Electron transport across the plasmalemma of Lemna gibba G1

Lemna gibba L., grown in the presence or absence of Fe, reduced extracellular ferricyanide with a V _max of 3.09 mol · g^-1 fresh weight · h^-1 and a K _m of 115 M. However, Fe³⁺-ethylenediaminetetraacetic acid (EDTA) was reduced only after Fe-starvation. External electron acceptors such as ferricyanide, Fe³⁺-EDTA, 2,6-dichlorophenol indophenol or methylene blue induced a membrane depolarization of up to 100 mV, but electron donors such as ferrocyanide or NADH had no effect. Light or glucose enhanced ferricyanide reduction while the concomitant membrane depolarization was much smaller. Under anaerobic conditions, ferricyanide had no effect on electrical membrane potential difference (E_m). Ferricyanide reduction induced H⁺ and K⁺ release in a ratio of 1.16 H⁺+1 K⁺/2 e^- (in +Fe plants) and 1.28 H⁺+0.8 K⁺/2 e^- (in -Fe plants). Anion uptake was inhibited by ferricyanide reduction. It is concluded that the steady-state transfer of electrons and protons proceeds by separate mechanisms, by a redox system and by a H⁺-ATPase.Abbreviations E _m electrical membrane potential difference - EDTA ethylenediaminetetraacetic acid - DCPIP dichlorophenol indophenol - +Fe control plant - -Fe iron-deficient plant - FW fresh weight - H⁺ electrochemical proton gradient     

From START to FINISH: The Influence of Osmotic Stress on the Cell Cycle

The cell cycle is a sequence of biochemical events that are controlled by complex but robust molecular machinery. This enables cells to achieve accurate self-reproduction under a broad range of different conditions. Environmental changes are transmitted by molecular signalling networks, which coordinate their action with the cell cycle. The cell cycle process and its responses to environmental stresses arise from intertwined nonlinear interactions among large numbers of simpler components. Yet, understanding of how these pieces fit together into a coherent whole requires a systems biology approach. Here, we present a novel mathematical model that describes the influence of osmotic stress on the entire cell cycle of S. cerevisiae for the first time. Our model incorporates all recently known and several proposed interactions between the osmotic stress response pathway and the cell cycle. This model unveils the mechanisms that emerge as a consequence of the interaction between the cell cycle and stress response networks. Furthermore, it characterises the role of individual components. Moreover, it predicts different phenotypical responses for cells depending on the phase of cells at the onset of the stress. The key predictions of the model are: (i) exposure of cells to osmotic stress during the late S and the early G2/M phase can induce DNA re-replication before cell division occurs, (ii) cells stressed at the late G2/M phase display accelerated exit from mitosis and arrest in the next cell cycle, (iii) osmotic stress delays the G1-to-S and G2-to-M transitions in a dose dependent manner, whereas it accelerates the M-to-G1 transition independently of the stress dose and (iv) the Hog MAPK network compensates the role of the MEN network during cell division of MEN mutant cells. These model predictions are supported by independent experiments in S. cerevisiae and, moreover, have recently been observed in other eukaryotes.     

Human proximity and habitat fragmentation are key drivers of the rangewide bonobo distribution

Habitat loss and hunting threaten bonobos (Pan paniscus), Endangered (IUCN) great apes endemic to lowland rainforests of the Democratic Republic of Congo. Conservation planning requires a current, data-driven, rangewide map of probable bonobo distribution and an understanding of key attributes of areas used by bonobos. We present a rangewide suitability model for bonobos based on a maximum entropy algorithm in which data associated with locations of bonobo nests helped predict suitable conditions across the species’ entire range. We systematically evaluated available biotic and abiotic factors, including a bonobo-specific forest fragmentation layer (forest edge density), and produced a final model revealing the importance of simple threat-based factors in a data poor environment. We confronted the issue of survey bias in presence-only models and devised a novel evaluation approach applicable to other taxa by comparing models built with data from geographically distinct sub-regions that had higher survey effort. The model’s classification accuracy was high (AUC = 0.82). Distance from agriculture and forest edge density best predicted bonobo occurrence with bonobo nests more likely to occur farther from agriculture and in areas of lower edge density. These results suggest that bonobos either avoid areas of higher human activity, fragmented forests, or both, and that humans reduce the effective habitat of bonobos. The model results contribute to an increased understanding of threats to bonobo populations, as well as help identify priority areas for future surveys and determine core bonobo protection areas.     

