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1.
Four species in the order Dictyotales ( Dictyopteris latiuscula (Okamura) Okamura, D. prolifera (Okamura) Okamura, D. repens (Okamura) Børgesen, and Spatoglossum crassum J. Tanaka) were found to be highly acidic as in some species of the order Desmarestiales (Phaeophyceae). The pH within their cells, presumably that of the vacuole, was estimated to be 0.5 to 0.9 by pH measurements of their cell extracts in distilled water. However, other species of these genera ( D. divaricata (Okamura) Okamura, D. undulata Holmes, and S. pacificum Yendo) did not show high acidity. Ion chromatography of the cell extracts showed that those species contained high concentrations of SO within their cells, up to 10 times that in seawater but relatively low Cl −. The sum of cations examined (Na +, NH , K +, Mg 2+, Ca 2+) was significantly lower than that of anions (Cl −, Br −, NO , SO ), and the difference is presumed to represent protons (H +), causing the extremely low cell sap pH. Estimated cellular proton concentrations calculated from the pH data roughly agreed with those calculated from differences between the sum of cations and anions and that of anions. Although certain other, nonacidic, dictyotalean species also contained high concentrations of SO , these species contained high concentrations of Mg 2+, and the sums of cations and anions were balanced. 相似文献
2.
Cellular pH estimated from cell extract pH, and the ion compositions of major inorganic ions (Na +, NH 4+, K +, Mg 2+, Ca 2+, Cl ?, Br ?, NO 3?, S0 42‐) were studied by ion chromatography in 15 species of 4 orders (Cladophorales, Codiales, Siphonocladales and Ulvales) of Ulvophyceae and 49 species of 8 orders (Bangiales, Ceramiales, Corallinales, Cryptonemiales, Gelidiales, Gigartinales, Nemaliales and Rhodymeniales) of Rhodophyceae. Among the Rhodophyceae, relatively low intracellular pH (approximately 2.0 within cells) and high concentration of S0 42‐ was demonstrated in Plocamium telfairiae(Harvey) Harvey. Furthermore, five species of Hypnea Lamouroux were shown to contain high concentrations of S0 42‐ balanced by relatively high concentrations of Na +. Among the Ulvophyceae, Codium cylindricum Holmes and Ulva pertusa Kjellman contained high concentrations of S0 42‐ balanced by relatively high concentrations of Mg 2+. 相似文献
3.
Among five species of the genus Plocamium Lamouroux distributed around Japan, P. cartilagineum (Linnaeus) Dixon, P. recurvatum Okamura and P. telfairiae (Hooker and Harvey) Harvey are often difficult to distinguish morphologically from each other. Our previous study demonstrated that P. recurvatum and P. telfairiae were divided into two groups, A and C, based on RUBISCO spacer sequence and that the specimens belonging to group C had acidic cell saps. In this study, we inferred evolutionary relationships of these Plocamium species from internal transcribed spacer sequence of the ribosomal RNA genes and obtained a similar topology to the RUBISCO spacer tree. Color of the dried specimens in the acidic group C was darker red than that in the non‐acidic group A, although there was no difference in color in living thalli. The Br ? concentration in the cell sap of the acidic group C was 20 times higher than that of the non‐acidic group. We could not find any morphological differences to distinguish clearly between groups A and C despite exhaustive investigation of field‐collected and cultured thalli in both P. recurvatum and P. telfairiae. These results suggest that the color of dried specimens and the composition of intracellular inorganic ions are significant criteria for interpreting phylogenetic relationships in Japanese Plocamium spp. 相似文献
4.
