52 research outputs found
Sulfate-induced stomata closure requires the canonical ABA signal transduction machinery
No full textPhytohormone abscisic acid (ABA) is the canonical trigger for stomatal closure upon abiotic stresses like drought. Soil-drying is known to facilitate root-to-shoot transport of sulfate. Remarkably, sulfate and sulfide—a downstream product of sulfate assimilation—have been independently shown to promote stomatal closure. For induction of stomatal closure, sulfate must be incorporated into cysteine, which triggers ABA biosynthesis by transcriptional activation of NCED3. Here, we apply reverse genetics to unravel if the canonical ABA signal transduction machinery is required for sulfate-induced stomata closure, and if cysteine biosynthesis is also mandatory for the induction of stomatal closure by the gasotransmitter sulfide. We provide genetic evidence for the importance of reactive oxygen species (ROS) production by the plasma membrane-localized NADPH oxidases, RBOHD, and RBOHF, during the sulfate-induced stomatal closure. In agreement with the established role of ROS as the second messenger of ABA-signaling, the SnRK2-type kinase OST1 and the protein phosphatase ABI1 are essential for sulfate-induced stomata closure. Finally, we show that sulfide fails to close stomata in a cysteine-biosynthesis depleted mutant. Our data support the hypothesis that the two mobile signals, sulfate and sulfide, induce stomatal closure by stimulating cysteine synthesis to trigger ABA production
Local Historiography in Early Medieval Iran and the <i>Tārīkh-i Bayhaq</i>
No full textDuring the medieval period iran produced one of the richest repertoires of local histories in the Islamic world. Ibn Funduq, the author of the local history of Bayhaq studied here, enumerates 15 local histories of Khurasan alone. These include three local histories of Marv by al-ᶜAbbas b. Musᶜab b. Bishr, Abu'l-Hasan Ahmad b. Sayyar (198-268/814-881), and Abu'l-ᶜAbbas b. Saᶜid al-Maᶜdani (d. 375/986). (al-Sakhawi calls Musᶜab b. Bishr's work a “history of (the city).“) To these Ibn Funduq adds two local histories of Herat by Abu Ishaq Ahmad b. Muhammad b. Yunis (?) al-Bazzaz and Abu Ishaq Ahmad b. Muhammad b. Saᶜid al-Haddad. (Sakhawi, apparently confused, attributes both histories to Abu Ishaq Muhammad b. Yasin al-Harawi al-Haddad); a Tārīkh-i Bukhārā va Samarqand by Saᶜd b. Janah; two histories of Khwarazm by al-Sari b. Dalwiya and Abu ᶜAbdallah Muhammad b. Saᶜid respectively; a history of Balkh by Abu ᶜAbdallah Muhammad b. ᶜAqil al-Faqih;</jats:p
Electrocatalytic oxidations and reductions in ionic liquids
No full textIn this thesis, surface electrocatalysis of several energy-conversion-relevant redox reactions in ionic liquid electrolytes is described. The first oxidation process investigated is the formation of surface oxide films on Pt electrodes by trace water oxidation in protic ionic liquids (PILs). This is followed by investigation of the oxidation of hydrazine (N2H4), formic acid (HCOOH), ethanol (EtOH) and dimethyl ether (DME) in PILs and a description of the role played by surface oxides during each oxidation process. Finally, the electrocatalytic reduction of CO2 at a variety of electrode materials is explored in room temperature aprotic ionic liquids.
The data reveal that the surfaces of Pt electrodes become covered with oxide layers due to oxidation of trace water, which is omnipresent in PILs, at positive potentials (E > 1.0 V vs. Pd-H). X-ray photoelectron spectroscopy (XPS) shows that the oxide layers grow to form thick films as the potential is made more positive and as the temperature and water concentration of the PILs are increased. The mechanism and kinetics of oxide film growth are also discussed.
