共查询到20条相似文献,搜索用时 15 毫秒
1.
Background
The image formed by the eye''s optics is inherently blurred by aberrations specific to an individual''s eyes. We examined how visual coding is adapted to the optical quality of the eye.Methods and Findings
We assessed the relationship between perceived blur and the retinal image blur resulting from high order aberrations in an individual''s optics. Observers judged perceptual blur in a psychophysical two-alternative forced choice paradigm, on stimuli viewed through perfectly corrected optics (using a deformable mirror to compensate for the individual''s aberrations). Realistic blur of different amounts and forms was computer simulated using real aberrations from a population. The blur levels perceived as best focused were close to the levels predicted by an individual''s high order aberrations over a wide range of blur magnitudes, and were systematically biased when observers were instead adapted to the blur reproduced from a different observer''s eye.Conclusions
Our results provide strong evidence that spatial vision is calibrated for the specific blur levels present in each individual''s retinal image and that this adaptation at least partly reflects how spatial sensitivity is normalized in the neural coding of blur. 相似文献2.
Background
The image formed by the eye''s optics is blurred by the ocular aberrations, specific to each eye. Recent studies demonstrated that the eye is adapted to the level of blur produced by the high order aberrations (HOA). We examined whether visual coding is also adapted to the orientation of the natural HOA of the eye.Methods and Findings
Judgments of perceived blur were measured in 5 subjects in a psychophysical procedure inspired by the “Classification Images” technique. Subjects were presented 500 pairs of images, artificially blurred with HOA from 100 real eyes (i.e. different orientations), with total blur level adjusted to match the subject''s natural blur. Subjects selected the image that appeared best focused in each random pair, in a 6-choice ranked response. Images were presented through Adaptive Optics correction of the subject''s aberrations. The images selected as best focused were identified as positive, the other as negative responses. The highest classified positive responses correlated more with the subject''s Point Spread Function, PSF, (r = 0.47 on average) than the negative (r = 0.34) and the difference was significant for all subjects (p<0.02). Using the orientation of the best fitting ellipse of angularly averaged integrated PSF intensities (weighted by the subject''s responses) we found that in 4 subjects the positive PSF response was close to the subject''s natural PSF orientation (within 21 degrees on average) whereas the negative PSF response was almost perpendicularly oriented to the natural PSF (at 76 degrees on average).Conclusions
The Classification-Images inspired method is very powerful in identifying the internally coded blur of subjects. The consistent bias of the Positive PSFs towards the natural PSF in most subjects indicates that the internal code of blur appears rather specific to each subject''s high order aberrations and reveals that the calibration mechanisms for normalizing blur also operate using orientation cues. 相似文献3.
Background
The paired box 6 (PAX6) gene is considered as a master gene for eye development. Linkage of myopia to the PAX6 region on chromosome 11p13 was shown in several studies, but the results for association between myopia and PAX6 were inconsistent so far.Methodology/Principal Findings
We genotyped 16 single nucleotide polymorphisms (SNPs) in the PAX6 gene and its regulatory regions in an initial study for 300 high myopia cases and 300 controls (Group 1), and successfully replicated the positive results with another independent group of 299 high myopia cases and 299 controls (Group 2). Five SNPs were genotyped in the replication study. The spherical equivalent of subjects with high myopia was ≤−8.0 dioptres. The PLINK package was used for genetic data analysis. No association was found between each of the SNPs and high myopia. However, exhaustive sliding-window haplotype analysis highlighted an important role for rs12421026 because haplotypes containing this SNP were found to be associated with high myopia. The most significant results were given by the 4-SNP haplotype window consisting of rs2071754, rs3026393, rs1506 and rs12421026 (P = 3.54×10−10, 4.06×10−11 and 1.56×10−18 for Group 1, Group 2 and Combined Group, respectively) and the 3-SNP haplotype window composed of rs3026393, rs1506 and rs12421026 (P = 5.48×10−10, 7.93×10−12 and 6.28×10−23 for the three respective groups). The results remained significant after correction for multiple comparisons by permutations. The associated haplotyes found in a previous study were also successfully replicated in this study.Conclusions/Significance
PAX6 haplotypes are associated with susceptibility to the development of high myopia in Chinese. The PAX6 locus plays a role in high myopia. 相似文献4.
