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1.
Photochemical oxidation of the primary electron donor P in reaction centers (RCs) of the filamentous anoxygenic phototrophic
bacterium Chloroflexus (C.) aurantiacus was examined by light-induced Fourier transform infrared (FTIR) difference spectroscopy at 95 K in the spectral range of
4000–1200 cm−1. The light-induced P+QA−/PQA IR spectrum of C. aurantiacus RCs is compared to the well-characterized FTIR difference spectrum of P photooxidation in the purple bacterium Rhodobacter (R.) sphaeroides R-26 RCs. The presence in the P+QA−/PQA FTIR spectrum of C. aurantiacus RCs of specific low-energy electronic transitions at ∼2650 and ∼2200 cm−1, as well as of associated vibrational (phase-phonon) bands at 1567, 1481, and 1294–1285 cm−1, indicates that the radical cation P+ in these RCs has dimeric structure, with the positive charge distributed between the two coupled bacteriochlorophyll a molecules. The intensity of the P+ absorbance band at ∼1250 nm (upon chemical oxidation of P at room temperature) in C. aurantiacus RCs is approximately 1.5 times lower than that in R. sphaeroides R-26 RCs. This fact, together with the decreased intensity of the absorbance band at ∼2650 cm−1, is interpreted in terms of the weaker coupling of bacteriochlorophylls in the P+ dimer in C. aurantiacus compared to R. sphaeroides R-26. In accordance with the previous (pre)resonance Raman data, FTIR measurements in the carbonyl stretching region show
that in C. aurantiacus RCs (i) the 131-keto C=O groups of PA and PB molecules constituting the P dimer are not involved in hydrogen bonding in either neutral or photooxidized state of P and
(ii) the 31-acetyl C=O group of PB forms a hydrogen bond (probably with tyrosine M187) absorbing at 1635 cm−1. Differential signals at 1757(+)/1749(−) and 1741(+)/1733(−) cm−1 in the FTIR spectrum of C. aurantiacus RCs are attributed to the 133-ester C=O groups of P in different environments. 相似文献
2.
An effect of desiccation (a decrease of relative water content from 97% to 10% within 35 h) on Photosystem II was studied
in barley leaf segments (Hordeum vulgare L. cv. Akcent) using chlorophyll a fluorescence and thermoluminescence (TL). The O-J-I-P fluorescence induction curve revealed a decrease of FP and a slight shift of the J step to a shorter time with no change in its height. The analysis of the fluorescence decline
after a saturating light flash revealed an increased portion of slow exponential components with increasing desiccation. The
TL bands obtained after excitation by continuous light were situated at about –27°C (Zv band – recombination of P680+QA
−), –14 °C (A band – S3QA
−), +12 °C (B band – S2/3QB
−) and +45 °C (C band – TyrD+QA
−). The bands related to the S-states of oxygen evolving complex (A and B) were reduced by desiccation and shifted to higher
and lower temperatures, respectively. In accordance with this, the band observed at about +27 °C (S2QB
−) after excitation by 1 flash fired at –10 °C and band at about +20 °C (S2/3QB
−) after 2 flashes decreased with increasing water deficit and shifted to lower temperatures. A new band around 5 °C appeared
in both regimes of TL excitation for a relative water content of under 42% and was attributed to the Q band (S2QA
−). It is suggested that under desiccation, an inhibition of the formation of S2- and S3-states in OEC occurred simultaneously with a lowering of electron transport on the acceptor side of PS II. The temperature
down-shift of the TL bands obtained after the flash excitation was induced at the initial phases of water stress, indicating
a decrease of the activation energy for the S2/3QB
−recombination.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
A. G. Yakovlev T. A. Shkuropatova V. A. Shkuropatova V. A. Shuvalov 《Biochemistry. Biokhimii?a》2010,75(4):412-422
Coherent processes in an initial phase of charge transfer in reaction centers (RCs) of the triple mutant S(L178)K/G(M203)D/L(M214)H
of Rhodobacter sphaeroides were investigated by difference (light — dark) absorption spectroscopy with 18 fsec time resolution. Electron transfer in
the B cofactor branch is activated in this mutant, while the A-branch electron transfer is slowed in comparison with native
