Comparing the xylose reductase/xylitol dehydrogenase and xylose isomerase pathways in arabinose and xylose fermenting Saccharomyces cerevisiae strains

Background

Ethanolic fermentation of lignocellulosic biomass is a sustainable option for the production of bioethanol. This process would greatly benefit from recombinant Saccharomyces cerevisiae strains also able to ferment, besides the hexose sugar fraction, the pentose sugars, arabinose and xylose. Different pathways can be introduced in S. cerevisiae to provide arabinose and xylose utilisation. In this study, the bacterial arabinose isomerase pathway was combined with two different xylose utilisation pathways: the xylose reductase/xylitol dehydrogenase and xylose isomerase pathways, respectively, in genetically identical strains. The strains were compared with respect to aerobic growth in arabinose and xylose batch culture and in anaerobic batch fermentation of a mixture of glucose, arabinose and xylose.

Results

The specific aerobic arabinose growth rate was identical, 0.03 h^-1, for the xylose reductase/xylitol dehydrogenase and xylose isomerase strain. The xylose reductase/xylitol dehydrogenase strain displayed higher aerobic growth rate on xylose, 0.14 h^-1, and higher specific xylose consumption rate in anaerobic batch fermentation, 0.09 g (g cells)^-1 h^-1 than the xylose isomerase strain, which only reached 0.03 h^-1 and 0.02 g (g cells)^-1h^-1, respectively. Whereas the xylose reductase/xylitol dehydrogenase strain produced higher ethanol yield on total sugars, 0.23 g g^-1 compared with 0.18 g g^-1 for the xylose isomerase strain, the xylose isomerase strain achieved higher ethanol yield on consumed sugars, 0.41 g g^-1 compared with 0.32 g g^-1 for the xylose reductase/xylitol dehydrogenase strain. Anaerobic fermentation of a mixture of glucose, arabinose and xylose resulted in higher final ethanol concentration, 14.7 g l^-1 for the xylose reductase/xylitol dehydrogenase strain compared with 11.8 g l^-1 for the xylose isomerase strain, and in higher specific ethanol productivity, 0.024 g (g cells)^-1 h^-1 compared with 0.01 g (g cells)^-1 h^-1 for the xylose reductase/xylitol dehydrogenase strain and the xylose isomerase strain, respectively.

Conclusion

The combination of the xylose reductase/xylitol dehydrogenase pathway and the bacterial arabinose isomerase pathway resulted in both higher pentose sugar uptake and higher overall ethanol production than the combination of the xylose isomerase pathway and the bacterial arabinose isomerase pathway. Moreover, the flux through the bacterial arabinose pathway did not increase when combined with the xylose isomerase pathway. This suggests that the low activity of the bacterial arabinose pathway cannot be ascribed to arabitol formation via the xylose reductase enzyme.     

Inhibition kinetics of a commercial mixed culture by ammonium sulfate

The inhibitory effect of ammonium sulfate on a commercial mixed culture, used in biological waste-water treatment was studied under aerobic batch conditions. Several mathematical models of enzyme and growth kinetics including a death factor were analyzed through nonlinear regression to find the best fit to corresponding data of inhibition. The best fit model was found to be the generalized Monod type with a death factor having the biokinetic parameters; μ_max 0.681 h⁻¹, K_s 0.224 g dm⁻³, K_i 56240 g dm⁻³, K 0.055 g dm⁻³ and k_d 0.052 h⁻¹ to represent the experimental data accurately. The low saturation coefficient value along with high maximum specific growth rate and inhibition coefficient denotes the competitive characteristics of commercial mixed cultures in the biological treatment of high ammonium polluted waste waters.     

A review of data needed to parameterize a dynamic model of measles in developing countries

Background

Dynamic models of infection transmission can project future disease burden within a population. Few dynamic measles models have been developed for low-income countries, where measles disease burden is highest. Our objective was to review the literature on measles epidemiology in low-income countries, with a particular focus on data that are needed to parameterize dynamic models.

Methods

We included age-stratified case reporting and seroprevalence studies with fair to good sample sizes for mostly urban African and Indian populations. We emphasized studies conducted before widespread immunization. We summarized age-stratified attack rates and seroprevalence profiles across these populations. Using the study data, we fitted a "representative" seroprevalence profile for African and Indian settings. We also used a catalytic model to estimate the age-dependent force of infection for individual African and Indian studies where seroprevalence was surveyed. We used these data to quantify the effects of population density on the basic reproductive number R ₀.

