Mesophyll Resistance and Carboxylase Activity: A Comparison under Water Stress Conditions

The response of several leaf gas exchange parameters were monitored with decreasing leaf water potential in Phaseolus vulgaris L. leaflets. These included photosynthesis, transpiration, CO₂ compensation point, ribulose 1,5-diphosphate carboxylase activity, boundary layer plus stomatal, and mesophyll resistance to diffusion of CO₂. Mesophyll resistance was calculated under two assumptions: (a) the CO₂ concentration at the chloroplast was zero, and (b) it was equal to the CO₂ compensation point.     

Importance of Aerodynamic Resistance to Water Use Efficiency in Three Conifers under Field Conditions

The quantitative importance of aerodynamic resistance to H₂O vapor and CO₂ exchange was determined for shoots from saplings of three conifers (Abies lasiocarpa [Hook] Nutt., Pinus contorta Dougl., Juniperus communis L.) under natural conditions in the field. A combination of relatively low stomatal resistances (<300 seconds per centimeter) and low wind speeds (<30 centimeters per second) led to substantial contributions of the aerodynamic resistance (R_wv^a) to water use efficiency (WUE = photosynthesis/transpiration) for all three species. For A. lasiocarpa, transpiration was calculated to be 44% less and photosynthesis 17% less due to the presence of R_wv^a, which led to a predicted increase in WUE of 57% compared to the calculated WUE when R_wv^a was assumed negligible. Similar increases in WUE were computed for P. contorta (48%) with somewhat smaller values for J. communis (34%). These results are discussed in terms of the estimated importance of R_wv^a on water and photosynthetic relations of plants that have relatively low stomatal resistances and grow in microhabitats with low winds.     

Shoot Resistance to Water Flow in Cotton

Studies using excised cotton (Gossypium hirsutum L.) plants,attached to a free water source and undergoing transpirationcycles, were conducted at intervals over a 2 year period inorder to quantify shoot resistance components of cotton canopies.Leaf water potential was found to be a linear function of transpirationrate at rates above 0.1 mm h^–1, so shoot resistance wasevaluated as the slope of this function. The value of 4.8 104h (0.48 MPa h mm^–1) total shoot resistance was consistentfor 1.10 m tall, well irrigated, fruit-bearing cotton plants.Further tests, with pre-wrapped and exposed leaves, revealedthat total shoot resistance was comprised of an axial component(40%) and a leaf component (60%). The total shoot resistanceof 0.48 MPa h mm^–1 is likely to be relevant for modellingcotton water relations when LWP is evaluated on exposed, topof the canopy leaves, such as in the ‘big leaf’type models. Key words: Leaf water potential, axial resistance, leaf resistance     

Resistance to Water Flow in Xylem Vessels

Experimental data on flow resistances in xylem vessels withdifferent lumen wall surface sculptures are presented. The techniqueinvolved using determinable forces at menisci to pull waterthrough isolated undamaged metaxylem and protoxylem vesselswhich were empty but had water-saturated walls. In the horizontalorientation, the surface tension forces moved the water at velocitiesthat the resisting viscous forces at the vessel walls wouldallow since inertial forces were found negligible. A high speedcamera was used to determine the meniscus translation rates.Vessel diameters as well as average dimensions of the microscopicinternal surface irregularities were measured with respect toaxial position from the inlet. From these, flow resistanceswere determined in terms of dimensionless friction factor, f,as functions of Reynolds number, Re. It was found that, at certain helical ring thicknesses and spacing,resistance to flow was lowest. Deviations from these parametervalues cause dramatic increases in resistance to flow. Resultsare applicable to normal flow in plants, i.e. without meniscipresent.     

A Biomechanical Model for Fluidization of Cells under Dynamic Strain

Recent experiments have investigated the response of smooth muscle cells to transient stretch-compress (SC) and compress-stretch (CS) maneuvers. The results indicate that the transient SC maneuver causes a sudden fluidization of the cell while the CS maneuver does not. To understand this asymmetric behavior, we have built a biomechanical model to probe the response of stress fibers to the two maneuvers. The model couples the cross-bridge cycle of myosin motors with a viscoelastic Kelvin-Voigt element that represents the stress fiber. Simulation results point to the sensitivity of the myosin detachment rate to tension as the cause for the asymmetric response of the stress fiber to the CS and SC maneuvers. For the SC maneuver, the initial stretch increases the tension in the stress fiber and suppresses myosin detachment. The subsequent compression then causes a large proportion of the myosin population to disengage rapidly from actin filaments. This leads to the disassembly of the stress fibers and the observed fluidization. In contrast, the CS maneuver only produces a mild loss of myosin motors and no fluidization.     