RCs of Rba. sphaeroides. A bulk of absorption difference spectra was analyzed in the 940–1060 nm range (stimulated emission of excited bacteriochlorophyll
dimer P* and absorption of bacteriochlorophyll anions BA− and β−, where β is a bacteriochlorophyll substituting the native bacteriopheophytin HA) and in the 735–775 nm range (bleaching of the absorption band of the bacteriopheophytin HB in the B-branch) in the −0.1 to 4 psec range of delays with respect to the moment of photoexcitation of P at 870 nm. Spectra
were measured at 293 and 90 K. The kinetics of P* stimulated emission at 940 nm shows its decay with a time constant of ∼14
psec at 90 K and ∼18 psec at 293 K, which is accompanied by oscillations with a frequency of ∼150 cm−1. A weak absorption band is found at 1018 nm that is formed ∼100 fsec after excitation of P and reflects the electron transfer
from P* to β and/or BA with accumulation of the P+β− and/or P+BA− states. The kinetics of ΔA at 1018 nm contains the oscillations at ∼150 cm−1 and distinct low-frequency oscillations at 20–100 cm−1; also, the amplitude of the oscillations at 150 cm−1 is much smaller at 293 than at 90 K. The oscillations in the kinetics of the 1018 nm band do not contain a 32 cm−1 mode that is characteristic for native Rba. sphaeroides RCs having water molecule HOH55 in their structure. The ΔA kinetics at 751 nm reflects the electron transfer to HB with formation of the P+HB− state. The oscillatory part of this kinetics has the form of a single peak with a maximum at ∼50 fsec completely decaying
at ∼200 fsec, which might reflect a reversible electron transfer to the B-branch. The results are analyzed in terms of coherent
nuclear wave packet motion induced in the P* excited state by femtosecond light pulses, of an influence of the incorporated
mutations on the mutual position of the energy levels of charge separated states, and of the role of water HOH55 in the dynamics
of the initial electron transfer. 相似文献
4.
Conidia of Beauveria bassiana and Metarhizium spp. smeared on glass slides were assayed for their responses to irradiation with weighted 312-nm UV-B and 365-nm UV-A at
gradient doses of 0.005–1.1 and 1.0–18.0 J cm−2, respectively. All inverted, sigmoid dose–survival trends showed good fit to a survival model (r
2 ≥ 0.97), yielding respective UV-B LD50s of 0.23–0.59 and 0.05–0.65 J cm−2 for 24 B. bassiana and 36 Metarhizium isolates, and UV-A LD50s of 2.78–10.46 J cm−2 for 24 Metarhizium isolates. Myzus persicae apterae on detached leaves were sprayed with a concentrated spore suspension of B. bassiana or M. anisopliae, followed by exposure to the UV-B doses to cause 10–90% viability losses. These doses caused aphid mortality reductions as
expected but affected neither spray-to-death period nor fungal growth on cadavers. The results highlight the merits of using
UV-tolerant candidates and photoprotection measures in fungal formulations for pest control. 相似文献
5.
The tolerances of 20 Beauveria bassiana isolates derived from host insects worldwide to UV-B irradiation were assessed quantitatively in multi-dose bioassays. Conidial
suspensions of the isolates smeared on glass slides were exposed to the gradient UV-B doses of 0.1–1.6 J cm−2 (D), which generated from 0.75 to 10.17 min irradiation of weighted 312-nm wavelength at 2.0–2.61 mW cm−2. Irradiated conidia were then incubated for 24 h at 25°C under saturated humidity. The ratio of germination at each dose
over that in the blank control was defined as survival index (I
s). For all isolates, the I
s − D observations fit well with the survival model I
s = 1/[1 + exp(a + bD)] (0.94 ≤ r
2 ≤ 0.99) generated widely spanned lethal doses of 0.154–0.928, 0.240–1.139, and 0.383–1.493 J cm−2 for their losses of 50%, 75%, and 95% viabilities, respectively. These were far below the solar UV-B dose of 2.439 J cm−2 measured in a sunny day during the summer. The large variation of UV-B tolerance among the isolates indicates a necessity
to select UV-tolerant candidates for formulations applied to insect control during summer. The highly efficient bioassay method
was developed to measure accurately the UV-B tolerances of fungal biocontrol agents as lethal doses. 相似文献
6.