Background
Telomere length has been proposed as a marker of aging. However, our knowledge of lifestyle risk factors determining telomere length is limited.Methods
We evaluated the associations between years of rotating night shifts, self-reported sleep duration, and telomere length in 4,117 female participants from the Nurses'' Health Study. Telomere length in peripheral blood leukocytes was determined by Real-Time PCR assay. Information on rotating night shifts and sleep duration was collected via questionnaires prior to blood collection. We used multivariable linear regression to investigate the associations between rotating night shifts, sleep duration, and telomere length.Results
Compared with women in the category (9 hours), those in the lowest category of sleep duration (≤6 hours) had a 0.12 unit decrease in z score after adjustment for age, BMI and cigarette smoking (equivalent to 9-year telomere attrition, P for trend = 0.05). Significant positive association between sleep duration and telomere length was seen among women under age of 50 (P for trend = 0.004), but not among those over 50 (P for trend = 0.33) (P for interaction = 0.005). In addition, we observed that women with a longer history of rotating night shifts tended to have shorter telomere length, but this relation was not statistically significant (P for trend = 0.36).Conclusion
We found that sleep duration was positively associated with telomere length among women under 50 years old. Further research is needed to confirm the observed associations. 相似文献5.
Purpose
To investigate the utility of uncorrected visual acuity measures in screening for refractive error in white school children aged 6-7-years and 12-13-years.Methods
The Northern Ireland Childhood Errors of Refraction (NICER) study used a stratified random cluster design to recruit children from schools in Northern Ireland. Detailed eye examinations included assessment of logMAR visual acuity and cycloplegic autorefraction. Spherical equivalent refractive data from the right eye were used to classify significant refractive error as myopia of at least 1DS, hyperopia as greater than +3.50DS and astigmatism as greater than 1.50DC, whether it occurred in isolation or in association with myopia or hyperopia.Results
Results are presented from 661 white 12-13-year-old and 392 white 6-7-year-old school-children. Using a cut-off of uncorrected visual acuity poorer than 0.20 logMAR to detect significant refractive error gave a sensitivity of 50% and specificity of 92% in 6-7-year-olds and 73% and 93% respectively in 12-13-year-olds. In 12-13-year-old children a cut-off of poorer than 0.20 logMAR had a sensitivity of 92% and a specificity of 91% in detecting myopia and a sensitivity of 41% and a specificity of 84% in detecting hyperopia.Conclusions
Vision screening using logMAR acuity can reliably detect myopia, but not hyperopia or astigmatism in school-age children. Providers of vision screening programs should be cognisant that where detection of uncorrected hyperopic and/or astigmatic refractive error is an aspiration, current UK protocols will not effectively deliver. 相似文献6.
Chihiro Mayama Tae Tsutsumi Hitomi Saito Ryo Asaoka Atsuo Tomidokoro Aiko Iwase Shinichiro Otani Kazunori Miyata Makoto Araie 《PloS one》2014,9(1)
Purpose
This study was performed to first investigate the morphological differences in the optic nerve head between highly myopic non-glaucomatous controls and highly myopic glaucomatous eyes in comparison with the differences between emmetropic non-glaucomatous controls and emmetropic glaucomatous eyes using confocal scanning laser ophthalmoscopy. Further, the ability of the apparatus in glaucoma diagnosis in highly myopic eyes was compared with that in emmetropic eyes.Methods
Healthy subjects and age-matched patients with early-stage open-angle glaucoma were divided into two groups: emmetropic eyes (−1.0 to +1.0 diopters) and highly myopic eyes (−12.0 to −5.0 diopters).The participants were comprised of 65 emmetropic normal eyes, 59 emmetropic glaucomatous eyes, 62 highly myopic normal eyes, and 68 highly myopic glaucomatous eyes and eyes with pathologic myopia were carefully excluded. Confocal scanning laser tomographic parameters were compared among all subjects after adjustment for age and disc area. The ROC curves and sensitivity and specificity for glaucoma detection using several clinical methods were then compared between the emmetropic and highly myopic eyes.Results
Rim area, cup/disc area ratio, mean cup depth, and cup shape measure of glaucoma eyes are significantly different from those of normal eyes in both highly myopic eyes and emmetropic eyes. Methodological overestimation of retinal nerve fiber layer cross sectional area due to optic disc tilting was suggested in the highly myopic eyes. The diagnostic performance of glaucoma using several discriminant methods significantly deteriorated in the highly myopic eyes.Conclusions
In the highly myopic glaucomatous eyes, confocal scanning laser tomographic parameters were significantly different from that of non-glaucomatous highly myopic eyes but diagnostic performance of glaucoma was deteriorated than that in emmetropic eyes. These findings demonstrate the utility and limitations of the apparatus in diagnosing glaucoma in highly myopic patients. 相似文献7.