Polyunsaturated aldehydes (PUA) have recently been shown to induce reactive oxygen species (ROS) and possibly reactive nitrogen species (RNS, e.g., peroxynitrite) in the diatom Skeletonema marinoi ( S. marinoi), which produces high amounts of PUA. We now are attempting to acquire better understanding of which reactive molecular species are involved in the oxidative response of S. marinoi to PUA. We used flow cytometry, the dye dihydrorhodamine 123 (DHR) as the main indicator of ROS (but which is also known to partially detect RNS), and different scavengers and inhibitors of both nitric oxide (NO) synthesis and superoxide dismutase activity (SOD). Both the scavengers Tempol (for ROS) and uric acid (UA, for peroxynitrite) induced a lower DHR‐derived green fluorescence in S. marinoi cells exposed to the PUA, suggesting that both reactive species were produced. When PUA‐exposed S. marinoi cells were treated with the NO scavenger 2‐4‐carboxyphenyl‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (cPTIO), an opposite response was observed, with an increase in DHR‐derived green fluorescence. A higher DHR‐derived green fluorescence was also observed in the presence of sodium tungstate (ST), an inhibitor of NO production via nitrate reductase. In addition, two different SOD inhibitors, 2‐methoxyestradiol (2ME) and sodium diethyldithiocarbamate trihydrate (DETC), had an effect, with DETC inducing the strongest inhibition after 20 min. These results indicate the involvement of O 2? generation and SOD activity in H 2O 2 formation (with downstream ROS generation dependent from H 2O 2) in response to PUA exposure. This is relevant as it refines the biological impact of PUA and identifies the specific molecules involved in the response. It is speculated that in PUA‐exposed S. marinoi cells, beyond a certain threshold of PUA, the intracellular antioxidant system is no longer able to cope with the excess of ROS, thus resulting in the observed accumulation of both O 2?? and H 2O 2. This might be particularly relevant for population dynamics at sea, during blooms, when cell lysis increases and PUA are released. It can be envisioned that in the final stages of blooms, higher local PUA concentrations accumulate, which in turn induces intracellular ROS generation that ultimately leads to cell death and bloom decay. 相似文献
5.
Low‐molecular‐weight thiol (LMWT) synthesis has been reported to be directly induced by arsenic (As) in Pteris vittata, an As hyperaccumulator. Sulphur (S) is a critical component of LMWTs. Here, the effect of As treatment on the uptake and distribution of S in P. vittata was investigated. In P. vittata grown under low S conditions, the presence of As in the growth medium enhanced the uptake of SO 42?, which was used for LMWT synthesis in fronds. In contrast, As application did not affect SO 42? uptake in Nephrolepis exaltata, an As non‐hyperaccumulator. Moreover, the isotope microscope system revealed that S absorbed with As accumulated locally in a vacuole‐like organelle in epidermal cells, whereas S absorbed alone was distributed uniformly. These results suggest that S is involved in As transport and/or accumulation in P. vittata. X‐ray absorption near‐edge structure analysis revealed that the major As species in the fronds and roots of P. vittata were inorganic As(III) and As(V), respectively, and that As–LMWT complexes occurred as a minor species. Consequently, in case of As accumulation in P. vittata, S possibly acts as a temporary ligand for As in the form of LMWTs in intercellular and/or intracellular transport (e.g. vacuolar sequestration). 相似文献
6.
Over the last decade, Na‐ion batteries have been extensively studied as low‐cost alternatives to Li‐ion batteries for large‐scale grid storage applications; however, the development of high‐energy positive electrodes remains a major challenge. Materials with a polyanionic framework, such as Na superionic conductor (NASICON)‐structured cathodes with formula Na xM 2(PO 4) 3, have attracted considerable attention because of their stable 3D crystal structure and high operating potential. Herein, a novel NASICON‐type compound, Na 4MnCr(PO 4) 3, is reported as a promising cathode material for Na‐ion batteries that deliver a high specific capacity of 130 mAh g ?1 during discharge utilizing high‐voltage Mn 2+/3+ (3.5 V), Mn 3+/4+ (4.0 V), and Cr 3+/4+ (4.35 V) transition metal redox. In addition, Na 4MnCr(PO 4) 3 exhibits a high rate capability (97 mAh g ?1 at 5 C) and excellent all‐temperature performance. In situ X‐ray diffraction and synchrotron X‐ray diffraction analyses reveal reversible structural evolution for both charge and discharge. 相似文献
7.
