Low-temperature synthesis of high-entropy amorphous metal oxides (HEOs) for enhanced oxygen evolution performance.

The rational design of multiple metal ions into high-entropy oxide electrode material via a single-step hydrothermal process is applicable to the evolution of oxygen molecules (O2) through simple water electrolysis. Their cost-effectiveness, high performance, and durable nature are the key factors of non-precious high-entropy multiple metal-based electrocatalysts, which can be used as replaceable catalysts instead of precious ones. This article reports a low-temperature synthesis of the cauliflower-type morphology of high-entropy amorphous metal oxides, and their electrochemical performances towards the oxygen evolution reaction (OER) are investigated. The multiple metal ion (Mn2+, Fe3+, Co2+, Ni2+, Cu2+) oxide electrode material shows an acceptable oxygen evolution reaction (OER) with an overpotential of 290 mV at a current density of 10 mA cm-2 and a lower Tafel slope value of 85 mV dec-1, respectively. Moreover, the 20 h durability test with negligible change in overpotential shows the efficacy of the modified electrode material in harsh alkaline media. The observed electrochemical results towards the OER correspond to the amorphous nature of the active material that displayed a cauliflower-type morphology, having a large specific surface area (240 m2 g-1) and providing higher electrochemical active sites as well. Consequently, post-stability characterization studies (such as PXRD, FESEM, TEM, and XPS) provide more information for understanding the post-structural and morphological results of the high-entropy amorphous metal oxide.

Chlorophyll Biosynthetic Reactions during Senescence of Excised Barley (Hordeum vulgare L. cv IB 65) Leaves.

The chlorophyll (Chl) biosynthetic reactions were monitored during senescence of dark-incubated excised barley (Hordeum vulgare L. cv IB 65) leaves floated in double-distilled water or kinetin solution. Kinetin abolished the degradation of Chl but failed to check the net degradation of protochlorophyllide (Pchlide), suggesting that different sets of enzymes, i.e. kinetin sensitive and insensitive, are responsible for the degradation of Chl and Pchlide, respectively. Upon exposure of the leaves to light, the dark-accumulated Pchlide was efficiently phototransformed to chorophyllide (Chlide), even on the 7th d of dark incubation, demonstrating that the activity of Pchlide reductase, one of the late enzymes of the Chl biosynthetic pathway, is not substantially affected during senescence. The senescing leaves continued to synthesize Pchlide and Chlide until the 7th d, although at a reduced rate (20% of the 1st d). The decline of the rate of synthesis of Pchlide and Chlide is due to the loss of activity of two early enzymes of the Chl biosynthetic pathway, i.e. 5-aminolevulinic acid dehydratase and porphobilinogen deaminase. Kinetin substantially checked the loss of activity of these two enzymes.

Inhibition of Photosystem I and Photosystem II in Wheat Seedlings with their Root-shoot Transition Zones Exposed to Red Light.

The present study was conducted to observe the role of the root-shoot transition zone in the development of PS I and PS II in red light. The development of PS II and PS I was severely inhibited when root-shoot transition zones of wheat seedlings were exposed to red light (670 nm) of intensity 500 micromol m(-2) s(-1). Chlorophyll biosynthesis was also inhibited in these seedlings. Most of the PS I and PS II proteins (D1, LHCPII, CP47, OEC33) and their transcript levels were severely inhibited but cyt b6f complex proteins were only partially inhibited. Protein and transcript levels of Rubisco large subunit and protochlorophyllide (Pchlide) biosynthesis were also severely inhibited in these seedlings. When incubated in the dark with or without the precursor of chlorophyll biosynthesis ALA, these plants accumulated most of the Pchlide, as non-phototransformable Pchlide, suggesting low activity of NADPH:protochlorophyllide oxidoreductase (EC 1.6.99.1) in these plants. These effects were not observed when the seedlings were grown in red light with their root-shoot transition zones covered. These results suggest that the root-shoot transition zone plays an important role in the overall greening process involving transcription and translation of photosynthetic genes.

Oxidative stress in cucumber (Cucumis sativus L) seedlings treated with acifluorfen.