Results

The peak attack rate usually occurred at age 1 year in Africa, and 1 to 2 years in India, which is earlier than in developed countries before mass vaccination. Approximately 60% of children were seropositive for measles antibody by age 2 in Africa and India, according to the representative seroprevalence profiles. A statistically significant decline in the force of infection with age was found in 4 of 6 Indian seroprevalence studies, but not in 2 African studies. This implies that the classic threshold result describing the critical proportion immune (p _c) required to eradicate an infectious disease, p _c = 1-1/R ₀, may overestimate the required proportion immune to eradicate measles in some developing country populations. A possible, though not statistically significant, positive relation between population density and R ₀ for various Indian and African populations was also found. These populations also showed a similar pattern of waning of maternal antibodies. Attack rates in rural Indian populations show little dependence on vaccine coverage or population density compared to urban Indian populations. Estimated R ₀ values varied widely across populations which has further implications for measles elimination.

Conclusions

It is possible to develop a broadly informative dynamic model of measles transmission in low-income country settings based on existing literature, though it may be difficult to develop a model that is closely tailored to any given country. Greater efforts to collect data specific to low-income countries would aid in control efforts by allowing highly population-specific models to be developed.     

Mathematical description of bikaverin production in a fluidized bed bioreactor

Summary  Growth of Gibberella fujikuroi in submerged cultures occurs as micelles or filamentous hyphae dispersed in fluid and pellets or stable, spherical agglomerations. Gibberella fujikuroi growth, substrate consumption and bikaverin production kinetics obtained from submerged batch fermentation were fitted to three different sigmoid models: two and three-parameter Gompertz models and one Logistic model. Growth fitting was used to compare between models and select the best one by means of an F test. The best model for describing growth was the two-parameter Gompertz model and was used for glucose consumption and bikaverin production fitting. Data from eight different schemes of fermentations were analysed and parameter estimation was carried out by means of minimization of residual sum of squares. Some characteristic values obtained with the two-parameter Gompertz model fit are: μ=0.028 h⁻¹, Y_x/s=0.1089 g substrate/g biomass, α =0.1384 g product/g biomass.     

Association between line per se and testcross performance for eight agronomic and quality traits in winter rye

Key message

We investigated associations between line per se and testcross performance in rye and suggested that selection for per se performance is valuable for several traits in multi-stage selection programs.

Abstract

Genotypic correlation between line per se and testcross performance is an important quantitative-genetic parameter for optimizing hybrid breeding programs. The main goal of this survey was to study the association of line per se and testcross performance at the phenotypic level. We used experimental data from the line per se and testcross performance of two segregating winter rye populations (A, B) with each of 220 progenies tested in six environments for eight agronomic and quality traits. Genotypic variances were considerably larger for per se than for testcross performance of all investigated traits resulting in higher heritabilities of the former in most instances. Genotypic correlations (r _g) between testcross and line per se performance decreased with increasing complexity of the trait as shown by the respective heritabilities. They were highest (r _g ≥ 0.7) for plant height and test weight in population B, and thousand-kernel weight, falling number and starch content in both populations. A selection of these traits for line per se performance in early generations will save field plots in further testing testcross performance and increase efficiency of hybrid breeding.     

The uncoupling protein 1 gene, UCP1, is expressed in mammalian islet cells and associated with acute insulin response to glucose in African American families from the IRAS Family Study

Background

Variants of uncoupling protein genes UCP1 and UCP2 have been associated with a range of traits. We wished to evaluate contributions of known UCP1 and UCP2 variants to metabolic traits in the Insulin Resistance and Atherosclerosis (IRAS) Family Study.

Methods

We genotyped five promoter or coding single nucleotide polymorphisms (SNPs) in 239 African American (AA) participants and 583 Hispanic participants from San Antonio (SA) and San Luis Valley. Generalized estimating equations using a sandwich estimator of the variance and exchangeable correlation to account for familial correlation were computed for the test of genotypic association, and dominant, additive and recessive models. Tests were adjusted for age, gender and BMI (glucose homeostasis and lipid traits), or age and gender (obesity traits), and empirical P-values estimated using a gene dropping approach.