Background
Accurate objective assessment of sedentary and physical activity behaviours during childhood is integral to the understanding of their relation to later health outcomes, as well as to documenting the frequency and distribution of physical activity within a population.Purpose
To calibrate the Actigraph GT1M accelerometer, using energy expenditure (EE) as the criterion measure, to define thresholds for sedentary behaviour and physical activity categories suitable for use in a large scale epidemiological study in young children.Methods
Accelerometer-based assessments of physical activity (counts per minute) were calibrated against EE measures (kcal.kg−1.hr−1) obtained over a range of exercise intensities using a COSMED K4b2 portable metabolic unit in 53 seven-year-old children. Children performed seven activities: lying down viewing television, sitting upright playing a computer game, slow walking, brisk walking, jogging, hopscotch and basketball. Threshold count values were established to identify sedentary behaviour and light, moderate and vigorous physical activity using linear discriminant analysis (LDA) and evaluated using receiver operating characteristic (ROC) curve analysis.Results
EE was significantly associated with counts for all non-sedentary activities with the exception of jogging. Threshold values for accelerometer counts (counts.minute−1) were <100 for sedentary behaviour and ≤2240, ≤3840 and ≥3841 for light, moderate and vigorous physical activity respectively. The area under the ROC curves for discrimination of sedentary behaviour and vigorous activity were 0.98. Boundaries for light and moderate physical activity were less well defined (0.61 and 0.60 respectively). Sensitivity and specificity were higher for sedentary (99% and 97%) and vigorous (95% and 91%) than for light (60% and 83%) and moderate (61% and 76%) thresholds.Conclusion
The accelerometer cut points established in this study can be used to classify sedentary behaviour and to distinguish between light, moderate and vigorous physical activity in children of this age. 相似文献8.
Proctor MC 《Annals of botany》2012,109(5):1019-1026
Background and Aims
Hymenophyllaceae (filmy ferns) are typically plants of shady, constantly moist habitats. They attain greatest species diversity and biomass in humid tropical montane forests and temperate hyperoceanic climates. This paper presents ecophysiological data bearing on their worldwide ecological niche space and its limits.Methods
Chlorophyll fluorescence was used to monitor recovery in desiccation experiments, and for measurements of 95 % saturating irradiance [photosynthetic photon flux density (PPFD95 %)] of photosynthetic electron flow and other parameters, in the New Zealand Hymenophyllum sanguinolentum, and three species each of Hymenophyllum and Trichomanes from forests in Trinidad and Venezuela.Key Results
Hymenophyllum sanguinolentum was comparable in desiccation tolerance and light responses with the European species. The more common species in the two tropical forests showed PPFD95 % >100 µmol m−2 s−1, and withstood moderate desiccation (–40 MPa) for several days. The four most shade-adapted species had PPFD95 % ≤51 µmol m−2 s−1, and were sensitive to even mild and brief desiccation (–22 MPa for 3 d).Conclusions
Light and desiccation responses of filmy ferns can be seen as an integrated package. At low light and windspeed in humid forests, net radiation and saturation deficit are low, and diffusion resistance high. Water loss is slow and can be supported by modest conduction from the sub-stratum. With higher irradiance, selection pressure for desiccation tolerance increases progressively. With low light and high humidity, the filmy fern pattern of adaptation is probably optimal, and the vascular plant leaf with mesophyll and stomata offers no advantage in light capture, water economy or CO2 uptake. Trade-offs between light adaptation and desiccation tolerance, and between stem conduction and water absorption through the leaf surface, underlie adaptive radiation and niche differentiation of species within the family. Hymenophyllaceae are a rare example of an evolutionary shift of adaptive strategy from typical vascular plant adaptation to the poikilohydry most typical of bryophytes. 相似文献9.