Yakovlev AG Vasilieva LG Shkuropatov AY Shuvalov VA 《Biochemistry. Biokhimii?a》2011,76(10):1107-1119
Primary stage of charge separation and transfer of charges was studied in reaction centers (RCs) of point mutants LL131H and
LL131H/LM160H/FM197H of the purple bacterium Rhodobacter sphaeroides by differential absorption spectroscopy with temporal resolution of 18 fsec at 90 K. Difference absorption spectra measured
at 0–4 psec delays after excitation of dimer P at 870 nm with 30 fsec step were obtained in the spectral range of 935–1060
nm. It was found that a decay of P* due to charge separation is considerably slower in the mutant RCs in comparison with native
RCs of Rba. sphaeroides. Coherent oscillations were found in the kinetics of stimulated emission of the P* state at 940 nm. Fourier analysis of the
oscillations revealed a set of characteristic bands in the frequency range of 20–500 cm−1. The most intense band has the frequency of −30 cm−1 in RCs of mutant LL131H and in native RCs and the frequency of ∼100 cm−1 in RCs of the triple mutant. It was found that an absorption band of bacteriochlorophyll anion BA− which is registered in the difference absorption spectra of native RCs at 1020 nm is absent in the analogous spectra of the
mutants. The results are analyzed in terms of the participation of the BA molecule in the primary electron transfer in the presence of a nuclear wave packet moving along the inharmonic surface of
P* potential energy. 相似文献
7.
Phase behaviour and crystallinity of plant cuticular waxes studied by Fourier transform infrared spectroscopy 总被引:1,自引:0,他引:1
The phase behaviour of cuticular waxes from leaves of Hedera helix L. and Juglans regia L. was studied by Fourier transform infrared spectroscopy. For this purpose reconstituted waxes, isolated cuticular membranes,
dewaxed polymer matrix membranes and whole leaves were studied in the horizontal attenuated total reflection and transmission
modes. Melting curves of cuticular waxes were derived from temperature-dependent changes in the absorption maximum of the
symmetric stretching mode of CH2 groups (νs, at approx. 2856–2848 cm−1). With increasing temperature absorption band doublets due to CH2 scissoring (δsciss) and rocking (δrock) movements (at approx. 1473–1471 and 730–720 cm−1, respectively) indicative of an orthorhombic arrangement of alkyl chains merged into a single peak. The area ratio of the
peaks at approx. 720 and 730 cm−1 was used as a measure for aliphatic crystallinity of plant cuticular waxes at a given temperature. The investigations of
reconstituted cuticular waxes and those still embedded in isolated cuticles or in situ on the leaf produced comparable results.
The findings are discussed in terms of the properties of the cuticular transport barrier.
Received: 21 March 1997 / Accepted: 25 April 1997 相似文献
8.
The objectives of this study were to investigate the moisture-induced protein aggregation of whey protein powders and to elucidate
the relationship of protein stability with respect to water content and glass transition. Three whey protein powder types
were studied: whey protein isolate (WPI), whey protein hydrolysates (WPH), and beta-lactoglobulin (BLG). The water sorption
isotherms were determined at 23 and 45°C, and they fit the Guggenheim–Andersson–DeBoer (GAB) model well. Glass transition
was determined by differential scanning calorimeter (DSC). The heat capacity changes of WPI and BLG during glass transition
were small (0.1 to 0.2 Jg−1 °C−1), and the glass transition temperature (T
g) could not be detected for all samples. An increase in water content in the range of 7 to 16% caused a decrease in T
g from 119 down to 75°C for WPI, and a decrease from 93 to 47°C for WPH. Protein aggregation after 2 weeks’ storage was measured
by the increase in insoluble aggregates and change in soluble protein fractions. For WPI and BLG, no protein aggregation was
observed over the range of 0 to 85% RH, whereas for WPH, ∼50% of proteins became insoluble after storage at 23°C and 85% RH
or at 45°C and ≥73% RH, caused mainly by the formation of intermolecular disulfide bonds. This suggests that, at increased
water content, a decrease in the T
g of whey protein powders results in a dramatic increase in the mobility of protein molecules, leading to protein aggregation
in short-term storage. 相似文献
9.