Life cycle assessment of lightweight and end-of-life scenarios for generic compact class passenger vehicles

Goal, Scope and Background  The automotive industry has a long history in improving the environmental performance of vehicles - fuel economy and emission improvements, introduction of recycled and renewable materials, etc. The European Union also aims at improving the environmental performance of products by reducing, in particular, waste resulting from End-of-Life Vehicles (ELVs) for example. The European Commission estimates that ELVs contribute to approximately 1 % of the total waste in Europe [9]. Other European Union strategies are considering more life cycle aspects, as well as other impacts including resource or climate change. This article is summarizing the results of a European Commission funded project (LIRECAR) that aims at identifying the environmental impacts and relevance for combinations of recycling / recovery and lightweight vehicle design options over the whole life cycle of a vehicle - i.e. manufacturing, use and recycling/recovery. Three, independent and scientific LCA experts reviewed the study according to ISO 14040. From the beginning, representatives of all Life Cycle Stakeholders have been involved (European materials & supplier associations, an environmental Non-Governmental Organization, recycler’s association). Model and System Definition  The study compared 3 sets of theoretical vehicle weight scenarios: 1000 kg reference (material range of today’s end-of-life, mid-sized vehicles produced in the early 1990’s) and 2 lightweight scenarios for 100 kg and 250 kg less weight based on reference functions (in terms of comfort, safety, etc.) and a vehicle concept. The scenarios are represented by their material range of a broad range of lightweight strategies of most European car manufacturers. In parallel, three End-of-Life (EOL) scenarios are considered: EOL today and two theoretical extreme scenarios (100% recycling, respectively, 100% recovery of shredder residue fractions that are disposed of today). The technical and economical feasibility of the studied scenarios is not taken into consideration (e.g. 100% recycling is not possible). Results and Discussion  Significant differences between the various, studied weight scenarios were determined in several scenarios for the environmental categories of global warming, ozone depletion, photochemical oxidant creation (summer smog), abiotic resource depletion, and hazardous waste. However, these improvement potentials can be only realized under well defined conditions (e.g. material compositions, specific fuel reduction values and EOL credits) based on case-by-case assessments for improvements over the course of the life cycle. Looking at the studied scenarios, the relative contribution of the EOL phase represents 5% or less of the total life cycle impact for most selected impact categories and scenarios. The EOL technology variations studied do not impact significantly the considered environmental impacts. Exceptions include total waste, as long as stockpile goods (overburden, tailings and ore/coal processing residues) and EOL credits are considered. Conclusions and Recommendations  LIRECAR focuses only on lightweight/recycling, questions whereas other measures (changes in safety or comfort standards, propulsion improvements for CO₂, user behavior) are beyond the scope of the study. The conclusions are also not necessarily transferable to other vehicle concepts. However, for the question of end-of-life options, it can be concluded that LIRECAR cannot support any general recommendation and/or mandatory actions to improve recycling if lightweight is affected. Also, looking at each vehicle, no justification could be found for the general assumption that lightweight and recycling greatly influence the affected environmental dimension (Global Warming Potential or resource depletion and waste, respectively). LIRECAR showed that this general assumption is not true under all analyzed circumstances and not as significant as suggested. Further discussions and product development targets shall not focus on generic targets that define the approach/technology concerned with how to achieve environmental improvement (weight reduction [kg], recycling quota [%]), but on overall life cycle improvement). To enable this case-by-case assessment, exchanges of necessary information with suppliers are especially relevant.     

