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41.
Three-dimensional pore space quantification of apple tissue using X-ray computed microtomography 总被引:1,自引:0,他引:1
The microstructure and the connectivity of the pore space are important variables for better understanding of the complex
gas transport phenomena that occur in plant tissues. In this study, we present an experimental procedure for image acquisition
and image processing to quantitatively characterize in 3D the pore space of apple tissues (Malus domestica Borkh.) for two cultivars (Jonagold and Braeburn) taken from the fleshy part of the cortex using X-ray computer microtomography.
Preliminary sensitivity analyses were performed to determine the effect of the resolution and the volume size (REV, representative
elementary volume analysis) on the computed porosity of apple samples. For comparison among cultivars, geometrical properties
such as porosity, specific surface area, number of disconnected pore volumes and their distribution parameters were extracted
and analyzed in triplicate based on the 3D skeletonization of the pore space (medial axis analysis). The results showed that
microtomography provides a resolution at the micrometer level to quantitatively analyze and characterize the 3D topology of
the pore space in apple tissue. The computed porosity was confirmed to be highly dependent of the resolution used, and the
minimum REV of the cortical flesh of apple fruit was estimated to be 1.3 mm3. Comparisons among the two cultivars using a resolution of 8.5 μm with a minimum REV cube showed that in spite of the complexity
and variability of the pore space network observed in Jonagold and Braeburn apples, the extracted parameters from the medial
axis were significantly different (P-value < 0.05). Medial axis parameters showed potential to differentiate the microstructure between the two evaluated apple
cultivars. 相似文献
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Cardiovascular disease accounts for significant morbidity and mortality in the elderly. The clinical trial data available to guide therapy in this growing population subset are relatively limited. This review will focus on treatment approaches and recommendations obtained from subgroup analyses of elderly patients from major clinical trials for the management of chronic stable angina, acute coronary syndromes (unstable angina and non-ST-segment elevation myocardial infarction), and coronary revascularization. Recent advances in the treatment of stable angina have shown that use of angiotensin-converting enzyme inhibitors and lipid-lowering therapy as adjunctive measures show benefit in the elderly by reducing the occurrence of death, nonfatal myocardial infarction, and unstable angina. However, if patients experience disabling or unstable anginal symptoms despite effective medical therapy, coronary revascularization must be considered. Several clinical trials have shown a significant reduction in major adverse cardiac events when using intravenous glycoprotein receptor antagonists periprocedurally during percutaneous revascularization approaches in elderly patients with unstable angina or non-ST-segment elevation myocardial infarction, especially when these measures are performed as soon as possible. However, the success of myocardial revascularization by a percutaneous or surgical approach is highly dependent on the patient's associated comorbidities, especially in patients over age 80 years. 相似文献
44.
The first step of many metabolomics studies is quenching, a technique vital for rapidly halting metabolism and ensuring that the metabolite profile remains unchanging during sample processing. The most widely used approach is to plunge the sample into prechilled cold methanol; however, this led to significant metabolite loss in Synecheococcus sp. PCC 7002. Here we describe our analysis of the impacts of cold methanol quenching on the model marine cyanobacterium Synechococcus sp. PCC 7002, as well as our brief investigation of alternative quenching methods. We tested several methods including cold methanol, cold saline, and two filtration approaches. Targeted central metabolites were extracted and metabolomic profiles were generated using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results indicate that cold methanol quenching induces dramatic metabolite leakage in Synechococcus, resulting in a majority of central metabolites being lost prior to extraction. Alternatively, usage of a chilled saline quenching solution mitigates metabolite leakage and improves sample recovery without sacrificing rapid quenching of cellular metabolism. Finally, we illustrate that metabolite leakage can be assessed, and subsequently accounted for, in order to determine absolute metabolite pool sizes; however, our results show that metabolite leakage is inconsistent across various metabolite pools and therefore must be determined for each individually measured metabolite. 相似文献
45.