Quan-fu Wang Yan-hua Hou Jin-lai Miao Guang-you Li 《Acta Physiologiae Plantarum》2009,31(6):1097-1102
The effect of ultraviolet-B (UV-B) radiation on Antarctic phytoplankton has become an attractive ecological issue as a result
of annual springtime ozone depletion. The effects of UV-B radiation on the growth and antioxidant enzymes were investigated
using Antarctic sea ice microalgae Chlamydomonas sp. ICE-L as the material in this study. The results demonstrated that UV-B radiation could notably inhibit the growth, especially
at high UV-B radiation intensity (70 μW cm−2). Malondialdehyde and O2
·− content in ICE-L increased rapidly in early days (1–3 days) exposed to UV-B radiation enhancement, then decreased rapidly.
In the stress of UV-B radiation enhancement, the superoxide dismutase, peroxidase and Catalase activities of 1–4 days in ICE-L
were obviously higher than those in the control, and their activities became higher at high UV-B radiation intensity (70 μW cm−2). These enzymes activity of 7 days would kept stable at low UV-B radiation intensity (35 μW cm−2), but kept high level at high UV-B radiation intensity (70 μW cm−2). However, the ascorbate peroxidase activity in ICE-L kept stable under the stress of UV-B radiation enhancement. The above
experimental results indicated that the antioxidant enzyme system played an important role in the adaptation of Antarctic
ice microalgae under the UV-B radiation change of Antarctic ecosystems. 相似文献
10.
Jordi Urmeneta Óscar Alcoba Efrén Razquín Elena Tarroja Antoni Navarrete Ricardo Guerrero 《Current microbiology》1998,37(3):151-155
Photosynthetic and respiratory activities at low light intensities (300 μE m−2 s−1) in the microbial mats of the Ebro Delta were measured by the oxygen exchange method in the laboratory. The response to H2S concentration, a significant factor in the dynamics of that ecosystem, was assessed. Total photosynthesis reached 23.78–28.17
μg O2 cm−2 h−1. Photosynthetic activity was not significantly different at the two temperatures tested. Respiratory activity reached a consumption
of 6.95–8.56 μg O2 cm−2 h−1 at 25°C and 11.42–11.70 μg O2 cm−2 h−1 at 35°C. The Q10 value for respiration was 1.37–1.64. Oxygen production in Microcoleus chthonoplastes, the most abundant cyanobacterium in those microbial mats, was highly resistant to sulfide inhibition. Concentrations less
than 0.02 mM sulfide did not affect the rate of photosynthesis. Concentrations up to 0.1 mM sulfide caused different degrees
of partially reversible inhibition, with a maximum of 67% at 0.78 mM sulfide. Primary production (g C assimilated/m2/year) in those microbial mats was also assessed and compared with data from other ecosystems.
Received: 24 October 1997 / Accepted: 18 December 1997 相似文献
11.
Dalila Serpa Manuela Falcão Pedro Duarte Luís Cancela da Fonseca Carlos Vale 《Biogeochemistry》2007,82(3):291-304
During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and
Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and
phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved
in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater
ammonium profiles evidenced a peak in the top-most muddy sediment (380 μM) suggesting higher mineralization rate when oxygen
is more available, while maximum phosphate concentration (113 μM) occurred in the sub-oxic layer probably due to phosphorus
desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were
always lower than in intertidal muddy sediments, ranging annually from 20 μM to 100 μM for ammonium and from 0.05 μM to 16 μM
for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, in both muddy (104 nmol cm−2 d−1––NH4+; 8 nmol cm−2 d−1––HPO4−2) and sandy sediments (26 nmol cm−2 d−1––NH4+; 1 nmol cm−2 d−1––HPO4−2), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated
annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal
areas (22 ton year−1––NH4+; 2 ton year−1––HPO4−2), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated
with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH4+ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance. 相似文献
12.
