A cytoskeletal network contributes significantly to intracellular regulation of mechanical stresses, cell motility and cellular mechanics. Thus, it plays a vital role in defining the mechanical behaviour of the cell. Among the wide range of models proposed for dynamic behaviour of cytoskeleton, the soft glassy rheology model has gained special attention due to the resemblance of its predictions with the mechanical data measured from experiment. The soft glassy material, theory of soft glassy rheology and experiment on cytoskeleton has been discussed, which leads to a discussion of the unique features and flaws of the model. The soft glassy rheological model provides a unique explanation of the cytoskeleton ability to deform, flow and remodel. and Obsahuje seznam literatury
This paper presents an adroit utilization of dimensional analysis-based model theory by which the deformation of a structure - however complex - can be elegantly and easily obtained. The structure is loaded by a concentrated lateral load of arbitrary location and magnitude. The relevant technique is outlined in some details; therefore the reader is advised to follow the presented routine closely. By doing so, he will be impressed by the prowees and economy of the described process. In the Preamble, the more important relevant theorems and relations - without proofs - are given in greatly condensed forms. This summary will help the reader to understand the subsequent application presented. Full treatment of the theories and practice of applied dimensional model theory can be found in [1], which the interested and motivated reader is advised to consult. and Obsahuje seznam literatury
Based on the crystal structure and spectral properties of C-phycocyanin (C-PC) from cyanobacteria, models for complexes with 2 and 3 C-PC hexamer disks were built and the energy transfer dynamic properties were studied by the use of stochastic computer simulation approach. In addition, an experimental parameter of 0.056 ps-1, corresponding to a time constant of 18 ps, derived from the previous time-resolved measurement, was used for simulation of the energy transfer process from the three terminal symmetrically equivalent β84 chromophores of the core-linked disk to an α84 chromophore of the allophycocyanin (APC) core. The simulation showed: (1) The disk-to-disk energy transfer can be as fast as several picoseconds. (2) The energy transfer efficiencies from the first disk to the core would depend on the length of the rod (i.e. the number of disks). Efficiencies of 0.95, 0.87, and 0.75 were found for the rods with 1, 2 and 3 hexamer disks, respectively. (3) The energy transfer along a rod in a native phycobilisome (PBS) is probably very close to the one-way manner. It is the core of PBS that makes the excitation energy be transferred fast in a nearly one-way manner. and Jie Xie, Jing-quan Zhao, Chenghang Peng.
Prediction of reservoir level fluctuation is important in the operation, design, and security of dams. In this paper, Artificial Neural Networks (ANN) is used for modeling. In such modeling approaches, it is possible to determine dam reservoir level and water balance (budget) by taking the monthly average precipitation and needed parameters into consideration. The basic data are available for over 29 years at the Tahtakőprű Dam in the southeast Mediterranean region of Turkey. As a sub-approach of ANN, a multi layer perceptron (MLP) is used. Bayesian regularization back-propagation training algorithm is employed for optimization of the network. MLP results are compared with the results of conventional multiple linear regression (MLR) and autoregressive (AR) models. The comparison shows that the ANN model provides better performance than the mentioned models in reservoir level estimation.
Energy transfer of aromatic amino acids in photosystem 2 (PS2) core antenna complexes CP43 and CP47 was studied using absorption spectroscopy, fluorescence spectroscopy, and the 0.35 nm crystal structure of PS2 core complex. The energy of tyrosines (Tyrs) was not effectively transferred to tryptophans (Trps) in CP43 and CP47. The fluorescence emission spectrum of CP43 and CP47 by excitation at 280 nm should be a superposition of the Tyr and Trp fluorescence emission spectra. The aromatic amino acids in CP43 and CP47 could transfer their energy to chlorophyll (Chl) a molecules by the Dexter mechanism and the Föster mechanism, and the energy transfer efficiency in CP47 was much higher than that in CP43. In CP47 the Föster mechanism must be the dominant energy transfer mechanism between aromatic amino acids and Chl a molecules, whereas in CP43 the Dexter mechanism must be the dominant one. Hence solar ultraviolet radiation brings not only damages but also benefits to plants. and Y. G. Qu .... [et al.].