Knowing your habitat: linking patch-encounter rate and patch exploitation in parasitoids

According to optimal foraging theory, animals should decidewhether or not to leave a resource patch by comparing the currentprofitability of the patch with the expected profitability ofsearching elsewhere in the habitat. Although there is abundantevidence in the literature that foragers in general are wellable to estimate the value of a single resource patch, theirdecision making has rarely been investigated with respect tohabitat quality. This is especially true for invertebrates.We have conducted experiments to test whether parasitic waspsadjust patch residence time and exploitation in relation tothe abundance of patches within the environment. We used thebraconid Asobara tabida, a parasitoid of Drosophila larvae,as our model species. Our experiments show that these waspsreduce both the residence time and the degree of patch exploitationwhen patches become abundant in their environment, as predictedby optimal foraging models. Based upon a detailed analysis ofwasp foraging behavior, we discuss proximate mechanisms thatmight lead to the observed response. We suggest that parasitoidsuse a mechanism of sensitization and desensitization to chemicalsassociated with hosts and patches, in order to respond adaptivelyto the abundance of patches within their environment.     

Molecular dynamics simulations of photoactive yellow protein (PYP) in three states of its photocycle: a comparison with X-ray and NMR data and analysis of the effects of Glu46 deprotonation and mutation

Photoactive yellow protein (PYP) is a prototype of the PAS domain superfamily of signaling proteins. The signaling process is coupled to a three-state photocycle. After the photoinduced trans-cis isomerization of the chromophore, 4-hydroxycinnamic acid (pCA), an early intermediate (pR) is formed, which proceeds to a second intermediate state (pB) on a sub-millisecond time scale. The signaling process is thought to be connected to the conformational changes upon the formation of pB and its recovery to the ground state (pG), but the exact signaling mechanism is not known. Experimental studies of PYP by solution NMR and X-ray crystallography suggest a very flexible protein backbone in the ground as well as in the signaling state. The relaxation from the pR to the pB state is accompanied by the protonation of the chromophore's phenoxyl group. This was found to be of crucial importance for the relaxation process. With the goal of gaining a better understanding of these experimental observations on an atomistic level, we performed five MD simulations on the three different states of PYP: a 1 ns simulation of PYP in its ground state [pG(MD)], a 1 ns simulation of the pR state [pR(MD)], a 2 ns simulation of the pR state with the chromophore protonated (pRprot), a 2 ns simulation of the pR state with Glu46 exchanged by Gln (pRGln) and a 2 ns simulation of PYP in its signaling state [pB(MD)]. Comparison of the pG simulation results with X-ray and NMR data, and with the results obtained for the pB simulation, confirmed the experimental observations of a rather flexible protein backbone and conformational changes during the recovery of the pG from the pB state. The conformational changes in the region around the chromophore pocket in the pR state were found to be crucially dependent on the strength of the Glu46-pCA hydrogen bond, which restricts the mobility of the chromophore in its unprotonated form considerably. Both the mutation of Glu46 with Gln and the protonation of the chromophore weaken this hydrogen bond, leading to an increased mobility of pCA and large structural changes in its surroundings. These changes, however, differ considerably during the pRGln and pRprot simulations, providing an atomistic explanation for the enhancement of the rate constant in the Gln46 mutant. Electronic supplementary material to this article is available at and is accessible for athorized users. Electronic Publication     

Oxidative DNA damage in circulating leukocytes occurs as an early event in chronic HCV infection

