Submillisievert Computed Tomography of the Chest Using Model-Based Iterative Algorithm: Optimization of Tube Voltage With Regard to Patient Size.

OBJECTIVE: The aim of this study was to define optimal tube potential for soft tissue and vessel visualization in dose-reduced chest CT protocols using model-based iterative algorithm in average and overweight patients. METHODS: Thirty-six patients receiving chest CT according to 3 protocols (120 kVp/noise index [NI], 60; 100 kVp/NI, 65; 80 kVp/NI, 70) were included in this prospective study, approved by the ethics committee. Patients' physical parameters and dose descriptors were recorded. Images were reconstructed with model-based algorithm. Two radiologists evaluated image quality and lesion conspicuity; the protocols were intraindividually compared with preceding control CT reconstructed with statistical algorithm (120 kVp/NI, 20). Mean and standard deviation of attenuation of the muscle and fat tissues and signal-to-noise ratio of the aorta were measured. RESULTS: Diagnostic images (lesion conspicuity, 95%-100%) were acquired in average and overweight patients at 1.34, 1.02, and 1.08 mGy and at 3.41, 3.20, and 2.88 mGy at 120, 100, and 80 kVp, respectively. Data are given as CT dose index volume values. CONCLUSIONS: Model-based algorithm allows for submillisievert chest CT in average patients; the use of 100 kVp is recommended.

Symbiodinium sp. cells produce light-induced intra- and extracellular singlet oxygen, which mediates photodamage of the photosynthetic apparatus and has the potential to interact with the animal host in coral symbiosis.

Coral bleaching is an important environmental phenomenon, whose mechanism has not yet been clarified. The involvement of reactive oxygen species (ROS) has been implicated, but direct evidence of what species are involved, their location and their mechanisms of production remains unknown. Histidine-mediated chemical trapping and singlet oxygen sensor green (SOSG) were used to detect intra- and extracellular singlet oxygen ((1) O2 ) in Symbiodinium cultures. Inhibition of the Calvin-Benson cycle by thermal stress or high light promotes intracellular (1) O2 formation. Histidine addition, which decreases the amount of intracellular (1) O2 , provides partial protection against photosystem II photoinactivation and chlorophyll (Chl) bleaching. (1) O2 production also occurs in cell-free medium of Symbiodinium cultures, an effect that is enhanced under heat and light stress and can be attributed to the excretion of (1) O2 -sensitizing metabolites from the cells. Confocal microscopy imaging using SOSG showed most extracellular (1) O2 around the cell surface, but it is also produced across the medium distant from the cells. We demonstrate, for the first time, both intra- and extracellular (1) O2 production in Symbiodinium cultures. Intracellular (1) O2 is associated with photosystem II photodamage and pigment bleaching, whereas extracellular (1) O2 has the potential to mediate the breakdown of symbiotic interaction between zooxanthellae and their animal host during coral bleaching.

Characterization of wave phenomena in the relaxation of flash-induced chlorophyll fluorescence yield in cyanobacteria.

Fluorescence yield relaxation following a light pulse was studied in various cyanobacteria under aerobic and microaerobic conditions. In Synechocystis PCC 6803 fluorescence yield decays in a monotonous fashion under aerobic conditions. However, under microaerobic conditions the decay exhibits a wave feature showing a dip at 30-50 ms after the flash followed by a transient rise, reaching maximum at ~1s, before decaying back to the initial level. The wave phenomenon can also be observed under aerobic conditions in cells preilluminated with continuous light. Illumination preconditions cells for the wave phenomenon transiently: for few seconds in Synechocystis PCC 6803, but up to one hour in Thermosynechocystis elongatus BP-1. The wave is eliminated by inhibition of plastoquinone binding either to the QB site of Photosystem-II or the Qo site of cytochrome b6f complex by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, respectively. The wave is also absent in mutants, which lack either Photosystem-I or the NAD(P)H-quinone oxidoreductase (NDH-1) complex. Monitoring the redox state of the plastoquinone pool revealed that the dip of the fluorescence wave corresponds to transient oxidation, whereas the following rise to re-reduction of the plastoquinone pool. It is concluded that the unusual wave feature of fluorescence yield relaxation reflects transient oxidation of highly reduced plastoquinone pool by Photosystem-I followed by its re-reduction from stromal components via the NDH-1 complex, which is transmitted back to the fluorescence yield modulator primary quinone electron acceptor via charge equilibria. Potential applications of the wave phenomenon in studying photosynthetic and respiratory electron transport are discussed. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

Investigating the photoprotective role of cytochrome b-559 in photosystem II in a mutant with altered ligation of the haem.

