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1.
Unequal absorption of photons between photosystems I and II, and between bundle-sheath and mesophyll cells, are likely to affect the efficiency of the CO2-concentrating mechanism in C4 plants. Under steady-state conditions, it is expected that the biochemical distribution of energy (ATP and NADPH) and photosynthetic metabolite concentrations will adjust to maintain the efficiency of C4 photosynthesis through the coordination of the C3 (Calvin-Benson-Bassham) and C4 (CO2 pump) cycles. However, under transient conditions, changes in light quality will likely alter the coordination of the C3 and C4 cycles, influencing rates of CO2 assimilation and decreasing the efficiency of the CO2-concentrating mechanism. To test these hypotheses, we measured leaf gas exchange, leaf discrimination, chlorophyll fluorescence, electrochromatic shift, photosynthetic metabolite pools, and chloroplast movement in maize (Zea mays) and Miscanthus × giganteus following transitional changes in light quality. In both species, the rate of net CO2 assimilation responded quickly to changes in light treatments, with lower rates of net CO2 assimilation under blue light compared with red, green, and blue light, red light, and green light. Under steady state, the efficiency of CO2-concentrating mechanisms was similar; however, transient changes affected the coordination of C3 and C4 cycles in M. giganteus but to a lesser extent in maize. The species differences in the ability to coordinate the activities of C3 and C4 cycles appear to be related to differences in the response of cyclic electron flux around photosystem I and potentially chloroplast rearrangement in response to changes in light quality.The CO2-concentrating mechanism in C4 plants reduces the carbon lost through the photorespiratory pathway by limiting the oxygenation of ribulose-1,5-bisphosphate (RuBP) by the enzyme Rubisco (Brown and Smith, 1972; Sage, 1999). Through the compartmentalization of the C4 cycle in the mesophyll cells and the C3 cycle in the bundle-sheath cells (Hatch and Slack, 1966), C4 plants suppress RuBP oxygenation by generating a high CO2 partial pressure around Rubisco (Furbank and Hatch, 1987). To maintain high photosynthetic rates and efficient light energy utilization, the metabolic flux through the C3 and C4 cycles must be coordinated. However, coordination of the C3 and C4 cycles is likely disrupted due to rapid changes in environmental conditions, particularly changes in light availability (Evans et al., 2007; Tazoe et al., 2008).Spatial and temporal variations in light environments, including both light quantity and quality, are expected to alter the coordination of the C3 and C4 cycles. For example, it has been suggested that the coordination of C3 and C4 cycles is altered by changes in light intensity (Henderson et al., 1992; Cousins et al., 2006; Tazoe et al., 2006, 2008; Kromdijk et al., 2008, 2010; Pengelly et al., 2010). However, more recent publications indicate that some of the proposed light sensitivity of the CO2-concentrating mechanisms in C4 plants can be attributed to oversimplifications of leaf models of carbon isotope discrimination (Δ13C), in particular, errors in estimates of bundle-sheath CO2 partial pressure and omissions of respiratory fractionation (Ubierna et al., 2011, 2013). Alternatively, there is little information on the effects of light quality on the coordination of C3 and C4 cycle activities and the subsequent impact on net rate of CO2 assimilation (Anet).In C3 plants, Anet is reduced under blue light compared with red or green light (Evans and Vogelmann, 2003; Loreto et al., 2009). This was attributed to differences in absorbance and wavelength-dependent differences in light penetration into leaves, where red and green light penetrate farther into leaves compared with blue light (Vogelmann and Evans, 2002; Evans and Vogelmann, 2003). Differences in light quality penetration into a leaf are likely to have profound impacts on C4 photosynthesis, because the C4 photosynthetic pathway requires the metabolic coordination of the mesophyll C4 cycle and the bundle-sheath C3 cycle. Indeed, Evans et al. (2007) observed a 50% reduction in the rate of CO2 assimilation in Flaveria bidentis under blue light relative to white light at a light intensity of 350 µmol quanta m−2 s−1. This was attributed to poor penetration of blue light into the bundle-sheath cells and subsequent insufficient