Net CO 2 flux measurements conducted during the summer and winter of 1994–96 were scaled in space and time to provide estimates of net CO 2 exchange during the 1995–96 (9 May 1995–8 May 1996) annual cycle for the Kuparuk River Basin, a 9200 km 2 watershed located in NE Alaska. Net CO 2 flux was measured using dynamic chambers and eddy covariance in moist‐acidic, nonacidic, wet‐sedge, and shrub tundra, which comprise 95% of the terrestrial landscape of the Kuparuk Basin. CO 2 flux data were used as input to multivariate models that calculated instantaneous and daily rates of gross primary production (GPP) and whole‐ecosystem respiration ( R) as a function of meteorology and ecosystem development. Net CO 2 flux was scaled up to the Kuparuk Basin using a geographical information system (GIS) consisting of a vegetation map, digital terrain map, dynamic temperature and radiation fields, and the models of GPP and R. Basin‐wide estimates of net CO 2 exchange for the summer growing season (9 May?5 September 1995) indicate that nonacidic tundra was a net sink of ?31.7 ± 21.3 GgC (1 Gg = 10 9 g), while shrub tundra lost 32.5 ± 6.3 GgC to the atmosphere (negative values denote net ecosystem CO 2 uptake). Acidic and wet sedge tundra were in balance, and when integrated for the entire Kuparuk River Basin (including aquatic surfaces), whole basin summer net CO 2 exchange was estimated to be in balance (?0.9 ± 50.3 GgC). Autumn to winter (6 September 1995–8 May 1996) estimates of net CO 2 flux indicate that acidic, nonacidic, and shrub tundra landforms were all large sources of CO 2 to the atmosphere (75.5 ± 8.3, 96.4 ± 11.4, and 43.3 ± 4.7 GgC for acidic, nonacidic, and shrub tundra, respectively). CO 2 loss from wet sedge surfaces was not substantially different from zero, but the large losses from the other terrestrial landforms resulted in a whole basin net CO 2 loss of 217.2 ± 24.1 GgC during the 1995–96 cold season. When integrated for the 1995–96 annual cycle, acidic (66.4 + 25.25 GgC), nonacidic (64.7 ± 29.2 GgC), and shrub tundra (75.8 ± 8.4 GgC) were substantial net sources of CO 2 to the atmosphere, while wet sedge tundra was in balance (0.4 + 0.8 GgC). The Kuparuk River Basin as a whole was estimated to be a net CO 2 source of 218.1 ± 60.6 GgC over the 1995–96 annual cycle. Compared to direct measurements of regional net CO 2 flux obtained from aircraft‐based eddy covariance, the scaling procedure provided realistic estimates of CO 2 exchange during the summer growing season. Although winter estimates could not be assessed directly using aircraft measurements of net CO 2 exchange, the estimates reported here are comparable to measured values reported in the literature. Thus, we have high confidence in the summer estimates of net CO 2 exchange and reasonable confidence in the winter net CO 2 flux estimates for terrestrial landforms of the Kuparuk river basin. Although there is larger uncertainty in the aquatic estimates, the small surface area of aquatic surfaces in the Kuparuk river basin (≈ 5%) presumably reduces the potential for this uncertainty to result in large errors in basin‐wide CO 2 flux estimates. 相似文献
8.
The mechanism of inorganic carbon (C i) acquisition by the economic brown macroalga, Hizikia fusiforme (Harv.) Okamura (Sargassaceae), was investigated to characterize its photosynthetic physiology. Both intracellular and extracellular carbonic anhydrase (CA) were detected, with the external CA activity accounting for about 5% of the total. Hizikia fusiforme showed higher rates of photosynthetic oxygen evolution at alkaline pH than those theoretically derived from the rates of uncatalyzed CO 2 production from bicarbonate and exhibited a high pH compensation point (pH 9.66). The external CA inhibitor, acetazolamide, significantly depressed the photosynthetic oxygen evolution, whereas the anion‐exchanger inhibitor 4,4′‐diisothiocyano‐stilbene‐2,2′‐disulfonate had no inhibitory effect on it, implying the alga was capable of using HCO 3? as a source of C i for its photosynthesis via the mediation of the external CA. CO 2 concentrations in the culture media affected its photosynthetic properties. A high level of CO 2 (10,000 ppmv) resulted in a decrease in the external CA activity; however, a low CO 2 level (20 ppmv) led to no changes in the external CA activity but raised the intracellular CA activity. Parallel to the reduction in the external CA activity at the high CO 2 was a reduction in the photosynthetic CO 2 affinity. Decreased activity of the external CA in the high CO 2 grown samples led to reduced sensitiveness of photosynthesis to the addition of acetazolamide at alkaline pH. It was clearly indicated that H. fusiforme, which showed CO 2‐limited photosynthesis with the half‐saturating concentration of C i exceeding that of seawater, did not operate active HCO 3? uptake but used it via the extracellular CA for its photosynthetic carbon fixation. 相似文献
9.