Despite many years of study, the physiological role of cytochrome b-559 (Cyt b-559) within the photosystem II (PSII) complex still remains unclear. Here we describe the analysis of a mutant of the green alga Chlamydomonas reinhardtii in which the His ligand to the haem, provided by the alpha subunit, has been replaced by a Cys residue. The mutant is unable to grow photoautotrophically but can assemble oxygen-evolving PSII supercomplexes to 15-20% of the levels found in the wild-type control. Haem is still detected in the isolated PSII supercomplexes but at sub-stoichiometric levels consistent with weaker binding to the mutated cytochrome. Analysis of PSII activity in cells indicates slowed electron transfer in the mutant between plastoquinones QA and QB. We show that PSII activity in the mutant is more sensitive to chronic photoinhibition than the WT control because of two effects: a faster rate of damage and an impaired PSII repair cycle at the level of synthesis and/or incorporation of D1 into PSII. We also demonstrate that Cyt b-559 plays a role during the critical stage of assembling the Mn4CaO5 cluster. Overall we conclude that Cyt b-559 optimises electron transfer on the acceptor side of PSII and plays physiologically important roles in the assembly, repair and maintenance of the complex.

Endoleak and in-stent thrombus detection with CT angiography in a thoracic aortic aneurysm phantom at different tube energies using filtered back projection and iterative algorithms.

PURPOSE: To determine the lower limit of dose reduction with hybrid and fully iterative reconstruction algorithms in detection of endoleaks and in-stent thrombus of thoracic aorta with computed tomographic (CT) angiography by applying protocols with different tube energies and automated tube current modulation. MATERIALS AND METHODS: The calcification insert of an anthropomorphic cardiac phantom was replaced with an aortic aneurysm model containing a stent, simulated endoleaks, and an intraluminal thrombus. CT was performed at tube energies of 120, 100, and 80 kVp with incrementally increasing noise indexes (NIs) of 16, 25, 34, 43, 52, 61, and 70 and a 2.5-mm section thickness. NI directly controls radiation exposure; a higher NI allows for greater image noise and decreases radiation. Images were reconstructed with filtered back projection (FBP) and hybrid and fully iterative algorithms. Five radiologists independently analyzed lesion conspicuity to assess sensitivity and specificity. Mean attenuation (in Hounsfield units) and standard deviation were measured in the aorta to calculate signal-to-noise ratio (SNR). Attenuation and SNR of different protocols and algorithms were analyzed with analysis of variance or Welch test depending on data distribution. RESULTS: Both sensitivity and specificity were 100% for simulated lesions on images with 2.5-mm section thickness and an NI of 25 (3.45 mGy), 34 (1.83 mGy), or 43 (1.16 mGy) at 120 kVp; an NI of 34 (1.98 mGy), 43 (1.23 mGy), or 61 (0.61 mGy) at 100 kVp; and an NI of 43 (1.46 mGy) or 70 (0.54 mGy) at 80 kVp. SNR values showed similar results. With the fully iterative algorithm, mean attenuation of the aorta decreased significantly in reduced-dose protocols in comparison with control protocols at 100 kVp (311 HU at 16 NI vs 290 HU at 70 NI, P ≤ .0011) and 80 kVp (400 HU at 16 NI vs 369 HU at 70 NI, P ≤ .0007). CONCLUSION: Endoleaks and in-stent thrombus of thoracic aorta were detectable to 1.46 mGy (80 kVp) with FBP, 1.23 mGy (100 kVp) with the hybrid algorithm, and 0.54 mGy (80 kVp) with the fully iterative algorithm.

Emergency CT head and neck imaging: effects of swimmer's position on dose and image quality.

