Inhibition by light of CO2 evolution from dark respiration: Comparison of two gas exchange methods

Two approaches to determine the fraction (μ) of mitochondrial respiration sustained during illumination by measuring CO₂ gas exchange are compared. In single leaves, the respiration rate in the light (`day respiration' rate R<sub>d</sub>) is determined as the ordinate of the intersection point of A–c<sub>i</sub> curves at various photon flux densities and compared with the CO<sub>2</sub> evolution rate in darkness (`night respiration' rate R_n). Alternatively, using leaves with varying values of CO₂ compensation concentration (Γ), intracellular resistance (r_i) and R_n, an average number for μ can be derived from the linear regression between Γ and the product r_iċR_n. Both methods also result in a number c* for that intercellular CO₂ concentration at which net CO₂ uptake rate is equal to –R_d. c* is an approximate value of the photocompensation point Γ* (Γ in the absence of mitochondrial respiration), which is related to the CO₂/O₂ specificity factor of Rubisco S_c/o. The presuppositions and limitations for application of both approaches are discussed. In leaves of Nicotiana tabacum, at 22 °C, single leaf measurements resulted in mean values of μ = 0.71 and c_* = 34 μmol mol⁻¹. At the photosynthetically active photon flux density of 960 μmol quanta m⁻² s⁻¹, nearly the same numbers were derived from the linear relationship between Γ and r_iċR_n. c* and R_d determined by single leaf measurements varied between 31 and 41 μmol mol⁻¹ and between 0.37 and 1.22 μmol m⁻² s⁻¹, respectively. A highly significant negative correlation between c* and R_d was found. From the regression equation we obtained estimates for Γ* (39 μmol mol⁻¹), S_c/o (96.5 mol mol⁻¹) and the mesophyll CO₂ transfer resistance (7.0 mol⁻¹ m² s). This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetic model of ethopropazine interaction with horse serum butyrylcholinesterase and its docking into the active site.

The action of a potent tricyclic cholinesterase inhibitor ethopropazine on the hydrolysis of acetylthiocholine and butyrylthiocholine by purified horse serum butyrylcholinesterase (EC 3.1.1.8) was investigated at 25 and 37 degrees C. The enzyme activities were measured on a stopped-flow apparatus and the analysis of experimental data was done by applying a six-parameter model for substrate hydrolysis. The model, which was introduced to explain the kinetics of Drosophila melanogaster acetylcholinesterase [Stojan et al. (1998) FEBS Lett. 440, 85-88], is defined with two dissociation constants and four rate constants and can describe both cooperative phenomena, apparent activation at low substrate concentrations and substrate inhibition by excess of substrate. For the analysis of the data in the presence of ethopropazine at two temperatures, we have enlarged the reaction scheme to allow primarily its competition with the substrate at the peripheral site, but the competition at the acylation site was not excluded. The proposed reaction scheme revealed, upon analysis, competitive effects of ethopropazine at both sites; at 25 degrees C, three enzyme-inhibitor dissociation constants could be evaluated; at 37 degrees C, only two constants could be evaluated. Although the model considers both cooperative phenomena, it appears that decreased enzyme sensitivity at higher temperature, predominantly for the ligands at the peripheral binding site, makes the determination of some expected enzyme substrate and/or inhibitor complexes technically impossible. The same reason might also account for one of the paradoxes in cholinesterases: activities at 25 degrees C at low substrate concentrations are higher than at 37 degrees C. Positioning of ethopropazine in the active-site gorge by molecular dynamics simulations shows that A328, W82, D70, and Y332 amino acid residues stabilize binding of the inhibitor.     