Walleska De Jesús-Bonilla Anthony Cruz Ariel Lewis José Cerda Daniel E. Bacelo Carmen L. Cadilla Juan López-Garriga 《Journal of biological inorganic chemistry》2006,11(3):334-342
Ferryl compounds [Fe(IV)=O] in living organisms play an essential role in the radical catalytic cycle and degradation processes
of hemeproteins. We studied the reactions between H2O2 and hemoglobin II (HbII) (GlnE7, TyrB10, PheCD1, PheE11), recombinant hemoglobin I (HbI) (GlnE7, PheB10, PheCD1, PheE11),
and the HbI PheB10Tyr mutant of L. pectinata. We found that the tyrosine residue in the B10 position tailors, in two very distinct ways, the reactivity of the ferryl
species, compounds I and II. First, increasing the reaction pH from 4.86 to 7.50, and then to 11.2, caused the the second-order
rate constant for HbII to decrease from 141.60 to 77.78 M−1 s−1, and to 2.96 M−1 s−1, respectively. This pH dependence is associated with the disruption of the heme–tyrosine (603 nm) protein moiety, which controls
the access of the H2O2 to the hemeprotein active center, thus regulating the formation of the ferryl species. Second, the presence of compound I
was evident in the UV–vis spectra (648-nm band) in the reactions of HbI and recombinant HbI with H2O2, This band, however, is completely absent in the analogous reaction with HbII and the HbI PheB10Tyr mutant. Therefore, the
existence of a hydrogen-bonding network between the heme pocket amino acids (i.e., TyrB10) and the ferryl compound I created
a path much faster than 3.0×10−2 s−1 for the decay of compound I to compound II. Furthermore, the decay of the heme ferryl compound I to compound II was independent
of the proximal HisF8 trans-ligand strength. Thus, the pH dependence of the heme–tyrosine moiety complex determined the overall reaction rate of the
oxidative reaction limiting the interaction with H2O2 at neutral pH. The hydrogen-bonding strength between the TyrB10 and the heme ferryl species suggests the presence of a cycle
where the ferryl consumption by the ferric heme increases significantly the pseudoperoxidase activity of these hemeproteins. 相似文献
13.
P. Meier J. Zettel 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):297-304
In the Swiss Prealps Entomobrya nivalis hibernates in an inactive state, hidden under bark flakes on spruce. For freeze avoidance it relies on thermal hysteresis
proteins (THPs) and polyols (mainly ribitol, with small amounts arabitol and threitol). Polyols are present only during the
inactive state, THPs additionally protect during the transition phase in spring and autumn, when animals are still active
but frosts may occur. Peak values were recorded in February/March for THPs (3.5 °C hysteresis between melting and freezing
point) and for polyols (26 μg mg−1 FW; hemolymph osmolality 680 mosmol l−1). E. nivalis is able to control its hemolymph osmolality independently of body water content. Mean osmolality in summer was 350– 440 mosmol l−1, in winter it was elevated to 650 mosmol l−1, due to a synthesis mainly of ribitol. Body water content varied between 1.8 and 3.3 mg H2O mg−1 DW, depending on humidity conditions. Experiments on triggering of antifreeze synthesis showed the action of temperature
and photoperiod as cues, but there was also evidence for an endogenous rhythm. No clear correlation between antifreeze concentration
and supercooling ability could be established, suggesting that gut content or other parameters also play an inportant role.
Accepted: 18 November 1995 相似文献
14.
Miyuki Sakaguchi Kyoko Shinzawa-Itoh Shinya Yoshikawa Takashi Ogura 《Journal of bioenergetics and biomembranes》2010,42(3):241-243
In the resting oxidized state (the fully oxidized “as-isolated” state) of cytochrome c oxidase (CcO) preparation, a resonance Raman band is observed at 755 cm-1 upon 647.1 nm excitation in resonance with an absorption band at 655 nm. Addition of cyanide eliminates the Raman band concomitant
with loss of the absorption band at 655 nm. These results strongly suggest that the Raman band at 755 cm-1 originates from the O−O stretching mode of the bridging peroxide (Fe−O-−O-−Cu) in the O2 reduction site of the fully oxidized “as-isolated” CcO. Although the peroxide bridged structure has been proposed on the basis of X-ray crystallography and reductive titration
experiments, the present vibrational spectroscopic analyses reveal conclusively the chemical nature of the bridging ligand
at the O2 reduction site of the fully oxidized “as-isolated” bovine heart CcO. 相似文献
15.