Treatment of diphenyl ether herbicide acifluorfen-Na (AF-Na) to intact cucumber (Cucumis sativus L cv Poinsette) seedlings induced overaccumulation of protoporphyrin IX in light (75 mumole m-2 s-1). The extra-plastidic protoporphyrin IX accumulated during the light exposure disappeared within two hours of transfer of acifluorofen-treated seedlings to darkness. The dark disappearance was due to re-entry of migrated protoporphyrin IX into the plastid and its subsequent conversion to protochlorophyllide. In light, protoporphyrin IX acted as a photosensitizer and caused generation of active oxygen species. The latter caused damage to the cellular membranes by peroxidation of membrane lipids that resulted in production of malondialdehyde. Damage to the plastidic membranes resulted in damage to photosystem I and photosystem II reactions. Dark-incubation of herbicide-sprayed plants before their exposure to light enhanced photodynamic damage due to diffusion of the herbicide to the site of action. Compared to control, in treated samples the cation-induced increases in variable fluorescence/maximum fluorescence ratio and increase in photosystem II activity was lower due to reduced grana stacking in herbicide-treated and light-exposed plants.

Additive action on boehmite precipitation in sodium aluminate solution.

Precipitation of boehmite (Al(2)O(3)·H(2)O) instead of gibbsite (Al(2)O(3)·3H(2)O) from sodium aluminate liquor can be an energy saving option for alumina production. Gibbsite is stable at precipitation temperature lower than 90 °C. Thus when boehmite is precipitated below 90 °C it is always accompanied with a gibbsite phase. However, the addition of certain organic additives favours precipitation of a monophase product i.e. boehmite at a temperature lower than 90 °C. At a temperature as low as 60 °C additives like tartaric acid, xylose and glucose could favour the precipitation of single phase boehmite precipitation. The role of the additive is proposed to be complete inhibition of gibbsite formation and facilitation of boehmite nucleation through different extent of complex formation by multidentate ligands.

Neuroprotective and anti-ageing effects of curcumin in aged rat brain regions.

This study investigated the influence of chronically administered curcumin on normal ageing-related parameters: lipid peroxidation, lipofuscin concentration and intraneuronal lipofuscin accumulation, activities of the enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx), and Na(+), K(+), -adenosine triphosphatase (Na(+), K(+), -ATPase) in different brain regions (cerebral cortex, hippocampus, cerebellum and medulla) of 6- and 24-month-old rats. In normal ageing, lipid peroxidation and lipofuscin concentration were found to increase with ageing, the activities of SOD, GPx and Na(+), K(+), -ATPase, however, decreased with ageing. Chronic curcumin treatment of both 6 and 24 months old rats resulted in significant decreases in lipid peroxide and the lipofuscin contents in brain regions, the activities of SOD, GPx and Na(+), K(+), -ATPase however, showed significant increase in various brain regions. The present study, thus, demonstrated the antioxidative, antilipofusinogenesic and anti-ageing effects of curcumin in the brain.

Microgravity effects on thylakoid, single leaf, and whole canopy photosynthesis of dwarf wheat.

The concept of using higher plants to maintain a sustainable life support system for humans during long-duration space missions is dependent upon photosynthesis. The effects of extended exposure to microgravity on the development and functioning of photosynthesis at the leaf and stand levels were examined onboard the International Space Station (ISS). The PESTO (Photosynthesis Experiment Systems Testing and Operations) experiment was the first long-term replicated test to obtain direct measurements of canopy photosynthesis from space under well-controlled conditions. The PESTO experiment consisted of a series of 21-24 day growth cycles of Triticum aestivum L. cv. USU Apogee onboard ISS. Single leaf measurements showed no differences in photosynthetic activity at the moderate (up to 600 micromol m(-2) s(-1)) light levels, but reductions in whole chain electron transport, PSII, and PSI activities were measured under saturating light (>2,000 micromol m(-2) s(-1)) and CO(2) (4000 micromol mol(-1)) conditions in the microgravity-grown plants. Canopy level photosynthetic rates of plants developing in microgravity at approximately 280 micromol m(-2) s(-1) were not different from ground controls. The wheat canopy had apparently adapted to the microgravity environment since the CO(2) compensation (121 vs. 118 micromol mol(-1)) and PPF compensation (85 vs. 81 micromol m(-2) s(-1)) of the flight and ground treatments were similar. The reduction in whole chain electron transport (13%), PSII (13%), and PSI (16%) activities observed under saturating light conditions suggests that microgravity-induced responses at the canopy level may occur at higher PPF intensity.