Simulations of voltage clamping poorly space-clamped voltage-dependent conductances in a uniform cylindrical neurite

Significant error is made by using a point voltage clamp to measure active ionic current properties in poorly space-clamped cells. This can even occur when there are no obvious signs of poor spatial control. We evaluated this error for experiments that employ an isochronal I(V) approach to analyzing clamp currents. Simulated voltage clamp experiments were run on a model neuron having a uniform distribution of a single voltage-gated inactivating ionic current channel along an elongate, but electrotonically compact, process. Isochronal Boltzmann I(V) and kinetic parameter values obtained by fitting the Hodgkin-Huxley equations to the clamp currents were compared with the values originally set in the model. Good fits were obtained for both inward and outward currents for moderate channel densities. Most parameter errors increased with conductance density. The activation rate parameters were more sensitive to poor space clamp than the I(V) parameters. Large errors can occur despite normal-looking clamp curves.     

Effects of Thallus Temperature and Hydration on Photosynthetic Parameters of Cetraria Islandica from Contrasting Habitats

Two methods of induced in vivo chlorophyll (Chl) fluorescence were used to investigate the effects of varying thallus temperature and hydration on the performance of photosynthetic apparatus of a foliar lichen Cetraria islandica: slow Chl fluorescence induction kinetic with the analysis of quenching mechanisms, and rapid irradiance response curves of photosynthesis derived from quantum yield of photochemical reactions of photosystem 2 (₂) recorded at increasing irradiances. We compared responses of photosynthetic apparatus in populations of C. islandica growing in lower altitude (LAP: 1 350 m a.s.l.) and in higher altitude (HAP: 2 000 m a.s.l.). At each altitude, the samples were collected both in fully irradiated sites (HI) and in shade (LI). Temperature optimum of photosynthetic processes was the same for LAP and HAP thalli of LI populations (18 °C), while it was significantly lower for HI HAP (14 °C). Gradual dehydration of fully hydrated thalli led to initial increase (up to 20 % of water saturation deficit, WSD) in F_V/F_M and ₂, no change at 20–50 % WSD, and a dramatic decrease of the parameters within 50–80 % of WSD. LI HAP of C. islandica was the best adapted population to low temperature having higher rates of photochemical processes of photosynthesis than HI HAP within temperature range of –5 to +5 °C. The differences between populations were apparent also in Chl content and thallus morphology.     

An Arsenic Exposure Model: Probabilistic Validation Using Empirical Data

This paper describes development of a multi-pathway arsenic exposure model. The model uses information on arsenic concentrations in food, water, soil, and dust, combined with estimates of intake and medium-specific absorption. Urinary arsenic is predicted assuming that 60% of absorbed arsenic is excreted in urine under steady state conditions. Fecal arsenic is predicted assuming all unabsorbed arsenic is excreted in feces. We applied this model at a former copper smelter site. Site specific distributions were available for the following parameters: soil and dust arsenic concentration (geometric mean approximately 100 to 200?ppm and 50 to 100?ppm, respectively); the combined childhood soil and dust ingestion rate (geometric mean of 20?mg/d); soil and dust arsenic relative bioavailability (geometric mean 0.20 and 0.28, respectively); exposure duration; water arsenic concentration; air arsenic concentration; and total arsenic in food. Monte Carlo simulation was used to predict daily arsenic uptake and excretion in urine and feces for children. Predicted urine arsenic levels were less than measured levels (73% to 88% of measured values, depending on region of site). On the other hand, predicted fecal arsenic levels exceeded measured levels by a factor of 1.7 to 4.6. We were able to improve the correspondence between predicted and measured arsenic excretion rates by decreasing the assumed value of the combined soil and dust ingestion rate, and increasing the assumed bioavailability of arsenic in soil and dust.     

Gondwanan radiation of the Southern Hemisphere crayfishes (Decapoda: Parastacidae): evidence from fossils and molecules