Voltammetric analysis shows that the presence of residual surface oxides activates Pt electrodes towards electrooxidation of N2H4. Furthermore, immersion of oxidized Pt electrodes in N2H4-containing PILs deactivates the electrode indicating that N2H4 reacts with the residual surface oxides. Oxidation of HCOOH at Pt catalyst in PILs occurs mainly by dehydration plus COads oxidation at a potential that coincides with the onset of the formation of Pt surface oxides. Compared to Pt electrocatalysts, the overpotential for electrooxidation of HCOOH is higher at Au catalyst but lower at Pd catalyst.
Oxidation of trace water in PILs at Pt also plays a pivotal role during the electrocatalytic oxidation of EtOH and DME in the PILs. Oxidation of both EtOH and DME coincides with coverage of the Pt surface by the adsorbed oxide species that helps to activate both processes by oxidizing the adsorbed poisoning CO and CO-like intermediate species via a 'bifunctional' reaction mechanism. Generally, higher overpotentials are observed for each oxidation, and higher activation energies are measured for EtOH oxidation in PILs than in aqueous electrolytes.
Finally, it is shown that CO2 electroreduction takes place at lower overpotentials at Au and Ag electrocatalysts than at Cu, Pt and boron doped diamond (BDD) electrodes in the presence of ionic liquid electrolytes. Ag electrocatalysts reduce CO2 at ~0.2 V lower potential when 1-ethyl-3-methylimidazolium ethylsulphate [emim][EtSO4] is used as supporting electrolyte in acetonitrile compared to when the conventional supporting electrolyte tetrabutylammonium hexaflourophosphate [TBA][PF6] is used. CO is a product of CO2 reduction at Ag catalyst and the results highlight that Ag and imidazolium-based ILs could be a promising system for reduction of CO2 to CO at low overpotentials
Electrocatalytic oxidations and reductions in ionic liquids
No full textIn this thesis, surface electrocatalysis of several energy-conversion-relevant redox reactions in ionic liquid electrolytes is described. The first oxidation process investigated is the formation of surface oxide films on Pt electrodes by trace water oxidation in protic ionic liquids (PILs). This is followed by investigation of the oxidation of hydrazine (N2H4), formic acid (HCOOH), ethanol (EtOH) and dimethyl ether (DME) in PILs and a description of the role played by surface oxides during each oxidation process. Finally, the electrocatalytic reduction of CO2 at a variety of electrode materials is explored in room temperature aprotic ionic liquids.
The data reveal that the surfaces of Pt electrodes become covered with oxide layers due to oxidation of trace water, which is omnipresent in PILs, at positive potentials (E > 1.0 V vs. Pd-H). X-ray photoelectron spectroscopy (XPS) shows that the oxide layers grow to form thick films as the potential is made more positive and as the temperature and water concentration of the PILs are increased. The mechanism and kinetics of oxide film growth are also discussed.
Voltammetric analysis shows that the presence of residual surface oxides activates Pt electrodes towards electrooxidation of N2H4. Furthermore, immersion of oxidized Pt electrodes in N2H4-containing PILs deactivates the electrode indicating that N2H4 reacts with the residual surface oxides. Oxidation of HCOOH at Pt catalyst in PILs occurs mainly by dehydration plus COads oxidation at a potential that coincides with the onset of the formation of Pt surface oxides. Compared to Pt electrocatalysts, the overpotential for electrooxidation of HCOOH is higher at Au catalyst but lower at Pd catalyst.
Oxidation of trace water in PILs at Pt also plays a pivotal role during the electrocatalytic oxidation of EtOH and DME in the PILs. Oxidation of both EtOH and DME coincides with coverage of the Pt surface by the adsorbed oxide species that helps to activate both processes by oxidizing the adsorbed poisoning CO and CO-like intermediate species via a 'bifunctional' reaction mechanism. Generally, higher overpotentials are observed for each oxidation, and higher activation energies are measured for EtOH oxidation in PILs than in aqueous electrolytes.