OBJECTIVES: To compare the effects of different arm positions on dose exposure and image quality (IQ) in cervical spine CT after trauma in different patient groups. METHODS: Patients in standard (STD = 126) and in swimmer's position (SWIM = 254) were included. Body mass index (BMI subgroup 1 = underweight to subgroup 4 = obese), anterior-posterior diameter (AP), left-right diameter (LR), area of an ellipse (AoE) and angle between the humeral heads (optimal STD < 3°, optimal SWIM > 10°) were used as grouping criteria. Computed tomography dose index (CTDI) was documented. Two radiologists rated the IQ at three levels (CV1/2, CV4/5, CV7/T1) using a semi-quantitative scale (0 = not diagnostic, 1 = diagnostic with limitations, 2 = diagnostic without limitations). The Mann-Whitney U test correlations of grouping criteria with dose effects and intra-class correlation (ICC) were calculated. RESULTS: ICC was 0.87. BMI grouping showed the strongest correlation with dose effects: CTDI of optimal STD versus optimal SWIM positioning was 3.17 mGy versus 2.46 mGy (subgroup 1), 5.47 mGy versus 3.97 mGy (subgroup 2), 7.35 mGy versus 5.96 mGy (subgroup 3) and 8.71 mGy versus 8.18 mGy (subgroup 4). Mean IQ at CV7/T1 was 1.65 versus 1.23 (subgroup 1), 1.27 versus 1.46 (subgroup 2), 1.06 versus 1.46 (subgroup 3), 0.79 versus 1.5 (subgroup 4). CONCLUSION: Patients with a BMI > 20 kg/m(2) benefited from both potential dose reduction and improved image quality at the critical cervicothoracic junction when swimmer's position was used. KEY POINTS: • BMI is a useful metric for personalized optimization in CT for the c-spine. • Using swimmer's position, patients can benefit from dose reduction. • In some patients a superior image quality can be achieved with swimmer's position. • For swimmer's positioning an angle of more than 10° is optimal.

Filtered back projection, adaptive statistical iterative reconstruction, and a model-based iterative reconstruction in abdominal CT: an experimental clinical study.

PURPOSE: To compare objective and subjective image quality parameters of three image reconstruction algorithms of different generations at routine multidetector computed tomographic (CT) examinations of the abdomen. MATERIALS AND METHODS: This institutional review board-approved study included 22 consecutive patients (mean age, 56.1 years ± 15.8 [standard deviation]; mean weight, 79.1 kg ± 14.8) who underwent routine CT examinations of the abdomen. A low-contrast phantom was used for objective quality control. Raw data sets were reconstructed by using filtered back projection (FPB), adaptive statistical iterative reconstruction (ASIR), and a model-based iterative reconstruction (MBIR). Radiologists used a semiquantitative scale (-3 to +3) to rate subjective image quality and artifacts, comparing both FBP and MBIR images with ASIR images. The Wilcoxon test and the intraclass correlation coefficient were used to evaluate the data. Measurements of objective noise and CT numbers of soft tissue structures were compared with analysis of variance. RESULTS: The phantom study revealed an improved detectability of low-contrast targets for MBIR compared with ASIR or FBP. Subjective ratings showed higher image quality for MBIR, with better resolution (median value, 2; range, 1 to 3), lower noise (2; range, 1 to 3), and finer contours (2; range, 1 to 2) compared with ASIR (all P < .001). FBP performed inferiorly (0, range, -2 to 0]; -1 [range, -3 to 0]; 0 [range, -1 to 0], respectively; all, P < .001). Mean interobserver correlation was 0.9 for image perception and 0.7 for artifacts. Objective noise for FBP was 14%-68% higher and for MBIR was 18%-47% lower than that for ASIR (P < .001). CONCLUSION: The MBIR algorithm considerably improved objective and subjective image quality parameters of routine abdominal multidetector CT images compared with those of ASIR and FBP.

Electron transfer from Cyt b(559) and tyrosine-D to the S2 and S3 states of the water oxidizing complex in photosystem II at cryogenic temperatures.