Results

UCP1 A-3826G was associated with AIR_g in AA (P = 0.006) and approached significance in Hispanic families (P = 0.054); and with HDL-C levels in SA families (P = 0.0004). Although UCP1 expression is reported to be restricted to adipose tissue, RT-PCR indicated that UCP1 is expressed in human pancreas and MIN-6 cells, and immunohistochemistry demonstrated co-localization of UCP1 protein with insulin in human islets. UCP2 A55V was associated with waist circumference (P = 0.045) in AA, and BMI in SA (P = 0.018); and UCP2 G-866A with waist-to-hip ratio in AA (P = 0.016).

Conclusion

This study suggests a functional variant of UCP1 contributes to the variance of AIR_g in an AA population; the plausibility of this unexpected association is supported by the novel finding that UCP1 is expressed in islets.     

Mass action models versus the Hill model: An analysis of tetrameric human thymidine kinase 1 positive cooperativity

Background

The Hill coefficient characterizes the extent to which an enzyme exhibits positive or negative cooperativity, but it provides no information regarding the mechanism of cooperativity. In contrast, models based on the equilibrium concept of mass action can suggest mechanisms of cooperativity, but there are often many such models and often many with too many parameters.

Results

Mass action models of tetrameric human thymidine kinase 1 (TK1) activity data were formed as pairs of plausible hypotheses that per site activities and binary dissociation constants are equal within contiguous stretches of the number of substrates bound. Of these, six 3-parameter models were fitted to 5 different datasets. Akaike's Information Criterion was then used to form model probability weighted averages. The literature average of the 5 model averages was K = (0.85, 0.69, 0.65, 0.51) μM and k = (3.3, 3.9, 4.1, 4.1) sec^-1 where K and k are per-site binary dissociation constants and activities indexed by the number of substrates bound to the tetrameric enzyme.

Conclusion

The TK1 model presented supports both K and k positive cooperativity. Three-parameter mass action models can and should replace the 3-parameter Hill model.

Reviewers

This article was reviewed by Philip Hahnfeldt, Fangping Mu (nominated by William Hlavacek) and Rainer Sachs.     

A simple model for estimating Ni availability and leaf Ni accumulation for the Ni-hyperaccumulator Leptoplax emarginata

Aims

The aim of the present study was to predict kinetics of both Ni concentration in soil solution and leaf Ni mass for the Ni-hyperaccumulator Leptoplax emarginata cultivated on a fertilized and Ni-contaminated sandy topsoil.

Methods

The 0-D (independent of space) one-site rate-limited desorption model proposed by Ingwersen et al. (J Environ Qual 35:2055–2065, 2006) was modified. The plant sink term of the model was approximated by the biophysical equation which assumes that the leaf nickel mass is equal to the triple product of the Intact Plant Transpiration Stream Concentration Factor for Ni IPTSCF_Ni (xylem:solution Ni concentration ratio), Ni concentration in solution and the volume of transpired water. The model input variables were the constant mean IPTSCF_Ni value, determined from independent leaf Ni accumulation kinetics, and the exponential law fitting the transpiration rate kinetics. Using the best calibration, the model was validated and a sensitivity analysis was carried out thereafter. Models were formulated as sets of ordinary differential equation systems which were solved using the fourth-order Runge–Kutta method.

Results

The best model calibration was the joint parameter optimization: the two parameters of the Freundlich Ni adsorption isotherm and of the Ni desorption rate coefficient are obtained using the kinetics of Ni concentrations in the soil solutions for the reference unplanted Ni-contaminated topsoils. The model was validated reasonably well for both Ni concentration in soil solution and leaf Ni mass.

Conclusions

The joint parameter optimization of the two parameters of the Freundlich nickel sorption isotherm and of the Ni desorption rate was successful whereas the Freundlich batch Ni sorption isotherm dramatically overestimated Ni sorption. This joint approach is therefore recommended for any plant metal uptake model. The 0-D one-site rate-limited desorption model linked to a biophysical coupled Ni and water uptake model reasonably validated the kinetics of both Ni concentration in solution and leaf Ni mass. This promising simplified model for predicting both metal concentration in solution and leaf metal mass for metal needs further validations in culture chambers and further improvements in order to use it in the field as a one-dimensional model, taking into account soil moisture dynamics.     

A computational model for functional mapping of genes that regulate intra-cellular circadian rhythms

Background

Development of the mathematical models that adequately describe biochemical reactions and molecular-genetic mechanisms is one of the most important tasks in modern bioinformatics. Because the enzyme adenylosuccinate synthetase (AdSS) has long been extensively studied, a wealth of kinetic data has been accumulated.