Speciation of Arsenic under Dynamic Conditions

In periodically flooded soils, reductive conditions can occur, which favor the dissolution of Fe (hydr)oxides. Fe (hydr)oxides such as goethite are important sorbents for arsenate (As^V), which is the dominant As species in soils under aerobic conditions. Hence, the dissolution of Fe (hydr)oxides under reductive conditions can result in the mobilization and reduction of As^V and, thus, in an increase in the bioavailability of arsenic. The temporal dynamics of these processes and possible re‐sorption or precipitation of arsenite (As^III) formed are poorly understood. Under controlled laboratory conditions, the temporal change in the redox potential and arsenic speciation with time after a simulated flooding event in a quartz‐goethite organic matter substrate, spiked with As^V, was examined. During a period of 6 weeks, substrate solutions were sampled weekly using micro‐suction cups and analyzed for pH, As^III and As^V, Fe, Mn and P concentrations. Redox potentials and matric potentials were determined in situ in the substrate‐bearing cylinders. The redox potential and the ratio between As^III and As^V concentrations remained unchanged during the experiment without organic matter application. With organic matter applied, the redox potential decreased and the As^III concentrations in the substrate solution increased while the total As concentrations in the substrate solution strongly decreased. An addition of goethite (1 g/kg) per se led to a decrease of the total As in the substrate solution (almost 50 %). In respect to the potential As availability for plants, and consequently, the transfer into the food chain, the results are difficult to evaluate. The lower the total As concentrations in the substrate solution, determined with decreasing redox potential, the least plant As uptake will occur. This effect may however be compensated by a shift of the molar P/As^V ratio in the solution in favor of As^V which is expected to increase the As uptake.     

A Novel Approach for Dynamic Testing of Total Hip Dislocation under Physiological Conditions

Constant high rates of dislocation-related complications of total hip replacements (THRs) show that contributing factors like implant position and design, soft tissue condition and dynamics of physiological motions have not yet been fully understood. As in vivo measurements of excessive motions are not possible due to ethical objections, a comprehensive approach is proposed which is capable of testing THR stability under dynamic, reproducible and physiological conditions. The approach is based on a hardware-in-the-loop (HiL) simulation where a robotic physical setup interacts with a computational musculoskeletal model based on inverse dynamics. A major objective of this work was the validation of the HiL test system against in vivo data derived from patients with instrumented THRs. Moreover, the impact of certain test conditions, such as joint lubrication, implant position, load level in terms of body mass and removal of muscle structures, was evaluated within several HiL simulations. The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces. For a deep maneuver with femoral adduction, lubrication was shown to cause less friction torques than under dry conditions. Similarly, it could be demonstrated that less cup anteversion and inclination lead to earlier impingement in flexion motion including pelvic tilt for selected combinations of cup and stem positions. Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads. Muscle removal emulating a posterior surgical approach indicated alterations in THR loading and the instability process in contrast to a reference case with intact musculature. Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.     

A Probabilistic Dynamic Material Flow Analysis Model for Chinese Urban Housing Stock

The stock‐driven dynamic material flow analysis (MFA) model is one of the prevalent tools to investigate the evolution and related material metabolism of the building stock. There exists substantial uncertainty inherent to input parameters of the stock‐driven dynamic building stock MFA model, which has not been comprehensively evaluated yet. In this study, a probabilistic, stock‐driven dynamic MFA model is established and China's urban housing stock is selected as the empirical case. This probabilistic dynamic MFA model has the ability to depict the future evolution pathway of China's housing stock and capture uncertainties in its material stock, inflow, and outflow. By means of probabilistic methods, a detailed and transparent estimation of China's housing stock and its material metabolism behavior is presented. Under a scenario with a saturation level of the population, urbanization, and living space, the median value of the urban housing stock area, newly completed area, and demolished area would peak at around 49, 2.2, and 2.2 billion square meters, respectively. The corresponding material stock and flows are 79, 3.5, and 3.3 billion tonnes, respectively. Uncertainties regarding housing stock and its material stock and flows are non‐negligible. Relative uncertainties of the material stock and flows are above 50%. The uncertainty importance analysis demonstrates that the material intensity and the total population are major contributions to the uncertainty. Policy makers in the housing sector should consider the material efficiency as an essential policy to mitigate material flows of the urban building stock and to lower the risk of policy failures.     