The Mn(4)CaO(5) cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with Tyrosine(Z) and P(680), which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine(D) (Y(D)) and Cytochrome b(559) (Cyt b(559)) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b(559) and Y(D) to the S(2) and S(3) states at 195 K. First, Y(D)(•) and Cyt b(559) were chemically reduced. The S(2) and S(3) states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S(1) state. EPR signals of the WOC (the S(2)-state multiline signal, ML-S(2)), Y(D)(•) and oxidized Cyt b(559) were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S(2) population decayed to S(1) in the S(2) samples by following a single exponential decay. Differently, S(3) samples showed an initial increase in the ML-S(2) intensity (due to S(3) to S(2) conversion) and a subsequent slow decay due to S(2) to S(1) conversion. In both cases, only a minor oxidation of Y(D) was observed. In contrast, the signal intensity of the oxidized Cyt b(559) showed a two-fold increase in both the S(2) and S(3) samples. The electron donation from Cyt b(559) was much more efficient to the S(2) state than to the S(3) state.

Pure forms of the singlet oxygen sensors TEMP and TEMPD do not inhibit Photosystem II.

In a recent article (Hakala-Yatkin and Tyystjärvi BBA 1807 (2011) 243-250) it was reported that the singlet oxygen spin traps 2,2,6,6-tetramethylpiperidine (TEMP) and 2,2,6,6-tetramethyl-4-piperidone (TEMPD) inhibit Photosystem II (PSII), the water oxidizing enzyme. O2 evolution, chlorophyll fluorescence and thermoluminescence were measured and were shown to be greatly affected by these chemicals. This work casts doubts over an earlier body of work in which these chemicals were used as spin traps for monitoring ¹O2 production when PSII was inhibited by high light intensities. Here we show that these spin probes hardly affect PSII. We show that the commercial batches of TEMPD and TEMP used by Hakala-Yatkin and Tyystjärvi contained impurities and/or derivatives that inhibited PSII and caused the specific effects on fluorescence. Earlier work that used pure spin traps to measure ¹O2 during photoinhibition, thus remains valid. However, concern must be expressed towards using these spin traps without proper controls.

Is It Possible to Replace Conventional Radiography (CR) with a Dose Neutral Computed Tomography (CT) of the Cervical Spine in Emergency Radiology-An Experimental Cadaver Study.

The purpose of this experimental study on recently deceased human cadavers was to investigate whether (I) the radiation exposure of the cervical spine CT can be reduced comparable to a dose level of conventional radiography (CR); and (II) whether and which human body parameters can be predictive for higher dose reduction potential (in this context). MATERIALS AND METHODS: Seventy serial CT scans of the cervical spine of 10 human cadavers undergoing postmortem virtual autopsy were taken using stepwise decreasing upper limits of the tube current (300 mAs, 150 mAs, 110 mAs, 80 mAs, 60 mAs, 40 mAs, and 20 mAs) at 120 kVp. An additional scan acquired at a fixed tube current of 300 mAs served as a reference. Images were reconstructed with filtered back projection and the upper (C1-4) and lower (C4-7) cervical spine were evaluated by three blinded readers for image quality, regarding diagnostic value and resolution of anatomical structures according to a semiquantitative three-point-scale. Dose values and individual physical parameters were recorded. The relationship of diagnostic IQ, dose reduction level, and patients' physical parameters were investigated. The high-contrast resolution of the applied CT protocols was tested in an additional phantom study. RESULTS: The IQ of the upper cervical spine was diagnostic at 1.69 ± 0.58 mGy (CTDI) corresponding to 0.20 ± 0.07 mSv (effective dose) in all cadavers. IQ of the lower cervical spine was diagnostic at 4.77 ± 1.86 mGy corresponding to 0.560 ± 0.21 mSv (effective dose) in seven cadavers and at 2.60 ± 0.93 mGy corresponding to 0.31 ± 0.11 mSv in four cadavers. Significant correlation was detected for BMI (0.8366; p = 0.002548) and the anteroposterior (a.p.) chest diameter (0.8363; p = 0.002566), shoulder positioning (0.79799; p = 0.00995), and radiation exposure. CONCLUSIONS: Conventional radiography can be replaced with a nearly dose-neutral CT scan of the cervical spine.