Chronic hepatitis C virus (HCV) infection is associated with an increased production of reactive oxygen species within the liver that are responsible for the oxidation of intracellular macromolecules. To ascertain whether the increased risk of hepatocellular carcinoma in individuals with chronic HCV infection is related to an accumulation of oxidative DNA damage, the 8-hydroxydeoxyguanosine (8-OHdG) content in the DNA of liver tissue and leukocytes of 87 individuals with HCV- or HBV-related liver disease and of 10 healthy controls was measured. Serum levels of thiobarbituric acid reactive substances (TBARS) were also assessed as an index of lipid peroxidation. RESULTS: The 8-OHdG content in the circulating leukocytes correlated with that of liver tissue (r = 0.618, p < .0004). HCV patients had the highest median 8-OHdG levels (p < .0004). 8-OHdG leukocyte levels in HCV patients were higher than in HBV patients (p < .04) and they significantly correlated with the clinical diagnosis (p < .025), the serum ferritin levels (p < .05), and the amount of liver steatosis (p < .001). No correlation was found with age, gender, history of drinking or smoking, ALT or GGT levels, ESR, alpha-1, or gamma-globulin level and Ishak score. TBARS levels were significantly higher in cirrhotics than in noncirrhotics (p < .01). CONCLUSIONS: The 8-OHdG level in circulating leukocytes is a reliable marker of oxidative stress occurring in the liver of individuals with chronic HCV infection. DNA oxidative damage appears to be an early and unique event in the natural history of HCV-related hepatitis. This injury increases the risk of genomic damage and may be one of the important factors involved in the carcinogenic process in cases of HCV-related chronic liver disease.     

Effect of anoxia on intracellular ATP, Na+i, Ca2+i, Mg2+i, and cytotoxicity in rat hepatocytes.

The effects of anoxia were studied in freshly isolated rat hepatocytes maintained in agarose gel threads and perfused with Krebs-Henseleit bicarbonate buffer (KHB). Cytosolic free calcium (Ca2+i) was measured with aequorin, intracellular sodium (Na+i) with SBFI, intracellular pH (pHi) with BCECF, lactic dehydrogenase (LDH) by the increase in NADH absorbance during lactate oxidation to pyruvate, ATP by 31P NMR spectroscopy in real time, and intracellular free Mg2+ (Mg2+i) from the chemical shift of beta-ATP relative to alpha-ATP in the NMR spectra. Anoxia was induced by perfusing the cells with KHB saturated with 95% N2, 5% CO2. After 1 h of anoxia, beta-ATP fell 66%, and 85% after 2 h, while the Pi/ATP ratio increased 10-fold from 2.75 to 28.3. Under control conditions, the resting cytosolic free calcium was 127 +/- 6 nM. Anoxia increased Ca2+i in two distinct phases: a first rise occurred within 15 min and reached a mean value of 389 +/- 35 nM (p less than 0.001). A second peak reached a maximum value of 1.45 +/- 0.12 microM (p less than 0.001) after 1 h. During the first hour of anoxia, Na+i increased from 15.9 +/- 2.4 mM to 32.2 +/- 1.2 mM (p less than 0.001), Mg2+i doubled from 0.51 +/- 0.05 to 1.12 +/- 0.01 mM (p less than 0.001), and pHi decreased from 7.41 +/- 0.03 to 7.06 +/- 0.1 (p less than 0.001). LDH release doubled during the first hour and increased 6-fold during the second hour of anoxia. Upon reoxygenation, ATP, Ca2+i, Mg2+i, Na+i, and LDH returned near the control levels within 45 min. To determine whether the increased LDH release was related to the rise in Ca2+i, and whether the increased Ca2+i was caused by Ca2+ influx, the cells were perfused with Ca(2+)-free KHB (+ 0.1 mM EGTA) during the anoxic period. After 2 h of anoxia in Ca(2+)-free medium, beta-ATP again fell 90%, but Ca2+i, after the first initial peak, fell below control levels, and LDH release increased only 2.7-fold. During reoxygenation, Ca2+i, ATP, Na+i, and LDH returned near the control levels within 45 min. These results suggest that the rise in Ca2+i induced by anoxia is caused by an influx of Ca2+ from the extracellular fluid, and that LDH release and cell injury may be related to the resulting rise in Ca2+i.