Estimation of the Gelatinization Temperature of Noodles from Water Sorption Curves under Temperature-Programmed Heating Conditions

Both free and conjugated brassinosteroids (BRs) in the pollen and anthers of Erythronium japonicum Decne. were investigated. As a free form of BRs, typhasterol was identified by GC-MS. Polar conjugated BRs occurred only in the anther, and non-polar con-jugated BRs occurred both in the pollen and mainly in the anther.

BR parts of acid hydrolysis of the former were identified to be teasterone (major) and castasterone (minor). Those of alkaline hydrolysis of the latter were identified to be typhasterol (major) and teasterone (minor).     

Water Import Rate in Tomato Fruit: A Resistance Model

A model of the water import rate in tomato fruit is proposed.It compares the fruit to a hollow sphere (P) with external radiusR and internal radius R_G, corresponding to pericarp, and containingan internal spherical part (G). The pathway limiting water inputrate at any point I at a distance r from the fruit centre wasassumed to be proportional: (a) in P, to the length of the arcwhich has a radius r and which goes from I to the pedicel extension;(b) in G, to r. The water input rate at I was modelled basedon a law similar to Darcy's law which takes into account thedifference between the water potential at entry of fruit andthe water potential at point I. This latter potential was thesum of fruit osmotic potential and pressure potential due toresistance of tissue to deformation. This potential was proportionalto R-r or R_G -r. The model was expressed at fruit level by alaw such that water mass imported per unit time per unit surfacearea of fruit (f_rw) was a linear function of R. The model wascompared to linear regressions of this rate in terms of R whichhad been found during fruit swelling from published results,and which were obtained at different values of nutrient solutionsalinity. The results suggested that water input in tomato fruitis conditioned by passive forces depending on fruit size.Copyright1994, 1999 Academic Press Fruit, growth, model, resistance, salinity, size, tomato, transfer, water     

Empirical Dynamic Material Flow Model for Tungsten in the USA

Multivariate polynomial regression (MPR) analysis was implemented to develop a nonlinear dynamic material flow model (DMFM) of tungsten in the United States for the years 1975–2000 without assumptions for lifetime distributions within reservoirs. Two external economic factors, the Consumer Price Index and the Industrial Production Index, were included as possible exogenous variables. Six types of vector time‐series models were developed using multilinear, simple interaction, and MPR models, each with and without the exogenous economic variables. The DMFMs developed in this work make one‐step‐ahead predictions. That is, the material flows in a given year were predicted using flows and exogenous variables from previous years. In contrast to approaches that utilize assumed lifetime distributions for material within reservoirs, such as the Weibull distribution, the approach used here is completely data driven. MPR models produced statistically better results than linear models for all 13 flows that were modeled. Four of these models used simple interaction terms (which we call linear interaction terms), and two of these incorporated exogenous variables. The other nine models utilized higher‐degree terms with interactions (called multivariate polynomial terms), and two of these incorporated exogenous variables. We conclude that nonlinear vector time series are capable of identifying complex relationships among material flows and exogenous variables. An understanding of these relationships has potential for managing, conserving, and/or forecasting the use of a resource.     

An Oxygenase-Independent Cholesterol Catabolic Pathway Operates under Oxic Conditions

Cholesterol is one of the most ubiquitous compounds in nature. The 9,10-seco-pathway for the aerobic degradation of cholesterol was established thirty years ago. This pathway is characterized by the extensive use of oxygen and oxygenases for substrate activation and ring fission. The classical pathway was the only catabolic pathway adopted by all studies on cholesterol-degrading bacteria. Sterolibacterium denitrificans can degrade cholesterol regardless of the presence of oxygen. Here, we aerobically grew the model organism with ¹³C-labeled cholesterol, and substrate consumption and intermediate production were monitored over time. Based on the detected ¹³C-labeled intermediates, this study proposes an alternative cholesterol catabolic pathway. This alternative pathway differs from the classical 9,10-seco-pathway in numerous important aspects. First, substrate activation proceeds through anaerobic C-25 hydroxylation and subsequent isomerization to form 26-hydroxycholest-4-en-3-one. Second, after the side chain degradation, the resulting androgen intermediate is activated by adding water to the C-1/C-2 double bond. Third, the cleavage of the core ring structure starts at the A-ring via a hydrolytic mechanism. The ¹⁸O-incorporation experiments confirmed that water is the sole oxygen donor in this catabolic pathway.     