Three‐dimensional microscale modelling of CO2 transport and light propagation in tomato leaves enlightens photosynthesis 下载免费PDF全文
Quang Tri Ho Herman N. C. Berghuijs Rodrigo Watté Pieter Verboven Els Herremans Xinyou Yin Moges A. Retta Ben Aernouts Wouter Saeys Lukas Helfen Graham D. Farquhar Paul C. Struik Bart M. Nicolaï 《Plant, cell & environment》2016,39(1):50-61
We present a combined three‐dimensional (3‐D) model of light propagation, CO2 diffusion and photosynthesis in tomato (Solanum lycopersicum L.) leaves. The model incorporates a geometrical representation of the actual leaf microstructure that we obtained with synchrotron radiation X‐ray laminography, and was evaluated using measurements of gas exchange and leaf optical properties. The combination of the 3‐D microstructure of leaf tissue and chloroplast movement induced by changes in light intensity affects the simulated CO2 transport within the leaf. The model predicts extensive reassimilation of CO2 produced by respiration and photorespiration. Simulations also suggest that carbonic anhydrase could enhance photosynthesis at low CO2 levels but had little impact on photosynthesis at high CO2 levels. The model confirms that scaling of photosynthetic capacity with absorbed light would improve efficiency of CO2 fixation in the leaf, especially at low light intensity. 相似文献
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Shigeki Shibata Masami Niwa Akihiko Himeno Nanette G. Gana Kazuto Shigematsu Masanori Matsumoto Kimihiro Yamashita Kohji Sumikawa Kohtaro Taniyama 《Cellular and molecular neurobiology》1997,17(1):151-156
1. The receptor autoradiographic method done on the rat lower brain stem and cerebellum plus 125I-endothelin-1, BQ-123, an antagonist for the endothelin ETA receptor, and sarafotoxin S6c, an agonist for the ETB receptor, revealed minute amounts of the ETA receptor coexisting with the ETB receptor in the caudal solitary tract nucleus of the rat lower brain stem.2. The ETB receptor is present predominantly in other parts of the lower brain stem.3. Knowledge of the heterogeneous distribution of the central endothelin receptor subtypes aids in understanding the neurophysiology of endothelins. 相似文献
49.
Hausmann R Bodnar M Woltersdorf R Wang H Fuchs M Messemer N Qin Y Günther J Riedel T Grohmann M Nieber K Schmalzing G Rubini P Illes P 《The Journal of biological chemistry》2012,287(17):13930-13943
The aim of the present experiments was to clarify the subunit stoichiometry of P2X2/3 and P2X2/6 receptors, where the same subunit (P2X2) forms a receptor with two different partners (P2X3 or P2X6). For this purpose, four non-functional Ala mutants of the P2X2, P2X3, and P2X6 subunits were generated by replacing single, homologous amino acids particularly important for agonist binding. Co-expression of these mutants in HEK293 cells to yield the P2X2 WT/P2X3 mutant or P2X2 mutant/P2X3 WT receptors resulted in a selective blockade of agonist responses in the former combination only. In contrast, of the P2X2 WT/P2X6 mutant and P2X2 mutant/P2X6 WT receptors, only the latter combination failed to respond to agonists. The effects of α,β-methylene-ATP and 2-methylthio-ATP were determined by measuring transmembrane currents by the patch clamp technique and intracellular Ca(2+) transients by the Ca(2+)-imaging method. Protein labeling, purification, and PAGE confirmed the assembly and surface trafficking of the investigated WT and WT/mutant combinations in Xenopus laevis oocytes. In conclusion, both electrophysiological and biochemical investigations uniformly indicate that one subunit of P2X2 and two subunits of P2X3 form P2X2/3 heteromeric receptors, whereas two subunits of P2X2 and one subunit of P2X6 constitute P2X2/6 receptors. Further, it was shown that already two binding sites of the three possible ones are sufficient to allow these receptors to react with their agonists. 相似文献
50.
Transport of CO2 in leaves was investigated by combining a 2-D, microscale CO2 transport model with photosynthesis kinetics in wheat (Triticum aestivum L.) leaves. The biophysical microscale model for gas exchange featured an accurate geometric representation of the actual 2-D leaf tissue microstructure and accounted for diffusive mass exchange of CO2. The resulting gas transport equations were coupled to the biochemical Farquhar-von Caemmerer-Berry model for photosynthesis. The combined model was evaluated using gas exchange and chlorophyll fluorescence measurements on wheat leaves. In general a good agreement between model predictions and measurements was obtained, but a discrepancy was observed for the mesophyll conductance at high CO2 levels and low irradiance levels. This may indicate that some physiological processes related to photosynthesis are not incorporated in the model. The model provided detailed insight into the mechanisms of gas exchange and the effects of changes in ambient CO2 concentration or photon flux density on stomatal and mesophyll conductance. It represents an important step forward to study CO2 diffusion coupled to photosynthesis at the leaf tissue level, taking into account the leaf''s actual microstructure. 相似文献