production of ATP in the bundle-sheath cells to match the rates of mesophyll cell CO2 pumping (Evans et al., 2007). Recently, Sun et al. (2012) observed similar low rates of steady-state CO2 assimilation under blue light relative to red, green, and blue light (RGB), red light, and green light at a constant light intensity of 900 µmol quanta m−2 s−1.Because the light penetration into a leaf depends on light quality, with blue light penetrating the least, this potentially results in changes in the energy available for carboxylation reactions in the bundle-sheath (C3 cycle) and mesophyll (C4 cycle) cells. Changes in the balance of energy driving the C3 and C4 cycles can alter the efficiency of the CO2-concentrating mechanisms, often represented by leakiness (ϕ), the fraction of CO2 that is pumped into the bundle-sheath cells that subsequently leaks back out (Evans et al., 2007). Unfortunately, ϕ cannot be measured directly, but it can be estimated through the combined measured and modeled values of Δ13C (Farquhar, 1983). Using measurements of Δ13C, it has been demonstrated that under steady-state conditions, changes in light quality do not affect ϕ (Sun et al., 2012); however, it remains unknown if ϕ is also constant during the transitions between different light qualities. In fact, sudden changes of light quality could temporally alter the coordination of the C3 and C4 cycles.To understand the effects of light quality on C4 photosynthesis and the coordination of the activities of C3 and C4 cycles, we measured transitional changes in leaf gas exchange and Δ13C under RGB and broad-spectrum red, green, and blue light in the NADP-malic enzyme C4 plants maize (Zea mays) and Miscanthus × giganteus. Leaf gas exchange and Δ13C measurements were used to estimate ϕ using the complete model of C4 leaf Δ13C (Farquhar, 1983; Farquhar and Cernusak, 2012). Additionally, we measured photosynthetic metabolite pools, Rubisco activation state, chloroplast movement, and rates of linear versus cyclic electron flow during rapid transitions from red to blue light and blue to red light. We hypothesized that the limited penetration of blue light into the leaf would result in insufficient production of ATP in the bundle-sheath cells to match the rate of mesophyll cell CO2 pumping. We predicted that rapid changes in light quality would affect the coordination of the C3 and C4 cycles and cause an increase in ϕ, but this would equilibrate as leaf metabolism reached a new steady-state condition.  相似文献   
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Glioma is a huge threat for human being because it was hard to be completely removed owing to both the infiltrating growth of glioma cells and integrity of blood brain barrier. Thus effectively imaging the glioma cells may pave a way for surgical removing of glioma. In this study, a fluorescent probe, Cy3, was anchored onto the terminal of AS1411, a glioma cell targeting aptamer, and then TGN, a BBB targeting peptide, was conjugated with Cy3-AS1411 through a PEG linker. The production, named AsT, was characterized by gel electrophoresis, 1H NMR and FTIR. In vitro cellular uptake and glioma spheroid uptake demonstrated the AsT could not only be uptaken by both glioma and endothelial cells, but also penetrate through endothelial cell monolayer and uptake by glioma spheroids. In vivo, AsT could effectively target to glioma with high intensity. In conclusion, AsT could be used as an effective glioma imaging probe.  相似文献   
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A study of the species composition of mayfly communities in connection with environmental parameters was made in headwater streams of the Pieniny Mts. The rhithral zone is inhabited maximally by 19 mayfly species. In most of the streams studied the mayfly communities were found to be similar, however the vertical zonation which reflected human impact was visible (NMDS analysis). The main factors responsible for mayfly communities at all the sites studied were stream regulation and organic pollution, followed by type of bottom substrate (pebble and gravel), riparian vegetation (shrubs), pH and water temperature. At undisturbed sites the most important factors were pH, substrate type, distance from the source, current velocity and riparian vegetation (CCA analysis). Analysis of mayfly communities and environmental characteristics in different seasons showed that occurrence of mayfly species varied substantially depending on the season. Only in early spring and autumn do mayfly communities occur which are dependent on many environmental factors, the most significant of which are substrate type, phosphate, distance from source and altitude (CCA analysis).  相似文献   