Sediment and water samples collected from one acidic and three alkaline high temperature hot springs at the Tengchong terrestrial geothermal field, Southwest China, were examined using mineralogical, geochemical, and molecular biological techniques. The mineralogical and geochemical analyses suggested that these hot springs contained relatively high concentrations of S, Fe and N chemical species. Specifically, the acidic water was rich in Fe 2+, SO 42? and NH 4+, while the alkaline waters were high in NO 3?, H 2S and S 2O 3?. Analyses of 16S rRNA gene sequences showed their bacterial communities were dominated by phyla Aquificae, Cyanobacteria, Deinococci-Thermus, Firmicutes, Proteobacteria, and Thermodesulfobacteria, while the archaeal clone libraries were dominated by orders Desulfurococcales, Sulfolobales, and Thermoproteales. Potential S-, N- and Fe-metabolizing prokaryotes were present at a relatively high proportion, but with large differences in the diversity and metabolic functions of each sample. These findings provide implications for uncovering microbial functions in elemental biogeochemical cycles within the Tengchong geothermal environments: i). the distinct differences in abundance and diversity of microbial communities in geothermal sediments were related to different in situ physicochemical conditions; ii). the S-, N- and Fe-related prokaryotes would take advantage of the strong chemical disequilibria in the hot springs; and iii). in return, their metabolic activities could promote the transformation of the S, Fe and N chemical species, thereby forming the basis of biogeochemical cycles in the terrestrial geothermal environments. 相似文献
10.
Young beech ( Fagus sylvatica) and spruce ( Picea abies) trees from different provenances or genotypes were grown in competition in large model ecosystems and were exposed to two concentrations of atmospheric CO 2 (370 vs 570 μmol mol ?1), two levels of wet nitrogen deposition (7 vs 70 kg N ha ?1 yr ?1), and two native forest soils (acidic vs calcareous) for four years in open‐top chambers. The 2×2×2 factorial experimental design was fully replicated ( n=4) with each CO 2×N combination applied to each soil type. Exposure to atmospheric CO 2 enrichment stimulated daytime net ecosystem CO 2 flux (NEC) as measured during sunny days in the middle of the third growing season. Nevertheless, we observed substantial down‐regulation of NEC, with larger adjustments on acidic than on calcareous soil. NEC adjustment was associated with slightly reduced leaf area index (LAI) on the acidic soil (no response on calcareous soil), enhanced soil CO 2 efflux from both substrate types, and, most importantly, with down‐regulation of CO 2 uptake at the leaf scale. Downward adjustment of light‐saturated single‐leaf photosynthesis ( A) and of Rubisco was more pronounced in beech than in spruce and these species‐specific differences increased over time. By year four, A adjustment (except in one specific treatment combination in each species) had become complete in beech but had disappeared in spruce. At no time did we observe a genotype or provenance effect on the downward adjustment of carbon fluxes, and nitrogen deposition rate generally had little effect as well. Overall, our results suggest that tree species and soil quality will have profound effects on ecosystem CO 2 fluxes under continued atmospheric CO 2 enrichment. 相似文献
11.