Alberto Migliore Umberto Massafra Emanuele Bizzi Francesca Vacca Severino Martin-Martin Mauro Granata Andrea Alimonti Sandro Tormenta 《Arthritis research & therapy》2009,11(6):R183
Introduction
Comparison of intra-articular bacterial-derived hyaluronic acid (Hyalubrix®) (HA) with local analgesia (mepivacaine) for osteoarthritis (OA) of the hip.Methods
A pilot prospective, double-blind, 6-month randomized trial of 42 patients with hip OA. HA or mepivacaine was administered twice (once a month) under ultrasound guidance. Efficacy measurements included the Lequesne''s algofunctional index, a visual analog scale for pain, concomitant use of analgesia, patient and physician global measurement, and safety.Results
Patients in the HA group exhibited a significantly reduced Lequesne''s algofunctional index 3 and 6 months after treatment (P < 0.001) and significantly reduced visual analog scale pain scores 3 and 6 months after treatment (P < 0.05) compared with the local anesthetic group. All primary and secondary measures were significantly improved versus baseline, but other than the above were not different from each other at 3 or 6 months. Adverse effects were minimal.Conclusions
This comparative study suggests a beneficial effect and safety of intra-articular HA in the management of hip OA.Trial registration number
ISRCTN39397064. 相似文献10.
Background and Aims
Modellers often define growth as the development of plant structures from endogenous resources, thus making a distinction between structural (WS) and total (W) dry biomass, the latter being the sum of WS and the weight of storage compounds. In this study, short-term C and N reserves were characterized experimentally (forms, organ distribution, time changes) in relation to light and nutrition signals, and organ structural growth in response to reserve levels was evaluated.Methods
Tomato plants (Solanum lycopersicum) were grown hydroponically in a growth room with a 12-h photoperiod and an adequate supply of NO3− (3 mol m−3). Three experiments were carried out 18 d after sowing: [NO3−] was either maintained at 3 mol m−3, changed to 0·02 mol m−3 or to 0 mol m−3. Plants were sampled periodically throughout the light/dark cycles over 24–48 h. Organ WS was calculated from W together with the amount of different compounds that act as C and N resources, i.e. non-structural carbohydrates and carboxylates, nitrate and free amino acids.Key Results
With adequate nutrition, carbohydrates accumulated in leaves during light periods, when photosynthesis exceeded growth needs, but decreased at night when these sugars are the main source of C for growth. At the end of the night, carbohydrates were still high enough to fuel full-rate growth, as WS increased at a near constant rate throughout the light/dark cycle. When nitrate levels were restricted, C reserves increased, but [NO3−] decreased progressively in stems, which contain most of the plant N reserves, and rapidly in leaves and roots. This resulted in a rapid restriction of structural growth.Conclusions
Periodic darkness did not restrict growth because sufficient carbohydrate reserves accumulated during the light period. Structural growth, however, was very responsive to NO3− nutrition, because N reserves were mostly located in stems, which have limited nitrate reduction capacity.Key words: Solanum lycopersicum, tomato, nitrogen, carbon, structural growth, reserves, nitrate, amino acids, carbohydrate, carboxylate 相似文献11.
Lepez T Vandewoestyne M Hussain S Van Nieuwerburgh F Poppe K Velkeniers B Kaufman JM Deforce D 《PloS one》2011,6(12):e29646
Context
Hashimoto''s thyroiditis (HT) and Graves'' disease (GD), two autoimmune thyroid diseases (AITD), occur more frequently in women than in men and show an increased incidence in the years following parturition. Persisting fetal cells could play a role in the development of these diseases.Objective
Aim of this study was to detect and characterize fetal cells in blood of postpartum women with and without an AITD.Participants
Eleven patients with an AITD and ten healthy volunteers, all given birth to a son maximum 5 years before analysis, and three women who never had been pregnant, were included. None of them had any other disease of the thyroid which could interfere with the results obtained.Methods
Fluorescence in situ hybridization (FISH) and repeated FISH were used to count the number of male fetal cells. Furthermore, the fetal cells were further characterized.Results
In patients with HT, 7 to 11 fetal cells per 1.000.000 maternal cells were detected, compared to 14 to 29 fetal cells in patients with GD (p = 0,0061). In patients with HT, mainly fetal CD8+ T cells were found, while in patients with GD, fetal B and CD4+ T cells were detected. In healthy volunteers with son, 0 to 5 fetal cells were observed, which was significantly less than the number observed in patients (p<0,05). In women who never had been pregnant, no male cells were detected.Conclusion
This study shows a clear association between fetal microchimeric cells and autoimmune thyroid diseases. 相似文献12.