Reduction in Radiation Exposure of CT Perfusion by Optimized Imaging Timing Using Temporal Information of the Preceding CT Angiography of the Carotid Artery in the Stroke Protocol.

(1) Background: CT perfusion (CTP) is a fast, robust and widely available but dose-exposing imaging technique for infarct core and penumbra detection. Carotid CT angiography (CTA) can precede CTP in the stroke protocol. Temporal information of the bolus tracking series of CTA could allow for better timing and a decreased number of scans in CTP, resulting in less radiation exposure, if the shortening of CTP does not alter the calculated infarct core and penumbra or the resulting perfusion maps, which are essential for further treatment decisions. (2) Methods: 66 consecutive patients with ischemic stroke proven by follow-up imaging or endovascular intervention were included in this retrospective study approved by the local ethics committee. In each case, six simulated, stepwise shortened CTP examinations were compared with the original data regarding the perfusion maps, infarct core, penumbra and endovascular treatment decision. (3) Results: In simulated CTPs with 26, 28 and 30 scans, the infarct core, penumbra and PRR values were equivalent, and the resulting clinical decision was identical to the original CTP. (4) Conclusions: The temporal information of the bolus tracking series of the carotid CTA can allow for better timing and a lower radiation exposure by eliminating unnecessary scans in CTP.

Functional characterization and quantification of the alternative PsbA copies in Thermosynechococcus elongatus and their role in photoprotection.

The D1 protein (PsbA) of photosystem II (PSII) from Thermosynechococcus elongatus is encoded by a psbA gene family that is typical of cyanobacteria. Although the transcription of these three genes has been studied previously (Kós, P. B., Deák, Z., Cheregi, O., and Vass, I. (2008) Biochim. Biophys. Acta 1777, 74-83), the protein quantification had not been possible due to the high sequence identity between the three PsbA copies. The successful establishment of a method to quantify the PsbA proteins on the basis of reverse phase-LC-electrospray mass ionization-MS/MS (RP-LC-ESI-MS/MS) enables an accurate comparison of transcript and protein level for the first time ever. Upon high light incubation, about 70% PsbA3 could be detected, which closely corresponds to the transcript level. It was impossible to detect any PsbA2 under all tested conditions. The construction of knock-out mutants enabled for the first time a detailed characterization of both whole cells and also isolated PSII complexes. PSII complexes of the ΔpsbA1/psbA2 mutant contained only copy PsbA3, whereas only PsbA1 could be detected in PSII complexes from the ΔpsbA3 mutant. In whole cells as well as in isolated complexes, a shift of the free energy between the redox pairs in the PsbA3 complexes in comparison with PsbA1 could be detected by thermoluminescence and delayed fluorescence measurements. This change is assigned to a shift of the redox potential of pheophytin toward more positive values. Coincidentally, no differences in the Q(A)-Q(B) electron transfer could be observed in flash-induced fluorescence decay or prompt fluorescence measurements. In conclusion, PsbA3 complexes yield a better protection against photoinhibition due to a higher probability of the harmless dissipation of excess energy.

Differential regulation of psbA and psbD gene expression, and the role of the different D1 protein copies in the cyanobacterium Thermosynechococcus elongatus BP-1.