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The endophytic bacterium Gluconacetobacter diazotrophicus colonizes a broad range of host plants. Its plant growth-promoting capability is related to the capacity to perform biological nitrogen fixation, the biosynthesis of siderophores, antimicrobial substances and the solubilization of mineral nutrients. Colonization of and survival in these endophytic niche requires a complex regulatory network. Among these, quorum sensing systems (QS) are signaling mechanisms involved in the control of several genes related to microbial interactions, host colonization and stress survival. G. diazotrophicus PAL5 possesses a QS composed of a luxR and a luxI homolog, and produces eight molecules from the AHL family as QS signals. In this report data are provided showing that glucose concentration modifies the relative levels of these signal molecules. The activity of G. diazotrophicus PAL5 QS is also altered in presence of other carbon sources and under saline stress conditions. Inactivation of the QS system of G. diazotrophicus PAL5 by means of a quorum quenching strategy allowed the identification of extracellular and intracellular proteins under the control of this regulatory mechanism.  相似文献   
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Wheat is the most important cereal grown in the European Union and Spain is its fifth largest wheat producer. There is little information about Fusarium species associated with wheat in Spain. Phylogenetic diversity of 51 strains belonging to Fusarium incarnatum-equiseti species complex (FIESC) isolated from Spanish wheat was investigated using partial sequences of the translation elongation factor gene (EF-1α). Maximum-parsimony and Bayesian analysis of aligned DNA sequences resolved 18 haplotypes and 7 phylogenetic species. Strains morphologically identified as F. equiseti belonged to two different phylogenetic species, FIESC-5 and FIESC-14. Some correlation between phylogenetic species and geographical region was found. The present results highlight the potential contribution of FIESC to the mycotoxin contamination of Spanish wheat.  相似文献   
8.
摘要:【目的】筛选可产生抗血栓活性物质的细菌。【方法】利用VY/4平板、酪蛋白平板从水样、土样、兔粪、羊粪、朽木等20多个样品中筛选目的菌株;利用纤维蛋白平板和纤维蛋白试管检测抗血栓活性;利用形态学特征、理化性质、16S rRNA序列同源性鉴定目的菌株。【结果】得到5株可产生抗血栓活性物质的细菌,重点研究了菌株LDS33,发现其分泌的胞外蛋白在纤维蛋白平板上和纤维蛋白试管中均显示出强烈的溶栓活性,通过试管法发现此蛋白质同时具有较强的抗凝活性。结合形态学、理化性质、16S rDNA序列及进化树分析,发现该菌株属于硬壁菌门芽孢杆菌目芽孢杆菌科芽孢杆菌属的短小芽孢杆菌,将其命名为Bacillus pumilus LDS.33。【结论】短小芽孢杆菌LDS33可产生高活性的抗凝溶栓双活性蛋白。  相似文献   
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Evaluation of diagnostic performance is typically based on the receiver operating characteristic (ROC) curve and the area under the curve (AUC) as its summary index. The partial area under the curve (pAUC) is an alternative index focusing on the range of practical/clinical relevance. One of the problems preventing more frequent use of the pAUC is the perceived loss of efficiency in cases of noncrossing ROC curves. In this paper, we investigated statistical properties of comparisons of two correlated pAUCs. We demonstrated that outside of the classic model there are practically reasonable ROC types for which comparisons of noncrossing concave curves would be more powerful when based on a part of the curve rather than the entire curve. We argue that this phenomenon stems in part from the exclusion of noninformative parts of the ROC curves that resemble straight‐lines. We conducted extensive simulation studies in families of binormal, straight‐line, and bigamma ROC curves. We demonstrated that comparison of pAUCs is statistically more powerful than comparison of full AUCs when ROC curves are close to a “straight line”. For less flat binormal ROC curves an increase in the integration range often leads to a disproportional increase in pAUCs’ difference, thereby contributing to an increase in statistical power. Thus, efficiency of differences in pAUCs of noncrossing ROC curves depends on the shape of the curves, and for families of ROC curves that are nearly straight‐line shaped, such as bigamma ROC curves, there are multiple practical scenarios in which comparisons of pAUCs are preferable.  相似文献   
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