress and combined stresses on roots of chickpea by reduction of H2O2 production, enhancing or keeping the existent activity of antioxidant enzymes, thereby preventing membrane peroxidation.Öğe The effect of salt stress on lipid peroxidation, antioxidative enzymes and proline content of sesame cultivars(Pergamon-Elsevier Science Ltd, 2007) Koca, Hulusi; Bor, Melike; Ozdemir, Filiz; Turkan, IsmailThe effect of increasing NaCl concentrations was studied on two different cultivars (cv. Orhangazi and cv. Cumhuriyet) of Sesamum indicum. Seedlings were grown for 40 days in half strength Hoagland solution and after 40 days treated with different NaCl concentrations (0, 50 and 100 mM) for 21 days. Differences in growth parameters, lipid peroxidation, antioxidative enzyme activities and proline accumulation were tested in order to put forward the relative tolerance or sensitivity of the cultivars. Results indicated that both parameters differ according to the cultivar's ability in coping oxidative stress caused by salinity. Constitutive levels of antioxidative enzyme activities were almost the same between the cultivars; however, cv. Cumhuriyet was able to induce antioxidative enzyme activities more efficiently when subjected to salt stress. Growth parameters, lipid peroxidation and proline accumulation results are also in good correlation with supporting this cultivar's being relatively tolerant. (C) 2007 Elsevier B.V. All rights reserved.Öğe The effects of boron toxicity on root antioxidant systems of two chickpea (Cicer arietinum L.) cultivars(Springer, 2009) Ardic, Murat; Sekmen, Askim Hediye; Turkan, Ismail; Tokur, Sueleyman; Ozdemir, FilizSignificant differences in the antioxidant systems of the roots of two chickpea (Cicer arietinum L.) cultivars differing in tolerance to drought were observed in under toxic boron (B) conditions. Three-week-old chickpea seedlings were subjected to 0.05 mM (control), 1.6 mM or 6.4 mM B in the form of boric acid (H3BO3) for 7 days. At the end of the treatment period, root length, dry weight, boron concentration, malondialdehyde (MDA) content, and the activities of antioxidant enzymes-superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), ascorbate peroxidase (APOX) and glutathione reductase (GR)-were measured. Root length of the drought-tolerant Gokce cultivar did not change under 1.6 mM B but increased under 6.4 mM B. On the contrary, root length decreased in the drought-sensitive Kusmen cultivar under both B concentrations. While root dry weight was unaffected in Gokce, it decreased in Kusmen under both B concentrations. Boron concentration was significantly higher in Kusmen than in Gokce at both B levels. Significant increases in SOD and POX activities were observed in roots of both cultivars under 1.6 and 6.4 mM B. Root extracts exhibited three SOD and three POX activity bands in both cultivars under B stress when compared to control groups. Although CAT activity in Gokce was increased, it decreased in Kusmen at the highest B concentration as compared to control groups. Roots of both cultivars showed no significant change in APOX activity under B toxicity (except in 1.6 mM B treated roots of Kusmen) when compared to control groups. GR activity in the roots of Kusmen decreased significantly with increasing B concentration. However, a significant increase in GR activity was found in Gokce under 1.6 mM B stress. In addition, lipid peroxidation levels of drought-sensitive Kusmen increased, indicating more damage to membrane lipids due to B toxicity. Lipid peroxidation did not change in the drought-tolerant Gokce cultivar at either B concentration. These results suggest that roots of Gokce are better protected from B-stress-induced oxidative stress due to enhanced SOD, CAT and POX activities under high B levels.Öğe The Effects of Melatonin on Transcriptional Profile of Unfolded Protein Response Genes Under Endoplasmic Reticulum Stress in Arabidopsis thaliana(Springer, 2017) Ozgur, Rengin; Uzilday, Baris; Turkan, Ismail; Sekmen, A. HediyeWhen the load of secretory pathway is increased or folding capacity in the endoplasmic reticulum (ER) is insufficient, unfolded proteins might accumulate in ER lumen causing a phenomenon called ER stress. During ER stress, normal cell functions are suppressed and unfolded protein response (UPR) is induced. Studies in animal systems suggest that melatonin alleviates the detrimental effects of ER stress; however, there is no study in plants in this respect. Hence, in this study, we investigated the possible role of melatonin on alleviation of ER stress in model plant Arabidopsis thaliana. Tunicamycin (Tm) was used to specifically induce ER stress. Melatonin treatment (10 and 25 mu M but not 1 mu M) increased root growth under Tm treatment, but it did not reach control levels. ER stress induced the expressions of ER stress sensor/transducer genes, ER chaperones and folding helper genes, ER-associated degradation (ERAD) genes, and ER stress-associated apoptosis genes in roots and shoots (a total of 16 genes). Among them, the expressions of ER stress sensor/transducer bZIP17, bZIP28, IRE1A, IRE1B, ERAD-related SEL1, and apoptosis genes AGB1 were decreased back to control levels with 25 mu M melatonin under ER stress in roots. Moreover, Tm + melatonin treatments decreased the expressions of these genes when compared to only Tm-treated plants. Downregulation of UPR components with increased concentrations of melatonin under Tm treatment demonstrated that melatonin alleviated the detrimental effects of ER stress.