1. Softwater lakes are generally dominated by slow growing, small, isoetid plant species that are adapted to the carbon‐ and nutrient‐limited conditions in these lakes. We investigated the strategy of a fast growing species, Sparganium angustifolium, for occupying softwater lakes. A field survey was carried out in Norwegian carbon‐limited Isoëteto‐Lobelietum softwater lakes to compare abiotic conditions at locations with and without S. angustifolium. In addition, long term abiotic changes (1995–2008) related to the sudden establishment of the species on experimentally limed plots were studied. Based on the results, the carbon acquisition mechanism of S. angustifolium was tested in eco‐physiological laboratory experiments. 2. The redox potential was significantly lower at locations with S. angustifolium (220 ± 2.3) compared to locations without S. angustifolium (338.1 ± 13.9). The lower redox potential was accompanied by significantly higher concentrations of HCO 3?, CO 2 and Fe 2+ in the sediment pore water, indicating in‐lake alkalinity generation due to higher iron reduction rates in the generally iron‐rich sediments. In addition, the lower redox potential was accompanied by a higher nutrient availability (NH 4+ and PO 43?) in the sediment pore water. Since there were no differences in water quality between the lakes, the ability of S. angustifolium to grow in softwater lakes very likely depends upon the higher dissolved inorganic carbon (DIC) and nutrient concentrations present in the sediment pore water. 3. Results from the liming experiment revealed that appearance of S. angustifolium on limed plots was related to the dissolution of Ca and Mg carbonates and development of a lower redox potential in the sediment. These processes were accompanied by a sustained increase in the availability of DIC in the sediment pore water. 4. The eco‐physiological experiments indicated that S. angustifolium can increase in biomass and produce floating leaves at a relatively high DIC availability in the root medium. In addition, it appeared that S. angustifolium can take up CO 2 by the roots. As far as we know, the ability to use sediment CO 2 has only been described as an adaptation typical for isoetid plant species. Use of the relatively large sediment CO 2 pools present in these sediment types (>1000 μmol L ?1) to enable development of long floating leaves for additional uptake of atmospheric CO 2 is a very different strategy to colonise softwater lakes as compared to isoetid plant species. 相似文献
12.
The etiology of astrocyte dysfunction is not well understood even though neuronal defects have been extensively studied in a variety of neuronal degenerative diseases. Astrocyte defects could be triggered by the oxidative stress that occurs during physiological aging. Here, we provide evidence that intracellular or mitochondrial reactive oxygen species (ROS) at physiological levels can cause hippocampal (neuronal) dysfunctions. Specifically, we demonstrate that astrocyte defects occur in the hippocampal area of middle‐aged Tet‐mev‐1 mice with the SDHC V69E mutation. These mice are characterized by chronic oxidative stress. Even though both young adult and middle‐aged Tet‐mev‐1 mice overproduced MitoSOX Red‐detectable mitochondrial ROS compared to age‐matched wild‐type C57BL/6J mice, only young adult Tet‐mev‐1 mice upregulated manganese and copper/zinc superoxide dismutase (Mn‐ and Cu/Zn‐SODs) activities to eliminate the MitoSOX Red‐detectable mitochondrial ROS. In contrast, middle‐aged Tet‐mev‐1 mice accumulated both MitoSOX Red‐detectable mitochondrial ROS and CM‐H 2DCFDA‐detectable intracellular ROS. These ROS levels appeared to be in the physiological range as shown by normal thiol and glutathione disulfide/glutathione concentrations in both young adult and middle‐aged Tet‐mev‐1 mice relative to age‐matched wild‐type C57BL/6J mice. Furthermore, only middle‐aged Tet‐mev‐1 mice showed JNK/SAPK activation and Ca 2+ overload, particularly in astrocytes. This led to decreasing levels of glial fibrillary acidic protein and S100β in the hippocampal area. Significantly, there were no pathological features such as apoptosis, amyloidosis, and lactic acidosis in neurons and astrocytes. Our findings suggest that the age‐dependent physiologically relevant chronic oxidative stress caused astrocyte defects in mice with impaired mitochondrial electron transport chain functionality. 相似文献
13.
