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121.
122.
Robert M. Scheller Alec M. Kretchun E. Louise Loudermilk Matthew D. Hurteau Peter J. Weisberg Carl Skinner 《Ecosystems》2018,21(4):643-656
Climate-driven increases in wildfires, drought conditions, and insect outbreaks are critical threats to forest carbon stores. In particular, bark beetles are important disturbance agents although their long-term interactions with future climate change are poorly understood. Droughts and the associated moisture deficit contribute to the onset of bark beetle outbreaks although outbreak extent and severity is dependent upon the density of host trees, wildfire, and forest management. Our objective was to estimate the effects of climate change and bark beetle outbreaks on ecosystem carbon dynamics over the next century in a western US forest. Specifically, we hypothesized that (a) bark beetle outbreaks under climate change would reduce net ecosystem carbon balance (NECB) and increase uncertainty and (b) these effects could be ameliorated by fuels management. We also examined the specific tree species dynamics—competition and release—that determined NECB response to bark beetle outbreaks. Our study area was the Lake Tahoe Basin (LTB), CA and NV, USA, an area of diverse forest types encompassing steep elevation and climatic gradients and representative of mixed-conifer forests throughout the western United States. We simulated climate change, bark beetles, wildfire, and fuels management using a landscape-scale stochastic model of disturbance and succession. We simulated the period 2010–2100 using downscaled climate projections. Recurring droughts generated conditions conducive to large-scale outbreaks; the resulting large and sustained outbreaks significantly increased the probability of LTB forests becoming C sources over decadal time scales, with slower-than-anticipated landscape-scale recovery. Tree species composition was substantially altered with a reduction in functional redundancy and productivity. Results indicate heightened uncertainty due to the synergistic influences of climate change and interacting disturbances. Our results further indicate that current fuel management practices will not be effective at reducing landscape-scale outbreak mortality. Our results provide critical insights into the interaction of drivers (bark beetles, wildfire, fuel management) that increase the risk of C loss and shifting community composition if bark beetle outbreaks become more frequent. 相似文献
123.
The structure of the tightly bound complex of the globular myosin head with F-actin is the key to understanding important details of the mechanism of how the actin-myosin motor functions. The current notion on this complex is based on the docking of known atomic structures of constituent proteins into low-resolution electron-density maps. The atomic structure of the complex was refined by the molecular mechanics method, which consists in minimizing the energy of molecular interaction and which makes it possible to optimize not only the relative position of protein backbones as rigid bodies, but also the position of side chains on the protein interface. The structure calculated using ICM-Pro software, on the one hand, is close to the model obtained using electron microscopy; on the other hand, it ensures the best calculated interaction energy and accounts for the results of mutagenesis experiments. On the basis of the structure obtained, we can suggest the molecular mechanisms underlying the actin-activated release of ATP hydrolysis products from myosin and the decrease in the affinity of myosin for actin upon binding of nucleotides. 相似文献
124.
125.
The morphology of dissociated single cerebellar Purkinje cells obtained from wild-type P1 CD1 mice was assessed in the absence
and in the presence of glia. A dedicated noninvasive technique based on optical microscopy was developed. Image processing
algorithms were implemented to extract metrical features characterizing cell structure and dendritic arborization. The morphological
features were analyzed in order to identify quantitative differences in Purkinje cell morphology due to interactions with
astrocytes. 相似文献
126.
D. Padilla F. Acosta J. A. García F. Real Jose R. Vivas 《Archives of microbiology》2009,191(3):191-198
Hafnia alvei, a Gram negative bacillus related to the Enterobacteriaceae family, is considered an opportunistic pathogen of several animal species and humans. In this communication, we describe
fimbrial-like structures from different strains of H. alvei that cannot be easily ascribed to any of the previously reported fimbrial types in this species (type I or type III). Polymerase
chain reaction (PCR) and immunofluorescence assays were carried out to study fimbriae and flagella in H. alvei strains isolated from different sources. No correlation between the results obtained by PCR and those obtained by phenotypic
methods were found, and the antibodies used gave cross or different recognition patterns of the surface structures present
in these strains. We report as well that strain and growth temperature influence fimbriation and expression of flagella in
human and animal isolates of H. alvei. This study also indicates that the absence of fimbriae have a significant positive influence on the initial adhesion of
H. alvei to human epithelial cells. 相似文献
127.