Results

We describe a mathematical model for the reaction catalyzed by AdSS. The model's parameters were fitted to experimental data obtained from published literature. The advantage of our model is that it includes relationships between the reaction rate, the concentrations of three substrates (GTP, IMP and ASP), the effects of five inhibitors (GMP, GDP, AMP, ASUC and SUCC), and the influence of Mg²⁺ ions.

Conclusion

Our model describes the reaction catalyzed by AdSS as a fully random process. The model structure implies that each of the inhibitors included in it is only competitive to one of the substrates. The model was tested for adequacy using experimental data published elsewhere. The values obtained for the parameters are as follows: V _max = 1.35·10^-3 mM/min, Km _GTP = 0.023 mM, Km _IMP = 0.02 mM, Km _ASP = 0.3 mM, Ki _GMP = 0.024 mM, Ki _GDP = 8·10^-3 mM, Ki _AMP = 0.01 mM, Ki _ASUC = 7.5·10^-3 mM, Ki _SUCC = 8 mM, Km _Mg = 0.08 mM.     

Kinetics study of pyridine biodegradation by a novel bacterial strain,Rhizobium sp. NJUST18

Biodegradation of pyridine by a novel bacterial strain, Rhizobium sp. NJUST18, was studied in batch experiments over a wide concentration range (from 100 to 1,000 mg l^?1). Pyridine inhibited both growth of Rhizobium sp. NJUST18 and biodegradation of pyridine. The Haldane model could be fitted to the growth kinetics data well with the kinetic constants μ* = 0.1473 h^?1, K _s = 793.97 mg l^?1, K _i = 268.60 mg l^?1 and S _m = 461.80 mg l^?1. The true μ _max, calculated from μ*, was found to be 0.0332 h^?1. Yield coefficient Y _X/S depended on S _i and reached a maximum of 0.51 g g^?1 at S _i of 600 mg l^?1. V _max was calculated by fitting the pyridine consumption data with the Gompertz model. V _max increased with initial pyridine concentration up to 14.809 mg l^?1 h^?1. The q _S values, calculated from $V_{ \hbox{max} }$ , were fitted with the Haldane equation, yielding q _Smax = 0.1212 g g^?1 h^?1 and q* = 0.3874 g g^?1 h^?1 at S _m′ = 507.83 mg l^?1, K _s′ = 558.03 mg l^?1, and K _i′ = 462.15 mg l^?1. Inhibition constants for growth and degradation rate value were in the same range. Compared with other pyridine degraders, μ _max and S _m obtained for Rhizobium sp. NJUST18 were relatively high. High K _i and K _i′ values and extremely high K _s and K _s′ values indicated that NJUST18 was able to grow on pyridine within a wide concentration range, especially at relatively high concentrations.     

Frequency preference in two-dimensional neural models: a linear analysis of the interaction between resonant and amplifying currents

Many neuron types exhibit preferred frequency responses in their voltage amplitude (resonance) or phase shift to subthreshold oscillatory currents, but the effect of biophysical parameters on these properties is not well understood. We propose a general framework to analyze the role of different ionic currents and their interactions in shaping the properties of impedance amplitude and phase in linearized biophysical models and demonstrate this approach in a two-dimensional linear model with two effective conductances g _L and g ₁. We compute the key attributes of impedance and phase (resonance frequency and amplitude, zero-phase frequency, selectivity, etc.) in the g _L ???g ₁ parameter space. Using these attribute diagrams we identify two basic mechanisms for the generation of resonance: an increase in the resonance amplitude as g ₁ increases while the overall impedance is decreased, and an increase in the maximal impedance, without any change in the input resistance, as the ionic current time constant increases. We use the attribute diagrams to analyze resonance and phase of the linearization of two biophysical models that include resonant (I _h or slow potassium) and amplifying currents (persistent sodium). In the absence of amplifying currents, the two models behave similarly as the conductances of the resonant currents is increased whereas, with the amplifying current present, the two models have qualitatively opposite responses. This work provides a general method for decoding the effect of biophysical parameters on linear membrane resonance and phase by tracking trajectories, parametrized by the relevant biophysical parameter, in pre-constructed attribute diagrams.     