Vis JC De Bruin-Bon HA Bouma BJ Huisman SA Imschoot L van den Brink K Mulder BJ 《Netherlands heart journal》2012,20(6):264-269
Objective
Physical fitness is reduced in adults with Down syndrome (DS). The present study was conducted to elucidate the exercise response in adults with DS.Design
Case controlled before-after trial.Setting
Residential centre for people with intellectual disabilities.Participants
96 Adults with DS, 25 non-DS adults with an intellectual disability, 33 controls.Interventions
Echocardiography to exclude heart defects and to measure cardiac index (CI) in the supine position, supine position with raised legs, and following ten knee bends.Main outcome measure
Exercise testingResults
At rest, mean CI was not significantly different between persons with DS and controls (2.3 vs. 2.4 l/min/m2, p = 0.3). However, mean CI after exercise was significantly lower in DS (2.9 vs. 3.7 l/min/m2, p < 0.001) and mean CI increase from rest to exercise was more than 50% lower in DS. On the contrary, CI after exercise was similar among controls and non-DS adults with an intellectual disability. Significantly lower stroke volumes in DS were found with insufficient heart rate response.Conclusions
CI at rest was similar in adults with DS and controls; however persons with DS have a diminished cardiac response to exercise. Stroke volumes were significantly lower in DS during exercise and a compensated heightened heart rate was absent. 相似文献13.
Background
How the visual system combines information from the two eyes to form a unitary binocular representation of the external world is a fundamental question in vision science that has been the focus of many psychophysical and physiological investigations. Ding & Sperling (2006) measured perceived phase of the cyclopean image, and developed a binocular combination model in which each eye exerts gain control on the other eye''s signal and over the other eye''s gain control. Critically, the relative phase of the monocular sine-waves plays a central role.Methodology/Principal Findings
We used the Ding-Sperling paradigm but measured both the perceived contrast and phase of cyclopean images in three hundred and eighty combinations of base contrast, interocular contrast ratio, eye origin of the probe, and interocular phase difference. We found that the perceived contrast of the cyclopean image was independent of the relative phase of the two monocular gratings, although the perceived phase depended on the relative phase and contrast ratio of the monocular images. We developed a new multi-pathway contrast-gain control model (MCM) that elaborates the Ding-Sperling binocular combination model in two ways: (1) phase and contrast of the cyclopean images are computed in separate pathways, although with shared cross-eye contrast-gain control; and (2) phase-independent local energy from the two monocular images are used in binocular contrast combination. With three free parameters, the model yielded an excellent account of data from all the experimental conditions.Conclusions/Significance
Binocular phase combination depends on the relative phase and contrast ratio of the monocular images but binocular contrast combination is phase-invariant. Our findings suggest the involvement of at least two separate pathways in binocular combination. 相似文献14.
Cipriani S Mencarelli A Chini MG Distrutti E Renga B Bifulco G Baldelli F Donini A Fiorucci S 《PloS one》2011,6(10):e25637
Background
GP-BAR1, a member G protein coupled receptor superfamily, is a cell surface bile acid-activated receptor highly expressed in the ileum and colon. In monocytes, ligation of GP-BAR1 by secondary bile acids results in a cAMP-dependent attenuation of cytokine generation.Aims
To investigate the role GP-BAR1 in regulating intestinal homeostasis and inflammation-driven immune dysfunction in rodent models of colitis.Methods
Colitis was induced in wild type and GP-BAR1−/− mice by DSS and TNBS administration. Potential GP-BAR1 agonists were identified by in silico screening and computational docking studies.Results
GP-BAR1−/− mice develop an abnormal morphology of colonic mucous cells and an altered molecular architecture of epithelial tight junctions with increased expression and abnormal subcellular distribution of zonulin 1 resulting in increased intestinal permeability and susceptibility to develop severe colitis in response to DSS at early stage of life. By in silico screening and docking studies we identified ciprofloxacin as a GP-BAR1 ligand. In monocytes, ciprofloxacin increases cAMP concentrations and attenuates TNFα release induced by TLR4 ligation in a GP-BAR1 dependent manner. Treating mice rendered colitic by TNBS with ciprofloxacin and oleanolic acid, a well characterized GP-BAR1 ligand, abrogates signs and symptoms of colitis. Colonic expression of GP-BAR1 mRNA increases in rodent models of colitis and tissues from Crohn''s disease patients. Flow cytometry analysis demonstrates that ≈90% of CD14+ cells isolated from the lamina propria of TNBS-treated mice stained positively for GP-BAR1.Conclusions
GP-BAR1 regulates intestinal barrier structure. Its expression increases in rodent models of colitis and Crohn''s disease. Ciprofloxacin is a GP-BAR1 ligand. 相似文献15.