Although nitrate is a macronutrient and can serve as good nitrogen source for many species of phytoplankton, high nitrate
concentrations do not benefit the growth of phytoplankton. We hypothesise that algae cultured under high nitrate concentrations
can accumulate intracellular nitrite, which is produced by nitrate reductase (NR) and can inhibit the growth of algae. To
assess the validity of this hypothesis, Microcystis aeruginosa was grown under different nitrate concentrations from 3.57 to 21.43 mM in low CO 2 and high CO 2 conditions for 15 days. We observed that, with increasing nitrate concentrations, the intracellular nitrite concentrations
of the alga increased and the growth rates and photosynthesis declined. When grown under high CO 2 conditions, M. aeruginosa showed lower intracellular nitrite concentrations and higher growth rates and
\text P\textm\textchla {\text{P}}_{\text{m}}^{{\text{chl}}a} ,
\text R\textd\textchla {\text{R}}_{\text{d}}^{{\text{chl}}a} , α chla
than under low CO 2 conditions. These results suggest that the accumulation of intracellular nitrite could be the cause of inhibition of algal
growth under high nitrate concentrations. 相似文献
14.
We report that two mitogen‐activated protein kinases (MAPKs), MPK9 and MPK12, positively regulate abscisic acid (ABA)‐induced stomatal closure in Arabidopsis thaliana. Yeast elicitor (YEL) induced stomatal closure accompanied by intracellular reactive oxygen species (ROS) accumulation and cytosolic free calcium concentration ([Ca 2+] cyt) oscillation. In this study, we examined whether these two MAP kinases are involved in YEL‐induced stomatal closure using MAPKK inhibitors, PD98059 and U0126, and MAPK mutants, mpk9, mpk12 and mpk9 mpk12. Both PD98059 and U0126 inhibited YEL‐induced stomatal closure. YEL induced stomatal closure in the mpk9 and mpk12 mutants but not in the mpk9 mpk12 mutant, suggesting that a MAPK cascade involving MPK9 and MPK12 functions in guard cell YEL signalling. However, YEL induced extracellular ROS production, intracellular ROS accumulation and cytosolic alkalisation in the mpk9, mpk12 and mpk9 mpk12 mutants. YEL induced [Ca 2+] cyt oscillations in both wild type and mpk9 mpk12 mutant. These results suggest that MPK9 and MPK12 function redundantly downstream of extracellular ROS production, intracellular ROS accumulation, cytosolic alkalisation and [Ca 2+] cyt oscillation in YEL‐induced stomatal closure in Arabidopsis guard cells and are shared with ABA signalling. 相似文献
15.
Elevated atmospheric carbon dioxide concentrations ([CO 2]) generally increase plant photosynthesis in C 3 species, but not in C 4 species, and reduce stomatal conductance in both C 3 and C 4 plants. In addition, tissue nitrogen concentration ([N]) often fails to keep pace with enhanced carbon gain under elevated CO 2, particularly in C 3 species. While these responses are well documented in many species, implications for plant growth and nutrient cycling in native ecosystems are not clear. Here we present data on 18 years of measurement of above and belowground biomass, tissue [N] and total standing crop of N for a Scirpus olneyi‐dominated (C 3 sedge) community, a Spartina patens‐dominated (C 4 grass) community and a C 3–C 4‐mixed species community exposed to ambient and elevated (ambient +340 ppm) atmospheric [CO 2] in natural salinity and sea level conditions of a Chesapeake Bay wetland. Increased biomass production (shoots plus roots) under elevated [CO 2] in the S. olneyi‐dominated community was sustained throughout the study, averaging approximately 35%, while no significant effect of elevated [CO 2] was found for total biomass in the C 4‐dominated community. We found a significant decline in C 4 biomass (correlated with rising sea level) and a concomitant increase in C 3 biomass in the mixed community. This shift from C 4 to C 3 was accelerated by the elevated [CO 2] treatment. The elevated [CO 2] stimulation of total biomass accumulation was greatest during rainy, low salinity years: the average increase above the ambient treatment during the three wettest years (1994, 1996, 2003) was 2.9 t ha −1 but in the three driest years (1995, 1999, 2002), it was 1.2 t ha −1. Elevated [CO 2] depressed tissue [N] in both species, but especially in the S. olneyi where the relative depression was positively correlated with salinity and negatively related with the relative enhancement of total biomass production. Thus, the greatest amount of carbon was added to the S. olneyi‐dominated community during years when shoot [N] was reduced the most, suggesting that the availability of N was not the most or even the main limitation to elevated [CO 2] stimulation of carbon accumulation in this ecosystem. 相似文献
16.