Selection of Kentucky Bluegrass for Drechslera poae Resistance under Greenhouse Conditions

Resistance to leaf spot and melting out caused by Drechslera poae was evaluated in eight cultivars and seven breeding lines of Poa pratensis under greenhouse conditions. The results obtained in this study were compared with levels of resistance scored after natural infection under field conditions during 1994–1997 in sun and shade lawn maintenance, as described before. It was found that resistance assessed in the greenhouse as leaf spots in the three‐leaf seedling stage 10–14 days after the first inoculation (assessment I) and resistance assessed as severity of melting out on the crown 56 days after the first inoculation (assessment IV) showed the highest repeatability with the scores obtained in the field under sun and shade conditions during 1994–1997.     

Planktonic Replication Is Essential for Biofilm Formation by Legionella pneumophila in a Complex Medium under Static and Dynamic Flow Conditions

Legionella pneumophila persists for a long time in aquatic habitats, where the bacteria associate with biofilms and replicate within protozoan predators. While L. pneumophila serves as a paradigm for intracellular growth within protozoa, it is less clear whether the bacteria form or replicate within biofilms in the absence of protozoa. In this study, we analyzed surface adherence of and biofilm formation by L. pneumophila in a rich medium that supported axenic replication. Biofilm formation by the virulent L. pneumophila strain JR32 and by clinical and environmental isolates was analyzed by confocal microscopy and crystal violet staining. Strain JR32 formed biofilms on glass surfaces and upright polystyrene wells, as well as on pins of “inverse” microtiter plates, indicating that biofilm formation was not simply due to sedimentation of the bacteria. Biofilm formation by an L. pneumophila fliA mutant lacking the alternative sigma factor σ²⁸ was reduced, which demonstrated that bacterial factors are required. Accumulation of biomass coincided with an increase in the optical density at 600 nm and ceased when the bacteria reached the stationary growth phase. L. pneumophila neither grew nor formed biofilms in the inverse system if the medium was exchanged twice a day. However, after addition of Acanthamoeba castellanii, the bacteria proliferated and adhered to surfaces. Sessile (surface-attached) and planktonic (free-swimming) L. pneumophila expressed β-galactosidase activity to similar extents, and therefore, the observed lack of proliferation of surface-attached bacteria was not due to impaired protein synthesis or metabolic activity. Cocultivation of green fluorescent protein (GFP)- and DsRed-labeled L. pneumophila led to randomly interspersed cells on the substratum and in aggregates, and no sizeable patches of clonally growing bacteria were observed. Our findings indicate that biofilm formation by L. pneumophila in a rich medium is due to growth of planktonic bacteria rather than to growth of sessile bacteria. In agreement with this conclusion, GFP-labeled L. pneumophila initially adhered in a continuous-flow chamber system but detached over time; the detachment correlated with the flow rate, and there was no accumulation of biomass. Under these conditions, L. pneumophila persisted in biofilms formed by Empedobacter breve or Microbacterium sp. but not in biofilms formed by Klebsiella pneumoniae or other environmental bacteria, suggesting that specific interactions between the bacteria modulate adherence.     

可交换条件下多维结构回归模型总体平均处理效应的估计

在可交换条件下，当响应变量为多维时，利用结构回归模型研究总体平均处理效应的估计。     

Resistance to Water Flow in the Seminal Roots of Wheat

Water uptake by the seminal root system of wheat is describedby a model which incorporates radial and axial resistance toflow in the root and the resistance to flow in the soil. Inan experiment where wheat plants were dependent on subsoil waterextracted from below 45 cm by one, three, or five seminal roots,calculations indicated that the axial resistance was the dominantresistance within the soil-root system and that flow rate changedpredictably with changing axial resistance. The model also indicatedthat the observed shape of the metaxylem vessel in the seminalaxes has important effects on the pattern of water uptake.     