Asghar Mesbahi Vahid Jafarzadeh Nahideh Gharehaghaji 《Reports of Practical Oncology and Radiotherapy》2012,17(3):146-150
Background
Application of less toxic normoxic polymer gel of N-isopropyl acrylamide (NIPAM) for radiation therapy has been studied in recent years.Aim
In the current study the optical and NMR properties of NIPAM were studied for radiation therapy dosimetry application.Materials and methods
NIPAM normoxic polymer gel was prepared and irradiated by 9 MV photon beam of a medical linac. The optical absorbance was measured using a conventional laboratory spectrophotometer in different wavelengths ranging from 390 to 860 nm. R2 measurements of NIPAM gels were performed using a 1.5 T scanner and R2–dose curve was obtained.Results
Our results showed R2 dose sensitivity of 0.193 ± 0.01 s−1 Gy−1 for NIPAM gel. Both R2 and optical absorbance showed a linear relationship with dose from 1.5 to 11 Gy for NIPAM gel dosimeter. Moreover, absorbance–dose response varied considerably with light wavelength and highest sensitivity was seen for the blue part of the spectrum.Conclusion
Our results showed that both optical and NMR approaches have acceptable sensitivity and accuracy for dose determination with NIPAM gel. However, for optical reading of the gel, utilization of an optimum optical wavelength is recommended. 相似文献16.
Lehmann LE Hauser S Malinka T Klaschik S Weber SU Schewe JC Stüber F Book M 《PloS one》2011,6(2):e17146
Background
Urinary tract infections (UTI) are frequent in outpatients. Fast pathogen identification is mandatory for shortening the time of discomfort and preventing serious complications. Urine culture needs up to 48 hours until pathogen identification. Consequently, the initial antibiotic regimen is empirical.Aim
To evaluate the feasibility of qualitative urine pathogen identification by a commercially available real-time PCR blood pathogen test (SeptiFast®) and to compare the results with dipslide and microbiological culture.Design of study
Pilot study with prospectively collected urine samples.Setting
University hospital.Methods
82 prospectively collected urine samples from 81 patients with suspected UTI were included. Dipslide urine culture was followed by microbiological pathogen identification in dipslide positive samples. In parallel, qualitative DNA based pathogen identification (SeptiFast®) was performed in all samples.Results
61 samples were SeptiFast® positive, whereas 67 samples were dipslide culture positive. The inter-methodological concordance of positive and negative findings in the gram+, gram- and fungi sector was 371/410 (90%), 477/492 (97%) and 238/246 (97%), respectively. Sensitivity and specificity of the SeptiFast® test for the detection of an infection was 0.82 and 0.60, respectively. SeptiFast® pathogen identifications were available at least 43 hours prior to culture results.Conclusion
The SeptiFast® platform identified bacterial DNA in urine specimens considerably faster compared to conventional culture. For UTI diagnosis sensitivity and specificity is limited by its present qualitative setup which does not allow pathogen quantification. Future quantitative assays may hold promise for PCR based UTI pathogen identification as a supplementation of conventional culture methods. 相似文献17.