Suaeda fruticosa and S. monoica are important halophytes for ecological rehabilitation of saline lands. We report differential physio-chemical, photosynthetic, and chlorophyll fluorescence responses in these halophytes under 100 mM sodium chloride (NaCl), 50% strength (16.25 ppt) of seawater (SW)-imposed salinity, and 10% polyethylene glycol 6000 imposed osmotic stress at 380 (ambient) and 1200 (elevated) µmol mol–1 CO2 concentrations. SW salinity enhanced the growth in both species; however, compared with S. fruticosa, the S. monoica exhibited comparatively better growth and biomass accumulation under saline conditions at elevated CO2. Results demonstrated better photosynthetic performances of S. monoica under stress conditions at both levels of CO2, and this resulted in higher accumulation of carbon, nitrogen, sugar, and starch contents. S. monoica exhibited improved antenna size, electron transfer at PSII donor side, and efficient working of photosynthetic machinery at elevated CO2, which might be due to efficient upstream utilization of reducing power to fix the CO2. The δ13C results supported the operation of C4 CO2 fixation in S. monoica and C3 or intermediate pathway of CO2 fixation in S. fruticosa. Lower accumulation of reactive oxygen species, reduced membrane damage, lowered solute potential, and higher accumulation of proline and polyphenol contents indicated elevated CO2-induced abiotic stress tolerance in Suaeda. Higher activity of antioxidant enzymes in both species at both levels of CO2 help plants to combat the oxidative stress. Upregulation of NADP-dependent malic enzyme and NADP-dependent malate dehydrogenase genes indicated their role in abiotic stress tolerance as well as photosynthetic carbon (C) sequestration. Operation of C4 type CO2 fixation in S. monoica and an intermediate CO2 fixation in S. fruticosa could be the possible reason for the superior photosynthetic efficiency of S. monoica under stress conditions at elevated CO2. 相似文献
17.
The photosynthetic efficiency of the CO 2‐concentrating mechanism in two forms of single‐cell C 4 photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid‐type single‐cell C 4 uses peripheral and central cytoplasmic compartments ( Bienertia sinuspersici), while the Borszczowioid single‐cell C 4 uses distal and proximal compartments of the cell ( Suaeda aralocaspica). C 4 photosynthesis within a single‐cell raises questions about the efficiency of this type of CO 2‐concentrating mechanism compared with the Kranz‐type. We used measurements of leaf CO 2 isotope exchange (Δ 13C) to compare the efficiency of the single‐cell and Kranz‐type forms of C 4 photosynthesis under various temperature and light conditions. Comparisons were made between the single‐cell C 4 and a sister Kranz form, S. eltonica[NAD malic enzyme (NAD ME) type], and with Flaveria bidentis[NADP malic enzyme (NADP‐ME) type with Kranz Atriplicoid anatomy]. There were similar levels of Δ 13C discrimination and CO 2 leakiness ( ?) in the single‐cell species compared with the Kranz‐type. Increasing leaf temperature (25 to 30 °C) and light intensity caused a decrease in Δ 13C and ? across all C 4 types. Notably, B. sinuspersici had higher Δ 13C and ? than S. aralocaspica under lower light. These results demonstrate that rates of photosynthesis and efficiency of the CO 2‐concentrating mechanisms in single‐cell C 4 plants are similar to those in Kranz‐type. 相似文献
18.