Oscillations in many of photosynthetic quantities with a period of about 1 min can be routinely measured with higher plant leaves after perturbation of the steady state by sudden change in gas phase. Among all hypotheses suggested so far to explain the oscillations, an effect of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activation status to control the oscillations is highly probable, at least upon high temperature (HT) treatment when in vivo RuBPCO activity controlled by RuBPCO activase (RuBPCO-A) decreases. Therefore, we measured the oscillations in fluorescence signal coming from barley leaves (Hordeum vulgare L. cv. Akcent) after their exposure for various time intervals to different HTs in darkness. We also evaluated steady state fluorescence and CO2 exchange parameters to have an insight to functions of electron transport chain within thylakoid membrane and Calvin cycle before initiation of the oscillations. The changes in period of the oscillations induced by moderate HT (up to 43 °C) best correlated with changes in non-photochemical fluorescence quenching (qN) that in turn correlated with changes in gross photosynthetic rate (PG) and rate of RuBPCO activation (kact). Therefore, we suggest that changes in period of the oscillations caused by moderate HT are mainly controlled by RuBPCO activation status. For more severe HT (45 °C), the oscillations disappeared which was probably caused by an insufficient formation of NADPH by electron transport chain within thylakoid membrane as judged from a decrease in photochemical fluorescence quenching (qP). Suggestions made on the basis of experimental data were verified by theoretical simulations of the oscillations based on a model of Calvin cycle and by means of a control analysis of the model. and D. Lazár ... [et al.].
Meteorological parameters inside and outside an open-top chamber (OTC) fumigation facility were recorded and the primary photosynthetic response of four tree species measured with chlorophyll (Chl) a fluorescence emission. Parameters extracted from the Chl a fluorescence transient were used to calculate photosynthetic activity of the leaves using a performance index. Measurements were made during the night throughout a single growing season. The seasonal primary photosynthetic performance in all species was significantly altered by growth in the OTCs, and the degree of response was dependent upon the species. Wind was an important effectual component of the altered environment. The average temperature was consistently 1.94±0.70 °C higher within the OTCs, whereas wind speed fluctuated substantially more between inside and outside the OTCs (0 to 8 m -1). There was a correlation between the photosynthetic performance index and wind speed in Fagus sylvatica, Fraxinus excelsior, and Prunus serotina. The response to wind was also particular to each species; the photosynthetic performance of F. sylvatica increased with wind speed (1 to 7 m s-1), decreased with F. excelsior (0 to 6.5 m s-1) and P. serotina (0 to 5.5 m s-1). Abies alba, in contrast, was almost insensitive to wind. A model was proposed and tested for the conversion of the photosynthetic performance values collected in OTCs to predict the photosynthetic performance outside OTCs. The wide variety of responses to wind and temperature of the four species conformed to linear functions that describe the relationship of the wind speed and temperature responses with the difference in photosynthetic performance between the OTC and open environments. Specific coefficients for wind and temperature were proposed. The photosynthetic response to wind of each species depends on its ecophysiological specialisation. and A. J. Clark ... [et al.].
Two types of photosystem 2-light-harvesting complex 2 (PS2-LHC2) supercomplexes with similar pigment and protein composition were isolated directly from thylakoid membranes by sucrose density gradient centrifugation. Electron microscopy and single particle image analysis revealed the first Type as single unpaired PS2-LHC2 supercomplexes, whereas the second Type was characterized as pairs of two PS2-LHC2 supercomplexes attached together by their stromal sides. Unstacking of thylakoid membranes resulted in a spontaneous disintegration of the paired supercomplexes into single unpaired particles. A model of the organisation of the pigment-protein complexes in grana region is proposed. and L. Bumba, M. Hušák, F. Vácha.
A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses of 30-d-old carrot seedlings to the combined effects of CO2 concentration (50-1 050 µmol mol-1) and moisture deficits (-5, -30, -55, and -70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola model. The estimated parameters were compared for effects of moisture deficit and elevated CO2 concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (-30 kPa) under EC when compared to the unstressed control. However, moderate (-55 kPa) and extreme (-70 kPa) moisture deficits reduced α under EC. Maximum net photosynthetic rate (PNmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced PNmax by nearly 85 % compared to controls. Dark respiration rate (RD) showed no consistent response to moisture deficit. The CO2 compensation concentration (Γ) was 324 µmol mol-1 for -75 kPa and ranged 63-93 µmol mol-1 for other moisture regimes. Interaction between moisture deficit and EC was noticed for PN, ratio of intercellular and ambient CO2 concentration (Ci/Ca), stomatal conductance (gs), and transpiration rate (E). PN was maximum and Ci/Ca was minimum at -30 kPa moisture deficit and at C a of 350 µmol mol-1. The gs and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture deficit up to -55 kPa and declined thereafter. EC showed a positive influence towards sustaining PN and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture deficits. and A. Thiagarajan, R. R. Lada.
Scanning tunnelling microscopy of intact D1/D2/CP47/CP43 photosystem 2 (PS2) core complexes and CP43-deleted D1/D2/CP47 core complexes shows definitively that the CP43 subunits reside at the ends of the dimeric core complex. The CP43-removal procedure produces CP43-deleted cores with minimal conformational distortion to the D1/D2/CP47 residual core complex. There was excellent agreement between the X-ray and STM structures for the intact core complex, and between the STM image for the CP43-deleted core complex and the X-ray model with the components assigned to CP43 omitted. and C. S. Barton, P. B. Lukins.