Optimization of biotechnological systems through geometric programming

Background

Due to the increasing importance of identifying insulin resistance, a need exists to have a reliable mathematical model representing the glucose/insulin control system. Such a model should be simple enough to allow precise estimation of insulin sensitivity on a single patient, yet exhibit stable dynamics and reproduce accepted physiological behavior.

Results

A new, discrete Single Delay Model (SDM) of the glucose/insulin system is proposed, applicable to Intra-Venous Glucose Tolerance Tests (IVGTTs) as well as to multiple injection and infusion schemes, which is fitted to both glucose and insulin observations simultaneously. The SDM is stable around baseline equilibrium values and has positive bounded solutions at all times. Applying a similar definition as for the Minimal Model (MM) S_I index, insulin sensitivity is directly represented by the free parameter K_xgI of the SDM. In order to assess the reliability of Insulin Sensitivity determinations, both SDM and MM have been fitted to 40 IVGTTs from healthy volunteers. Precision of all parameter estimates is better with the SDM: 40 out of 40 subjects showed identifiable (CV < 52%) K_xgI from the SDM, 20 out of 40 having identifiable S_I from the MM. K_xgI correlates well with the inverse of the HOMA-IR index, while S_I correlates only when excluding five subjects with extreme S_I values. With the exception of these five subjects, the SDM and MM derived indices correlate very well (r = 0.93).

Conclusion

The SDM is theoretically sound and practically robust, and can routinely be considered for the determination of insulin sensitivity from the IVGTT. Free software for estimating the SDM parameters is available.     

Physiological characterization of recombinant inbred lines of barley with contrasting levels of carbon isotope discrimination

Background and Aims

Carbon isotope discrimination (Δ¹³C) in C₃ plants used as an indirect measure of water-use efficiency (WUE) provides a tool for selecting crops with high WUE under dry environments.

Methods

We evaluated the physiology and Δ¹³C of a set of 8 F₅ recombinant inbred lines (RILs) with contrasting levels of leaf Δ¹³C derived from two parents, ‘W89001002003’ (low Δ¹³C) and ‘I60049’ (high Δ¹³C) of six-row barley (Hordeum vulgare L.) in a greenhouse and under field conditions in three locations (Lacombe, Vegreville and Castor). In the greenhouse experiment, seven days of water deficit was imposed at the stem elongation stage followed by re-watering to pre-deficit level.

Results

A significant negative relationship between WUE and leaf Δ¹³C was observed. Under water-deficit conditions, both photosynthetic rate (A) and stomatal conductance (g _s ) were significantly reduced with a strong positive correlation (r = 0.89) between the two, and the variation in g _s was proportionally greater than A. The low leaf-Δ¹³C RIL ‘147’ maintained the highest A and g _s among ten genotypes (RILs and parents) under water-deficit conditions. Leaf Δ¹³C was positively correlated with biomass and grain yield in the field trials. Multivariate analysis of leaf Δ¹³C, harvest index and plant height discriminated genotypes into three clusters: drought sensitive, drought tolerant and an intermediate type.

Conclusions

The study suggests that it is possible to select low Δ¹³C lines such as RIL ‘147’, which is able to maintain or produce high yields under low moisture conditions on the Canadian Prairies     

Use of linear mixed models for genetic evaluation of gestation length and birth weight allowing for heavy-tailed residual effects

Background

The distribution of residual effects in linear mixed models in animal breeding applications is typically assumed normal, which makes inferences vulnerable to outlier observations. In order to mute the impact of outliers, one option is to fit models with residuals having a heavy-tailed distribution. Here, a Student''s-t model was considered for the distribution of the residuals with the degrees of freedom treated as unknown. Bayesian inference was used to investigate a bivariate Student''s-t (BSt) model using Markov chain Monte Carlo methods in a simulation study and analysing field data for gestation length and birth weight permitted to study the practical implications of fitting heavy-tailed distributions for residuals in linear mixed models.

Methods

In the simulation study, bivariate residuals were generated using Student''s-t distribution with 4 or 12 degrees of freedom, or a normal distribution. Sire models with bivariate Student''s-t or normal residuals were fitted to each simulated dataset using a hierarchical Bayesian approach. For the field data, consisting of gestation length and birth weight records on 7,883 Italian Piemontese cattle, a sire-maternal grandsire model including fixed effects of sex-age of dam and uncorrelated random herd-year-season effects were fitted using a hierarchical Bayesian approach. Residuals were defined to follow bivariate normal or Student''s-t distributions with unknown degrees of freedom.