Regulation of protoporphyrin IX biosynthesis by intraplastidic compartmentalization and adenosine triphosphate.

Subplastidic preparations from cotyledons of cucumber (Cucumis sativus L.) were tested for their ability to synthesize protoporphyrin IX from the substrate 5-aminolevulinic acid. Envelope or thylakoid membranes failed to synthesize protoporphyrin IX from the substrate 5-aminolevulinic acid. Stromal preparations synthesized a very low amount of protoporphyrin IX. In a reconstitution experiment using stroma + envelope membranes, protoporphyrin IX synthesis from 5-aminolevulinic acid was enhanced by 660% over that of stroma alone. However, when thylakoids were added to the stroma + envelope mixture, protoporphyrin IX synthesis from 5-aminolevulinic acid was completely inhibited. In the reconstituted stroma + envelope membrane mixture, the reducing agent dithiothreitol enhanced the protoporphyrin IX-synthesizing ability and completely abolished the inhibition of protoporphyrin IX synthesis by thylakoids. This suggested that the oxidizing agents usually associated with the thylakoid membranes inhibited protoporphyrin IX biosynthesis and the inhibition was alleviated by the reducing power of dithiothreitol. This study exposes the weakness of in vitro reconstitution experiments in mimicking the in vivo-conditions. Addition of ATP stimulated protoporphyrin IX synthesis by 50% in the supernatant fraction of chloroplast lysate. This ATP-induced stimulation of protoporphyrin IX synthesis was due to the enhancement of the activities of uroporphyrinogen decarboxylase and protoporphyrinogen oxidase, involved in tetrapyrrole biosynthesis. The ATP-induced stimulation of porphyrinogen oxidase activity was an energy-dependent reaction.

5-Aminolevulinic Acid Induced Photodynamic Damage of the Photosynthetic Electron Transport Chain of Cucumber (Cucumis sativus L.) Cotyledons.

Cucumber (Cucumis sativus L. cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid (ALA) and then incubated in dark for 14 hours. Upon transfer to sunlight ( approximately 800 watts per square meter) the plants died after 5 hours of exposure due to photosensitization reaction of metalloporphyrins. Due to the photodynamic damage, photosystem II (PSII), photosystem I (PSI), and whole chain reactions were impaired. PSII activity was more susceptible to photodynamic damage than PSI. The variable fluorescence was significantly reduced in ALA-treated plants within 1 hour of exposure to sunlight. At low temperature (77 degrees K), the PSI fluorescence peak height (F(734)) was drastically reduced and blue shifted by 6 nanometers. The photodynamic damage was irreversible; rather, it continued upon dark incubation of ALA-treated cucumber plants exposed to sunlight for 15 minutes. In the latter experiment, continued production of malondialdehyde during dark treatment suggests the degradation of unsaturated membrane lipids.

Chloroplast Biogenesis 60 : Conversion of Divinyl Protochlorophyllide to Monovinyl Protochlorophyllide in Green(ing) Barley, a Dark Monovinyl/Light Divinyl Plant Species.