Aim The sequential break‐up of Gondwana is thought to be a dominant process in the establishment of shared biota across landmasses of the Southern Hemisphere. Yet similar distributions are shared by taxa whose radiations clearly post‐date the Gondwanan break‐up. Thus, determining the contribution of vicariance versus dispersal to seemingly Gondwanan biota is complex. The southern freshwater crayfishes (family Parastacidae) are distributed on Australia and New Guinea, South America, Madagascar and New Zealand and are unlikely to have dispersed via oceans, owing to strict freshwater limitations. We test the hypotheses that the break‐up of Gondwana has led to (1) a predominately east–west (((Australia, New Zealand: 80 Ma) Madagascar: 160–121 Ma) South America: 165–140 Ma), or (2) a southern (((Australia, South America: 52–35 Ma) New Zealand: 80 Ma) Madagascar: 160–121 Ma) pattern for parastacid crayfish. Further, we examine the evidence for a complete drowning of New Zealand and subsequent colonization by freshwater crayfish. Location Southern Hemisphere. Methods The evolutionary relationships among the 15 genera of Parastacidae were reconstructed using mitochondrial [16S, cytochrome c oxidase subunit I (COI)] and nuclear (18S, 28S) sequence data and maximum likelihood and Bayesian methods of phylogenetic reconstruction. A Bayesian (multidivtime ) molecular dating method using six fossil calibrations and phylogenetic inference was used to estimate divergence time among crayfish clades on Gondwanan landmasses. Results The South American crayfish are monophyletic and a sister group to all other southern crayfish. Australian crayfish are not monophyletic, with two Tasmanian genera, Spinastacoides and Ombrastacoides, forming a clade with New Zealand and Malagasy crayfish (both monophyletic). Divergence of crayfish among southern landmasses is estimated to have occurred around the Late Jurassic to Early Cretaceous (109–178 Ma). Main conclusions The estimated phylogenetic relationships and time of divergence among the Southern Hemisphere crayfishes were consistent with an east–west pattern of Gondwanan divergence. The divergence between Australia and New Zealand (109–160 Ma) pre‐dated the rifting at around 80 Ma, suggesting that these lineages were established prior to the break‐up. Owing to the age of the New Zealand crayfish, we reject the hypothesis that there was a complete drowning of New Zealand crayfish habitat.     

Prediction and interpretation of the antioxidant capacity of green tea from dissimilar chromatographic fingerprints

Previously, multivariate calibration techniques have been successfully applied to model and predict the antioxidant activity of green tea from its chromatographic fingerprint. Since the selectivity differences between dissimilar chromatographic systems have already been valuably used in several applications, in this paper it is studied whether combining the complementary information contained in two dissimilar fingerprints can improve the predictive capacity of the multivariate calibration model. The simplest way of combining the data is concatenating both fingerprints for each sample. The resulting matrix can then be subjected to Orthogonal Projections to Latent Structures (O-PLS). Unfortunately, this approach resulted in a more complex model with a prediction error of about the average of the errors obtained with the individual fingerprints. Secondly, only the peaks with high loading and low orthogonal loading from both chromatograms were included in the O-PLS model. This resulted in a reduced complexity, but not in better predictions, probably due to a lack of complementarity of the information concerning the antioxidant capacity. Finally, the concatenated fingerprints were subjected to stepwise multiple linear regression (MLR) in order to build a model based on the variables most correlated with the antioxidant capacity. The obtained prediction error was lower than those of both previous approaches, but still higher than the error of the model based on a single analysis. This is probably again caused by a lack of complementarity in the variables. Nevertheless, it was advantageous to develop fingerprints on dissimilar system, because it enables to choose the most suited chromatographic profile to build a multivariate calibration model for the considered purpose. In contrast to what was expected, the study showed that the most simple (so the worst separated) fingerprints resulted in the best predictions. On the other hand, a more complex fingerprint in which more compounds are separated is still important to improve the interpretability of the model.     