Finally, it is shown that CO2 electroreduction takes place at lower overpotentials at Au and Ag electrocatalysts than at Cu, Pt and boron doped diamond (BDD) electrodes in the presence of ionic liquid electrolytes. Ag electrocatalysts reduce CO2 at ~0.2 V lower potential when 1-ethyl-3-methylimidazolium ethylsulphate [emim][EtSO4] is used as supporting electrolyte in acetonitrile compared to when the conventional supporting electrolyte tetrabutylammonium hexaflourophosphate [TBA][PF6] is used. CO is a product of CO2 reduction at Ag catalyst and the results highlight that Ag and imidazolium-based ILs could be a promising system for reduction of CO2 to CO at low overpotentials
Electrochemistry of ethanol and dimethyl ether at a Pt electrode in a protic ionic liquid: the electrode poisoning mechanism
No full textA protic ionic liquid (PIL), N,N-diethyl-N-methyl ammonium trifluoromethane sulfonate, [dema][TfO] was synthesized and confirmed using 1H-NMR and ion chromatography (IC). The surface electrocatalysis of ethanol (EtOH) and dimethyl ether (DME) was investigated on a polycrystalline Pt electrode in a PIL using a cyclic voltammetry technique. The voltammetry response shows that surface Pt-oxides/hydroxides (PtOH/PtO) are formed due to the oxidation of trace water (240 ppm determined by coulometric Karl-Fischer (FT) titration) in [dema][TfO] which plays a pivotal role during the electrocatalytic oxidation of EtOH and DME in the PIL. Oxidation of EtOH and DME coincides with coverage of the Pt surface by the adsorbed oxide species that helps to activate both processes by oxidizing the adsorbed poisoning CO and CO-like intermediate species via a ‘bifunctional’ reaction mechanism. The influence of temperature was investigated to obtain quantitative and qualitative information on the kinetics of EtOH oxidation. Higher activation energies are measured for EtOH oxidation in [dema][TfO] than in aqueous electrolytes due to the low water content and high viscosity of the PIL. This study gave a basic insight into the mechanism of EtOH and DME oxidation reactions, and the Pt-electrode poisoning species formation mechanism in the neoteric electrolyte medium is electrochemically investigated and reported
Efficient electrocatalytic reduction of CO2 on an Ag catalyst in 1-ethyl-3-methylimidazolium ethylsulfate, with its co-catalytic role as a supporting electrolyte during the reduction in an acetonitrile medium
No full textCO2 electrochemical reduction reactions (CO2ERR) has shown great promise in reducing greenhouse gas emissions while also producing useful chemicals. In this contribution, we describe the CO2ERR at different catalysts using 1-ethyl-3-methylimidazolium ethyl sulfate [emim][EtSO4] ionic liquid (IL) as a solvent and as a supporting electrolyte. CO2ERR occurs at Ag and Cu catalysts at a lower overpotential than that at Au, Pt, and boron-doped diamond (BDD) catalysts. In addition, we report that ILs play a better co-catalytic role when used as a supporting electrolyte during CO2ERR in an acetonitrile (AcN) medium than the conventional supporting electrolyte, tetrabutylammonium hexafluorophosphate [TBA][PF6] in AcN. Furthermore, it is found that imidazolium-based cations ([emim]+) play a significant co-catalytic role during the reduction compared to [TBA]+ and pyrrolidinium [empyrr]+ cations, while anions of the ILs play no such role. The formation of CO from the CO2ERR was detected using cyclic voltammetry at an Ag catalyst both in [emim][EtSO4] as well as in an AcN solvent containing [emim][EtSO4] as a supporting electrolyte. The product of the CO2 reduction in this IL medium at the Ag catalyst is CO, which can be converted to synthetic liquid fuels by coupling the process with the Fischer–Tropsch process or through the conversion of CO2 into fuels based on green hydrogen by the Sabatier process, that is, methanation of CO2 on industrial scale, in the future.Godkänd;2025;Nivå 0;2025-05-09 (u8);Funder: University of Nottingham; Higher Education Commission (HEC), Pakistan; Islamia College, Peshawar;Full text license: CC BY</p
The role of sulfite reductase in assimilatory sulfate reduction in Arabidopsis thaliana