In higher plants, most of the chlorophyll a is formed via the divinyl and monovinyl chlorophyll monocarboxylic biosynthetic routes. These two routes are strongly interconnected prior to protochlorophyllide formation in barley (Hordeum vulgare L. cv Morex), a dark monovinyl-light divinyl plant species, but not in cucumber (Cucumis sativus L. cv Beit Alpha MR), a dark divinyl-light divinyl plant species (BC Tripathy, CA Rebeiz, 1986 J Biol Chem 261: 13556-13564). It is shown that in dark monovinyl-light divinyl plant species such as barley, the divinyl and monovinyl monocarboxylic routes become interconnected at the level of protochlorophyllide during transition from the divinyl to the monovinyl protochlorophyllide biosynthetic mode. In cucumber, a dark divinyl-light divinyl plant species, in which the monovinyl monocarboxylic biosynthetic route becomes preponderant only after an abnormally long sojourn in darkness, the conversion of divinyl to monovinyl protochlorophyllide does not take place on the barley time-scale of incubation.

Chloroplast biogenesis. Demonstration of the monovinyl and divinyl monocarboxylic routes of chlorophyll biosynthesis in higher plants.

It is shown that barley (Hordeum vulgare), a dark monovinyl/light divinyl plant species, and cucumber (Cucumis sativus L.) a dark divinyl/light divinyl plant species synthesize monovinyl and divinyl protochlorophyllide in darkness from monovinyl and divinyl protoporphyrin IX via two distinct monovinyl and divinyl monocarboxylic chlorophyll biosynthetic routes. Evidence for the operation of monovinyl monocarboxylic biosynthetic routes consisted (a) in demonstrating the conversion of delta-aminolevulinic acid to monovinyl protoporphyrin and to monovinyl Mg-protoporphyrins, and (b) in demonstrating the conversion of these tetrapyrroles to monovinyl protochlorophyllide by both isolated barley and cucumber etiochloroplasts. Likewise, evidence for the operation of divinyl monocarboxylic chlorophyll biosynthetic routes consisted (a) in demonstrating the biosynthesis of divinyl protoporphyrin and divinyl Mg-protoporphyrins from delta-aminolevulinic acid, and (b) in demonstrating the conversion of the latter tetrapyrroles to divinyl protochlorophyllide. Finally, it was shown that the divinyl tetrapyrrole substrates were metabolized differently by barley and cucumber. For example, divinyl protoporphyrin, divinyl Mg-protoporphyrin, and divinyl Mg-protoporphyrin monoester were converted predominantly to monovinyl protochlorophyllide and to smaller amounts of divinyl protochlorophyllide by barley etiochloroplasts. In contrast, cucumber etiochloroplasts converted the above substrates predominantly to divinyl protochlorophyllide, although smaller amounts of monovinyl protochlorophyllide were also formed. Furthermore, it was shown that monovinyl protochlorophyllide was not formed from divinyl protochlorophyllide either in barley or in cucumber etiochloroplasts. These metabolic differences are explained by the presence of strong biosynthetic interconnections between the divinyl and monovinyl monocarboxylic routes, prior to divinyl protochlorophyllide formation, in barley but not in cucumber.

Spectrofluorometric estimation of intermediates of chlorophyll biosynthesis: protoporphyrin IX, Mg-protoporphyrin, and protochlorophyllide.

A highly sensitive spectrofluorometric method for quantitative estimation of certain precursors of chlorophyll biosynthesis from the mixtures of plant tetrapyrroles having overlapping fluorescence emission spectra is developed. At room temperature (293 degrees K) protoporphyrin IX is monitored from its emission maximum, 633 nm, when excited at 400 nm (E400/F633). Protochlorophyllide is estimated at 638 nm, while being excited at 440 nm (E440/F638). Mg-protoporphyrin+Mg-protoporphyrin monoester pool has emission around 589-592 nm. Therefore the integration value of the emission band that extends from 580 to 610 nm is taken to calibrate its concentration. This spectrofluorometric method designed for the determination of protoporphyrin IX, esterified and nonesterified Mg-protoporphyrin pool, and protochlorophyllide is far superior to available spectrophotometric methods and estimates as low as 1 nM concentration of plant pigments. As minute quantities of individual pigments can be quantitatively analyzed from their mixtures, this method eliminates analytical uncertainties due to recovery losses caused by chromatography. However, only dilute samples can be estimated by this spectrofluorometric method as the quantitative relation between fluorescence and concentration deviates from linearity at high, i.e., above 150 nM, concentrations of pigment to be quantified.