Background
Globally plants are the primary sink of atmospheric CO2, but are also the major contributor of a large spectrum of atmospheric reactive hydrocarbons such as terpenes (e.g. isoprene) and other biogenic volatile organic compounds (BVOC). The prediction of plant carbon (C) uptake and atmospheric oxidation capacity are crucial to define the trajectory and consequences of global environmental changes. To achieve this, the biosynthesis of BVOC and the dynamics of C allocation and translocation in both plants and ecosystems are important.Methodology
We combined tunable diode laser absorption spectrometry (TDLAS) and proton transfer reaction mass spectrometry (PTR-MS) for studying isoprene biosynthesis and following C fluxes within grey poplar (Populus x canescens) saplings. This was achieved by feeding either 13CO2 to leaves or 13C-glucose to shoots via xylem uptake. The translocation of 13CO2 from the source to other plant parts could be traced by 13C-labeled isoprene and respiratory 13CO2 emission.Principal Finding
In intact plants, assimilated 13CO2 was rapidly translocated via the phloem to the roots within 1 hour, with an average phloem transport velocity of 20.3±2.5 cm h−1. 13C label was stored in the roots and partially reallocated to the plants'' apical part one day after labeling, particularly in the absence of photosynthesis. The daily C loss as BVOC ranged between 1.6% in mature leaves and 7.0% in young leaves. Non-isoprene BVOC accounted under light conditions for half of the BVOC C loss in young leaves and one-third in mature leaves. The C loss as isoprene originated mainly (76–78%) from recently fixed CO2, to a minor extent from xylem-transported sugars (7–11%) and from photosynthetic intermediates with slower turnover rates (8–11%).Conclusion
We quantified the plants'' C loss as respiratory CO2 and BVOC emissions, allowing in tandem with metabolic analysis to deepen our understanding of ecosystem C flux. 相似文献18.
Takuhei Shoji Hiroto Kuroda Masayuki Suzuki Motoyoshi Baba Masanori Hangai Makoto Araie Shin Yoneya 《PloS one》2014,9(12)
Purpose
To measure horizontal and vertical lamina cribrosa (LC) tilt angles and investigate associated factors using prototype optical coherence tomography (OCT) with a broad wavelength laser light source.Design
Cross sectional study.Methods
Twenty-eight no glaucoma eyes (from 15 subjects) and 25 glaucoma eyes (from 14 patients) were enrolled. A total of 300 optic nerve head B-scans were obtained in 10 µm steps and the inner edge of Bruch''s membrane opening (BMO) was identified as the reference plane. The vertical and horizontal angles between BMO line and approximate the best-fitting line for the surface of the LC were measured and potential associated factors were estimated with univariate and multivariate logistic regression analyses.Results
The median (interquartile range) horizontal and vertical tilt angles were 7.10 (2.43–11.45) degrees and 4.15 (2.60–6.85) degrees in eyes without glaucoma and 8.50 (4.40–14.10) degrees and 9.30 (6.90–14.15) degrees in glaucoma eyes, respectively. The refractive errors had a statistically significant association with horizontal LC tilt angles (coefficients, −1.53 per diopter) and glaucoma had a significant correlation with vertical tilt angles (coefficients, 6.56) using multiple logistic regression analysis (p<0.001).Conclusions
OCT allowed evaluation of the internal tilting of the LC compared with the BMO. The horizontal internal LC tilt angle was correlated with refractive errors, corresponding to myopic physiological changes, and vertical internal LC tilt was correlated with glaucoma, corresponding to glaucomatous pathological changes. These parameters have important implications for investigation of the correlation between myopia, glaucoma and LC morphological features. 相似文献19.
Background and Aims
Previous work has shown that the entire photosynthetic light response curve, based on both Mitscherlich and Michaelis–Menten functions, could be predicted in an interspecific context through allometric relations linking the parameters of these functions to two static leaf traits: leaf nitrogen (N) content and leaf mass per area (LMA). This paper describes to what extent these allometric relations are robust to changes in soil fertility and the growth irradiance of the plants.Methods
Plants of 25 herbaceous species were grown under controlled conditions in factorial combinations of low/high soil fertility and low/high growth irradiance. Net photosynthetic rates per unit dry mass were measured at light intensities ranging from 0 to 700 µmol m−2 s−1 photosynthetically active radiation (PAR).Key Results
The differing growth environments induced large changes in N, LMA and in each of the parameter estimates of the Mitscherlich and Michaelis–Menten functions. However, the differing growth environments induced only small (although significant) changes in the allometric relationships linking N and LMA to the parameters of the two functions. As a result, 88 % (Mitcherlich) and 89 % (Michaelis–Menten) of the observed net photosynthetic rates over the full range of light intensities (0–700 µmol m−2 s−1 PAR) and across all four growth environments could be predicted using only N and LMA using the same allometric relations.Conclusions
These results suggest the possibility of predicting net photosynthetic rates in nature across species over the full range of light intensities using readily available data. 相似文献20.