Results

Posterior mean estimates of degrees of freedom parameters seemed to be accurate and unbiased in the simulation study. Estimates of sire and herd variances were similar, if not identical, across fitted models. In the field data, there was strong support based on predictive log-likelihood values for the Student''s-t error model. Most of the posterior density for degrees of freedom was below 4. Posterior means of direct and maternal heritabilities for birth weight were smaller in the Student''s-t model than those in the normal model. Re-rankings of sires were observed between heavy-tailed and normal models.

Conclusions

Reliable estimates of degrees of freedom were obtained in all simulated heavy-tailed and normal datasets. The predictive log-likelihood was able to distinguish the correct model among the models fitted to heavy-tailed datasets. There was no disadvantage of fitting a heavy-tailed model when the true model was normal. Predictive log-likelihood values indicated that heavy-tailed models with low degrees of freedom values fitted gestation length and birth weight data better than a model with normally distributed residuals.Heavy-tailed and normal models resulted in different estimates of direct and maternal heritabilities, and different sire rankings. Heavy-tailed models may be more appropriate for reliable estimation of genetic parameters from field data.     

Construction of a large scale integrated map of macrophage pathogen recognition and effector systems

Background

Mathematical models provide abstract representations of the information gained from experimental observations on the structure and function of a particular biological system. Conferring a predictive character on a given mathematical formulation often relies on determining a number of non-measurable parameters that largely condition the model's response. These parameters can be identified by fitting the model to experimental data. However, this fit can only be accomplished when identifiability can be guaranteed.

Results

We propose a novel iterative identification procedure for detecting and dealing with the lack of identifiability. The procedure involves the following steps: 1) performing a structural identifiability analysis to detect identifiable parameters; 2) globally ranking the parameters to assist in the selection of the most relevant parameters; 3) calibrating the model using global optimization methods; 4) conducting a practical identifiability analysis consisting of two (a priori and a posteriori) phases aimed at evaluating the quality of given experimental designs and of the parameter estimates, respectively and 5) optimal experimental design so as to compute the scheme of experiments that maximizes the quality and quantity of information for fitting the model.

Conclusions

The presented procedure was used to iteratively identify a mathematical model that describes the NF-κB regulatory module involving several unknown parameters. We demonstrated the lack of identifiability of the model under typical experimental conditions and computed optimal dynamic experiments that largely improved identifiability properties.     

Concentric-tube airlift bioreactors

Mass transfer coefficients were measured in three concentric-tube airlift reactors of different scales (RIMP, V _L =0.07 m³;RIS?1,V _L =2.50 m³;RIS?2, V _L =5.20 m³). The effects of top and bottom clearance and flow resistances at downcorner entrance were studied in water-air system. Experimental results show that h _s ,h _B and A _d /A _R ratio affect K _L a values as a result of their influence on gas holdup and liquid velocity. The gas-liquid mass-transfer coefficients for all the geometric variables were successfully correlated as Sherwood number with Froude and Galilei numbers, the bottom spatial ratio (B=h _B /D _R ), the top spatial ratio , the gas separation ratio and the downcomer flow resistance ratio (R=A _d /A _R ). The proposed empirical model satisfactorily fitted the experimental data obtained in large airlift reactors and some data presented in literature.     

A systems-based mathematical modelling framework for investigating the effect of drugs on solid tumours

Background and Purpose

Most information on the dose-response of radiation-induced cancer is derived from data on the A-bomb survivors. Since, for radiation protection purposes, the dose span of main interest is between zero and one Gy, the analysis of the A-bomb survivors is usually focused on this range. However, estimates of cancer risk for doses larger than one Gy are becoming more important for radiotherapy patients. Therefore in this work, emphasis is placed on doses relevant for radiotherapy with respect to radiation induced solid cancer.

Materials and methods

For various organs and tissues the analysis of cancer induction was extended by an attempted combination of the linear-no-threshold model from the A-bomb survivors in the low dose range and the cancer risk data of patients receiving radiotherapy for Hodgkin's disease in the high dose range. The data were fitted using organ equivalent dose (OED) calculated for a group of different dose-response models including a linear model, a model including fractionation, a bell-shaped model and a plateau-dose-response relationship.