Involvement of Singlet Oxygen in 5-Aminolevulinic Acid-Induced Photodynamic Damage of Cucumber (Cucumis sativus L.) Chloroplasts.

Cucumber (Cucumis sativus L., cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid and then incubated in the dark for 14 hours. The intact chloroplasts were isolated from the above plants in the dark and were exposed to weak light (250 micromoles per square meter per second). Within 30 minutes, photosystem II activity was reduced by 50%. The singlet oxygen ((1)O(2)) scavengers, histidine and sodium azide (NaN(3)) significantly protected against the damage caused to photosystem II. The hydroxyl radical scavenger formate failed to protect the thylakoid membranes. The production of (1)O(2) monitored as N,N-dimethyl p-nitrosoaniline bleaching increased as a function of light exposure time of treated chloroplasts and was abolished by the (1)O(2) quencher, NaN(3). Membrane lipid peroxidation monitored as malondialdehyde production was also significantly reduced when chloroplasts were illuminated in the presence of NaN(3) and histidine. Protochlorophyllide was the most abundant pigment accumulated in intact chloroplasts isolated from 5-aminolevulinic acid-treated plants and was probably acting as type II photosensitizer.

Root-shoot interaction in the greening of wheat seedlings grown under red light.

Wheat seedlings grown with roots exposed to constant red light (300-500 micromoles m-2 s-1) did not accumulate chlorophyll in the leaves. In contrast, seedlings grown with their roots shielded from light accumulated chlorophylls. Chlorophyll biosynthesis could be induced in red-light-grown chlorophyll-deficient yellow plants by either reducing the red-light intensity at the root surface to 100 micromoles m-1 s-1 or supplementing with 6% blue light. The inhibition of chlorophyll biosynthesis was due to impairment of the Mg-chelatase enzyme working at the origin of the Mg-tetrapyrrole pathway. The root-perceived photomorphogenic inhibition of shoot greening demonstrates root-shoot interaction in the greening process.

Zinc-inhibited Electron Transport of Photosynthesis in Isolated Barley Chloroplasts.

In isolated barley chloroplasts, the presence of 2 millimolar ZnSO(4) inhibits the electron transport activity of photosystem II, as measured by photoreduction of dichlorophenolindophenol, O(2) evolution, and chlorophyll a fluorescence. The inhibition of photosystem II activity can be restored by the addition of the electron donor hydroxylamine or diphenylcarbazide, but not by benzidine and MnCl(2). These observations suggest that Zn inhibits electron flow at the oxidizing side of photosystem II at a site prior to the electron donating site(s) of hydroxylamine and diphenylcarbazide. No inhibition of photosystem I-dependent electron transport by 3 millimolar ZnSO(4) is observed. However, with concentrations of ZnSO(4) above 5 millimolar, photosystem I activity is partially inactivated. Washing Zn(2+)-treated chloroplasts partially restores the O(2)-evolving activity.

Antimycin-resistant alternate electron pathway to plastocyanin in bovine-heart complex III.

Bovine-heart Complex III can catalyze the reduction of spinach plastocyanin by a decyl analog of ubiquinol-2 at a rate comparable with the rate of plastocyanin reduction by plastoquinol as catalyzed by the cytochrome b6-f complex purified from spinach leaves. This plastocyanin reduction as catalyzed by Complex III was almost completely inhibited by myxothiazol at stoichiometric concentrations, partially inhibited by UHDBT (5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole) and funiculosin, and was relatively insensitive to antimycin and HQNO (2-n-heptyl-4-hydroxyquinoline-N-oxide). Cytochrome c reduction as catalyzed by Complex III displayed a residual, inhibitor-insensitive rate of 5% of the uninhibited rate for each of the three inhibitors, antimycin, myxothiazol, and UHDBT. However, the residual rate that was insensitive to each of the inhibitors added singly was inhibited further by addition of the remaining two inhibitors. From these results it is concluded that plastocyanin reduction involves an electron-transfer pathway through Complex III that is distinct from the pathway utilized for reduction of cytochrome c.