In Thermosynechococcus elongatus BP-1, which is the preferred organism in recent structural studies of PSII, three psbA and two psbD genes code for three D1 and one D2 protein isoforms, respectively. The regulation and function of these genes and protein products is largely unknown. Therefore, we used quantitative RT-PCR to follow changes in the mRNA level of the respective genes, in combination with biophysical measurements to detect changes in the electron transport activity of Photosystem II under exposure to different visible and UV light, and temperature conditions. In cells which are acclimated to 40 micromol m(-2)s(-1) growth light conditions at 40 degrees C the main populations of the psbA and psbD transcripts arise from the psbA1 and psbD1 genes, respectively. When the temperature is raised to 60 degrees C psbA1 becomes the single dominating psbA mRNA species. Upon exposure of the cells to 500 micromol m(-2)s(-1) intensity visible light psbA3 replaces psbA1 as the dominating psbA mRNA species, and psbD2 increases at the expense of psbD1. UV-B radiation also increases the abundance of psbA3, and psbD2 at the expense of psbA1 and psbD1, respectively. From the different extent of total D1 protein loss in the absence and presence of lincomycin it was estimated that the PsbA3 protein isoform replaces PsbA1 in about 65% of PSII centers after 2 h of high light acclimation. Under the conditions of different psbA transcript distributions chlorophyll fluorescence and thermoluminescence measurements were applied to monitor charge recombination characteristics of the S2Q(A)(-) and S2Q(B)(-) states. We obtained faster decay of flash-induced chlorophyll fluorescence in the presence of DCMU, as well as lower peak temperature of the Q and B thermoluminescence bands when PsbA3 replaced PsbA1 as the main D1 protein isoform. The relevance of dynamic changes in the abundance of psbA and psbD transcript levels, as well as D1 protein isoforms in the acclimation of T. elongatus to changing environmental conditions is discussed.

The extreme halophyte Salicornia veneta is depleted of the extrinsic PsbQ and PsbP proteins of the oxygen-evolving complex without loss of functional activity.

BACKGROUND AND AIMS: Photosystem II of oxygenic organisms is a multi-subunit protein complex made up of at least 20 subunits and requires Ca(2+) and Cl(-) as essential co-factors. While most subunits form the catalytic core responsible for water oxidation, PsbO, PsbP and PsbQ form an extrinsic domain exposed to the luminal side of the membrane. In vitro studies have shown that these subunits have a role in modulating the function of Cl(-) and Ca(2+), but their role(s) in vivo remains to be elucidated, as the relationships between ion concentrations and extrinsic polypeptides are not clear. With the aim of understanding these relationships, the photosynthetic apparatus of the extreme halophyte Salicornia veneta has been compared with that of spinach. Compared to glycophytes, halophytes have a different ionic composition, which could be expected to modulate the role of extrinsic polypeptides. METHODS: Structure and function of in vivo and in vitro PSII in S. veneta were investigated and compared to spinach. Light and electron microscopy, oxygen evolution, gel electrophoresis, immunoblotting, DNA sequencing, RT-PCR and time-resolved chlorophyll fluorescence were used. KEY RESULTS: Thylakoids of S. veneta did not contain PsbQ protein and its mRNA was absent. When compared to spinach, PsbP was partly depleted (30 %), as was its mRNA. All other thylakoid subunits were present in similar amounts in both species. PSII electron transfer was not affected. Fluorescence was strongly quenched upon irradiation of plants with high light, and relaxed only after prolonged dark incubation. Quenching of fluorescence was not linked to degradation of D1 protein. CONCLUSIONS: In S. veneta the PsbQ protein is not necessary for photosynthesis in vivo. As the amount of PsbP is sub-stoichiometric with other PSII subunits, this protein too is largely dispensable from a catalytic standpoint. One possibility is that PsbP acts as an assembly factor for PSII.

The sensitivity of Photosystem II to damage by UV-B radiation depends on the oxidation state of the water-splitting complex.

The water-oxidizing complex of Photosystem II is an important target of ultraviolet-B (280-320 nm) radiation, but the mechanistic background of the UV-B induced damage is not well understood. Here we studied the UV-B sensitivity of Photosystem II in different oxidation states, called S-states of the water-oxidizing complex. Photosystem II centers of isolated spinach thylakoids were synchronized to different distributions of the S(0), S(1), S(2) and S(3) states by using packages of visible light flashes and were exposed to UV-B flashes from an excimer laser (lambda=308 nm). The loss of oxygen evolving activity showed that the extent of UV-B damage is S-state-dependent. Analysis of the data obtained from different synchronizing flash protocols indicated that the UV-sensitivity of Photosystem II is significantly higher in the S(3) and S(2) states than in the S(1) and S(0) states. The data are discussed in terms of a model where UV-B-induced inhibition of water oxidation is caused either by direct absorption within the catalytic manganese cluster or by damaging intermediates of the water oxidation process.

Purification, crystallization and X-ray diffraction analyses of the T. elongatus PSII core dimer with strontium replacing calcium in the oxygen-evolving complex.