Bacterial Adhesion under Static and Dynamic Conditions

The deposition of various pseudomonads and coryneform bacteria with different hydrophobicities (water contact angles) and negative cell surface charges on negatively charged Teflon and glass surfaces was investigated. The levels of deposition varied between 5.0 × 10⁴ and 1.6 × 10⁷ cells cm^-2 and between 5.0 × 10⁴ and 3.6 × 10⁷ cells cm^-2 for dynamic column and static batch systems, respectively, indicating that there was a wide variation in physicochemical interactions. Batch and column results were compared in order to better distinguish between hydrodynamic and other system-dependent influences and method-independent physicochemical interactions. Despite the shorter suspension-solid contact time in columns (1 h) than in batch systems (4 h), the level of deposition (expressed as the number of cells that adhered) divided by the applied ambient cell concentration was 4.12 ± 1.63 times higher in columns than in batch sytems for 15 of 22 strain-surface combinations studied. This demonstrates that transport of microbial particles from bulk liquid to surfaces is more efficient in dynamic columns (transport dominated by convection and diffusion) than in static batch systems (transport by diffusion only). The relative constancy of this ratio for the 15 combinations shows that physicochemical interactions affect adhesion similarly in the two systems. The deviating deposition behavior of the other seven strain-surface combinations could be attributed to method-dependent effects resulting from specific cell characteristics (e.g., to the presence of capsular polymers, to an ability to aggregate, to large cell sizes, or to a tendency to desorb after passage through an air-liquid interface).     

The Pathway of Assimilate Flow from Source to Sink in Urtica dioica L., Studied with14C under Ambient Atmospheric Conditions

The contribution of individual vascular bundles of the stemto the flow of assimilates from a selected source leaf to thesink regions was investigated inUrtica dioica L., a plant witha decussate leaf arrangement. Two homologous sets of eight vascularstrands were recognized, arranged in mirror symmetry in thestem internodes. In each set, three of the bundles were identifiedas traces of one leaf merging into the vascular system of thestem one node below the origin of the leaf. The main bundleof a stem-half bifurcates at each end of the internode intotwo subdominant bundles, which combine in the next but one nodeto form the dominant bundle again. Each set of vascular strandsalso contains two minor bundles which pass more or less withoutinterruption through the whole stem. The uppermost mature source leaf (leaf number 5 as counted fromthe tip) was exposed to¹⁴CO₂in a closed gas circuit. The concentrationof the carbon-labelled CO₂was maintained at the ambient CO₂levelto maintain the natural source strength of the leaf. By theend of the usual nocturnal dark phase, carbon from the sourceleaf had been imported predominantly by sink leaves of the sameorthostichy. Lesser, but significant amounts of radiocarbonwere also incorporated into the sink leaves of the adjacenttwo orthostichies via the marginal leaf traces. In spite ofthe junction of the vascular strands in the nodes and an interfascicularconnection of the stem bundles, randomization of the photosynthatesfrom individual leaves was minimal in the vascular system ofthe stem in the upward direction, and also low in the flux tothe roots. Substantial amounts of radioactivity were also foundin the lately-formed xylem elements of the vascular strandsand their interfascicular connections, indicating active secondarygrowth. Assimilate distribution; source–sink connections; Urtica dioica ; vascular architecture     

A Dynamic Model for Photosynthesis

A dynamic mathematical model of the effect of radiant flux densityand CO₂ concentration on the rate of photosynthesis is proposed.An appropriate dynamic experimental method for ecological studiesof this subject is described. The methodology permits the analysisof numerous problems, including the effect of changes in CO₂concentration on photosynthesis and the effectiveness of energyconversion by a leaf of a plant in different environmental conditions. The dynamic model for photosynthesis is composed of two separateinteracting non-linear parts; one describes the dynamics ofthe complex set of light reactions, and the other describesthe dark reactions. The model explains the dynamics of leafphotosynthesis in a closed circuit flow system, and also explainsthe expressions for the equilibrium states of photosyntheticrate widely used in the literature. photosynthesis, mathematical model, carbon dioxide fixation, light reactions