Chloroplast biogenesis: quantitative determination of monovinyl and divinyl Mg-protoporphyrins and protochlorophyll(ides) by spectrofluorometry.

General equations which permit the determination of the amounts of any two closely related fluorescent compounds which can be distinguished by 77 degrees K but not by 293 degrees K spectrofluorometry have been described. This was achieved in the presence or absence of a third interfering compound, without prior separation of the fluorescent species. The adaptation of the generalized equations to the determination of the amounts of monovinyl (MV) and divinyl (DV) Mg-protoporphyrins or of MV and DV protochlorophyll(ides) in the presence or absence of Mg-Protos [Mg-protoporphyrin IX (Mg-Proto), Mg-Proto monoester, Mg-Proto diester or a mixture of those three tetrapyrroles] interference, was then demonstrated over a wide range of MV/DV tetrapyrrole proportions. These equations are likely to be very useful for the study of the intermediary metabolism of the monovinyl and divinyl chlorophyll biosynthetic routes in plants.

Chloroplast biogenesis 51 : modulation of monovinyl and divinyl protochlorophyllide biosynthesis by light and darkness in vitro.

It is shown that the monovinyl and divinyl protochlorophyllide biosynthetic patterns of etiolated maize (Zea mays L.), and cucumber (Cucumis sativus L.) seedlings and of their isolated etiochloroplasts can be modulated by light and darkness as was shown for green photoperiodically grown plants (E. E. Carey, C. A. Rebeiz 1985 Plant Physiol. 79: 1-6). In etiolated corn and cucumber seedlings and isolated etiochloroplasts poised in the divinyl protochlorophyllide biosynthetic mode by a 2 hour light pretreatment, darkness induced predominantly the biosynthesis of monovinyl protochlorophyllide in maize and of divinyl protochlorophyllide in cucumber. When etiolated seedlings and their isolated etiochloroplasts were poised in the monovinyl protochlorophyllide biosynthetic mode by a prolonged dark-pretreatment, light induced mainly the biosynthesis of divinyl protochlorophyllide in both maize and cucumber.

Growth and photosynthetic responses of wheat plants grown in space.

Growth and photosynthesis of wheat (Triticum aestivum L. cv Super Dwarf) plants grown onboard the space shuttle Discovery for 10 d were examined. Compared to ground control plants, the shoot fresh weight of space-grown seedlings decreased by 25%. Postflight measurements of the O2 evolution/photosynthetic photon flux density response curves of leaf samples revealed that the CO2-saturated photosynthetic rate at saturating light intensities in space-grown plants declined 25% relative to the rate in ground control plants. The relative quantum yield of CO2-saturated photosynthetic O2 evolution measured at limiting light intensities was not significantly affected. In space-grown plants, the light compensation point of the leaves increased by 33%, which likely was due to an increase (27%) in leaf dark-respiration rates. Related experiments with thylakoids isolated from space-grown plants showed that the light-saturated photosynthetic electron transport rate from H2O through photosystems II and I was reduced by 28%. These results demonstrate that photosynthetic functions are affected by the microgravity environment.

Effect of trypsin treatment of photosystem I particles on the electron donation to p700.

Proteolysis of photosystem I particles had no effect on P700 oxidation but did inhibit the rate of P700(+) reduction. The V(max) values were decreased for both dichlorophenol and plastocyanin, but the K(m) values were unaffected indicating that trypsin treatment altered electron transfer rather than the binding of the donor to the photosystem I complex. The salt dependence of P700(+) reduction was unaffected. The effects of P700(+) reduction were the same for the preparations of different workers (Shiozawa, Alberte, Thornber 1974 Arch Biochem Biophys 165: 388; and Bengis, Nelson 1975 J Biol Chem 250: 2783).In both cases, the 70-kilodalton, chlorophyll-containing polypeptide was digested confirming its role in transferring electrons from plastocyanin to P700. The fact that the preparation of Shiozawa et al. lacks subunit (III) but still used plastocyanin as the electron donor rules out a role for this subunit as "the plastocyanin binding protein." Subunit III was also digested in the Bengis and Nelson preparation.