Öğe Emerging roles for ROS and RNS - versatile molecules in plants(Oxford Univ Press, 2017) Turkan, IsmailIncreased cellular levels of potentially harmful reactive oxygen species (ROS) and reactive nitrogen species (RNS) come about as plants contend with harsh environmental conditions. At low concentrations, however, ROS and RNS can act as signals for the regulation of growth and development and for defence against biotic and abiotic stress. Indeed, we now know that they are involved in nearly every facet of plant metabolism and cell function. This virtual issue introduces active research in this rapidly moving field, as well as discussing the gaps in our knowledge and the technical developments which are opening up new vistas.Öğe Endoplasmic reticulum stress regulates glutathione metabolism and activities of glutathione related enzymes in Arabidopsis(Csiro Publishing, 2018) Uzilday, Baris; Ozgur, Rengin; Sekmen, A. Hediye; Turkan, IsmailStress conditions generate an extra load on protein folding machinery in the endoplasmic reticulum (ER) and if the ER cannot overcome this load, unfolded proteins accumulate in the ER lumen, causing ER stress. ER lumen localised protein disulfide isomerase (PDI) catalyses the generation of disulfide bonds in conjugation with ER oxidoreductase1 (ERO1) during protein folding. Mismatched disulfide bonds are reduced by the conversion of GSH to GSSG. Under prolonged ER stress, GSH pool is oxidised and H2O2 is produced via increased activity of PDI-ERO1. However, it is not known how glutathione metabolism is regulated under ER stress in plants. So, in this study, ER stress was induced with tunicamycin (0.15, 0.3, 0.45 mu g mL(-1) Tm) in Arabidopsis thaliana (L.) Heynh. Glutathione content was increased by ER stress, which was accompanied by induction of glutathione biosynthesis genes (GSH1, GSH2). Also, the apoplastic glutathione degradation pathway (GGT1) was induced. Further, the activities of glutathione reductase (GR), dehydroascorbate reductase (DHAR), glutathione peroxidase (GPX) and glutathione S-transferase (GST) were increased under ER stress. Results also showed that chloroplastic GPX genes were specifically downregulated with ER stress. This is the first report on regulation of glutathione metabolism and glutathione related enzymes in response to ER stress in plants.Öğe Endoplasmic reticulum stress triggers ROS signalling, changes the redox state, and regulates the antioxidant defence of Arabidopsis thaliana(Oxford Univ Press, 2014) Ozgur, Rengin; Turkan, Ismail; Uzilday, Baris; Sekmen, Askim H.Endoplasmic reticulum stress, which is induced by tunicamycin, triggers reactive oxygen species signalling via NADPH oxidase activity and also regulates the antioxidant defence system in Arabidopsis thaliana.Inefficient chaperone activity in endoplasmic reticulum (ER) causes accumulation of unfolded proteins and is called ER stress, which triggers the unfolded protein response. For proper oxidative protein folding, reactive oxygen species (ROS) such as H2O2 are produced in the ER. Although the role of ROS during abiotic stresses such as salinity is well documented, the role of ER-related ROS production and its signalling is not yet known. Moreover, how H2O2 production, redox regulation, and antioxidant defence are affected in salt-treated plants when ER protein-folding machinery is impaired needs to be elucidated. For this aim, changes in NADPH-oxidase-dependent ROS signalling and H2O2 content at sequential time intervals and after 48h of ER stress, induced by tunicamycin (Tm), salinity, and their combination were determined in Arabidopsis thaliana. The main root growth was inhibited by ER stress, while low levels of Tm caused an increase in lateral root density. Salt stress and Tm induced the expression of ER-stress-related genes (bZIP17, bZIP28, bZIP60, TIN1, BiP1, BiP3) and ERO1. Tm induced expression of RBOHD and RBOHF, which led to an early increase in H2O2 and triggered ROS signalling. This study is the first report that ER stress induces the antioxidant system and the AsadaHalliwell pathway of A. thaliana in a similar way to salinity. ER stress caused oxidative damage, as evident by increased H2O2 accumulation, lipid peroxidation, and protein oxidation. As a result, this study shows that ER stress triggers ROS signalling, changes the redox state, and regulates the antioxidant defence of A. thaliana.