The core complex of photosystem II (PSII) was purified from thermophilic cyanobacterium Thermosynechococcus elongatus grown in Sr(2+)-containing and Ca(2+)-free medium. Functional in vivo incorporation of Sr(2+) into the oxygen-evolving complex (OEC) was confirmed by EPR analysis of the isolated and highly purified SrPSII complex in agreement with the previous study of Boussac et al. [J. Biol. Chem. 279 (2004) 22809-22819]. Three-dimensional crystals of SrPSII complex were obtained which diffracted to 3.9 A and belonged to the orthorhombic space group P2(1)2(1)2(1) with unit cell dimensions of a=133.6 A, b=236.6 A, c=307.8 A. Anomalous diffraction data collected at the Sr K-X-ray absorption edge identified a novel Sr(2+)-binding site which, within the resolution of these data (6.5 A), is consistent with the positioning of Ca(2+) in the recent crystallographic models of PSII [Ferreira et al. Science 303 (2004) 1831-1838, Loll et al. Nature 438 (2005) 1040-1044]. Fluorescence measurements on SrPSII crystals confirmed that crystallized SrPSII was active in transferring electrons from the OEC to the acceptor site of the reaction centre. However, SrPSII showed altered functional properties of its modified OEC in comparison with that of the CaPSII counterpart: slowdown of the Q(A)-to-Q(B) electron transfer and stabilized S(2)Q(A)(-) charge recombination.

Contrasting response of biomass and grain yield to severe drought in Cappelle Desprez and Plainsman V wheat cultivars.

We report a case study of natural variations and correlations of some photosynthetic parameters, green biomass and grain yield in Cappelle Desprez and Plainsman V winter wheat (Triticum aestivum L.) cultivars, which are classified as being drought sensitive and tolerant, respectively. We monitored biomass accumulation from secondary leaves in the vegetative phase and grain yield from flag leaves in the grain filling period. Interestingly, we observed higher biomass production, but lower grain yield stability in the sensitive Cappelle cultivar, as compared to the tolerant Plainsman cv. Higher biomass production in the sensitive variety was correlated with enhanced water-use efficiency. Increased cyclic electron flow around PSI was also observed in the Cappelle cv. under drought stress as shown by light intensity dependence of the ratio of maximal quantum yields of Photosystem I and Photosystem II, as well by the plot of the Photosystem I electron transport rate as a function of Photosystem II electron transport rate. Higher CO2 uptake rate in flag leaves of the drought-stressed Plainsman cv. during grain filling period correlates well with its higher grain yield and prolonged transpiration rate through spikes. The increase in drought factor (DFI) and performance (PI) indices calculated from variable chlorophyll fluorescence parameters of secondary leaves also showed correlation with higher biomass in the Cappelle cultivar during the biomass accumulation period. However, during the grain filling period, DFI and PI parameters of the flag leaves were higher in the tolerant Plainsman V cultivar and showed correlation with grain yield stability. Our results suggest that overall biomass and grain yield may respond differentially to drought stress in different wheat cultivars and therefore phenotyping for green biomass cannot be used as a general approach to predict grain yield. We also conclude that photosynthetic efficiency of flag and secondary leaves is correlated with grain yield and green biomass, respectively. In addition, secondary trait associated mechanisms like delayed senescence and higher water-use efficiency also contribute to biomass stability. Our studies further prove that photosynthetic parameters could be used to characterize environmental stress responses.

Dose reduction in 64-row whole-body CT in multiple trauma: an optimized CT protocol with iterative image reconstruction on a gemstone-based scintillator.