Two gram‐negative, catalase‐negative, oxidase‐positive strains (PAGU 1467 T and PAGU 1468) isolated from patients with infective endocarditis were investigated to determine their taxonomic status. 16S rRNA gene sequence analysis indicated that the two strains were members of the Bergeyella‐Chryseobacterium‐Riemerella branch of the family Flavobacteriaceae. Strains PAGU 1467 T and PAGU 1468 were highly related to each other (98.8% 16S rRNA gene sequence similarity). Phylogenetically closely‐related species to PAGU 1467 T comprised Bergeyella zoohelcum (95.0% 16S rRNA gene sequence similarity), Riemerella anatipestifer (94.3%) and Cloacibacterium normanense (94.3%). The major fatty acids of the two isolates were iso‐C 15:0, iso‐C 17:0 3‐OH and iso‐C 15:0 3‐OH. The presence of C 16:0 3‐OH and iso‐C 15:0 2‐OH allowed these isolates to be distinguished from B. zoohelcum. Menaquinone MK‐6 was the only respiratory quinone in these organisms; this is a consistent characteristic of the family Flavobacteriaceae. The guanine‐plus‐cytosine content of the genomic DNA was 42.0%, which is higher than that of other close phylogenetic relatives. On the basis of their phenotypic properties and genetic distinctiveness, isolates PAGU 1467 T and PAGU 1468 were classified within the novel genus Spodiobacter, as Spodiobacter cordis gen. nov., sp. nov., which is also the type species. The type strain of S. cordis is PAGU 1467 T ( = CCUG 65564 T = NBRC 109998 T). 相似文献
19.
The difficulty in finding positive electrode materials for sodium‐ion (Na‐ion) batteries with a large specific energy has slowed down their commercialization. Layered transition metal (M) oxides Na xMO 2 with a two‐layer oxygen stacking (P2, 0.6 ≤ x ≤ 0.75), are promising candidates. However, the high average metal oxidation state needed during synthesis means that P2 Na xMO 2 cathodes often require the introduction of high‐valent cations (Mn 4+, Ti 4+, Sn 5+, or Te 6+), limiting the cathode's performance. Using a combination of first‐principles calculations and experiments, the feasibility of P2 cathodes containing only electrochemically active nickel and cobalt cations is investigated. It is found that P2 Na xNi yCo 1–yO 2 materials with x = 0.66, 0.75, and 0 ≤ y ≤ 0.33 are either thermodynamically stable or metastable yet close to the convex hull at typical P2 synthesis temperatures (≈1000 K). It is demonstrated that a novel P2 compound with y = 0.22 and both Ni 3+/4+ and Co 3+/4+ can be successfully synthesized. It is studied electrochemically and structurally, using in situ and ex situ X‐ray diffraction. It is demonstrated that the chemical space of P2 layered compounds is not fully explored yet and that ab initio phase diagrams allow the determination of new high‐specific energy positive electrodes to be targeted experimentally. 相似文献
20.
Anodically electrodeposited amorphous molybdenum sulfide (AE‐MoS x) has attracted significant attention as a non‐noble metal electrocatalyst for its high activity toward the hydrogen evolution reaction (HER). The [Mo 3S 13] 2? polymer‐based structure confers a high density of exposed sulfur moieties, widely regarded as the HER active sites. However, their intrinsic complexity conceals full understanding of their exact role in HER catalysis, hampering their full potential for water splitting applications. In this report, a unifying approach is adopted accounting for modifications in the inherent electrochemistry (EC), HER mechanism, and surface species to maximize the AE‐MoS x electroactivity over a broad pH region (0–10). Dramatic enhancements in HER performance by selective electrochemical cycling within reductive (overpotential shift, η HER ≈ ?350 mV) and electro‐oxidative windows (η HER ≈ ?290 mV) are accompanied by highly stable performance in mildly acidic electrolytes. Joint analysis of X‐ray photoelectron spectroscopy, Raman, and EC experiments corroborate the key role of bridging and terminal S ligands as active site generators at low pH, and reveal molybdenum oxysulfides (Mo 5+O xS y) to be the most active HER moiety in AE‐MoS x in mildly acidic‐to‐neutral environments. These findings will be extremely beneficial for future tailoring of MoS x materials and their implementation in commercial electrolyzer technologies. 相似文献
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