Results

The quality of the applied fits shows that the linear model fits best colon, cervix and skin. All other organs are best fitted by the model including fractionation indicating that the repopulation/repair ability of tissue is neither 0 nor 100% but somewhere in between. Bone and soft tissue sarcoma were fitted well by all the models. In the low dose range beyond 1 Gy sarcoma risk is negligible. For increasing dose, sarcoma risk increases rapidly and reaches a plateau at around 30 Gy.

Conclusions

In this work OED for various organs was calculated for a linear, a bell-shaped, a plateau and a mixture between a bell-shaped and plateau dose-response relationship for typical treatment plans of Hodgkin's disease patients. The model parameters (α and R) were obtained by a fit of the dose-response relationships to these OED data and to the A-bomb survivors. For any three-dimensional inhomogenous dose distribution, cancer risk can be compared by computing OED using the coefficients obtained in this work.     

Water loss regulation to soil drought associated with xylem vulnerability to cavitation in temperate ring-porous and diffuse-porous tree seedlings

Key message

Sustainable stomatal opening despite xylem cavitation occurs in ring-porous species and stomatal closure prior to cavitation in diffuse-porous species during soil drought.

Abstract

To elucidate the relationship between water loss regulation and vulnerability to cavitation associated with xylem structure, stomatal conductance (g _s), defoliation, vulnerability curves, and vessel features were measured on seedlings of ring-porous Zelkova serrata and Melia azedarach, and diffuse-porous Betula platyphylla var. japonica, Cerasus jamasakura and Carpinus tschonoskii. Under prolonged drought conditions, the percentage loss of hydraulic conductivity (PLC) increased and g _s decreased gradually with decreasing predawn (Ψ_pd) or xylem water potential (Ψ_xylem) in Z. serrata. During the gentle increase of PLC in M. azedarach, g _s increased in the early stages of dehydration while leaves were partly shed. A sharp reduction in g _s was observed before the onset of an increase in the PLC for drying plants of the three diffuse-porous species, suggesting cavitation avoidance by stomatal regulation. In the ring-porous species, xylem-specific hydraulic conductivity (K _s) was higher, whereas the vessel multiple fractions, the ratio of the number of grouped vessels to total vessels, was lower than that in the diffuse-porous species, suggesting that many were distributed as solitary vessels. This may explain the gradual increase in the PLC with decreasing Ψ_xylem because isolated vessels provide less opportunity for air seeding. Different water loss regulation to soil drought was identified among the species, with potential mechanisms being sustainable gas exchange at the expense of xylem dysfunction or partial leaf shedding, and the avoidance of xylem cavitation by strict stomatal regulation. These were linked to vulnerability to cavitation that appears to be governed by xylem structural properties.     

Proof of concept: nitrogen use efficiency of contrasting spring wheat varieties grown in greenhouse and field

Aims

Major aims were to test and evaluate a new concept for assessment of nitrogen use efficiency (NUE) of crops by growing six spring wheat varieties in greenhouse and field environments. NUE was calculated with a plant based concept integrating the entire crop life history and separating plant characteristics from environmental factors affecting NUE. Specific hypotheses were tested related to the varieties’ drought and nutrient fertilisation responses for NUE components, and coherence of those responses in field and greenhouse.

Methods

The wheat (Triticum aestivum L.) cultivated varieties ‘Diskett’, ‘Granary’, ‘Quarna’, ‘Stilett’, ‘Vinjett’, and a Swedish landrace (‘Dala’) were grown in field and greenhouse environments in Central Sweden. Two fertilisation treatments were included in a field and greenhouse experiment, and in the greenhouse also drought. The NUE components N uptake efficiency (U_N), grain-specific N efficiency (E_N,g) and grain N concentration (C_N,g) were assessed.

Results

Drought reduced yield and NUE through E_N,g, and more so when drought occurred prior to anthesis than after anthesis. Effect of fertilisation treatment on NUE components was similar in the two set-ups, but there were fewer variety × fertilisation interactions in the field. U_N was higher in the field and E_N,g was higher in the greenhouse, while C_N,g and overall NUE were similar in the two environments. Ranking of varieties regarding NUE and U_N was similar in the greenhouse and field, but different regarding E_N,g and C_N,g.

Conclusions

The NUE concept is a useful tool to describe and integrate important NUE components for crops grown in different treatments (nutrient fertilisation, drought) and experimental set-ups, i.e. greenhouse and field. Similar variety ranking in overall NUE across experimental set-ups indicates stable results in different environments.