Marine, intertidal, freshwater and terrestrial biodiversity of an isolated polar archipelago

Aim We ask how biodiverse is a polar archipelago; how this faunal richness is spread across marine, intertidal, freshwater, terrestrial and parasitic realms; and how fast species are accumulated with increased sampling effort. Location The South Orkney Islands (SOI), Scotia Arc, Southern Ocean. Methods We sampled mega‐ and macro‐benthos at the SOI using scuba in the shallows (0–10 m), a rough bottom otter trawl at 150–250 m and an Agassiz trawl and epibenthic sledge, both at depths of 200, 500, 1000 and 1500 m. We also collated species occurrence at the SOI in each realm from a century of literature and modern databases to investigate patterns in species accumulation, endemism, faunistic affinities and bathymetric ranges in three model taxa. Results Our 11 benthic samples showed that point biodiversity at the SOI is high, yielding 19 classes and 158 species. Nearly a third were new to the area, whilst five species and one genus were new to science. The shallowest samples were richest but had fewest new records of species. Known richness at the SOI is dominated by marine species (1026), of which 821 (83.3%) were benthic. Across all realms, 1224 species (50 classes, 24 phyla) were recorded, of which 43 were intertidal, 64 freshwater, 100 terrestrial, 60 parasitic and 40 birds. Species accumulation curves for model taxa showed new sampling yields about 0.75% per sample of known benthic richness, so by Antarctic standards we know the SOI quite well. Most species are Southern Ocean endemics, but very few occur only at the SOI. Main conclusions This first estimate of faunal biodiversity of a polar locality demonstrates both high richness and high levels of knowledge at the SOI. As suspected but never quantified, the benthos dominates polar biodiversity, at least at the SOI. Marine species there constitute 20% of those recently listed for the entire Southern Ocean, whilst > 60% of terrestrial species are known from Antarctica. The SOI, being one of the better‐studied polar locations, of known age and with a discrete shelf, represent an important source of comparison for biodiversity studies. Our data clearly show that richness and our knowledge of the polar fauna differ across environments.     

Bayesian Hierarchical Functional Data Analysis Via Contaminated Informative Priors

Summary .  A variety of flexible approaches have been proposed for functional data analysis, allowing both the mean curve and the distribution about the mean to be unknown. Such methods are most useful when there is limited prior information. Motivated by applications to modeling of temperature curves in the menstrual cycle, this article proposes a flexible approach for incorporating prior information in semiparametric Bayesian analyses of hierarchical functional data. The proposed approach is based on specifying the distribution of functions as a mixture of a parametric hierarchical model and a nonparametric contamination. The parametric component is chosen based on prior knowledge, while the contamination is characterized as a functional Dirichlet process. In the motivating application, the contamination component allows unanticipated curve shapes in unhealthy menstrual cycles. Methods are developed for posterior computation, and the approach is applied to data from a European fecundability study.     

扶桑绵粉蚧与长角立毛蚁的互惠关系及其对寄主棉花叶片叶绿素荧光特性的影响

【背景】草食动物对寄主植物的取食或损伤会诱导改变植物的光合作用,从而直接影响植株的健康生长。产蜜昆虫与蚂蚁的互惠关系是物种相互促进的一种重要的生态学现象,能够促进产蜜昆虫的种群数量,然而这种互惠关系及其对寄主植物光合生理的影响还知之甚少。【方法】在室内条件下,运用叶绿素荧光动力学技术研究了外来入侵害虫扶桑绵粉蚧与长角立毛蚁的互惠对寄主棉花叶片叶绿素荧光特性的影响。【结果】随着扶桑绵粉蚧危害时间的延续,寄主植物上蚂蚁和扶桑绵粉蚧的数量均呈现显著上升的趋势,而在危害后期,蚂蚁存在情况下扶桑绵粉蚧的数量要明显低于无蚂蚁处理;在扶桑绵粉蚧取食寄主棉花20 d后,有、无蚂蚁存在的棉花叶片的光合利用率α值较无虫处理分别下降了53.5%和37.0%;存在蚂蚁或扶桑绵粉蚧危害后期对棉花叶片最大相对电子传递效率r ETRmax有显著影响,然而扶桑绵粉蚧单独取食或与蚂蚁互作的情况下未显著影响棉花叶片对强光的耐受能力(Ek)。【结论与意义】研究明确了扶桑绵粉蚧与长角立毛蚁的互惠关系对寄主棉花叶片的光合生理产生了一定的负面效应,为进一步解释扶桑绵粉蚧入侵、扩散及暴发的生态学过程提供了科学依据。