No full textReductive assimilation of inorganic sulfate to sulfide is an essential metabolic process in higher plants for the synthesis of cysteine and all downstream compounds containing reduced sulfur in the cell. Sulfite reductase (SiR) palys a central role in the assimilatory sulfate reduction pathway by catalyzing the reduction of sulfite to sulfide. An Arabidopsis T-DNA insertion line (sir1-1) with an insertion in the promoter region of SiR was isolated in order to address the exact role of SiR in vivo. Detailed characterization of sir1-1 revealed that homozygous sir1-1 plants are viable, but severely affected in growth. Homozygous sir1-1 plants flower and set viable seeds, albeit later than wild-type plants grown under the same conditions. Evaluation of SiR transcript levels in the leaves of sir1-1 plants revealed that the mRNA was down-regulated to about 50% of wild-type level. Consequently, the amount of SiR protein and the SiR activity were reduced in the same manner. The significant differences between the leaves of sir1-1 and Col-0 plants for most of the sulfur-containing and other related compounds such as cysteine, O-acetylserine (OAS), sulfate, nitrate, total glucosinolates, total carbon (C), nitrogen (N), and sulfur (S) suggests strong perturbations in the entire metabolism of sir1-1 plants. A reduction of approximately 25.6-fold and 32.7-fold in the incorporation of 35S label into cysteine and GSH fractions, respectively, of sir1-1 leaves compared to wild-type plants was observed, suggesting the fact that the activity of SiR generates a severe bottleneck in the sulfur assimilation pathway. Investigations of the transcript levels through microarray analysis revealed that the expression of many genes related to sulfur metabolism was altered in response to reduced sulfide synthesis. Out of 920 selected genes related to sulfur metabolism, the expression of 67 genes in the leaves and 180 genes in the roots of sir1-1, were significantly up- or down-regulated compared to wild-type. The high affinity sulfate transporters, sulfate transporter 1;1 (SULTR 1;1) and sulfate transporter 1;2 (SULTR 1;2) showed a significant up-regulation in the roots of sir1-1 compared to Col-0. The up-regulation of the high affinity sulfate transporters in the roots of sir1-1 suggests that instead of steady-state sulfate levels, the amount of reduced sulfur present in the cell, likely forms the signal for their their induction. The preliminary results for a second T-DNA insertion line (sir1-2) strongly indicate that an insertion more closer to the gene, in the promoter region of SiR causes early seedling lethality. All results point towards the exclusiveness of SiR for sufite reduction and that its optimal activity is essential for the normal growth of Arabidopsis plants. Treatment of different Arabidopsis lines with selenate, which is quite similar to sulfate, caused an increase in the total sulfur and selenium contents of the plants. This might happen due to the up-regulation of sulfate transporters which might eventually lead to an increase in total sulfur and selenium due to elevated sulfate/selenate contents
Utilization of genes encoding osmoprotectants in transgenic plants for enhanced abiotic stress tolerance
No full textAbstractGlobal agriculture in the context of growing and expanding populations is under huge pressure to provide increased food, feed, and fiber. The recent phenomenon of climate change has further added fuel to the fire. It has been practically established now that the global temperature has been on the increase with associated fluctuations in annual rainfall regimes, and the resultant drought and flood events and increasing soil and water salinization. These challenges would be met with the introduction and utilization of new technologies coupled with conventional approaches. In recent years, transgenic technology has been proved very effective in terms of production of improved varieties of crop plants, resistant to biotic stresses. The abiotic stresses such as salt and drought are more complex traits, controlled by many genes. Transgenic plant development for these stresses has utilized many single genes. However, much emphasis has been placed on genes catalyzing the biosynthetic pathways of osmoprotectants. This review focuses on the current status of research on osmoprotectant genes and their role in abiotic stress tolerance in transgenic plants
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