Grube M Muter O Strikauska S Gavare M Limane B 《Journal of industrial microbiology & biotechnology》2008,35(11):1545-1549
Previous studies showed that cabbage leaf extract (CLE) added to the growth medium can noticeably promote the degradation
of nitro aromatic compounds by specific consortium of bacteria upon their growth. For further development of the approach
for contaminated soil remediation it was necessary to evaluate the qualitative and/or quantitative composition of different
origin CLE and their relevance on the growth of explosives-degrading bacteria. Six CLE (different by species, cultivars and
harvesting time) were tested and used as additives to the growth medium. It was shown that nitro aromatic compounds can be
identified in the FT-IR absorption spectra by the characteristic band at 1,527 cm−1, and in CLE by the characteristic band at 1,602 cm−1. The intensity of the CLE band at 1,602 cm−1 correlated with the concentration of total nitrogen (R
2 = 0.87) and decreased upon the growth of bacteria. The content of nitrogen in CLE differed (0.22–1.00 vol.%) and significantly
influenced the content of total carbohydrates (9.50–16.00% DW) and lipids [3.90–9.90% dry weight (DW)] accumulated in bacterial
cells while the content of proteins was similar in all samples. Though this study showed quantitative differences in the composition
of the studied CLE and the response of bacterial cells to the composition of the growth media, and proved the potential of
this additive for remediation of contaminated soil. It was shown that analysis of CLE and monitoring of the conversion of
nitro aromatic compounds can be investigated by FT-IR spectroscopy as well as by conventional chemical methods. 相似文献
16.
Ko-ichiro Miyamoto Parida Yamada Ryo-taro Yamaguchi Takami Muto Ayumi Hirano Yasuo Kimura Michio Niwano Hiroko Isoda 《Cytotechnology》2007,55(2-3):143-149
In this study, we report on an in situ monitoring system of living cultured cells using infrared absorption spectroscopy in
the geometry of multiple internal reflections (MIR-IRAS). In order to observe living cultured cells, the temperature in the
sample chamber of a FT-IR spectrometer was maintained at 37 °C and a humidified gas mixture containing 5% CO2 was introduced into the sample chamber. Human breast cell line MCF-7 cultured on Si MIR prisms were placed in the sample
chamber and infrared spectra of MCF-7 cells were collected for 5 h. It was found that the adhesion and metabolism of MCF-7
cells could be monitored by the absorption intensity of amide-II protein band (1,545 cm−1) and also by the absorption intensities of CH
x
bands (2,700–3,100 cm−1). These results suggest that our system is useful for a nondestructive and non-label monitoring of cell viability. Our method
based on infrared absorption spectroscopy has a potential for bioscreening application. 相似文献
17.
Cyanobacteria were a major constituent of phototrophic communities in the lakes, ponds and streams of Bylot Island, in the
Canadian high Arctic. The waters spanned a range of temperatures (1.8–16.8°C in late July), pH regimes (6.2–9.2) and conductivities
(1.5–1700 μS cm−1) but nutrient concentrations were consistently low (< 1 μg dissolved reactive P l−1 at all sites; < 10 μg NO3-N l−1 at most sites). Picoplanktonic species (Synechococcus spp.) were often the numerical dominants in the plankton, and periphytic filamentous species (Oscillatoriaceae) commonly
formed thick (5–50 mm) benthic mats. Bloom-forming species of cyanobacteria were either absent or poorly represented even
in Chla-rich ponds. The total community biomass ranged from 0.1 to 29.8 μg Chla l−1 in the plankton and from 1.1 to 34.8 μg Chla cm−2 in the benthos. The in vivo absorbance characteristics of isolates from these environments indicated a genetically diverse
range of species in each group of Arctic cyanobacteria. Growth versus irradiance relationships were determined for each of
the isolates and similarly revealed large genetic differences (maximum growth rates from 0.17 to 0.61 day−1), even between morphologically identical taxa. A comparison of nutrients, pigment concentrations and species composition
underscores the strong similarities between freshwater ecosystems in the north and south polar zones.