OBJECTIVE: Evaluation of potential dose savings by implementing adaptive statistical iterative reconstruction (ASiR) on a gemstone-based scintillator in a clinical 64-row whole-body CT (WBCT) protocol after multiple trauma. METHODS: Dose reports of 152 WBCT scans were analysed for two 64-row multidetector CT scanners (Scanners A and B); the main scanning parameters were kept constant. ASiR and a gemstone-based scintillator were used in Scanner B, and the noise index was adjusted (head: 5.2 vs 6.0; thorax/abdomen: 29.0 vs 46.0). The scan length, CT dose index (CTDI) and dose-length product (DLP) were analysed. The estimated mean effective dose was calculated using normalized conversion factors. Student's t-test was used for statistics. RESULTS: Both the mean CTDI (mGy) (Scanner A: 53.8 ± 2.0, 10.3 ± 2.5, 14.4 ± 3.7; Scanner B: 48.7 ± 2.2, 7.1 ± 2.3, 9.1 ± 3.6; p < 0.001, respectively) and the mean DLP (mGy cm) (Scanner A: 1318.9 ± 167.8, 509.3 ± 134.7, 848.8 ± 254.0; Scanner B: 1190.6 ± 172.6, 354.6 ± 128.3, 561.0 ± 246.7; p < 0.001, respectively) for the head, thorax and abdomen were significantly reduced with Scanner B. There was no relevant difference in scan length. The total mean effective dose (mSv) was significantly decreased with Scanner B (24.4 ± 6.0, 17.2 ± 5.8; p < 0.001). CONCLUSION: The implementation of ASiR and a gemstone-based scintillator allows for significant dose savings in a clinical WBCT protocol. ADVANCES IN KNOWLEDGE: Recent technical developments can significantly reduce radiation dose of WBCT in multiple trauma. Dose reductions of 10-34% can be achieved.

Iterative image reconstruction techniques: cardiothoracic computed tomography applications.

Iterative image reconstruction algorithms provide significant improvements over traditional filtered back projection in computed tomography (CT). Clinically available through recent advances in modern CT technology, iterative reconstruction enhances image quality through cyclical image calculation, suppressing image noise and artifacts, particularly blooming artifacts. The advantages of iterative reconstruction are apparent in traditionally challenging cases-for example, in obese patients, those with significant artery calcification, or those with coronary artery stents. In addition, as clinical use of CT has grown, so have concerns over ionizing radiation associated with CT examinations. Through noise reduction, iterative reconstruction has been shown to permit radiation dose reduction while preserving diagnostic image quality. This approach is becoming increasingly attractive as the routine use of CT for pediatric and repeated follow-up evaluation grows ever more common. Cardiovascular CT in particular, with its focus on detailed structural and functional analyses, stands to benefit greatly from the promising iterative solutions that are readily available.

The role of the PsbU subunit in the light sensitivity of PSII in the cyanobacterium Synechococcus 7942.

In the present study we investigated the role of the PsbU subunit in the electron transport characteristics and light sensitivity of the Photosystem II complex. The experiments were performed by using an earlier characterized PsbU-less mutant of the cyanobacterium Synechococcus PCC 7942, which has enhanced antioxidant capacity (Balint et al. FEBS Lett. 580 (2006) 2117-2122). Flash induced Chl fluorescence measurements in the presence and absence of the electron transport inhibitor DCMU showed that both the S(2)Q(A)(-) and the S(2)Q(B)(-) recombination is slowed down in the PsbU mutant relative to the WT strain. Thermoluminescence measurements confirmed the increased stability of the S(2)Q(A)(-) and S(2)Q(B)(-) charge pairs by showing an increased peak temperature of Q and B bands, which were measured in the presence and absence of DCMU, respectively. In addition, the intensity of the TL bands is also increased in the PsbU mutant (≈1.7 times for the B band), as compared to the WT. The PsbU mutant shows enhanced loss of Photosystem II activity under exposure to high light intensity both in the absence and presence of the protein synthesis inhibitor lincomycin. It is concluded from the data that the lack of the PsbU subunit in Synechococcus PCC 7942 affects the energetic stability of the S(2)Q(A)(-) and S(2)Q(B)(-) charge pairs by modifying both the PSII donor and acceptor side components. This effect is most likely caused by structural changes in the vicinity of the Mn cluster and in the inner part of the PSII complex, which are induced by the lack of the PsbU subunit from the lumenal part of the complex. The light sensitivity of Photosystem II in Synechococcus 7942 in the absence of the PsbU subunit is likely due to reactive oxygen species, which are produced as a consequence of disturbed donor side structure and/or due to the modified energetic properties of the primary radical pair.