128.
The status of the reproductive system is investigated in five species of Teleostei from the Teterev River and the Kiev Reservoir
(Ukraine), descendants of F42–F7 generations of fish exposed to radiation from the accident at the Chernobyl nuclear power plant. Twenty years after the accident,
a wide range of morphofuinctional anomalies of this system is present in fish. The most significant of them are: asymmetry
and anomalous morphology of gonads, proliferation of connective tissue—sterilization, mass destruction of follicular and sex
cells of various developmental stages, and hermaphroditism. Among the investigated species, disturbances of reproductive glands
were preset to the highest extent in pike Esox lucius and crucian carp Carassius carassius. In the series of investigated generations the maximum frequency of occurrence of gonad anomalies was noted in F4 and F5, due to prolonged mutagenesis (Dubinin, 1986). 相似文献
129.
The objective of this study is to compare the thermal stress changes in the tooth microstructures and the hydrodynamic changes of the dental fluid under hot and cold stimuli. The dimension of the microstructures of eleven cats’ teeth was measured by scanning electron microscopy, and the changes in thermal stress during cold and hot stimulation were calculated by 3D fluid–structure interaction modeling. Evaluation of results, following data validation, indicated that the maximum velocities in cold and hot stimuli were ??410.2?±?17.6 and +?205.1?±?8.7 µm/s, respectively. The corresponding data for maximum thermal stress were ??20.27?±?0.79 and +?10.13?±?0.24 cmHg, respectively. The thermal stress caused by cold stimulus could influence almost 2.9 times faster than that caused by hot stimulus, and the durability of the thermal stress caused by hot stimulus was 71% greater than that by cold stimulus under similar conditions. The maximum stress was on the tip of the odontoblast, while the stress in lateral walls of the odontoblast and terminal fibril was very weak. There is hence a higher possibility of pain transmission with activation of stress-sensitive ion channels at the tip of the odontoblast. The maximum thermal stress resulted from the cold stimulus is double that produced by the hot stimulus. There is a higher possibility of pain transmission in the lateral walls of the odontoblast and terminal fibril by releasing mediators during the cold stimulation than the hot stimulation. These two reasons can be associated with a greater pain sensation due to intake of cold liquids. 相似文献
130.
Vikas Yadav Patade Sujata Bhargava Penna Suprasanna 《Plant Cell, Tissue and Organ Culture》2012,108(2):279-286
In order to discriminate between the ionic and osmotic components of salt stress, sugarcane (Saccharum officinarum L. cv. Co 86032) calli were cultured on media containing NaCl or polyethylene glycol (PEG) 8000 that exerted the same osmotic
pressure (−0.7 MPa). PEG stress exposure for 15 days led to significant growth reduction and loss in water content than salt
stressed and control tissues. Osmotic adjustment (OA) was observed in callus tissues grown on salt, but was not evident in
callus grown on PEG. Oxidative damage to membranes, estimated in terms of accumulation of thiobarbituric acid reactive substances-TBARS
and electrolytic leakage was significantly higher in both the stressed calli than the control however, the extent of damage
was more in the PEG stressed calli. The stressed callus tissues showed inhibition of ascorbate peroxidase activity, while
catalase activity was increased. These results indicate sensitivity of cells to PEG-mediated stress than salt stress and differences
in their OA to these two stress conditions. The sensitivity to the osmotic stress indicate that expression of the stress tolerance
response requires the coordinated action of different tissues in a plant and hence was not expressed at the cellular level. 相似文献