Received: 3 June 1996 / Accepted: 3 November 1996 相似文献
18.
A. G. Yakovlev L. G. Vasilieva T. I. Khmelnitskaya V. A. Shkuropatova A. Ya. Shkuropatov V. A. Shuvalov 《Biochemistry. Biokhimii?a》2010,75(7):832-840
The role of tyrosine M210 in charge separation and stabilization of separated charges was studied by analyzing of the femtosecond
oscillations in the kinetics of decay of stimulated emission from P* and of a population of the primary charge separated state
P+BA− in YM210L and YM210L/HL168L mutant reaction centers (RCs) of Rhodobacter sphaeroides in comparison with those in native Rba. sphaeroides RCs. In the mutant RCs, TyrM210 was replaced by Leu. The HL168L mutation placed the redox potential of the P+/P pair 123 mV below that of native RCs, thus creating a theoretical possibility of P+BA− stabilization. Kinetics of P* decay at 940 nm of both mutants show a significant slowing of the primary charge separation
reaction in comparison with native RCs. Distinct damped oscillations in these kinetics with main frequency bands in the range
of 90–150 cm−1 reflect mostly nuclear motions inside the dimer P. Formation of a very small absorption band of BA− at 1020 nm is registered in RCs of both mutants. The formation of the BA− band is accompanied by damped oscillations with main frequencies from ∼10 to ∼150 cm−1. Only a partial stabilization of the P+BA− state is seen in the YM210L/HL168L mutant in the form of a small non-oscillating background of the 1020-nm kinetics. A similar
charge stabilization is absent in the YM210L mutant. A model of oscillatory reorientation of the OH-group of TyrM210 in the
electric fields of P+ and BA− is proposed to explain rapid stabilization of the P+BA− state in native RCs. Small oscillatory components at ∼330–380 cm−1 in the 1020-nm kinetics of native RCs are assumed to reflect this reorientation. We conclude that the absence of TyrM210
probably cannot be compensated by lowering of the P+BA− free energy that is expected for the double YM210L/HL168L mutant. An oscillatory motion of the HOH55 water molecule under
the influence of P+ and BA− is assumed to be another potential contributor to the mechanism of P+BA− stabilization. 相似文献
19.
Klaus Martin Meiners S. Papadimitriou D. N. Thomas L. Norman G. S. Dieckmann 《Polar Biology》2009,32(7):1055-1065
Physical, biogeochemical and photosynthetic parameters were measured in sea ice brine and ice core bottom samples in the north-western
Weddell Sea during early spring 2006. Sea ice brines collected from sackholes were characterised by cold temperatures (range
−7.4 to −3.8°C), high salinities (range 61.4–118.0), and partly elevated dissolved oxygen concentrations (range 159–413 μmol kg−1) when compared to surface seawater. Nitrate (range 0.5–76.3 μmol kg−1), dissolved inorganic phosphate (range 0.2–7.0 μmol kg−1) and silicic acid (range 74–285 μmol kg−1) concentrations in sea ice brines were depleted when compared to surface seawater. In contrast, NH4
+ (range 0.3–23.0 μmol kg−1) and dissolved organic carbon (range 140–707 μmol kg−1) were enriched in the sea ice brines. Ice core bottom samples exhibited moderate temperatures and brine salinities, but high
algal biomass (4.9–435.5 μg Chl a l−1 brine) and silicic acid depletion. Pulse amplitude modulated fluorometry was used for the determination of the photosynthetic
parameters F
v/F
m, α, rETRmax and E
k. The maximum quantum yield of photosystem II, F
v/F
m, ranged from 0.101 to 0.500 (average 0.284 ± 0.132) and 0.235 to 0.595 (average 0.368 ± 0.127) in the sea ice internal and
bottom communities, respectively. The fluorometric measurements indicated medium ice algal photosynthetic activity both in
the internal and bottom communities of the sea ice. An observed lack of correlation between biogeochemical and photosynthetic
parameters was most likely due to temporally and spatially decoupled physical and biological processes in the sea ice brine
channel system, and was also influenced by the temporal and spatial resolution of applied sampling techniques. 相似文献